Bacterial Carbon Research Articles

Assessment of Explicit Representation of Dynamic Viral Processes in Regional Marine Ecological Models.

Viruses, the most abundant microorganisms in the ocean, play important roles in marine ecosystems, mainly by killing their hosts and contributing to nutrient recycling. However, in models simulating ecosystems in real marine environments, the virus-mediated mortality (VMM) rates of their hosts are implicitly represented by constant parameters, thus ignoring the dynamics caused by interactions between viruses and hosts. Here, we construct a model explicitly representing marine viruses and the VMM rates of major hosts, heterotrophic bacteria, and apply it to two sites in the oligotrophic North Pacific and the more productive Arabian Sea. The impacts of the viral processes were assessed by comparing model results with the viral processes enabled and disabled. For reliable assessments, a data assimilation method was used to objectively optimize the model parameters in each run. The model generated spatiotemporally variable VMM rates, generally decreasing in the subsurface but increasing at the surface. Although the dynamics introduced by viruses could be partly stabilized by the ecosystems, they still caused substantial changes to the bacterial abundance, primary production and carbon export, with the changes greater at the more productive site. Our modeling experiments reveal the importance of explicitly simulating dynamic viral processes in marine ecological models.

Long‐term ground cover affects soil bacterial community and carbon metabolism in the Loess Plateau, China

AbstractFarmland mulching can maintain soil nutrients, which plays a positive role in agricultural planting in the arid area. However, the composition of the soil microbial community and the C cycle involved is unclear under farmland mulching. Based on the Changwu Agro‐Ecological Experiment Station, this study set up a long‐term positioning experiment to explore the effect on soil bacterial community structure and C metabolism capacity. In this study, we include five treatments: control uncovered (CK), plastic film mulching (PF), high amount of straw mulching carried out in July, August, and September every year (St90), low amount of straw mulch throughout the growth period (S45), and high amount of straw cover throughout the growth period (S90). We combined Illumina MiSeq sequencing and Biolog‐ECO technology to analyze the functional characterization of soil bacterial community composition in terms of C source metabolism. The results indicated that the soil bacteria showed a high degree of epistatic clustering, and the operational taxonomic unit numbers of soil bacteria decrease as St90, S45, PF, CK, and S90. Redundancy analysis showed that soil available P, NH4+–N, soil moisture content were the main environmental factors affecting bacterial community composition. Proteobacteria, Acidobacteria, and Actinobacteria are the main dominant flora in this area. Soil bacterial C metabolism was highest under PF treatment. Structural equation modeling (SEM) shows that surface cover has direct and indirect effects on bacterial C metabolism capacity and diversity through soil physicochemical properties. Reasonable mulching methods have a positive effect on the sustainable development of agro‐ecosystems in arid areas.

Bottom-Up Control of the Groundwater Microbial Food-Web in an Alpine Aquifer

Groundwater ecosystems are typically poor in organic carbon and productivity sustaining a low standing stock of microbial biomass. In consequence, microbial food webs in oligotrophic groundwater are hypothesized to be bottom-up controlled. To date, quantitative information on groundwater microbial communities, food web interactions, and carbon flow is relatively lacking in comparison to that of surface waters. Studying a shallow, porous alpine aquifer we collected data on the numbers of prokaryotes, virus-like particles and heterotrophic nanoflagellates (HNFs), the concentration of dissolved (DOC) and assimilable organic carbon (AOC), bacterial carbon production (BCP), and physical-chemical conditions for a 1 year hydrological cycle. The potential effects of protozoan grazing and viral lysis onto the prokaryotic biomass was tested. Flow of organic carbon through the microbial food web was estimated based on data from the literature. The abundance of prokaryotes in groundwater was low with 6.1 ± 6.9 × 104 cells mL–1, seasonally influenced by the hydrological dynamics, with higher densities coinciding with a lower groundwater table. Overall, the variability in cell numbers was moderate, and so it was for HNFs (179 ± 103 HNFs mL–1) and virus-like particles (9.6 ± 5.7 × 105 VLPs mL–1). The virus to prokaryotes and prokaryote to HNF ratios ranged between 2–230 and 33–2,084, respectively. We found no evidence for a viral control of prokaryotic biomass, and the biomass of HNFs being bottom-up controlled. First estimations point at carbon use efficiencies of 0.2–4.2% with prokaryotic production, and carbon consumed and recycled by HNFs and phages to be of minor importance. This first groundwater microbial food web analysis strongly hints at a bottom-up control on productivity and standing stock in oligotrophic groundwater ecosystems. However, direct measurement of protozoan grazing and phage mediated lysis rates of prokaryotic cells are urgently needed to deepen our mechanistic understanding. The effect of microbial diversity on the population dynamics still needs to be addressed.

Analysis of Bacteria–Phytoplankton relationships at three discrete locations in the Eastern Arabian Sea during winter

Bacterial abundance (BA), bacterial production (BP), chlorophyll a (Chl a) and primary production (PP) were estimated during Dec 2016–Jan 2017 at three discrete locations viz. the coastal waters, oceanic waters and near coral islands in the eastern Arabian Sea (EAS). During the study period, total bacterial counts were 0.2–1.2 × 109 cells L−1 and Chl a concentration was <0.1–1.2 mg m−3 in the EAS. Bacterial carbon (BC) was 50% of the Chl a-carbon representing phytoplankton biomass in all three locations. The BP (0.2–7.2 mg C m−3 d−1) was also high relative to the concomitantly measured PP (0.01–17 mg C m−3 d−1). Higher ratios of BC:Chl a-C and BP:PP compared to typical ratios in marine environments suggest dominance of allochthonous organic matter. Our analysis indicate that the dissolved organic carbon (DOC) pool which could result from the slow decomposition of the phytoplankton bloom of the preceding southwest monsoon (SWM) season, from the organic matter transported via estuaries and from anthropogenic activities comprises of labile as well as semi-labile components. It possibly fuels much of the bacterial carbon demand that greatly exceeds primary production in all three locations causing net heterotrophic condition which could contribute to increased flux of CO2 to the atmosphere, deoxygenation of coastal waters and threaten fisheries in the EAS during winter.

Large differences in bacterial community composition of nearby shallow lakes surrounded by Nothofagus pumilio forest in Patagonia (Argentina)

Abstract Freshwater ecosystems are integrated in a terrestrial landscape, receiving continuously soil and plant-derived material. In Patagonia, the deciduous beech Nothofagus pumilio constitutes an important source of organic matter for aquatic environments. Here, I attempted to analyze bacterial communities, including genetic diversity and metabolic functioning, in four nearby lakes located under a N. pumilio forest (Chall-Huaco Mountain, Argentina). I combined fieldwork and experiments to assess physicochemical characteristics, bacterial community composition (BCC) and Carbon (C)-consumption. Physicochemical variables analyzed with NMDS showed a clear segregation of all the studied lakes. Similarly, BCC differed among lakes, maintaining its differences regardless of the seasons. Variables that significantly affected bacterial community structuring were dissolved P concentration and protein-like DOM component. The number of specialist operational taxonomic units was higher than that of generalists, but the latter doubled specialists in number of sequences. The last suggests that generalists may be responsible for the differences in BCC among lakes, and species sorting appears to be the main mechanism structuring the metacommunity. These results showed that even at a small geographic scale distinctive bacterial communities can be developed in lakes under the influence of N. pumilio forest.

Seagrasses and local environment control the bacterial community structure and carbon substrate utilization in brackish sediments

Seagrasses are complex benthic coastal ecosystems that play a crucial role in organic matter cycling and carbon sequestration. However, little is known about how seagrasses influence the structure and carbon utilization potential of benthic bacterial communities. This study examined the bacterial communities in monospecific and mixed meadows of seagrasses and compared with bulk (unvegetated) sediments from Chilika, a brackish water coastal lagoon of India. High-throughput sequencing of 16S rRNA genes revealed a vegetation effect in terms of differences in benthic bacterial community diversity, composition, and abundances in comparison with bulk sediments. Desulfobacterales, Chromatiales, Enterobacteriales, Clostridiales, Vibrionales, and Acidimicrobiales were major taxa that contributed to differences between seagrass and bulk sediments. Seagrasses supported ∼5.94 fold higher bacterial abundances than the bulk due to rich organic carbon stock in their sediments. Co-occurrence network demonstrated much stronger potential interactions and connectedness in seagrass bacterial communities compared to bulk. Chromatiales and Acidimicrobiales were identified as the top two keystone taxa in seagrass bacterial communities, whereas, Dehalococcoidales and Rhizobiales were in bulk communities. Seagrasses and local environmental factors, namely, water depth, water pH, sediment salinity, redox potential, total organic carbon, available nitrogen, sediment texture, sediment pH, and sediment core depth were the major drivers of benthic bacterial community composition. Carbon metabolic profiling revealed that heterotrophic bacteria in seagrass sediments were much more metabolically diverse and active than bulk. The utilization of carbon substrate guilds, namely, amino acids, amines, carboxylic acids, carbohydrates, polymers, and phenolic compounds was enhanced in seagrass sediments. Metabolic mapping predicted higher prevalence of sulfate-reducer and N2 fixation metabolic functions in seagrass sediments. Overall, this study showed that seagrasses control benthic bacterial community composition and diversity, enhance heterotrophic carbon substrate utilization, and play crucial roles in organic matter cycling including degradation of hydrocarbon and xenobiotics in coastal sediments.

Local differences in paleohydrology have stronger influence on plant biomarkers than regional climate change across two Paleogene Laramide Basins, Wyoming, USA

Plant biomarkers in the geologic record are commonly used to reconstruct paleovegetation and paleoclimate. Yet the representativeness of these biomarker-based reconstructions is not entirely straightforward because both local and regional climatic influences are convolved in the recovered biomarker composition. Furthermore, geomorphic processes including sedimentation, deposition, burial rates, and surface and groundwater levels can also influence biomarker preservation and taphonomy. The combination of leaf compression fossils with the biomarker record provides a robust framework in which ecological reconstructions can be made. Herein we present a case study examining the biomarker responses to a major regional climatic signal, the Paleocene Eocene Thermal Maximum (PETM), from local effects in two basins with different paleohydrology: the Hanna Basin (HB) and Bighorn Basin (BHB), in Wyoming (USA). Data collected include (1) leaf wax n-alkanes and plant-derived non-steroidal di- and triterpenoids, (2) pristane/phytane vs. terrestrial to aquatic ratio (Pr/Ph:TAR), plant material source proxy (Paq), hopanes, and bacteria which provide constraints on organic matter sourcing, redox conditions, and bacterial inputs, and (3) carbon (δ13Cn-alk) and hydrogen (δ2Hn-alk) isotopic compositions of plant wax n-alkanes. We find the two basins differed significantly in weight % total organic carbon (TOC), alkane and terpenoid concentrations, and δ13Cn-alk and δ2Hn-alk values. We examined the effects of δ13Catm on δ13Cn-alk values by assuming comparable regional climate in the two basins. Differences in paleohydrology and paleovegetation were assessed using the above proxies and previously published paleobotanical data. Local paleohydrologic conditions, an abiotic factor, likely drove variability in plant biomarker preservation and paleovegetation structure. Notably, an abundance of water in the HB during the PETM created a conifer refugium while drying within the BHB caused a local extirpation. This study highlights the importance of considering the influence of local environment, specifically paleohydrology, on the local fossil record and the need to compare multiple sites to disentangle regional climate effects on terrestrial plant communities. Distinguishing local from regional differences is imperative if we are to understand how ecosystems respond to future climate change.

Depth distribution of organic carbon sources in Arctic Chukchi Sea sediments

Climate-induced changes in the composition of organic matter sources in Chukchi Sea sediments could have major implications on carbon cycling, carbon sequestration, and food sources for lower benthic trophic levels. The aim of this study was two-fold: (1) to identify the proportional contributions of organic matter from various primary producers (phytoplankton, terrestrial, and bacterial) to depth-stratified sediments (0–5 cm) across the Arctic Chukchi Sea shelf using essential amino acid (EAA) specific stable carbon isotope biomarkers; and (2) to experimentally evaluate sediment bacterial production under different temperature scenarios. Proportional contributions of EAA sources to surface sediments had little relationship with environmental variables across the Chukchi Shelf and only showed noticeably higher terrestrial proportions in surface sediments in a high-deposition region in the southern study area. Across all sediment depth strata, the majority of EAA in sediments (∼76%) originated from terrestrial sources and may be indicative of accumulation over time due to slow degradation processes of this source within sediments. The different EAA sources showed no significant differences in proportional contributions with sediment depth except for phytoplankton-derived EAA, which decreased with increasing sediment depth. These patterns indicate a well-mixed upper sediment horizon, possibly from bioturbation activities by the abundant benthos. One EAA source assumed to respond quickly to changing environmental conditions are bacteria. To evaluate if and how bacterial production would respond to elevated temperatures, sediment bacterial production was measured experimentally using phospholipid fatty acid (PLFA) analysis. Bacterial production was initially (first 24 h) higher at 5 °C than at 0 °C; however, a drawdown of substrate or potential increase in predation activity and viral lysis resulted in bacterial production to subsequently be similar at both temperature settings. Overall results of this study suggest that terrestrial and bacterial carbon sources may become more prominent in a future, warmer Arctic. Identifying current patterns and potential shifts in organic matter sources with changes in temperature can aid in the understanding of the consequences of climate change in terms of organic matter presence and flow through benthic consumers that use these shelf sediments as feeding grounds.

Environmental Regulation of Photosynthetically Produced Dissolved Organic Carbon by Phytoplankton Along a Subtropical Estuarine Bay

Photosynthetically produced dissolved organic carbon (PDOC) released by marine phytoplankton has an important significance on the marine carbon cycle and on the growth of heterotopic bacteria (HB). However, PDOC is often neglected in the estimation of global marine primary productivity and carbon sequestration capacity. This work studied the issue of PDOC and its environmental regulation mechanism through field investigation and lab experiments in an estuarine bay during southwest and northeast monsoon. We used the percentage of extracellular release (PER) as a key indicator to evaluate the contribution of PDOC to total primary productivity (TPP). We also compared PER among different seasons and sectors and then analyzed the inter-relationship between PDOC and bacterial carbon demand (BCD), size-fractionated phytoplankton, bacterial production (BP), and TPP. We finally discussed the impact factors of PDOC productivity. The results showed that the average contribution of PDOC to TPP in Qinzhou bay could reach 15% during two seasons, which satisfies about 25% of the carbon requirement by HB in the bay. Multiple factors contribute to the seasonal (SW monsoon 13% &amp;lt; NE monsoon 18%) and sectoral variation (outer bay 26% &amp;gt; middle bay 17% &amp;gt; inner bay 7%) in PER, the most significant of which are salinity and nitrogen to phosphorus ratios. PER is also related to phytoplankton community structure and nutrient limitation, the higher PER in the outer bay is attributed to the dual effect of picophytoplankton being the predominant species and a severe imbalance in the nitrogen to phosphorus ratio, both of which lead to increased phytoplankton PDOC release. On the other hand, the lower PER in the inner bay was mainly due to the dominance of microphytoplankton and nitrogen to phosphorus ratio which is close to the redfield ratio. There is still a non-uniform conclusion on the relationship between PER and TPP, suggesting that this relationship needs to be evaluated not only in a horizontal-independent way but also through seasonal and vertical dimensions. The non-linear relationship between PDOC and BCD found in this study potentially indicated weak coupling between phytoplankton exudation and bacterial metabolism. In addition to phytoplankton exudate, HB is still dependent on other sources of DOC to meet their carbon requirements.

Top-Down Controls of Bacterial Metabolism: A Case Study from a Temperate Freshwater Lake Ecosystem.

In freshwater environments, limited data exist on the impact of mortality forces (viruses and heterotrophic nanoflagellates) on bacterial growth efficiency (BGE, index of bacterial carbon metabolism) compared to resource availability. An investigation to determine the relative influence of viral lysis and flagellate predation (top-down forces) on BGE was conducted in a mesotrophic freshwater system (Lake Goule, France) with time and space. Viral abundance was significantly (p < 0.001) related to bacterial abundance by a power law function with an exponent less than 1, emphasizing that the increases in host population (bacteria) together with viruses were not proportionate. A lytic viral strategy was evident throughout the study period, with high lysis of the bacterial population (up to 60%) supported by viral production rates. Viral processes (lysis and production) that were influenced by bacterial production and heterotrophic nanoflagellate abundance had a positive impact on BGE. Estimates of BGE were variable (9.9–45.5%) due to uncoupling between two metabolic parameters—namely bacterial production and respiration. The existence of a synergistic relationship between viruses and flagellates with bacteria in Lake Goule highlighted the decisive impact of top-down agents in sustaining the bacterial carbon metabolism of non-infected population through the nature of vital resources released via mortality processes.

Multi-omics joint analysis of the effect of temperature on microbial communities, metabolism, and genetics in full-scale biogas reactors with food waste

Due to the diversity of microbiota and the high complexity of their interactions that mediate biogas production, a detailed understanding of the microbiota is essential for the overall stability and performance of the anaerobic digestion (AD) process. This study evaluated the microbial taxonomy, metabolism, function, and genetic differences in 14 full-scale biogas reactors and laboratory reactors operating under various conditions in China. This is the first known study of the microbial ecology of AD at food waste (FW) at a regional scale based on multi-omics (16S rRNA gene amplicon sequencing, metagenomics, and proteomics). Temperature significantly affected the bacterial and archaeal community structure (R2 = 0.996, P = 0.001; R2 = 0.846, P < 0.002) and total inorganic carbon(TIC) slightly changed the microbial structure (R2 = 0.532, P = 0.005; R2 = 0.349, P = 0.016). The Wood-Ljungdahl coupled with hydrogenotrophic methanogenic pathways were dominant in the thermophilic reactors, where the acs, metF, cooA, mer, mch and ftr genes were 10.1-, 2.8-, 16.2-, 1.74-, 4.15-, 1.04-folds of the mesophilic reactors (P < 0.01). However, acetoclastic and methylotrophic methanogenesis was the primary pathway in the mesophilic reactors, where the ackA, pta, cdh and mta genes were 2.2-, 3.2-, 14.3-, 1.88-folds of the thermophilic group (P < 0.01). Finally, the Wilcoxon rank-sum test was applied to explain the cause of the temperature affecting AD microbial activities. The findings have deepened the understanding of the effect of temperature on AD microbial ecosystems and are expected to guide the construction and management of full-scale FW biogas plants.

Response of Coastal Shewanella and Duganella Bacteria to Planktonic and Terrestrial Food Substrates.

Global warming scenarios indicate that in subarctic regions, the precipitation will increase in the future. Coastal bacteria will thus receive increasing organic carbon sources from land runoff. How such changes will affect the function and taxonomic composition of coastal bacteria is poorly known. We performed a 10-day experiment with two isolated bacteria: Shewanella baltica from a seaside location and Duganella sp. from a river mouth, and provided them with a plankton and a river extract as food substrate. The bacterial growth and carbon consumption were monitored over the experimental period. Shewanella and Duganella consumed 40% and 30% of the plankton extract, respectively, while the consumption of the river extract was low for both bacteria, ∼1%. Shewanella showed the highest bacterial growth efficiency (BGE) (12%) when grown on plankton extract, while when grown on river extract, the BGE was only 1%. Duganella showed low BGE when grown on plankton extract (< 1%) and slightly higher BGE when grown on river extract (2%). The cell growth yield of Duganella was higher than that of Shewanella when grown on river extract. These results indicate that Duganella is more adapted to terrestrial organic substrates with low nutritional availability, while Shewanella is adapted to eutrophied conditions. The different growth performance of the bacteria could be traced to genomic variations. A closely related genome of Shewanella was shown to harbor genes for the sequestration of autochthonously produced carbon substrates, while Duganella contained genes for the degradation of relatively refractive terrestrial organic matter. The results may reflect the influence of environmental drivers on bacterial community composition in natural aquatic environments. Elevated inflows of terrestrial organic matter to coastal areas in subarctic regions would lead to increased occurrence of bacteria adapted to the degradation of complex terrestrial compounds with a low bioavailability.

Modeling polar marine ecosystem functions guided by bacterial physiological and taxonomic traits

Abstract. Heterotrophic marine bacteria utilize organic carbon for growth and biomass synthesis. Thus, their physiological variability is key to the balance between the production and consumption of organic matter and ultimately particle export in the ocean. Here we investigate a potential link between bacterial traits and ecosystem functions in the rapidly warming West Antarctic Peninsula (WAP) region based on a bacteria-oriented ecosystem model. Using a data assimilation scheme, we utilize the observations of bacterial groups with different physiological traits to constrain the group-specific bacterial ecosystem functions in the model. We then examine the association of the modeled bacterial and other key ecosystem functions with eight recurrent modes representative of different bacterial taxonomic traits. Both taxonomic and physiological traits reflect the variability in bacterial carbon demand, net primary production, and particle sinking flux. Numerical experiments under perturbed climate conditions demonstrate a potential shift from low nucleic acid bacteria to high nucleic acid bacteria-dominated communities in the coastal WAP. Our study suggests that bacterial diversity via different taxonomic and physiological traits can guide the modeling of the polar marine ecosystem functions under climate change.

Identification of zooplankton carbon sources using fatty acid biomarkers in lakes and reservoirs at different trophic states in Nanjing and surrounding areas

脂肪酸在生物的摄食活动中相对稳定，可用于辨别消费者的食物来源.不同营养水平的湖泊与水库中浮游动物的碳源组成有差异，因而可能具有不同的脂肪酸组成特征.本研究对南京市及其周边21个湖库的颗粒有机物（POM）、浮游动物的脂肪酸组成进行了对比分析.结果表明，南京市及其周边湖库21个湖库由中营养、轻富营养、中富营养、重富营养共4个营养水平组成.中营养湖库总氮（TN）、总磷（TP）、叶绿素a（Chl.a）、浮游植物生物量均低于富营养湖库，透明度（SD）则相反.中营养湖库中POM脂肪酸的必需脂肪酸（EFA）平均浓度低于富营养湖库；而细菌特征脂肪酸∑C15+∑C17含量高于富营养湖库.随着湖库富营养化，POM中多不饱和脂肪酸（PUFA）浓度逐渐增大，单不饱和脂肪酸（MUFA）浓度则逐渐减少.中营养湖库中浮游动物PUFA浓度普遍低于富营养湖库，∑C15+∑C17含量高于富营养湖库；且浮游动物体内主要来源于藻类的必需脂肪酸EFA/C16：0比值与细菌源脂肪酸（∑C15+∑C17）/C16：0比值均大于其他湖库，表明中营养湖库中浮游动物摄食了较多细菌.随着湖库营养水平升高，浮游动物饱和脂肪酸（SFA）逐渐增多，MUFA浓度逐渐减少，EFA浓度增多，表明浮游动物主要摄食藻类，而外源碳对浮游动物的碳源贡献较小.冗余分析（RDA）结果显示，EFA/C16：0、（∑C15+∑C17）/C16：0与透明度呈正相关，与Chl.a、总磷、磷酸盐呈高度负相关，表明透明度较高、营养水平相对较低的湖库中，浮游动物可能利用较多的藻类与细菌碳；此外，陆源碳转化指标∑C24/C16：0与TN、硝态氮呈正相关性，表明随着营养水平升高，陆源碳对浮游动物碳源贡献呈增加趋势.总体而言，浮游动物更倾向于利用高质量的内源碳，但在内源碳不足以供给水生生物生长需求的中营养水体中，外源碳对生态系统的物质循环和能量流动会产生重要作用.;Fatty acids are relatively stable in the feeding activities of organisms and can be used to identify consumers' food sources. The carbon source composition of zooplankton in lakes and reservoirs with different nutrient levels is different, so they may have different fatty acid composition characteristics. This study compared the fatty acid composition of POM (particulate organic matter) and zooplankton in 21 lakes and reservoirs in Nanjing and its surrounding areas. The results show that the 21 lakes and reservoirs are composed of four nutritional levels:medium nutrition, light eutrophication, medium eutrophication, and heavy eutrophication. The total nitrogen (TN), total phosphorus (TP), chlorophyll-a (Chl.a), and phytoplankton biomass of mesotrophic lakes and reservoirs are lower than those of eutrophic lakes and reservoirs, while the transparency (SD) is the opposite. The average concentration of essential fatty acids (EFA) of POM fatty acids in mesotrophic lakes was lower than that of eutrophic lakes, while the content of bacterial characteristic fatty acids ∑C15+∑C17 was higher than that of eutrophic lakes. With nutrient increase, the concentration of polyunsaturated fatty acids (PUFA) in POM gradually increases, while the concentration of monounsaturated fatty acids (MUFA) gradually decreases. The PUFA of zooplankton in mesotrophic lakes and reservoirs is generally lower than that of eutrophic lakes and reservoirs, and the content of ∑C15+∑C17 is higher than that of eutrophic lakes and reservoirs; and the ratio of essential fatty acids EFA/C16:0, which are mainly derived from algae, and bacterial fatty acids in zooplankton (The ratio of ∑C15+∑C17)/C16:0 is larger than that of other lakes and reservoirs, indicating that zooplankton in the middle-nutrition lakes and reservoirs ingested more bacteria. As nutrient increases, zooplankton saturated fatty acids (SFA) gradually increase, MUFA gradually decreases, and EFA content increases, indicating that zooplankton mainly feeds on algae, while exogenous carbon contributes little to the carbon source of zooplankton. Redundancy analysis (RDA) show that EFA/C16:0, (∑C15+∑C17)/C16:0 are positively correlated with SD, and highly negatively correlated with Chl.a, TP, and phosphate, suggesting that zooplankton consumed more algal and bacterial carbon; and ∑C24/C16:0 is positively correlated with TN, nitrate nitrogen, indicating that zooplankton utilized more terrestrial carbon. In general, zooplankton is more inclined to use high-quality endogenous carbon, but in mesotrophic water bodies where endogenous carbon is not sufficient to supply the growing needs of aquatic organisms. Exogenous carbon plays an important role in the material circulation and energy flow of the ecosystem.

Nitrogen Fertilizers Prime Bacterial Necromass Formation and Carbon Sequestration in Soil

Nitrogen Fertilizers Prime Bacterial Necromass Formation and Carbon Sequestration in Soil

亚热带红壤区森林土壤剖面微生物残体碳分布及影响因素

土壤剖面中20cm以下土壤有机碳（SOC）储量占土壤剖面总SOC储量50%左右，由于土壤微生物残体碳（MRC）是稳定土壤碳库的重要来源，因此研究土壤剖面中MRC对SOC的贡献对于评估土壤碳储量具有重要意义。然而，目前关于MRC含量及其对SOC贡献的研究多数集中在土壤表层，在土壤剖面和母质中尚不清楚。选取江西省千烟洲亚热带典型森林红壤剖面，通过氨基糖与磷脂脂肪酸（PLFA）微生物标志物分析方法，分析红壤剖面和母质中MRC的影响机制及其对SOC贡献的分布特征。研究结果表明：（1）MRC含量随着土壤剖面深度增加而显著降低（P<0.05），在整个土壤剖面中，细菌MRC对SOC贡献为6%-12%，真菌MRC对SOC贡献为12%-36%，MRC对SOC贡献为18%-46%。从土壤表层至母质，真菌MRC对SOC贡献高于细菌MRC。（2）结构方程模型结果表明，在土壤剖面中，MRC含量主要受到微生物-PLFA含量、容重和溶解态有机碳含量的影响。研究量化了红壤剖面中MRC对SOC的贡献，表明在20cm以下土壤及母质中，微生物残体碳对红壤地区生态系统碳库具有重要贡献。;In soil profiles, soil organic carbon (SOC) storage beneath 20cm accounts for about 50% of the total SOC storage in the terrestrial ecosystem. Microbial residue carbon (MRC) is considered as an important constituent of persistent soil organic carbon. It is important to learn the role of MRC for soil carbon storage in deep soil as the main source of soil stable carbon pool. Until now, most studies involving MRC content and the contribution of MRC to SOC have mainly focused on surface soil, but seldom in deep soil and parent material. In this study, we selected typical red soil profiles in Qianyanzhou, Jiangxi province in subtropical region. We measured the microbial biomarkers of amino sugars and phospholipid fatty acids (PLFAs) which represent microbial residue carbon content and living microbial biomass content, respectively. The objective of the study was to analyze the influence factors of MRC and to quantify the contributions of MRC to SOC along the soil profiles from the surface to parent material. The results showed that (1) bacterial residue carbon (MRC_B), fungal residue carbon (MRC_F) and MRC contents decreased significantly with soil depth (P<0.05), and were about 0.08, 0.18, 0.25 g/kg at the parent material, respectively. The contributions of MRC to SOC along the soil profiles remained unchanged because of the same variation trend of MRC and SOC contents. Along the whole soil profiles, the contributions of MRC_B, MRC_F and MRC to SOC were about 6%-12%, 12%-36% and 18%-46%, respectively. The contribution of MRC_F to SOC was higher than that of MRC_B to SOC from surface soil to parent material. This may be caused by different components of cell walls in bacteria and fungi. The chitin in cell wall of fungi is more difficult to decompose than peptidoglycan in cell wall of bacteria. In addition, MRC_F could have more physical protection than MRC_B by soil aggregates since extracellular mycelia and polysaccharides are involved in the formation of soil aggregates. (2) The structural equation model showed that MRC content was largely determined by microbial biomass content of PLFA biomarkers, soil bulk density (Db) and dissolved organic carbon (DOC) content in the soil profiles, while Db and DOC indirectly influenced but microbial-PLFA content directly influenced the MRC content. Our study quantified the contribution of MRC to SOC along the soil profile and emphasized the contribution of MRC to the formation of ecosystem carbon pool beneath 20cm and in the parent material in red soil region.

Generous Hosts: 'Candidatus Liberibacter asiaticus' Growth in Madagascar Periwinkle (Catharanthus roseus) Highlights Its Nutritional Needs.

'Candidatus Liberibacter asiaticus', the putative causal agent of citrus greening, is not available in pure culture yet. In addition to trees of citrus and citrus relatives, 'Ca. L. asiaticus' can grow in Madagascar periwinkle (Catharanthus roseus). Using gas chromatography-mass spectrometry, we compared the phloem sap composition in sweet orange 'Valencia' (Citrus sinensis) and periwinkle plants after the infection with 'Ca. L. asiaticus'. Interestingly, in contrast to our previous studies of total leaf metabolites, we found that, compared with uninfected phloem sap, the organic acids implicated in the tricarboxylic acid cycle (TCA) cycle including citrate, isocitrate, succinate, fumarate, and malate were reduced significantly in the infected phloem saps of both species. As a result of the reduction of organic acids content, the pH of infected phloem saps was increased. We hypothesize that the bacterial growth induces the mitochondrial TCA cycle in parenchyma cells to produce more of these compounds to be used as a bacterial carbon source. Once these compounds reach a low level in the phloem sap, the bacterium may send a signal, yet to be identified, to initiate a feedback loop to further induce the TCA cycle. Phloem blockage might be another reason behind the reduced translocation of TCA cycle intermediates within the phloem. The net result, localized availability of organic acids, likely benefits bacterial growth and may explain the unequal distribution of 'Ca. L. asiaticus' within infected trees. These findings may help in designing media for the pure culturing of 'Ca. L. asiaticus'.

Chemical and biological vertical distributions within central Arctic (&gt;82°N) sea ice during late summer

We assessed the distribution of biota (autotrophs and heterotrophs) and associated carbonate chemistry variables in Arctic sea ice at latitudes &gt;82°N during late summer and early autumn 2018. The sampled sea ice was relatively thick (average 1.4 m) with variable snow cover (mean 7 cm) and low bulk salinities throughout. Most measured variables, including carbonate chemistry parameters, were low in the upper half of the ice cores, but increased with depth. Measurements of particulate organic carbon (POC), chlorophyll a (chl a), bacterial abundance, and particulate extracellular polysaccharide (pEPS) in the cores strongly suggested that detrital carbon was the major particulate organic pool. Near the ice-water interface, autotrophic material comprised ca. 50% of the total POC, whereas pEPS and bacterial carbon accounted for ca. 8 and 1% of the total POC, respectively. Under-ice water was nutrient poor, providing only a small input of nutrients to support autotrophic growth, at least during the time of our sampling. While the Arctic Ocean has substantial interannual variability in sea-ice concentration and thickness, these measurements enrich the available database and suggest that during years when autumn sea ice is &gt;1 m thick, sea-ice biota are limited in activity and biomass.

Effect of long-term tillage and cropping system on portion of fungal and bacterial necromass carbon in soil organic carbon

The microbial necromass carbon (M-C) is considered to be relatively stable and important part of SOC. However, knowledge about the contribution of M-C storage in increasing SOC storage and the influences of tillage and cropping systems on fungal and bacterial necromass carbon (F-C and B-C) is lacking, especially in the long-term. Here, a subset of treatments in a long-term 16-year study was used to evaluate these changes. The treatments selected for present study were: (1) NTCS: no-tillage with two year corn-soybean (CS) rotation (Zea mays L. – Glycine max Merr.); (2) MPCS: moldboard plowing with two year corn-soybean rotation; (3) NTCC: no-tillage with continuous corn (CC); (4) MPCC: moldboard plowing with continuous corn; (5) CTCC: conventional tillage with continuous corn and no residue return (traditional tillage practice in China). Amino sugars were measured to calculate the M-C, F-C and B-C and their storage. Three-way ANOVA showed that tillage, depth and their interactions had significant effect on all amino sugars. However, two-way ANOVA in separate layers showed the effects of tillage on all amino sugars mostly occurred in 0–5 cm layer. A decaying exponential model showed the relationship between the M-C and SOC (R2 = 0.87). Tillage showed great effects on the amount of M-C, F-C and B-C storage but had no influence on the proportion of their distribution in SOC storage (%). More than half of the increase in SOC storage existed as M-C storage under CC cropping due to returned residue, which was higher than CS. F-C storage % was not affected by agriculture management (residue return, tillage and cropping), whereas B-C storage % was affected by both quantity and quality of residue. The results suggested that CC cropping system was better for M-C sequestration and that bacteria were relatively more sensitive to agriculture management than fungi.

Seawater desalination based drinking water: Microbial characterization during distribution with and without residual chlorine

Monitoring the changes that occur to water during distribution is vital to ensure water safety. In this study, the biological stability of reverse osmosis (RO) produced drinking water, characterized by low cell concentration and low assimilable organic carbon, in combination with chlorine disinfection was investigated. Water quality at several locations throughout the existing distribution network was monitored to investigate whether microbial water quality changes can be identified. Results revealed that the water leaving the plant had an average bacterial cell concentration of 103 cells/mL. A 0.5–1.5 log increase in bacterial cell concentration was observed at locations in the network. The residual disinfectant was largely dissipated in the network from 0.5 mg/L at the treatment plant to less than 0.1 mg/L in the network locations. The simulative study involving miniature distribution networks, mimicking the dynamics of a distribution network, fed with the RO produced chlorinated and non-chlorinated drinking water revealed that distributing RO produced water without residual disinfection, especially at high water temperatures (25–30 °C), poses a higher chance for water quality change. Within six months of operation of the miniature network fed with unchlorinated RO produced water, the adenosine triphosphate (ATP) and total cell concentration (TCC) in the pipe biofilm were 4 × 102 pg ATP/cm2 and 1 × 107 cells/ cm2. The low bacterial cell concentration and organic carbon concentration in the RO-produced water did not prevent biofilm development inside the network with and without residual chlorine. The bacterial community analysis using 16S ribosomal RNA (rRNA) gene sequencing revealed that mesophilic bacteria with higher temperature tolerance and bacteria associated with oligotrophic, nutrient-poor conditions dominated the biofilm, with no indication of the existence of opportunistic pathogenic species. However, chlorination selected against most bacterial groups and the bacterial community that remained was mainly the bacteria capable of surviving disinfection regimes. Biofilms that developed in the presence of chlorine contained species classified as opportunistic pathogens. These biofilms have an impact on shaping the water quality received at the consumer tap. The presence of these bacteria on its own is not a health risk indicator; viability assessment and qPCRs targeting genes specific to the opportunistic pathogens as well as quantitative microbiological risk assessment (QMRA) should be included to assess the risk.The results from this study highlight the importance of implementing multiple barriers to ensure water safety. Changes in water quality detected even when high-quality disinfected RO-produced water is distributed highlight microbiological challenges that chlorinated systems endure, especially at high water temperatures.