Heterotrophic Microbial Activity Research Articles

Exploration of strategies to increase the nitrogen and phosphate content of solid waste landfill soil.

Several strategies were undertaken to increase the fertility of landfill soil as rapid urbanization remarkably decreases the agricultural land, posing challenges to the fast-growing human population. Towards this direction, soil microcosms were prepared wherein the addition of nutrient or biofertilizer or the combination of both increased the soil nitrogen and phosphate content considerably. The maximum amount of nitrogen fixation and phosphate solubilization occurred in microcosm treated with biofertilizer and nutrient. To investigate the underlying cause, we observed that separate application of nutrient or biofertilizer or combined application of both increased the abundance of nitrogen-fixing and phosphate-solubilizing bacteria in the microcosms. However, the highest abundance of nitrogen-fixing and phosphate-solubilizing bacteria was spotted in a microcosm challenged with nutrient and biofertilizer together. It was detected that with increasing population of nitrogen-fixing and phosphate-solubilizing bacteria, the soil nitrogen and phosphate level also got enhanced, respectively, thus establishing a strong positive correlation between them. The microcosm treated with biofertilizer and nutrient manifested the highest degree of heterotrophic microbial growth and microbial activity than the microcosms either treated with nutrient or biofertilizer. The microcosm treated with nutrient and biofertilizer was found to exhibit the highest functional diversity compared to others. A surface plot was constructed to demonstrate the association among microbial activity, functional diversity, and the availability of soil nitrogen and phosphate content of soil. The result indicates that the combined application of nutrient and biofertilizer increases the microbial activity leading to the formation of a heterogeneous ecosystem that enhances the nitrogen and phosphate content of landfill soil considerably.

Temporal and stoichiometric patterns of algal stimulation of litter‐associated heterotrophic microbial activity

Abstract Periphyton communities associated with submerged plant detritus contain interacting autotrophic and heterotrophic microbes, and are sites of extracellular enzymatic activity. The strength and nature of these interactions might be expected to change over time as microbial communities develop on plant litter. Microbial interactions and enzymatic activity can be altered by nutrient availability, suggesting that litter stoichiometry could also affect these phenomena. We grew wetland plants under ambient and nutrient‐enriched conditions to generate plant litter of differing nutrient content. In two experiments, we investigated: (1) the influence of algal photosynthesis on fungal and bacterial production and the activities of four extracellular enzymes throughout a 54‐day period of microbial colonisation and growth; and (2) the influence of litter stoichiometry on these relationships. Ambient and nutrient‐enriched standing‐dead plant litter was collected and then submerged in wetland pools to allow for natural microbial colonisation and growth. Litter samples were periodically retrieved and transported to the laboratory for experiments manipulating photosynthesis using the photosystem II inhibitor DCMU (which effectively prevents algal photosynthetic activity). Algal (14C‐bicarbonate), bacterial (3H‐leucine), and fungal (14C‐acetate) production, and β‐glucosidase, β‐xylosidase, leucine aminopeptidase, and phosphatase activities (MUF‐ or AMC‐labelled fluorogenic substrates) were measured under conditions of active and inhibited algal photosynthesis. Photosynthesis stimulated overall fungal and bacterial production in both experiments, although the strength of stimulation varied amongst sampling dates. Phosphatase activity was stimulated by photosynthesis during the first, but not the second, experiment. No other enzymatic responses to short‐term photosynthesis manipulations were observed. Microbial communities on high‐nutrient litter occasionally showed increased extracellular enzyme activity, fungal growth rates, and bacterial production compared to communities on non‐enriched litter, but algal and fungal production were not affected. Litter stoichiometry had no effects on fungal, bacterial, or enzymatic responses to photosynthesis, but the mean enzyme vector analysis angle (a measure of P‐ versus N‐acquiring enzyme activity) was positively correlated to litter N:P, suggesting that elevated litter N:P led to an increase in the relative activity of P‐acquiring enzymes. These results supported the hypothesis that algal photosynthesis strongly influences heterotrophic microbial activity on macrophyte leaf litter, especially that of fungi, throughout microbial community development. However, the strength of this photosynthetic stimulation does not generally depend on small differences in litter nutrient content. Stimulation of microbial heterotrophs by algal photosynthesis could drive diurnal shifts in periphyton community and aquatic ecosystem function, as well as linking green (photoautotroph‐based) and brown (detrital‐based) food webs.

Seasonal freshening of NW Mediterranean surface water impacts microbial heterotrophic activity and dissolved organic matter

The Rhone river represents the most important source of freshwater, nutrients and organic matter to the northwestern (NW) Mediterranean Sea and riverine input markedly affects biogeochemistry and ecosystem functioning in the estuarine and coastal zone. Structures of low salinity waters (LSW) originating near the river plume can also be transported along the continental shelf and offshore. The objective of the present study was to investigate the influence of LSW distant from their source, focusing on dissolved organic matter (DOM) and related microbial processes during two annual cycles (2007 and 2008) at a time series site characterized by the regular occurrence of LSW in spring (Microbial Observatory Laboratoire Arago). We observed enhanced bacterial heterotrophic production and community respiration and specific DOM features within these LSW, concurrently with low net community production. Our results suggest that LSW represent a mechanism of labile DOM supply, thereby sustaining enhanced heterotrophic microbial metabolism.

Source of organic detritus and bivalve biomass influences nitrogen cycling and extracellular enzyme activity in estuary sediments

In aquatic ecosystems, natural processes that remove nitrogen from the biologically available pool (e.g. denitrification) have been intensively studied as an ecosystem function that reduces eutrophication. The quantity of sediment organic matter is a key driver of denitrification with percent organic content positively related to rates of nitrogen removal; however, few studies have investigated the influence of the quality of organic matter on nitrogen cycling in estuarine sediments despite shifts in primary producers with eutrophication. This laboratory study using intact benthic communities investigates the influence of various organic detritus sources, which vary in their C:N ratio, on nitrogen gas (N2) and solute fluxes and extracellular enzyme activity in estuarine sediments. A custom-built tank with a removable front plate was used with a planar optode film to image sediment oxygenation. Mangrove leaf detritus significantly increased the net N2 production in sediments, while the deposition of other detrital sources and control sediments produced net N2 consumption. Sulfatase activity was significantly reduced in the mangrove leaves and seagrass treatments, suggesting alteration of heterotrophic microbial activity with reducing oxygen conditions. Leucine aminopeptidase activity, indicating nitrogen cycling, was reduced in all treatments, suggesting the organic detritus provided a nitrogen supplement or reduced the activity of extracellular enzymes producing microbes. Bivalve biomass increased net nitrogen gas fluxes in some treatments. Our results indicate different detrital sources may have varying impacts on the removal of bioavailable nitrogen through denitrification and show that feedbacks in biogeochemical cycles may occur with changes in organic detrital source pools.

Towards a simple global-standard bioassay for a key ecosystem process: organic-matter decomposition using cotton strips

Abstract Cotton-strip bioassays are increasingly used to assess ecosystem integrity because they provide a standardized measure of organic-matter decomposition – a fundamental ecosystem process. However, several different cotton-strip assays are routinely used, complicating the interpretation of results across studies, and hindering broader synthesis. Here, we compare the decay rates and assemblages of bacteria and fungi colonizing the three most commonly used cotton materials: Artist’s canvas, Calico cloth, and Empa fabric. Cotton strips from each material type were incubated in 10 streams that span a wide range of physicochemical properties across five ecoregions. Additionally, to evaluate responses to environmental stress without potentially confounding biogeographical effects, we deployed identical bioassays in five streams across an acidification gradient within a single ecoregion. Across all streams decomposition rates (as tensile strength loss [TSL]) differed among the three cotton materials; Calico cloth decomposed fastest (time to 50% TSL [T50] = 16.7 d), followed by the Empa fabric (T50 = 18.3 d) and then Artist’s canvas (T50 = 21.4 d). Despite these differences, rates of TSL of the three cotton materials responded consistently to variation in environmental conditions; TSL of each fabric increased with stream temperature, dissolved-nutrient concentrations and acid-neutralizing capacity, although Artist’s canvas and Calico cloth were more sensitive than Empa fabric. Microbial communities were similar among the materials, and values of community structure (e.g., phylotype richness and diversity) were comparable to those reported for decaying leaves in streams from the same region, the major natural basal carbon resource in forested-stream ecosystems. We present linear calibrations among pairs of assays so that past and future studies can be expressed in a “common currency” (e.g., Artist’s-fabric equivalents) ‘past and future studies’ repeated two times in the sentence. Lastly, given its relatively low within-site variability, and the large number of streams where it has been used (>700 across the globe), we recommend Artist’s fabric for future work. These results show that cotton provides an effective and realistic standardized substrate for studying heterotrophic microbial assemblages, and acts as a reasonable proxy for more chemically complex forms of detritus. These findings add to growing evidence that cotton-strip bioassays are simple, effective and easily standardized indicators of heterotrophic microbial activity and the ecosystem processes that result.

Specific Effect of Trace Metals on Marine Heterotrophic Microbial Activity and Diversity: Key Role of Iron and Zinc and Hydrocarbon-Degrading Bacteria.

Marine microbes are an important control on the biogeochemical cycling of trace metals, but simultaneously, these metals can control the growth of microorganisms and the cycling of major nutrients like C and N. However, studies on the response/limitation of microorganisms to trace metals have traditionally focused on the response of autotrophic phytoplankton to Fe fertilization. Few reports are available on the response of heterotrophic prokaryotes to Fe, and even less to other biogeochemically relevant metals. We performed the first study coupling dark incubations with next generation sequencing to specifically target the functional and phylogenetic response of heterotrophic prokaryotes to Fe enrichment. Furthermore, we also studied their response to Co, Mn, Ni, Zn, Cu (individually and mixed), using surface and deep samples from either coastal or open-ocean waters. Heterotrophic prokaryotic activity was stimulated by Fe in surface open–ocean, as well as in coastal, and deep open-ocean waters (where Zn also stimulated). The most susceptible populations to trace metals additions were uncultured bacteria (e.g., SAR324, SAR406, NS9, and DEV007). Interestingly, hydrocarbon-degrading bacteria (e.g., Thalassolituus, Marinobacter, and Oleibacter) benefited the most from metal addition across all waters (regions/depths) revealing a predominant role in the cycling of metals and organic matter in the ocean.

Negative Effects of Copper Oxide Nanoparticles on Carbon and Nitrogen Cycle Microbial Activities in Contrasting Agricultural Soils and in Presence of Plants.

Metal-oxide nanoparticles (NPs) such as copper oxide (CuO) NPs offer promising perspectives for the development of novel agro-chemical formulations of pesticides and fertilizers. However, their potential impact on agro-ecosystem functioning still remains to be investigated. Here, we assessed the impact of CuO-NPs (0.1, 1, and 100 mg/kg dry soil) on soil microbial activities involved in the carbon and nitrogen cycles in five contrasting agricultural soils in a microcosm experiment over 90 days. Additionally, in a pot experiment, we evaluated the influence of plant presence on the toxicity of CuO-NPs on soil microbial activities. CuO-NPs caused significant reductions of the three microbial activities measured (denitrification, nitrification, and soil respiration) at 100 mg/kg dry soil, but the low concentrations (0.1 and 1 mg/kg) had limited effects. We observed that denitrification was the most sensitive microbial activity to CuO-NPs in most soil types, while soil respiration and nitrification were mainly impacted in coarse soils with low organic matter content. Additionally, large decreases in heterotrophic microbial activities were observed in soils planted with wheat, even at 1 mg/kg for soil substrate-induced respiration, indicating that plant presence did not mitigate or compensate CuO-NP toxicity for microorganisms. These two experiments show that CuO-NPs can have detrimental effects on microbial activities in soils with contrasting physicochemical properties and previously exposed to various agricultural practices. Moreover, we observed that the negative effects of CuO-NPs increased over time, indicating that short-term studies (hours, days) may underestimate the risks posed by these contaminants in soils.

Periphytic algae decouple fungal activity from leaf litter decomposition via negative priming.

1. Well-documented in terrestrial settings, priming effects describe stimulated heterotrophic microbial activity and decomposition of recalcitrant carbon by additions of labile carbon. In aquatic settings, algae produce labile exudates which may elicit priming during organic matter decomposition, yet the directions and mechanisms of aquatic priming effects remain poorly tested. 2. We tested algal-induced priming during decomposition of two leaf species of contrasting recalcitrance, Liriodendron tulipifera and Quercus nigra, in experimental streams under light or dark conditions. We measured litter-associated algal, bacterial, and fungal biomass and activity, stoichiometry, and litter decomposition rates over 43 days. 3. Light increased algal biomass and production rates and increased bacterial abundance 141-733% and fungal production rates 20-157%. Incubations with a photosynthesis inhibitor established that algal activity directly stimulated fungal production rates in the short-term. 4. Algal-stimulated fungal production rates on both leaf species were not coupled to long-term increases in fungal biomass accrual or litter decomposition rates, which were 154-157% and 164-455% greater in the dark, respectively. The similar patterns on fast- vs. slow-decomposing L. tulipifera and Q. nigra, respectively, indicated that substrate recalcitrance may not mediate priming strength or direction. 5. In this example of negative priming, periphytic algae decoupled fungal activity from decomposition, likely by providing labile carbon invested toward greater fungal growth and reproduction instead of recalcitrant carbon degradation. If common, algal-induced negative priming could stimulate heterotrophy reliant on labile carbon yet suppress decomposition of recalcitrant carbon, modifying energy and nutrients available to upper trophic levels and enhancing organic carbon storage or export in well-lit aquatic habitats.

Soil heterotrophic respiration: Measuring and modeling seasonal variation and silvicultural impacts

To determine the effectiveness of forests in sequestering atmospheric carbon (C), we must know the amount of fixed carbon dioxide (CO2) that is subsequently lost due to heterotrophic microbial activity in the soil. Furthermore, the heterotrophic proportion of total soil respiration (Rs) must be quantified as it changes between different physiographic regions, seasons, and silvicultural treatments. This research quantified heterotrophic contributions to Rs in loblolly pine (Pinus taeda) plantations in the Piedmont (n = 3) and Upper Coastal Plain (n = 3) of the Southeastern USA under control, fertilized, and herbicide treatments over an annual cycle. Heterotrophic respiration (Rh) was separated in the field from autotrophic root respiration (Ra) using metal root-excluding collars. The Rh proportion of Rs was not significantly different between regions or treatments, but demonstrated some seasonal variance. The average Rh proportion across the study was found to be ∼73 ± 2% but ranged from ∼70% in winter, spring, and summer to 82% in the fall. Statistical models using microbial biomass, temperature, moisture, and other soil characteristics explained 82% and 75% of Rs and Rh variability, respectively. In contrast, the process based DAYCENT model, parameterized for each site to model Rs, Rh, and Rh proportion compared poorly to field measurements. Model predicted mean seasonal Rh proportions also extended beyond the range of those measured (65–88%) from 61 ± 1.3% to 94 ± 0.4%. DAYCENT performed slightly better (i.e., lower root mean square error) for Piedmont than Coastal Plain sites. DAYCENT does not simulate CO2 fluxes below 20 cm and may be missing substantial fluxes from deeper roots and microbial activity. The results from this study suggest that statistical models such as multiple regression may provide more accurate estimates of Rh proportion for regional extrapolation than the current formulation of the process based DAYCENT model. It is unclear, however, if either approach captures seasonal variation in Rh or how strongly Rh varies with season. Finally, the empirical field data suggest the use of fertilizer and herbicides in these ecosystems increases ecosystem productivity without increasing Rh, which results in an increase in net ecosystem productivity that may lead to greater rates of C sequestration.

Nitrogen Limitations on Microbial Degradation of Plant Substrates Are Controlled by Soil Structure and Moisture Content.

Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO2 emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one.

Autotrophic and heterotrophic indicators of ecological impairment in Toronto Harbour and coastal Lake Ontario

The Toronto and Region Area of Concern (also known as Toronto Harbour) includes 42 km of Lake Ontario coastline and 6 watersheds. Over 4 million people reside within its boundaries which includes the City of Toronto (Ontario, Canada). We sampled eleven sites along the Lake Ontario coastline approximately monthly with 6 cruises from May to early November. Our analyses included standard water quality indicators (total phosphorus, nitrate + nitrite, chlorophyll a) in addition to a robust suite of autotrophic and heterotrophic indicators of ecosystem health, specifically: primary productivity and bacterial growth assays, phytoplankton biomass assessments, and microbial loop assessments. The sites were compared using mean values from May – November. Results from the offshore waters of Lake Ontario, the Bay of Quinte and Hamilton Harbour have also been presented for comparative purposes. The highest mean values observed in Toronto Harbour for total phosphorus (26.5 µg l−1) and chlorophyll a (6.2 µg l−1) which were both in the inner harbour suggested mesotrophic conditions, although the majority of observations suggested oligotrophy. With respect to autotrophic indicators, primary productivity at the mouth of the Humber River as well as the inner harbour (averaging 15 – 20 mg C m−3 h−1) suggested mesotrophy whereas the remaining sites were more oligotrophic. Phytoplankton biomass (≈400 – 1000 mg m−3) suggested oligotrophy. There was a surprising amount of heterotrophic microbial activity at the Humber Bay and inner harbour sites which were influenced by the Humber and Don Rivers. This included elevated rates of bacterial production (≈2 – 3 mg C m−3 h−1) and a high biomass of heterotrophic nanoflagellates (≈1300 – 2600 mg m−3) which was not likely sustained by the autotrophic production. Our findings suggest that a significant amount of organic matter is being deposited by these two rivers and shunted to the microbial food web. Such findings are not obvious from standard indicators (e.g. total phosphorus, chlorophyll a). More work is needed to quantify the sources of organic carbon and assess its utility as ecological indicators.

Effects of dissolved organic matter and nitrification on biodegradation of pharmaceuticals in aerobic enrichment cultures

Natural dissolved organic matter (DOM) and nitrification can play an important role in biodegradation of pharmaceutically active compounds (PhACs) in aerobic zones of constructed wetlands (CWs). This study used an enrichment culture originating from CW sediment to study the effect of DOM and nitrification on aerobic biodegradation of seven PhACs. The enriched culture degraded caffeine (CAF), metoprolol (MET), naproxen (NAP), and ibuprofen (IBP) with a consistent biodegradability order of CAF>MET>NAP>IBP. Biodegradation of propranolol, carbamazepine, and diclofenac was insignificant (<15%). CAF biodegradation was inhibited by the easily biodegradable DOM. Conversely, DOM enhanced biodegradation of MET, NAP, and IBP, potentially by contributing more biomass capable of degrading PhACs. Nitrification enhanced biodegradation of NAP and IBP and mineralization of the PhAC mixture as well as less biodegradable DOM, which may result from co-metabolism of ammonia oxidizing bacteria or enhanced heterotrophic microbial activity under nitrification. MET biodegradation was inhibited in the presence of nitrification. DOM and nitrification effects on PhAC biodegradation in CWs gained from this study can be used in strategies to improve CW operation, namely: designing hydraulic retention times based on the biodegradability order of specific PhACs; applying DOM amendment; and introducing consistent ammonium streams to increase removal of PhACs of interest.

Spatio-temporal reproducibility of the microbial food web structure associated with the change in temperature: Long-term observations in the Adriatic Sea

Global and atmospheric climate change is altering the thermal conditions in the Adriatic Sea and, consequently, the marine ecosystem. Along the eastern Adriatic coast sea surface temperature (SST) increased by an average of 1.03 °C during the period from 1979 to 2015, while in the recent period, starting from 2008, a strong upward almost linear trend of 0.013 °C/month was noted. Being mainly oligotrophic, the middle Adriatic Sea is characterized by the important role played by the microbial food web in the production and transfer of biomass and energy towards higher trophic levels. It is very important to understand the effect of warming on microbial communities, since small temperature increases in surface seawater can greatly modify the microbial role in the global carbon cycle. In this study, the Self-Organizing Map (SOM) procedure was used to analyse the time series of a number of microbial parameters at two stations with different trophic status in the central Adriatic Sea. The results show that responses of the microbial food web (MFW) structure to temperature changes are reproducible in time. Furthermore, qualitatively similar changes in the structure of the MFW occurred regardless of the trophic status. The rise in temperature was associated with: (1) the increasing importance of microbial heterotrophic activities (increase bacterial growth and bacterial predator abundance, particularly heterotrophic nanoflagellates) and (2) the increasing importance of autotrophic picoplankton (APP) in the MFW.

Impact of nutrient enrichment on productivity of coastal water along the SE Mediterranean shore of Israel - A bioassay approach

The coastal waters of the southeastern Mediterranean-Sea (SEMS) are routinely enriched with naturally-occurring and anthropogenic land-based nutrient loads. These external inputs may affect autotrophic and heterotrophic microbial biomass and activity. Here, we conducted 13 microcosm bioassays with different additions of inorganic NO3-(N), PO4-(P) and Si(OH)4-(Si) in different seasons along the Mediterranean coast of Israel. Our results indicate that cyanobacteria are mainly N-limited, whereas N or Si (or both) limit pico-eukaryotes. Furthermore, the degree to which N affects phytoplankton depends on the ambient seawater's inorganic N and N:P characteristics. Heterotrophic bacteria displayed no response in all treatments, except when all nutrients were added simultaneously, suggesting a possible co-limitation by nutrients. These results contrast the N+P co-limitation of phytoplankton and the P-limitation of bacteria in the open waters of the SEMS. These observations enable the application for a better science-based environmental monitoring and policy implementation along the SEMS coast of Israel.

Cryptic serpulid-microbialite bioconstructions in the Kakoskali submarine cave (Cyprus, Eastern Mediterranean)

The biostalactites from the Kakoskali cave in Cyprus represent a new example of the complex biotic relationships between skeletal organisms and microbial communities in building bioconstructions of cryptic marine environments. Biostalactites are mainly constituted of polychaetes of the family Serpulidae and, to a lesser degree, foraminifers and bryozoans. Within the skeletal framework of these organisms, two types of microcrystalline calcite (micrite) have been recognized: autochthonous and detrital micrite. The autochthonous fraction is syndepositionally lithified and occurs as clotted peloidal and, subordinately, aphanitic (structureless) textures, suggesting the presence of heterotrophic microbial activities thriving on decaying metazoan organic matter. This fraction is limited to the protected portions of the bioconstructions, especially in the inner and lower parts. The presence of iron and manganesiferous oxidizing bacteria is suggested by the deposition of ferromanganesiferous crusts and Frutexites-like structures. These microbial-induced biomineralizations are the main evidence of carbonatogenetic and Fe–Mn, autotrophic and chemoheterotrophic, bacterial activities. The Kakoskali cave is frequently visited by divers who, during their immersions, resuspend the fine bottom sediment, which later covers the surface of the bioconstructions, disturbing the delicate equilibrium of the biotic association. This perturbation, which is also caused by strong waves and currents, during winter months, reflects on the bioconstruction morphologies, community composition, and colonization pattern. Bioconstructions exhibit an upper smooth surface, produced by few taxa (e.g., polychaetes, foraminifers), hosting a low number of living individuals, and a lower comparably rough surface, colonized by a more abundant community showing a higher species richness. The ratio surface roughness/smoothness is related to micrite sediment type: the upper part is mainly characterized by loose detrital micrite while the internal and lower parts by syndepositional cemented autochthonous micrite.

Short-term effects of SWRO desalination brine on benthic heterotrophic microbial communities

Seawater reverse osmosis (SWRO) desalination discharge brine-waste as part of the process with immediate (short-term) and chronic (long-term) impacts to marine coastal environment. Brine-waste is often denser than the receiving environment, therefore sinks and flows as a saline plume in adjacency to the sea floor. We suggest that the saline flow over the bottom may impose an osmotic stress, and alter benthic heterotrophic microbial diversity, activity and growth. In this study, we examined the short-term (48h) effects of different salinities on benthic heterotrophic bacteria attached to the sediment at the eastern Mediterranean coast. To this end, 12 cylinders were filled with sediment and incubated in full darkness with rising salinities ranging from 2% to 20% over the ambient levels. During the summer experiments, heterotrophic bacterial abundance has reduced by 60% at salinity levels >5% above the ambient concentration. Further, bacterial cell specific activity significantly increased following high salinity scenarios. Our experimental results provide the first scientifically-based data on the immediate effects of SWRO brine over benthic heterotrophic bacteria. However, we stress that long-term studies are imperative at the outfall of operating desalination facilities to determine the chronic effects of brine on benthic bacteria.

Predominant terminal electron accepting processes during organic matter degradation: Spatio-temporal changes in Ashtamudi estuary, Kerala, India

Anaerobic microbial communities in the anoxic zones degrade organic matter in estuarine sediments. Thermodynamic energy yield for the oxidation reactions with various electron acceptors decreases in the order of O2> NO3- > Mn4+> Fe3+> SO42- > CO2. The predominant terminal electron accepting (TEA) process has an influence on the biogeochemical cycles of nutrients as well as the production of important greenhouse gases such as nitrous oxide and methane from estuarine sediments. The research questions of this study were (1) what are the environmental factors (pH, salinity, organic carbon, sulphate, redox potential) explaining variability in TEA activities such as nitrate reduction rate (NRR), iron reduction rate (IRR), sulphate reduction rate (SRR) and methane production rate (MPR) and (2) which is the predominant TEA process during degradation of organic matter. To determine the TEA activities, sediment samples collected from 13 sampling stations of Ashtamudi estuary during monsoon 2014 and summer 2015 were incubated with sulphate depleted artificial seawater, under anaerobic conditions for 72 h, in microcosms. Spatial variations dominated temporal variations for environmental variables. Nevertheless, biogeochemical processes showed a distinct seasonal variation. Total TEA activity was higher during summer than monsoon, indicating the higher heterotrophic microbial activity favored by high temperature. Individually, SRR was the maximum during summer, while NRR, IRR and MPR were the maximum during monsoon. Sulphate reduction was observed to be the predominant electron accepting process in all sampling stations with cumulative values of 3125.79 and 4046.07 nmol cm-3 day-1 during monsoon and summer respectively. This was followed by NRR, IRR and MPR. Although thermodynamically more favorable, NRR could not predominate due to scarcity of nitrate in sediments. Nevertheless, two-fold and five-fold increase in methanogenesis and denitrification were observed respectively during monsoon in sampling stations, which cannot be ignored, owing to the importance of methane and nitrous oxide as a potent greenhouse gas.

Warmer night-time temperature promotes microbial heterotrophic activity and modifies stream sediment community.

Diel temperature patterns are changing because of global warming, with higher temperatures being predicted to be more pronounced at night. Biological reactions are temperature dependent, with some occurring only during the daylight hours (e.g., light photosynthesis) and other during the entire day (e.g., respiration). Consequently, we expect the modification of daily temperature cycles to alter microbial biological reactions in stream sediments. Here, we aimed to study the effect of warming and changes of the diel temperature patterns on stream sediment biofilm functions tied to organic carbon decomposition, as well as on biofilm meiofaunal community structure. We performed an eight-week experiment with 12 artificial streams subjected to three different diel temperature patterns: warming, warmer nights and control. Significant effects of warming on biofilm function and structure were mainly detected in the long term. Our results showed that warming altered biofilm function, especially in the warmer nights' treatment, which enhanced β-glucosidase enzyme activity. Interestingly, clear opposite diel patterns were observed for dissolved organic carbon and β-glucosidase activity, suggesting that, at night, sediment bacteria quickly consume the input of photosynthetic dissolved organic carbon labile compounds created during light-time. The biofilm structure was also altered by warming, as both warming and warmer night treatments enhanced copepod abundance and diminished abundances of turbellaria and nematodes, which, in turn, controlled bacterial, algal and ciliate communities. Overall, we conclude that warming has strong effect on sediment biofilm structure and enhanced microbial organic matter degradation which might, consequently, affect higher trophic levels and river carbon cycling.

No‐tillage with half‐amount residue retention enhances microbial functional diversity, enzyme activity and glomalin‐related soil protein content within soil aggregates

AbstractA 3‐year field tillage and residue management experiment established in North China was used to analyse topsoil (0–15 cm) aggregation, and microbial functional diversity, enzyme activity and glomalin‐related soil protein (GRSP) content within aggregates. Compared with conventional tillage (CT), no‐tillage (NT) alone significantly (P &lt; 0.05) increased organic C contents in 50–250 and &lt;2 μm aggregates and decreased the proportion of C accumulated by 2–50 μm aggregates and microbial functional diversity indices in &lt;2 μm aggregates. Regardless of tillage practice, both half‐amount (C50) and full (C100) residue retention tended to increase organic C and GRSP contents, or dehydrogenase and invertase activities, in certain aggregates. Under CT, a poorer performance of C50 than C100 was observed in maintaining Shannon index (H′) and Simpson index (D) in &gt;250 and &lt;2 μm aggregates, and also McIntosh index (U) in &lt;2 μm aggregates, owing to insufficient residue and possible decreases in the distribution of decomposer micro‐organisms. Under NT, however, C50 was more effective than C100 in maintaining/elevating H′, D and U in all soil aggregates except for 50–250 μm, suggesting that surplus residue may induce worse soil conditions, decreasing heterotrophic microbial activities. Thus, NT with half‐amount residue retention improved soil physical–chemical–biological properties and could be a useful management practice in North China.

Dendrotelmata (Water-Filled Tree Holes) as Fungal Hotspots - A Long Term Study

Abstract Water-filled tree holes (dendrotelmata) are mostly ephemeral micro-ecosystems characterized by high level of heterotrophic microbial activity sustained by allochthonous organic matter. In this paper, description of a five-year long observation of fungal consortia in a Norway maple tree-hole is presented. Overall, 139 fungal taxa were detected. Among them, Excipularia fusispora, Ellisembia leptospora, Rebentischia unicaudata, Tricladium castaneicola, Thielavia terricola and Alternaria spp. occurred most frequently. Our observations suggest that even an individual dendrotelma represents an exceptional microhabitat, forming a hot-spot for microfungi due to its role as a natural spore trap and its (temporarily) aquatic environment. Our results show that this aquatic micro-ecosystem supports highly diverse mycobiota with continuous temporal dynamics, with an important fraction of sporadic taxa.