Adaptation Of Microbial Communities Research Articles

Elucidating microbial community adaptation to anaerobic co-digestion of fats, oils, and grease and food waste

Despite growing interest in co-digestion and demonstrated process improvements (e.g., enhanced stability and biogas production), few studies have evaluated how co-digestion impacts the anaerobic digestion (AD) microbiome. Three sequential bench-scale respirometry experiments were conducted at thermophilic temperature (50 °C) with various combinations of primary sludge (PS); thickened waste activated sludge (TWAS); fats, oils, and grease (FOG); and food waste (FW). Two additional runs were then performed to evaluate microbial inhibition at higher organic fractions of FOG (30–60% volatile solids loading (VSL; v/v)). Co-digestion of PS, TWAS, FOG, and FW resulted in a 26% increase in methane production relative to digestion of PS and TWAS. A substantial lag time was observed in biogas production for vessels with FOG addition that decreased by more than half in later runs, likely due to adaptation of the microbial community. 30% FOG with 10% FW showed the highest increase in methane production, increasing 53% compared to digestion of PS and TWAS. FOG addition above 50% VSL was found to be inhibitory with and without FW addition and resulted in volatile fatty acid (VFA) accumulation. Methane production was linked with high relative activity and abundance of syntrophic fatty-acid oxidizers alongside hydrogenotrophic methanogens, signaling the importance of interspecies interactions in AD. Specifically, relative activity of Syntrophomonas was significantly correlated with methane production. Further, methane production increased over subsequent runs along with methyl coenzyme M reductase (mcrA) gene expression, a functional gene in methanogens, suggesting temporal adaptation of the microbial community to co-digestion substrate mixtures. The study demonstrated the benefits of co-digestion in terms of performance enhancement and enrichment of key active microbial populations.

Characterisation of bioavailability of Surat Basin Walloon coals for biogenic methane production using environmental microbial consortia

The study sets out to characterise the bioavailability of six Surat Basin Walloon coals from different stratigraphic layers in a single borehole to environmental methanogenic consortia. Factors that control bioavailability have also been investigated on grounds of coal petrographic composition and the organic composition of solvent-extractable matter. Finely crushed coal core samples were inoculated with digested sludge culture from domestic wastewater treatment in serum bottles kept anoxically before incubation at mesophilic temperature over 30days for biomethane production. Degradation of coal compounds was demonstrated via GC–MS characterisation of methanol and dichloromethane (DCM) extracts, in combination with aqueous volatile fatty acids and alcohols and total organic carbon (TOC) analysis on fresh and microbially-digested coal samples. The resulting methane yields ranged from 14 to 33μmol/g, with an average of 21μmol/g (0.515m3/t), comparable to those previously reported for subbituminous coals. Organic solvent-extractable materials that accounted for 3.8 to 12% of coal weight were generally dominated by aliphatic compounds, composed of mainly medium-long-chain n-alkanes, n-alcohols and esters. Aromatics were detected up to three fused rings, and are rich in dibenzofuran, alkyl benzene, diphenyls and alkyl PAH (polymeric aromatic hydrocarbon). The abundance of solvent-extractable matter was found to be positively associated with liptinite content, particularly suberinite, sporinite and liptodetrinite. Preservation of these compounds was thought to rely on vitrinite, such as telinite and collotelinite that are rich in micropores, serving as storage for the hydrocarbons. Environmental factors, such as microbe-carrying groundwater might compromise coal extractability by converting coal hydrocarbons to biogas. Bioavailability of coal was shown to be controlled by three factors: 1) Water solubility - Bioassay eliminated an average 98% of aqueous compounds (based on TOC), which were dominated by volatile fatty acids and alcohols, and to a lesser degree, medium-chain (primarily C10 to C20) n-alcohols, esters and aliphatic amine; 2) Solvent extractability – 34.5% of solvent-extractable compounds were shown to be biodegraded (based on peak intensity in GC–MS), with methanol extracts being more bioavailable than DCM's; 3) Heterogeneous moieties, particularly aliphatic hydroxyl group, ester bond, ether bond and CN bond in aliphatic amine - These functional groups present heteroatoms that can lower the activation energy of nearby bonds, making them vulnerable for microbial cleavage. Compound degradation in bioassays was shown to be clearly associated with methane yield, but only a small proportion degraded was converted to methane. Further improvement may be achieved via proper adaptation of the current microbial community.

Adaptation of microbial community of the anode biofilm in microbial fuel cells to temperature

Temperature as an important ecological factor affects biofilm development and microbial metabolic activity. Here, the performances and microbial communities of microbial fuel cells (MFCs) at different temperature were analyzed. As the temperature decreased, the power output of MFCs declined. A maximum power density of 894.3±48.6mW/m2 was obtained in MFCs operating at 30°C, which was 18.5% and 64.5% higher than that in MFCs at 20°C and 10°C, respectively. Illumina sequencing of 16S rRNA gene amplicons showed that a distinct difference in microbial community structure of the anode biofilms occurred. This resulted in different power outputs of MFCs. Species diversity analyses indicated that species evenness of the anode biofilms shifted beyond species richness at different temperatures. The predominant populations of the anode biofilm shifted from Geobacter and Azonexus (30°C) to Pelobacter (20°C) or Acidovorax, Zoogloea and Simplicispira, (10°C). These results indicate that temperature plays an important role in shaping microbial communities of the anode biofilms in MFCs through changes in species evenness.

The fate of nitrogen is linked to iron(II) availability in a freshwater lake sediment

The fate of nitrogen in natural environments is controlled by anaerobic nitrate-reducing processes by which nitrogen is removed as N2 or retained as NH4+. These processes can potentially be driven by oxidation of reduced inorganic compounds at oxic-anoxic interfaces. Several studies have investigated the use of Fe2+ as an electron donor in nitrate reduction in bacterial cultures, however current information on this process in the environment is sparse. We aimed to determine whether nitrate-reducing processes in the freshwater Lake Almind (Silkeborg, Denmark) were linked to Fe2+ oxidation. Anaerobic sediment slurries were supplemented with 15N-substrates and electron donors (Fe2+ and/or acetate) to characterize nitrate-reducing processes under environmentally relevant substrate concentrations and at higher concentrations traditionally used in microbial enrichment studies.Dissimilatory nitrate reduction to ammonium, DNRA, was stimulated by Fe2+ addition in 7 of 10 slurry experiments and in some cases, denitrification was concomitantly reduced. The determined kinetic parameters (Vmax and Km) for Fe2+-driven DNRA were 4.7µmolNL−1d−1 and 33.8µmolFe2+L−1, respectively and reaction stoichiometry for Fe2+:NH4+ (8.2:1) was consistent with that of predicted stoichiometry (8:1). Conversely, under enrichment conditions, denitrification was greatly increased while DNRA rates remained unchanged. Increased Fe2+ concentrations may be exploited by DNRA organisms and have an inhibitory effect on denitrification, thus Fe2+ may play a role in regulating N transformations in Lake Almind. Furthermore, we suggest enrichment conditions may promote the adaptation or change of microbial communities to optimally utilize the available high substrate concentrations; misrepresenting metabolisms occurring in situ.

Composition and Environmental Adaptation of Microbial Community in Shibahe Copper Tailing in Zhongtiao Mountain in Shanxi

In order to reveal the effects of heavy metal pollution on microbial community compositions and microbial community diversity in tailing area,we conducted an experiment by examining the microbial community in tailing water,sediments and tailing sand in Shibahe copper tailing in Zhongtiao Mountain.Differences in microbial community compositions in different habitats and their relationships with environmental parameters were analyzed.The results showed that the richness and diversity of microbial community were the largest in tailing sand,but the lowest in tailing water.Microbial community compositions were similar between tailing water and sediments.There were significant positive correlations between the relative abundance of the dominant family (Sphingomonadaceae) and contents of heavy metals (Cd,Cu,Mn,Ni,Pb,Zn),while there were significant negative correlations between relative abundances of aulobacteraceae, Methylobacteriaceae, Nocardioidaceae, Microbacteriaceae, Micrococcaceae, Streptococcaceae and Paenibacillaceae and heavy metal contents.It showed that most of the bacteria were inhibited by heavy metals,but Sphingomonadaceae had a higher tolerance to heavy metals which may indicate that it has a potential for remediation of heavy metal contamination.

Metagenomic assembly unravel microbial response to redox fluctuation in acid sulfate soil

Acid sulfate soil (ASS) is sensitive to redox fluctuations induced by climate change and human activities. Oxidation of sulfur and sulfide in ASS leads to the release of acid and consequently metals, posing severe hazards to coastal environment, while microbial contribution and response to oxidation is poorly understood. Here we used metagenomic sequencing to delineate the shift in microbial community structures and functional genes in ASS upon exposure to aerobic conditions. Aerobic incubation resulted in significant shifts in microbial communities in both topsoil and parent material. Archaea decreased significantly in the parent material after aerobic incubation. The relative abundance of sulfur cycling genes in the parent material layer was significantly higher than those in the topsoil, and multiple sulfide oxidation genes increased after aerobic oxidation. Metagenomic assembly enabled construction of eight key draft genomes from ASS. Three of them (GS3, GS6 and GT3) are novel strains of Thermoplasmatales, Acidothermales (Acidothermus) and Acidimicrobiales, respectively. Functional gene annotation of these population genomes revealed a dominance of sulfur cycling genes and acid tolerant genes. These findings highlight the microbial response to environmental change and identify the ecological adaptation and survival strategies of microbial communities in acid sulfate soils.

Density-Mediated Earthworm Effects on Soil Respiration

Earthworms, as ecosystem engineers, strongly regulate microbial activities and microorganism-mediated processes in the soil; their effects differ among species and ecological groups. Lumbricids are suggested to have density-dependent regulation of species populations, but it is not known whether their effects on soil processes are density-dependent. In a field experiment, litter/soil microcosms contained monocultures of five common lumbricid species belonging to epigeic, anecic and endogeic ecological groups, at various density levels. After 6 and 15 weeks, respiration rates of soil systems were measured and (after subtraction of approximately calculated earthworm respiration) microbial respiration rates estimated. In the presence of earthworms, respiration of soil systems tended to increase. After 6 weeks, this increment was explained by earthworm's own respiration. However, after 15 weeks earthworm respiration comprised 12–80% of the respiration increment; hence, microbial respiration was stimulated by earthworm activities. In any earthworm species, total community and microbial respiration were correlated with its density increase. However, specific respiration increments (per unit earthworm biomass) were not significantly affected by lumbricid density. The lack of density-dependent patterns indicates a weak impact of lumbricid intraspecific interactions on soil respiration. However, specific respiration increments and stimulation of microbial respiration varied across earthworm species, being higher for endogeic than for epigeic/anecic species. This is explained by a relatively lower microbial grazing by endogeics and a depletion of litter (a resource and environment for the microbial community) by epigeic/anecic earthworms. Overall, the results support the view that microbial community adapts to the presence of earthworms by switching to a smaller, but a more active one.

Effects of pH variations on anodic marine consortia in a dual chamber microbial fuel cell

The effect of anodic pH on Microbial fuel cells (MFCs) inoculated with marine consortia was investigated to characterize the microbial community adaptation to possible pH environmental changes and to define the pH extreme boundaries beyond which MFCs do not run properly.Tests were conducted in triplicate using different feeding pH values (pHfeed) ranging from 3 to 13. The MFCs inoculated with marine consortia had a strong self-regulation ability and actively counterbalanced small variations in pHfeed maintaining the pH inside the anodic chamber (pHanode) close to neutrality.As soon as the pHanode deviated from neutrality it affected MFCs' performances. Alkaline conditions with pHanode values between 8 and 10 corresponded to the formation of a denser biofilm together with the best performance in terms of maximum power density (Pmax). Conversely, when the pHanode reached values lower than 5.5 or higher than 10, a sharp drop in MFC performances, as well as a decrease of viable population, were observed. Interestingly, the system was able to survive these extreme conditions and restart working effectively when neutrality was reset.The obtained results underline the high adaptability and recovery ability of anodic marine consortia even in extreme conditions, suggesting the employment of this inoculum for MFC applications as biosensors for on-site seawater monitoring or as power supply units to be installed in remote area.

Characterization and Adaptation of Anaerobic Sludge Microbial Communities Exposed to Tetrabromobisphenol A.

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential ecological and human health impacts. TBBPA is microbially transformed under anaerobic conditions to bisphenol A (BPA). However, little is known about which taxa degrade TBBPA and the adaptation of microbial communities exposed to TBBPA. The objectives of this study were to characterize the effect of TBBPA on microbial community structure during the start-up phase of a bench-scale anaerobic sludge reactor, and identify taxa that may be associated with TBBPA degradation. TBBPA degradation was monitored using LC/MS-MS, and the microbial community was characterized using Ion Torrent sequencing and qPCR. TBBPA was nearly completely transformed to BPA via reductive debromination in 55 days. Anaerobic reactor performance was not negatively affected by the presence of TBBPA and the bulk of the microbial community did not experience significant shifts. Several taxa showed a positive response to TBBPA, suggesting they may be associated with TBBPA degradation. Some of these taxa had been previously identified as dehalogenating bacteria including Dehalococcoides, Desulfovibrio, Propionibacterium, and Methylosinus species, but most had not previously been identified as having dehalogenating capacities. This study is the first to provide in-depth information on the microbial dynamics of anaerobic microbial communities exposed to TBBPA.

Diverse gene functions in a soil mobilome

Accessing bacterial mobilomes of any given environment enables the investigation of genetic traits encoded by circular genetic elements, and how their transfer drives the adaptation of microbial communities. Here we take advantage of Illumina HiSeq sequencing and report, for the first time, the soil mobilome sampled from a well-characterized field in Hygum, Denmark. Soil bacterial cells were obtained by Nycodenz extraction, total DNA was purified by removing sheared chromosomal DNA using exonuclease digestion, and the remaining circular DNA was amplified with the phi29 polymerase and finally sequenced. The soil mobilome represented a wide range of known bacterial gene functions and highlighted the enrichment of plasmids, transposable elements and phages when compared to a well-characterized soil metagenome that, on the other hand, was dominated by basic biosynthesis and metabolism functions. Approximately one eighth of the gene set was of plasmid-intrinsic traits, including replication, conjugation, mobilization and stability based on Pfam database analysis. Resistance determinants toward aminoglycosides, beta-lactams and glycopeptides as well as multi-drug functions indicated that a substantial fraction of the soil resistome is plasmid-encoded and potentially mobilizable. Additionally, we recovered more than half of all Pfam-listed plasmid replication protein families, of which the composition of both common and rare replication families was significantly different from a previously reported wastewater and rat cecum mobilome. This comprehensive analysis reveals a distinct plasmid gene pool in the soil environment and suggests the prevalence of specific plasmid groups and plasmid-encoded genetic traits in distinct ecological environments.

Microbial community adaptation influences long-chain fatty acid conversion during anaerobic codigestion of fats, oils, and grease with municipal sludge

Codigesting fats, oils, and greases with municipal wastewater sludge can greatly improve biomethane recovery at wastewater treatment facilities. Process loading rates of fats, oils, and greases have been previously tested with little knowledge of the digester microbial community structure, and high transient fat loadings have led to long chain fatty acid (LCFA) accumulation and digester upsets. This study utilized recently-developed quantitative PCR assays for syntrophic LCFA-degrading bacteria along with 16S amplicon sequencing to relate changes in microbial community structure to LCFA accumulation during transient loading increases to an anaerobic codigester receiving waste restaurant oil and municipal wastewater sludge. The 16S rRNA gene concentration of the syntrophic β-oxidizing genus Syntrophomonas increased to ∼15% of the Bacteria community in the codigester, but stayed below 3% in the control digester that was fed only wastewater sludge. Methanosaeta and Methanospirillum were the dominant methanogenic genera enriched in the codigester, and together comprised over 80% of the Archaea community by the end of the experimental period. Constrained ordination showed that changes in the codigester Bacteria and Archaea community structures were related to measures of digester performance. Notably, the effluent LCFA concentration in the codigester was positively correlated to the specific loading rate of waste oil normalized to the Syntrophomonas 16S rRNA concentration. Specific loading rates of 0–1.5 × 10−12 g VS oil/16S gene copies-day resulted in LCFA concentrations below 30 mg/g TS, whereas LCFA accumulated up to 104 mg/g TS at higher transient loading rates. Based on the community-dependent loading limitations found, enhanced biomethane production from high loadings of fats, oils and greases can be achieved by promoting a higher biomass of slow-growing syntrophic consortia, such as with longer digester solids retention times. This work also demonstrates the potential for controlling the loading rate of fats, oils, and greases based on the analysis of the codigester community structure, such as with quantitative PCR measurements of syntrophic LCFA-degrading bacteria abundance.

Spatial Patterns of bphA Gene Diversity Reveal Local Adaptation of Microbial Communities to PCB and PAH Contaminants.

Biphenyl dioxygenases, encoded by the bphA gene, initiate the oxidation of polychlorinated biphenyls (PCBs) and specify the substrate range of PCB congeners metabolized by bacteria. Increased bphA gene diversity within microbial communities may allow a broader range of PCB congeners to be catabolized, thus resulting in greater PCB degradation. To assess the role of PCBs in modulating bphA gene diversity, 16S ribosomal RNA (rRNA) gene and bphA environmental DNA libraries were generated from bacterial communities in sediments with a steep gradient of PCB contamination. Multiple measures of sequence diversity revealed greater heterogeneity of bphA sequences in polluted compared to unpolluted locations. Codon-based signatures of selection in bphA sequences provided evidence of purifying selection. Unifrac analysis of 16S rRNA sequences revealed independent taxonomic lineages from polluted and unpolluted locations, consistent with the presence of locally adapted bacterial communities. Phylogenetic analysis of bphA sequences indicated that dioxygenases from sediments were closely related to previously characterized dioxygenases that metabolize PCBs and polynuclear aromatic hydrocarbons (PAHs), consistent with high levels of these contaminants within the studied sediments. Structural analyses indicated that the BphA protein of Rhodococcus jostii, capable of metabolizing both PCBs and PAHs, provided a more optimal modeling template for bphA sequences reported in this study than a BphA homologue with more restricted substrate specificity. Results from this study suggest that PCBs and PAHs may drive local adaptation of microbial communities by acting as strong selective agents for biphenyl dioxygenases capable of metabolizing a wide range of congeners.

Adaptation of microbial communities in activated sludge to 1-decyl-3-methylimidazolium bromide.

The effects of 1-decyl-3-methylimidazolium bromide on activated sludge process and microbial composition were investigated. Ionic liquid (IL) was dosed continuously to the laboratory activated sludge system at an influent concentration from 1 to 20 mg l(-1) for about 1 month. As compared to the control test, mean values of degree of chemical oxygen demand removal and degree of biochemical oxygen demand removal were almost remaining constant at a high level, equaling 92.6% and 98.1%, respectively. In addition, no influence of IL on size and shape of flocs was observed. The values of the sludge biotic index indicate that sludge exposed on IL was stable and very well colonized with good biological activity. Increases in Proteobacteria (mainly Variovorax sp., Vogesella sp., Hydrogenophaga sp.), Bacteroidetes (mainly Lewinella sp., Haliscomenobacter sp., Runella sp.) and Nitrospirae were detected in sludge adapted to IL compared to the control system. The results showed that activated sludge can adapt to IL present in wastewater.

Cellular content of biomolecules in sub-seafloor microbial communities

Microbial biomolecules, typically from the cell envelope, can provide crucial information about distribution, activity, and adaptations of sub-seafloor microbial communities. However, when cells die these molecules can be preserved in the sediment on timescales that are likely longer than the lifetime of their microbial sources. Here we provide for the first time measurements of the cellular content of biomolecules in sedimentary microbial cells. We separated intact cells from sediment matrices in samples from surficial, deeply buried, organic-rich, and organic-lean marine sediments by density centrifugation. Amino acids, amino sugars, muramic acid, and intact polar lipids were analyzed in both whole sediment and cell extract, and cell separation was optimized and evaluated in terms of purity, separation efficiency, taxonomic resemblance, and compatibility to high-performance liquid chromatography and mass spectrometry for biomolecule analyses. Because cell extracts from density centrifugation still contained considerable amounts of detrital particles and non-cellular biomolecules, we further purified cells from two samples by fluorescence-activated cell sorting (FACS). Cells from these highly purified cell extracts had an average content of amino acids and lipids of 23–28fgcell−1 and 2.3fgcell−1, respectively, with an estimated carbon content of 19–24fgcell−1. In the sediment, the amount of biomolecules associated with vegetative cells was up to 70-fold lower than the total biomolecule content. We find that the cellular content of biomolecules in the marine subsurface is up to four times lower than previous estimates. Our approach will facilitate and improve the use of biomolecules as proxies for microbial abundance in environmental samples and ultimately provide better global estimates of microbial biomass.

Comparison of microbial taxonomic and functional shift pattern along contamination gradient.

BackgroundThe interaction mechanism between microbial communities and environment is a key issue in microbial ecology. Microbial communities usually change significantly under environmental stress, which has been studied both phylogenetically and functionally, however which method is more effective in assessing the relationship between microbial communities shift and environmental changes still remains controversial.ResultsBy comparing the microbial taxonomic and functional shift pattern along heavy metal contamination gradient, we found that both sedimentary composition and function shifted significantly along contamination gradient. For example, the relative abundance of Geobacter and Fusibacter decreased along contamination gradient (from high to low), while Janthinobacterium and Arthrobacter increased their abundances. Most genes involved in heavy metal resistance (e.g., metc, aoxb and mer) showed higher intensity in sites with higher concentration of heavy metals. Comparing the two shift patterns, there were correlations between them, because functional and phylogenetic β-diversities were significantly correlated, and many heavy metal resistance genes were derived from Geobacter, explaining their high abundance in heavily contaminated sites. However, there was a stronger link between functional composition and environmental drivers, while stochasticity played an important role in formation and succession of phylogenetic composition demonstrated by null model test.ConclusionsOverall our research suggested that the responses of functional traits depended more on environmental changes, while stochasticity played an important role in formation and succession of phylogenetic composition for microbial communities. So profiling microbial functional composition seems more appropriate to study the relationship between microbial communities and environment, as well as explore the adaptation and remediation mechanism of microbial communities to heavy metal contamination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0731-6) contains supplementary material, which is available to authorized users.

Analysis of the metatranscriptome of microbial communities of an alkaline hot sulfur spring revealed different gene encoding pathway enzymes associated with energy metabolism.

Alkaline sulfur hot springs notable for their specialized and complex ecosystem powered by geothermal energy are abundantly rich in different chemotrophic and phototrophic thermophilic microorganisms. Survival and adaptation of these organisms in the extreme environment is specifically related to energy metabolism. To gain a better understanding of survival mechanism of the organisms in these ecosystems, we determined the different gene encoding enzymes associated with anaerobic pathways of energy metabolism by applying the metatranscriptomics approach. The analysis of the microbial population of hot sulfur spring revealed the presence of both aerobic and anaerobic organisms indicating dual mode of lifestyle of the community members. Proteobacteria (28.1%) was the most dominant community. A total of 988 reads were associated with energy metabolism, out of which 33.7% of the reads were assigned to nitrogen, sulfur, and methane metabolism based on KEGG classification. The major lineages of hot spring communities were linked with the anaerobic pathways. Different gene encoding enzymes (hao, nir, nar, cysH, cysI, acs) showed the involvement of microbial members in nitrification, denitrification, dissimilatory sulfate reduction, and methane generation. This study enhances our understanding of important gene encoding enzymes involved in energy metabolism, required for the survival and adaptation of microbial communities in the hot spring.

Metabolic adaptation of microbial communities to ammonium stress in a high solid anaerobic digester with dewatered sludge.

A high solid digester with dewatered sludge was operated for 110 days to ascertain the interactions between bacterial and archaeal communities under ammonium stress, as well as the corresponding changes in bio-degradation mechanisms. The volatile solids reduction (95% confidence intervals in mean) changed from 31.6 ± 0.9% in the stable period (day 40–55) to 21.3 ± 1.5% in the last period (day 71–110) when ammonium concentration was elevated to be within 5,000–6,000 mgN/L. Biogas yield dropped accordingly from 11.9 ± 0.3 to 10.4 ± 0.2 L/d and carbon dioxide increased simultaneously from 35.2% to 44.8%. Anaerobranca better adapted to the ammonium stress, while the initially dominant protein-degrading microbes-Tepidimicrobium and Proteiniborus were suppressed, probably responsible for the increase of protein content in digestate. Meanwhile, Methanosarcina, as the dominant Archaea, was resistant to ammonium stress with the constant relative abundance of more than 92% during the whole operation. Nonmetric Multidimensional Scaling (NMDS) analysis was thus conducted which indicated that the gradually increased TAN dictated the bacterial clusters. The dominant Methanosarcina and the increased carbon dioxide content under ammonium stress suggested that, rather than the commonly acknowledged syntrophic acetate oxidation (SAO) with hydrogenotrophic methanogenesis, only SAO pathway was enhanced during the initial ‘ammonium inhibition’.

Exploring natural vs. synthetic minimal media to boost current generation with electrochemically-active marine bioanodes

One of the greatest challenges in the development of Microbial Electrochemical Technologies (METs) is the achievement of efficient bioanodes, which not only can operate for long term but which can also be effectively and promptly regenerated for the sustained and successive production of electricity out of waste organics contained in aqueous streams. Simple strategies that facilitate the engineering of these systems are then pursued. Sustainable electricity generation was here achieved using electrochemically-active marine biofilms, which reached up to 6.8Am−2 in the best case. These biofilms showed deteriorated current generation after successive transfers in fresh natural media. The electricity-generation functionality of these marine biofilms was recuperated after their relocation into synthetic minimal media (i.e. up to about 3.8Am−2 after a decay down to about 1–2Am−2). Upon this relocation, the overall electrochemical mechanisms were preserved. Fluctuating nutrient stress intensified the effect of minimal media on current generation. The change from natural to minimal media showed an important impact on the selection and adaptation of microbial communities, characterized by CE-SSCP profiles; yet, robust bioanodes in which some microbial species were preserved were obtained in synthetic minimal media, these being sufficient for a reproducible electrochemical functionality. The systematic cycling between natural media and minimal media, regarded as periodic stress conditioning, is therefore proposed as a convenient strategy to boost current generation in robust electrochemically-active marine bioanodes.

Influence of Oxygen and Nitrate on Fe (Hydr)oxide Mineral Transformation and Soil Microbial Communities during Redox Cycling.

Oscillations between reducing and oxidizing conditions are observed at the interface of anaerobic/oxic and anaerobic/anoxic environments, and are often stimulated by an alternating flux of electron donors (e.g., organic carbon) and electron acceptors (e.g., O2 and NO3(-)). In iron (Fe) rich soils and sediments, these oscillations may stimulate the growth of both Fe-reducing bacteria (FeRB) and Fe-oxidizing bacteria (FeOB), and their metabolism may induce cycling between Fe(II) and Fe(III), promoting the transformation of Fe (hydr)oxide minerals. Here, we examine the mineralogical evolution of lepidocrocite and ferrihydrite, and the adaptation of a natural microbial community to alternating Fe-reducing (anaerobic with addition of glucose) and Fe-oxidizing (with addition of nitrate or air) conditions. The growth of FeRB (e.g., Geobacter) is stimulated under anaerobic conditions in the presence of glucose. However, the abundance of these organisms depends on the availability of Fe(III) (hydr)oxides. Redox cycling with nitrate results in decreased Fe(II) oxidation thereby decreasing the availability of Fe(III) for FeRB. Additionally, magnetite is detected as the main product of both lepidocrocite and ferrihydrite reduction. In contrast, introduction of air results in increased Fe(II) oxidation, increasing the availability of Fe(III) and the abundance of Geobacter. In the lepidocrocite reactors, Fe(II) oxidation by dissolved O2 promotes the formation of ferrihydrite and lepidocrocite, whereas in the ferrihydrite reactors we observe a decrease in magnetite stoichiometry (e.g., oxidation). Understanding Fe (hydr)oxide transformation under environmentally relevant redox cycling conditions provides insight into nutrient availability and transport, contaminant mobility, and microbial metabolism in soils and sediments.

Variability of Microbial Biomass in Paleosols of Different-Age Burial Mounds of the Lower Volga Region in Relation to the Dynamics of Climate Humidity

The microbial biomass variability in buried chestnut and light chestnut soils of different ages under burial mounds and their modern background analogs in the Volga and Ergeni uplands were studied. It was shown that almost all microorganisms in chestnut paleosols of the Bronze Age are in the dormant state and provide no respiratory response to the addition of glucose. In the paleosol buried in the most arid period, an increase in the total microbial biomass and the abundance of colony-forming units was revealed. The maxi-mum values of active microbial biomass upon the minimum number of cells were found in soils buried in rel-atively humid periods. The increase in the total microbial biomass and the proportion of microbial cell carbon in the organic carbon of soils buried in extremely dry seasons at the turn of the III–II millennium BC may indicate the adaptation of microbial communities to unfavorable environmental conditions.