Microbial Carbon Source Research Articles

Effects of algal ponds on vertical flow constructed wetlands under different sewage application techniques

Algae can increase dissolved oxygen (DO) in water body by photosynthesis and affect the wastewater treatment performance of constructed wetlands (CWs). Two laboratory-scale vertical flow constructed wetlands combined with algal pond were designed and constructed to treat simulated wastewater in replicated experiments. The two units (half-vertical subsurface flow constructed wetlands and shallow algal pond-vertical subsurface flow constructed wetlands) could decrease chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) at low temperature condition (0–10°C). The study showed that algal pond significantly improved TN and TP removal by 26.2–30.6% and 16.5–21.2% in CWs, respectively. The COD removal was only increased by 16.8–20.2% probably due to microbial carbon source accumulation originated from dead algae and algal debris. The study suggested that the designed new system with algal pond might be a green water treatment solution.

Characterization of chromophoric dissolved organic matter and relationships among PARAFAC components and water quality parameters in Heilongjiang, China.

Chromophoric dissolved organic matter (CDOM) is an important optically active substance that can transports nutrients and pollutants from terrestrial to aquatic systems. Additionally, it is used as a measure of water quality. To investigate the source and composition of CDOM, we used chemical and fluorescent analyses to characterize CDOM in Heilongjiang. The composition of CDOM can be investigated by excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC). PARAFAC identified four individual components that were attributed to microbial humic-like (C1) and terrestrial humic-like (C2-4) in water samples collected from the Heilongjiang River. The relationships between the maximum fluorescence intensities of the four PARAFAC components and the water quality parameters indicate that the dynamic of the four components is related to nutrients in the Heilongjiang River. The relationships between the fluorescence component C3 and the biochemical oxygen demand (BOD5) indicates that component C3 makes a great contribution to BOD5 and it can be used as a carbon source for microbes in the Heilongjiang River. Furthermore, the relationships between component C3, the particulate organic carbon (POC), and the chemical oxygen demand (CODMn) show that component C3 and POC make great contributions to BOD5 and CODMn. The use of these indexes along with PARAFAC results would be of help to characterize the co-variation between the CDOM and water quality parameters in the Heilongjiang River.

Variations in microbial carbon sources and cycling in the deep continental subsurface

Deep continental subsurface fracture water systems, ranging from 1.1 to 3.3km below land surface (kmbls), were investigated to characterize the indigenous microorganisms and elucidate microbial carbon sources and their cycling. Analysis of phospholipid fatty acid (PLFA) abundances and direct cell counts detected varying biomass that was not correlated with depth. Compound-specific carbon isotope analyses (δ13C and Δ14C) of the phospholipid fatty acids (PLFAs) and carbon substrates combined with genomic analyses did identify, however, distinct carbon sources and cycles between the two depth ranges studied.In the shallower boreholes at circa 1kmbls, isotopic evidence indicated microbial incorporation of biogenic CH4 by the in situ microbial community. At the shallowest site, 1.05kmbls in Driefontein mine, this process clearly dominated the isotopic signal. At slightly deeper depths, 1.34kmbls in Beatrix mine, the isotopic data indicated the incorporation of both biogenic CH4 and dissolved inorganic carbon (DIC) derived from CH4 oxidation. In both of these cases, molecular genetic analysis indicated that methanogenic and methanotrophic organisms together comprised a small component (<5%) of the microbial community. Thus, it appears that a relatively minor component of the prokaryotic community is supporting a much larger overall bacterial community in these samples.In the samples collected from >3kmbls in Tau Tona mine (TT107, TT109 Bh2), the CH4 had an isotopic signature suggesting a predominantly abiogenic origin with minor inputs from microbial methanogenesis. In these samples, the isotopic enrichments (δ13C and Δ14C) of the PLFAs relative to CH4 were consistent with little incorporation of CH4 into the biomass. The most 13C-enriched PLFAs were observed in TT107 where the dominant CO2-fixation pathway was the acetyl-CoA pathway by non-acetogenic bacteria. The differences in the δ13C of the PLFAs and the DIC and DOC for TT109 Bh2 were ∼−24‰ and 0‰, respectively. The dominant CO2-fixation pathways were 3-HP/4-HB cycle>acetyl-CoA pathway>reductive pentose phosphate cycle.

Mechanism and Kinetics of Hexavalent Chromium Chemical Reduction with Sugarcane Molasses

Sugarcane molasses, which is a kind of microbial carbon source, is a viscous by-product of the refining of sugarcane into sugar. However, experiments were designed to ascertain the mechanism and kinetics of Cr(VI) reduction with sugarcane molasses without adding microbes in aqueous solution. Results indicated that sugarcane molasses can reduce Cr(VI) to Cr(III) at pH values that range from 2.0 to 6.1 when no bioreduction occurs in the reaction. Furthermore, the reaction mechanism was proven to be that Cr(VI) acts as an electrophile that readily accepts electrons from the phenolic hydroxyl group of plant polyphenol, and it is then reduced to Cr(III) and in the process oxidizes the phenolic hydroxyl group to a quinone. Meanwhile, the reaction could be described by the pseudo-first-order kinetic model with respect to Cr(VI) concentration. The reaction rate constants were 324.2, 65.9, 21.9, and 14.4 h−1 when pH values were 2.0, 3.5, 5.0, and 6.1, respectively, at 20 °C. The k obs increased 3.36, 7.02, and 13.48 times with the temperature adjusted from 5 to 10, 20, and 30 °C.

Responses of bacterial communities in seagrass sediments to polycyclic aromatic hydrocarbon-induced stress.

The seagrass meadows represent one of the highest productive marine ecosystems, and have the great ecological and economic values. Bacteria play important roles in energy flow, nutrient biogeochemical cycle and organic matter turnover in marine ecosystems. The seagrass meadows are experiencing a world-wide decline, and the pollution is one of the main reasons. Polycyclic aromatic hydrocarbons (PAHs) are thought be the most common. Bacterial communities in the seagrass Enhalus acoroides sediments were analyzed for their responses to PAHs induced stress. Dynamics of the composition and abundance of bacterial communities during the incubation period were explored by polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative PCR assay, respectively. Both the incubation time and the PAHs concentration played significant roles in determining the microbial diversity, as reflected by the detected DGGE bands. Analysis of sequencing results showed that the Gammaproteobacteria were dominant in the seagrass sediments, accounting for 61.29 % of all sequenced bands. As PAHs could be used as carbon source for microbes, the species and diversity of the PAH-added groups (group 1 and 2) presented higher Shannon Wiener index than the group CK, with the group 1 showing the highest values almost through the same incubation stage. Patterns of changes in abundance of the three groups over the experiment time were quite different. The bacterial abundance of the group CK and group 2 decreased sharply from 4.15 × 10(11) and 6.37 × 10(11) to 1.17 × 10(10) and 1.07 × 10(10) copies/g from day 2 to 35, respectively while bacterial abundance of group 1 increased significantly from 1.59 × 10(11) copies/g at day 2 to 8.80 × 10(11) copies/g at day 7, and then dropped from day 14 till the end of the incubation. Statistical analysis (UMPGA and PCA) results suggested that the bacterial community were more likely to be affected by the incubation time than the concentration of the PAHs. This study provided the important information about dynamics of bacterial community under the PAHs stress and revealed the high bacterial diversity in sediments of E. acoroides. Investigation results also indicated that microbial community structure in the seagrass sediment were sensible to the PAHs induced stress, and may be used as potential indicators for the PAHs contamination.

荒坡地种植巨菌草对土壤微生物群落功能多样性及土壤肥力的影响

研究种植于荒坡地、不同生长年限（1、2、3、5a）的巨菌草对土壤微生物群落功能多样性及肥力的影响。结果表明，不同生长年限巨菌草土壤微生物对不同碳源的利用随培养时间延长而增大，培养72-96 h变化最明显，培养144 h后各土壤AWCD值均达到最大值。总体上AWCD 值大小依次为：2年生 > 3年生 > 1年生 > 5年生 > CK，不同生长年限的巨菌草土壤AWCD值均比对照高，且差异显著，2年生AWCD 值最高，其次为3年生，1年生、5年生巨菌草土壤AWCD值差异不显著。对培养96 h土壤微生物利用碳源特性进行主成分分析，31个碳源中提取的与土壤微生物碳源利用相关的主成分8个，其中主成分1至主成分8分别能够解释变量方差的25.39%、18.89%、11.28%、9.31%、6.84%、5.60%、5.26%、4.71%，合计解释变量方差的87.27%；主成分1、主成分2能够区分不同生长年限巨菌草土壤的微生物群落特征，2年生、3年生巨菌草土壤微生物功能多样性与CK相比，差异显著；与主成分1显著相关的碳源主要是糖类，氨基酸，羧酸和多聚物，与主成分2显著相关的碳源主要是氨基酸。不同生长年限的巨菌草的Shannon （<em>H</em>）、均匀度、Brillouin指数均高于CK，且差异显著，2年生与3年生差异不显著，1年生与5年生差异不显著。总体上不同生长年限巨菌草的土壤的pH值、有机质、碱解氮、有效磷、速效钾的含量比对照高，其中3年生巨菌草的土壤有机质含量比对照高98.20%，5年生巨菌草土壤的碱解氮含量比对照高93.2%；除1年生巨菌草外，有机质、碱解氮含量均与对照差异显著。在荒坡地种植巨菌草，可增加土壤微生物群落功能多样性，在一定程度上提高土壤肥力，荒坡地种植巨菌草能产生一定的生态正效应。;Introduced from Africa by Fujian Agriculture and Forestry University in 2005, the Giant Juncao (<em> Pennisetum</em> sp.) had the features of tall, erect, forested with the high annual output of 200-400 t/hm². The crude protein content of the Giant Juncao was 10.8% after growth for 4 weeks, indicating the advantage of developed root system, strong stress resistance and quick growth variety. The Giant Juncao may be used to produce mushroom, fungi forage and forage additives successfully. Now, the Giant Juncao is used to control soil erosion and improve the soil properties. This paper studied the effects of the Giant Juncao on the soil microbial community functional diversity and fertility with different growth years (1, 2, 3 and 5 years) planted in the barren hillside. The results indicated that the utilization of carbon sources by soil microbes increased when culture time prolonged. The most obvious change happened in the culture time of 72-96 h. AWCD (Average Well Color Development) value reached the maximum in the culture time of 144 h. Generally, the order of AWCD value was 2 years> 3 years > 1 year > 5 years> CK. The values of AWCD of the Giant Juncao with different growth year was significantly higher than CK. AWCD was highest when the growth year of the Giant Juncao was 2 years, follow by 3 years. The difference of AWCD between 1 and 5 years was not significant. The principal component in the utilization of carbon source by soil microbes in the growth time of 96 h was analyzed. The results showed that the 8 principal components extracted from 31 carbon source were related to soil microbial carbon source utilization, the 1-8 principal components account for 25.39%, 18.89%, 11.28%, 9.31%, 6.84%, 5.60%, 5.26%, 5.60% of variables variance respectively, and account for 87.27% of the total variables variance. The principal component 1 and 2 could be used to distinguish the characteristics of soil microbial community with different growth years of Giant Juncao. The diversity of soil microbial community of the 2 and 3 years' Giant Juncao was significantly different with CK. The Shannon (<em>H</em>), Evenness and Brillouin indexes of soil microbial community with different growth time of Giant Juncao were significantly higher than CK. The Shannon (<em>H</em>), Evenness and Brillouin indexes of soil microbial community planted with Giant Juncao between 2 and 3 years, 1 and 5 years had no significant differences. Generally, pH value, organic matter, alkali solution nitrogen, effective phosphorus and rapidly-available potassium contents of soil planted with Giant Juncao were higher than CK. The content of organic matter of soil planted with 3 years old Giant Juncao was higher than CK by 98.20%. The content of alkaline hydrolysis nitrogen of soil planted with 5 years old Giant Juncao was higher than CK by 93.2%. The organic matter and alkali solution content of soil planted with 2, 3 and 5 years old Giant Juncao were significantly different to CK. The Giant Juncao planted in barren hillside could enhance soil microbial community functional diversity and improve soil fertility to a certain extent. Planting Giant Juncao in the Barren Hillside had certain positive ecological effect.

Impacts of the invasive annual herb Ambrosia artemisiifolia L. on soil microbial carbon source utilization and enzymatic activities

There is currently much interest in the interactions between exotic plants and soil organisms. Exotic invasive species can have profound effects on the microbial community of the soil and positive feedback of soil biota to invasive plants may facilitate their successful invasion. To better understand the impacts of Ambrosia artemisiifolia L. invasion on microbial carbon source utilization and related microbiological parameters, soils were sampled from two invaded sites, i.e., historically-invaded (HINVA), recently-invaded (LINVA) sites and two non-invaded sites, i.e., grassland (NINVA) and native-plant (NATIV) sites in late April. Soil biochemical properties, enzyme activities, and microbial biomass were determined. Meanwhile, carbon source utilization intensity was examined based on the Biolog community-level physiological profile (CLPP) method. The two invaded sites had significantly higher total phosphorus, available nitrogen and phosphorus than non-invaded sites. Microbial biomass nitrogen and phosphorus, and invertase and catalase activities were also significantly higher in soils from invaded sites. The soil microbial community from the HINVA site most profoundly improved soil fertility. Microbial utilization of carbohydrate groups significantly increased in the invaded sites relative to non-invaded sites, especially the utilization of carbohydrates and amines/amides. Soil from the HINVA site had higher efficiency in carbon source utilization, especially for carbohydrates and amino acids. Principal components analysis (PCA) of carbon substrate utilization data revealed distinct differentiation in soil microbial community functions among the four studied sites. Redundancy analysis (RDA) indicated that better soil biochemical conditions, especially the microbial quotient (Cmic/Corg) and available nitrogen values were associated with higher soil carbon utilization in A. artemisiifolia invaded sites. The improvement of soil fertility as well as microbial community function in invaded soils may be beneficial to A. artemisiifolia and contribute to its establishment in new habitats.

Control of the Escherichia coli Sialoregulon by Transcriptional Repressor NanR

NanR, one of >8,500 GntR superfamily helix-turn-helix transcriptional regulators, controls expression of the genes required for catabolism of sialic acids in Escherichia coli. It is predicted to do the same in related bacteria harboring orthologs of nanR. The sialic acids are a family of over 40 naturally occurring nine-carbon keto-sugar acids found mainly in the animal lineage, which includes starfish to humans in the deuterostome lineage. Sialic acids function in development, immunity, protein localization and stability, and homeostasis. They also serve as microbial carbon and nitrogen sources and ligands for cell recognition during host colonization. The importance of microbial sialic acid metabolism for host-microbe interactions has made it a target for therapeutic development. Exploiting this target depends on understanding sialometabolic pathways in a wide range of evolutionarily distinct bacteria. Here, we show by transcriptome, genetic, and biochemical analyses that the most common sialic acid, N-acetylneuraminate, induces the nanATEK-yhcH, yjhATS (nanCMS), and yjhBC operons by directly inactivating NanR, converting the predominantly dimeric form of the repressor to an inactive monomer of approximately 30-kDa. Additionally, other results identify critical amino acid residues and nucleotides in the regulator and operator, respectively. The combined results better define how sialic acids, acting through NanR, affect the metabolic flux of an important group of host-derived metabolites. Thus, E. coli serves as a valuable model for understanding sialocatabolic pathways in bacteria.

Assessing microbial carbon sources and potential PAH degradation using natural abundance 14C analysis

Natural abundance 14C analysis was applied to PLFAs collected from an industrial site in southern Ontario in order to assess microbial carbon sources and potential PAH biodegradation in soils. Δ14C of microbial phospholipid fatty acids (PLFA) at the site ranged from +54‰ to −697‰. Comparison of these values to surrounding carbon sources found that microbial carbon sources were derived primarily from vegetation and/or natural organic matter present in the soils rather than PAHs. This study highlights that microbes are able to utilize almost all available pools of organic matter including older pools which are thought to contain recalcitrant compounds. Furthermore, it shows that even with the presence of an active microbial community, there may be little biodegradation of PAHs. This study illustrates challenges in assessing microbial activity in the environment and the advantage of using natural abundance 14C analysis as a tool to elucidate microbial carbon sources.

Microbial Functional Diversity in Facilities Cultivation Soils of Nitrate Accumulation

Abstract There are increasing concerns over facilities cultivation soils of nitrate accumulation in China. Nitrate pollution in secondary salinization soil is regarded as having potential effects on soil microbial communities. Our study was conducted to evaluate effects of secondary salinization on soil microbial functional diversity with the BIOLOG method. The results showed that Average well-color development (AWCD) values declined with the rising of nitrate concentrations to some extent. The results also exhibited that the accumulation of nitrate in soil decreased the carbon sources utilization rates and the microbial species diversity indices. It indicated that nitrate has significantly negative effects on the sole-carbon-source metabolic ability of soil microbial communities. The cluster analysis intuitively demonstrated the distance and relationship between each sample: soil samples with high nitrate content were more close to each other, while soil samples with low were more similar in distances. The principal component analysis (PCA) result further validated that nitrate was inversely correlated to microbial carbon sources utilization intensity and microbial diversity. The four carbon substrates, Carbohydrates, Miscellaneous, Amino acids and Polymers, could reflect most of the information about carbon sources utilization. Microorganisms preferred these four carbon substrates were more vulnerable to nitrate. Thus, these four carbon substrates could be one of the prioritized microbe carbon sources in soil bioremediation.

Effects of different cropping system and fertilization on functional diversity in soil microbial community of Chrysanthemum morifolium

To study the effects of Chrysanthemum morifolium based on functional diversity in soil microbial community with different cropping system and fertilization and offer scientific basis for the establishment of the reasonable planting patterns. Combined yield and quality of Ch. morifolium, 8 treatments of different cropping system and fertilization on functional diversity in soil microbial community of Ch. morifolium were investigated by the Biolog. The AWCD of Ch. morifolium paddy-dryland rotation was higher than that of the continuous cropping, the AWCD of organic fertilizer and compound NPK > single organic fertilizer > single compound NPK > no fertilizer. The principal component analysis about Ch. morifolium soil microbial carbon source use showed that the contribution rate of principal component 1 was 45.5% and principal component 2 was 12.1%, which could explain most information about the variation. Different cropping system of Ch. morfolium differentiated in principal component 1 axis, different fertilization differentiated in principal component 2 axis. The yield of Ch. morifolium and volatile oil content paddy-dryland rotation was significantly higher than that of continuous cropping. The Ch. morifolium should be cultivated with organic fertilizer and compound NPK by paddy-dryland rotation patters.

Rapid biological oxidation of methanol in the tropical Atlantic: significance as a microbial carbon source

Abstract. Methanol is the second most abundant organic gas in the atmosphere after methane, and is ubiquitous in the troposphere. It plays a significant role in atmospheric oxidant chemistry and is biogeochemically active. Large uncertainties exist about whether the oceans are a source or sink of methanol to the atmosphere. Even less is understood about what reactions in seawater determine its concentration, and hence flux across the sea surface interface. We report here concentrations of methanol between 151–296 nM in parts of the oligotrophic North Atlantic, with corresponding microbial uptake rates between 2–146 nM d−1, suggesting turnover times as low as 1 day (1–25 days) in surface waters of the oligotrophic tropical North East Atlantic. Methanol is mainly (≥97%) used by microbes for obtaining energy in oligotrophic regions, which contrasts with shelf and coastal areas where between 20–50% can be used for cell growth. Comparisons of microbial methanol oxidation rates with parallel determinations of bacterial leucine uptake suggest that methanol contributes on average 13% to bacterial carbon demand in the central northern Atlantic gyre (maximum of 54%). In addition, the contribution that methanol makes to bacterial carbon demand varies as a power function of chlorophyll a concentrations; suggesting for concentrations &lt;0.2 μg l−1 that methanol can make a significant contribution to bacterial carbon demand. However, our low air to sea methanol flux estimates of 7.2–13 μmol m−2 d−1 suggest that the atmosphere is not a major methanol source. We conclude that there must be a major, as yet unidentified, in situ oceanic methanol source in these latitudes which we suggest is sunlight driven decomposition of organic matter.

Comparative analysis of DNA-based microbial community composition and substrate utilisation patterns of activated sludge microorganisms from wastewater treatment plants operated under different conditions

In this study, the microbial community structure and carbon source utilisation profile of activated sludge samples collected from full-scale municipal wastewater treatment plants (WWTPs) operated under different conditions were characterised and compared, respectively, using terminal-restriction fragment length polymorphism (T-RFLP) analysis and Biolog assay. Samples were collected from each biological treatment tank of six conventional activated sludge, two anaerobic-oxic, two anaerobic-anoxic-oxic, and one step-aeration processes in eight full-scale WWTPs in Osaka, Japan. Results of the T-RFLP analysis of eubacterial 16S rDNA showed that microbial communities of activated sludge differed greatly among samples, and that they were affected by process-based operational conditions. In contrast, the carbon source utilisation profiles of activated sludge samples were mutually similar, but appeared to be influenced slightly by aerated conditions at each reaction tank. Similar carbon source utilisation profiles among all samples suggest that the activated sludge community possesses functions that are necessary for wastewater treatment even if the phylogenetic composition is different. Different results from the T-RFLP analysis and Biolog assay suggest that the phylogenetic composition of microbial community might not necessarily reflect the wastewater treatment functions of the activated sludge.

Determination of Microbial Carbon Sources and Cycling during Remediation of Petroleum Hydrocarbon Impacted Soil Using Natural Abundance 14C Analysis of PLFA

In a petroleum impacted land-farm soil in Sarnia, Ontario, compound-specific natural abundance radiocarbon analysis identified biodegradation by the soil microbial community as a major pathway for hydrocarbon removal in a novel remediation system. During remediation of contaminated soils by a plant growth promoting rhizobacteria enhanced phytoremediation system (PEPS), the measured Delta(14)C of phospholipid fatty acid (PLFA) biomarkers ranged from -793 per thousand to -897 per thousand, directly demonstrating microbial uptake and utilization of petroleum hydrocarbons (Delta(14)C(PHC) = -1000 per thousand). Isotopic mass balance indicated that more than 80% of microbial PLFA carbon was derived from petroleum hydrocarbons (PHC) and a maximum of 20% was obtained from metabolism of more modern carbon sources. These PLFA from the contaminated soils were the most (14)C-depleted biomarkers ever measured for an in situ environmental system, and this study demonstrated that the microbial community in this soil was subsisting primarily on petroleum hydrocarbons. In contrast, the microbial community in a nearby uncontaminated control soil maintained a more modern Delta(14)C signature than total organic carbon (Delta(14)C(PLFA) = +36 per thousand to -147 per thousand, Delta(14)C(TOC) = -148 per thousand), indicating preferential consumption of the most modern plant-derived fraction of soil organic carbon. Measurements of delta(13)C and Delta(14)C of soil CO(2) additionally demonstrated that mineralization of PHC contributed to soil CO(2) at the contaminated site. The CO(2) in the uncontaminated control soil exhibited substantially more modern Delta(14)C values, and lower soil CO(2) concentrations than the contaminated soils, suggesting increased rates of soil respiration in the contaminated soils. In combination, these results demonstrated that biodegradation in the soil microbial community was a primary pathway of petroleum hydrocarbon removal in the PEPS system. This study highlights the power of natural abundance radiocarbon for determining microbial carbon sources and identifying biodegradation pathways in complex remediation systems.

Soil organic matter in soil depth profiles: Distinct carbon preferences of microbial groups during carbon transformation

This study investigates how carbon sources of soil microbial communities vary with soil depth. Microbial phospholipid fatty acids (PLFA) were extracted from 0–20, 20–40 and 40–60 cm depth intervals from agricultural soils and analysed for their stable carbon isotopes ( δ 13C values). The soils had been subjected to a vegetation change from C3 ( δ 13C≈−29.3‰) to C4 plants ( δ 13C≈−12.5‰) 40 years previously, which allowed us to trace the carbon flow from plant-derived input (litter, roots, and root exudates) into microbial PLFA. While bulk soil organic matter (SOM) reflected ≈12% of the C4-derived carbon in top soil (0–20 cm) and 3% in deeper soil (40–60 cm), the PLFA had a much higher contribution of C4 carbon of about 64% in 0–20 cm and 34% in 40–60 cm. This implies a much faster turnover time of carbon in the microbial biomass compared to bulk SOM. The isotopic signature of bulk SOM and PLFA from C4 cultivated soil decreases with increasing soil depth (−23.7‰ to −25.0‰ for bulk SOM and −18.3‰ to −23.3‰ for PLFA), which demonstrates decreasing influence of the isotopic signature of the new C4 vegetation with soil depth. In terms of soil microbial carbon sources this clearly shows a high percentage of C4 labelled and thus young plant carbon as microbial carbon source in topsoils. With increasing soil depth this percentage decreases and SOM is increasingly used as microbial carbon source. Among all PLFA that were associated to different microbial groups it could be observed that (a) depended on availability, Gram-negative and Gram-positive bacteria prefer plant-derived carbon as carbon source, however, (b) Gram-positive bacteria use more SOM-derived carbon sources while Gram-negative bacteria use more plant biomass. This tendency was observed in all three-depth intervals. However, our results also show that microorganisms maintain their preferred carbon sources independent on soil depth with an isotopic shift of 3–4‰ from 0–20 to 40–60 cm soil depth.

Short‐term controls on the age of microbial carbon sources in boreal forest soils

One predicted positive feedback of increasing temperatures in the boreal region is carbon (C) loss through enhanced microbial decomposition of soil organic matter (SOM). The degree to which temperature sensitivity for decomposition varies across a range of C‐substrates remains uncertain. Using incubations, we tested whether microorganisms shift to more recalcitrant substrates (with longer turnover times) at higher temperatures at low or increased soil moisture. We measured the radiocarbon (Δ14C) and stable isotope (δ13C) signature of CO2 respired from organic soils from six black spruce forests (0 to 150 years since fire). We identified major C substrates contributing to decomposition by comparing Δ14C of CO2 to Δ14C of roots, mosses, needles, and wood separated from bulk SOM. The Δ14C signatures of these components allow an estimation of their turnover times, further constraining their relative contribution to respiration. Fastest turnover rates were observed for herbaceous litter and needles (annual to &lt;decadal), the longest (&gt;decadal) for mosses, with intermediate turnover times for roots. Dominant microbial C sources in 5 to 40 year old stands were fire remnants and litter of early succession species, while substrates with longer turnover times accounted for a larger proportion of CO2 in mature stands. At both low and increased moisture levels, the increase in CO2 efflux at higher temperatures was accompanied by a decline in δ13CO2, but no shift in Δ14CO2. This suggests that temperature sensitivity is not greater for recalcitrant C and that changes in δ13C likely reflect temperature dependence of microbial fractionation processes rather than a substrate shift.

Positive roles of biofilm during the operation of membrane bioreactor for water reuse

Generally, membrane biofilm have been believed to be minimized during the operation of membrane bioreactor (MBR) for wastewater treatment and reuse. In this study, positive roles of membrane biofilm in the intermittently aerated MBR system were highlighted. During the long-term operation using real domestic wastewater, membrane biofilm played secondary filtration barrier for both low and high molecular weight organic matters. The biofilm on the membrane surface was responsible for the removal of low molecular weight organic matters by the use of easily degradable organic matters (i.e. <1 kDa) as microbial carbon and energy sources during the filtration. Also, track study showed that the significant denitrification took place by the membrane biofilm, proved by the degradation of carbon source and increase of alkalinity such as inorganic carbon. Nevertheless the necessity of further study, this study will give unique insight into positive roles of membrane biofilm, and also continue to aid both fundamental studies and developments of MBR processes.

Characteristics of feeding on dinoflagellates by newly hatched larval crabs

The zoeal larvae of brachyuran crabs must feed soon after hatching on a diet that includes large micro- and mesozooplankton in order to satisfy nutritional requirements. However, newly hatched larvae have been shown to ingest a variety of dinoflagellates, perhaps using microbial carbon sources to sustain them until they encounter more favored prey. Ingestion of dinoflagellates by larval crabs has been documented previously under conditions in which the larvae were exposed to algae provided in monoculture or in defined mixtures of cells. We report here on experiments conducted on the hatching stage of five crab species to determine if ingestion of dinoflagellates occurred when they were provided in combination with Artemia sp. nauplii or after a period of feeding on mesozooplankton. Quantitative measurements of chl a in the larval guts provided evidence of ingestion of algal cells. Active ingestion of the dinoflagellate Prorocentrum micans at specified intervals during an extended feeding period was determined on larvae of two crab species using fluorescently labeled cells provided for brief periods at prescribed time intervals. Stage 1 larvae of four of the five crab species ingested dinoflagellates when they were provided in combination with nauplii and larvae of all five species ingested cells after feeding solely on nauplii for 24 h. Ingestion of algal cells was first evident in the larval guts after 6 h of feeding at both low (200 cell ml−1) and high (1,000 cells ml−1) prey densities. Higher prey densities resulted in higher gut chl a. Larvae continuously exposed to dinoflagellates actively ingested cells at every 3 h interval tested over a 36 h period. Results confirm previous studies that larvae will ingest dinoflagellates even when they are encountered in a mixed prey field or when having previously fed. Ingestion of cells may occur on a continual basis over time.

Variable use of plant- and soil-derived carbon by microorganisms in agricultural soils

In this study we used compound specific 13C and 14C isotopic signatures to determine the degree to which recent plant material and older soil organic matter (SOM) served as carbon substrates for microorganisms in soils. We determined the degree to which plant-derived carbon was used as a substrate by comparison of the 13C content of microbial phospholipid fatty acids (PLFA) from soils of two sites that had undergone a vegetation change from C3 to C4 plants in the past 20–30 years. The importance of much older SOM as a substrate was determined by comparison of the radiocarbon content of PLFA from soils of two sites that had different 14C concentrations of SOM. The 13C shift in PLFA from the two sites that had experienced different vegetation history indicated that 40–90% of the PLFA carbon had been fixed since the vegetation change took place. Thus PLFA were more enriched in 13C from the new C4 vegetation than it was observed for bulk SOM indicating recent plant material as preferentially used substrate for soil microorganisms. The largest 13C shift of PLFA was observed in the soil that had high 14C concentrations of bulk SOM. These results reinforce that organic carbon in this soil for the most part cycles rapidly. The degree to which SOM is incorporated into microbial PLFA was determined by the difference in 14C concentration of PLFA derived from two soils one with high 14C concentrations of bulk SOM and one with low. These results showed that 0–40% of SOM carbon is used as substrate for soil microorganisms. Furthermore a different substrate usage was identified for different microorganisms. Gram-negative bacteria were found to prefer recent plant material as microbial carbon source while Gram-positive bacteria use substantial amounts of SOM carbon. This was indicated by 13C as well as 14C signatures of their PLFA. Our results find evidence to support ‘priming’ in that PLFA indicative of Gram-negative bacteria associated with roots contain both plant- and SOM-derived C. Most interestingly, we find PLFA indicative of archeobacteria (methanothrophs) that may indicate the use of other carbon sources than plant material and SOM to a substantial amount suggesting that inert or slow carbon pools are not essential to explain carbon dynamics in soil.

Determination of Microbial Carbon Sources in Petroleum Contaminated Sediments Using Molecular 14C Analysis

Understanding microbial carbon sources is fundamental to elucidating the role of microbial communities in carbon cycling and in the biodegradation of organic contaminants. Because the majority of anthropogenic contaminants are either directly or indirectly derived from fossil fuels that are devoid of 14C, radiocarbon can be used as a natural inverse tracer of contaminant carbon in the contemporary environment. Here, 14C analysis of individual microbial phospholipid fatty acids (PLFA) was used to characterize the carbon sources utilized bythe active microbial community in salt marsh sediments contaminated by the Florida oil spill of 1969 in Wild Harbor, West Falmouth, MA. A specific goal was to determine whether this community is actively degrading petroleum residues that persist in these sediments. The delta14C values of microbial PLFA in all sediment horizons (contaminated and noncontaminated) matched the delta14C of the total sedimentary organic carbon after petroleum removal, indicating that no measurable metabolism of petroleum residues was occurring. This result agrees with ancillary data such as the delta13C content and distribution of PLFA, and the residual hydrocarbon composition determined by comprehensive two-dimensional gas chromatography (GCxGC) analysis. We hypothesize that microbes have chosen to respire the natural organic matter rather than the residual petroleum hydrocarbons because the former is more labile. Future efforts directed at determining indices of microbial degradation of petroleum hydrocarbons should consider competition with natural organic matter.