Petrobacter succinatimandens gen. nov., sp. nov., a moderately thermophilic, nitrate-reducing bacterium isolated from an Australian oil well

Deciphering the core bacterial community structure and function and their response to environmental factors in activated sludge from pharmaceutical wastewater treatment plants

Pharmaceutical wastewater is recognized for its heightened concentrations of organic pollutants, and biological treatment stands out as an effective technology to remove these organic pollution. Therefore, a comprehensive exploration of core bacterial community compositions, functions, and their responses to environmental factors in pharmaceutical wastewater treatment plants (PWWTPs) is important for understanding the removal mechanism of these organic pollutants. This study comprehensively investigated 36 activated sludge (AS) samples from 15 PWWTPs in China. The results revealed that Proteobacteria (45.41%) was the dominant phylum in AS samples, followed by Bacteroidetes (19.54%) and Chloroflexi (4.13%). While the dominant genera were similar in both aerobic and anaerobic treatment processes, their relative abundances exhibited significant variations. Genera like HA73, Kosmotoga, and Desulfovibrio were more abundant during anaerobic treatment, while Rhodoplanes, Bdellovibrio, and Hyphomicrobium dominated during aerobic treatment. 13 and 10 core operational taxonomic units (OTUs) were identified in aerobic and anaerobic sludge, respectively. Further analysis revealed that core OTUs belonging to genera Kosmotoga, Desulfovibrio, Thauera, Hyphomicrobium, and Chelativorans, were associated with key functions, including sulfur metabolism, methane metabolism, amino acid metabolism, carbohydrate metabolism, toluene degradation, and nitrogen metabolism. Furthermore, this study highlighted the crucial roles of environmental factors, such as COD, NH4+-N, SO42-, and TP, in shaping both the structure and core functions of bacterial communities within AS of PWWTPs. Notably, these factors indirectly affect functional attributes by modulating the bacterial community composition and structure in pharmaceutical wastewater. These findings provide valuable insights for optimizing the efficiency of biochemical treatment processes in PWWTPs.

The discrepant metabolic pathways of PAHs by facultative anaerobic bacteria under aerobic and nitrate-reducing conditions

Studies regarding the facultative anaerobic biodegradation of polycyclic aromatic hydrocarbons (PAHs) were still in the initial stage. In this study, a facultative anaerobe which was identified as Bacillus Firmus and named as PheN7 was firstly isolated from the mixed petroleum-polluted soil samples using phenanthrene and nitrate as the solo carbon resource and electron acceptor under anaerobic condition. The degradation rates of PheN7 towards phenanthrene were detected as 33.17 μM/d, 13.81 μM/d and 7.11 μM/d at the initial phenanthrene concentration of 250.17 μM with oxygen, nitrate and sulfate as the electron acceptor, respectively. The metabolic pathways toward phenanthrene by PheN7 were deduced combining the metagenome analysis of PheN7 and intermediate metabolites of phenanthrene under aerobic and nitrate-reducing conditions. Dioxygenation and carboxylation were inferred as the initial activation reactions of phenanthrene degradation in these two pathways. This study highlighted the significance of facultative anaerobic bacteria in natural PAHs biodegradation, revealing the discrepant metabolic fates of PAHs by one solo bacteria under aerobic and anaerobic environments.

Thermophilic microorganisms involved in the nitrogen cycle in thermal environments: Advances and prospects

Thermophilic microorganisms mediated significant element cycles and material conversion in the early Earth as well as mediating current thermal environments. Over the past few years, versatile microbial communities that drive the nitrogen cycle have been identified in thermal environments. Understanding the microbial-mediated nitrogen cycling processes in these thermal environments has important implications for the cultivation and application of thermal environment microorganisms as well as for exploring the global nitrogen cycle. This work provides a comprehensive review of different thermophilic nitrogen-cycling microorganisms and processes, which are described in detail according to several categories, including nitrogen fixation, nitrification, denitrification, anaerobic ammonium oxidation, and dissimilatory nitrate reduction to ammonium. In particular, we assess the environmental significance and potential applications of thermophilic nitrogen-cycling microorganisms, and highlight knowledge gaps and future research opportunities.

Correlating bacterial and archaeal community with efficiency of a coking wastewater treatment plant employing anaerobic-anoxic-oxic process in coal industry

Coking wastewater (CWW) contains various complex pollutants, and biological treatment processes are frequently applied in the coking wastewater treatment plants (CWWTPs). The present work is to evaluate the contaminants removal of a full-scale CWWTP with an anaerobic-anoxic-oxic process (A/A/O), to reveal function of bacterial and archaeal community involved in different bioreactors, and to clarify the relationship between the performance and microbial community. Illumina Miseq sequencing of bacteria showed that β-proteobacteria dominated in three bioreactors with relative abundance of 60.2%~81.7%. 75.2% of sequences were assigned to Petrobacter in the bioreactor A1, while Thiobacillus dominated in A2 and O with relative abundance of 31.8% and 38.7%, respectively. Illumina Miseq sequencing of archaea revealed a high diversity of methanogens existed in A1 and A2 activated sludge. Moreover, Halostagnicola was the dominant archaea in A1 and A2 activated sludge with relative abundance of 41.8% and 66.5%, respectively. Function predicted analysis explored that function of bacteria was similar to that of archaea but the relative abundance differed from each other. A putative biodegradation model of CWW treatment in A/A/O process indicated that A1 and A2 activated sludge mainly reduced carbohydrate, protein, TN, phenol and cyanide, as well as methane production. Bacteria in the bioreactor O were responsible for aerobic biotransformation of residual carbohydrates, refractory organics and nitrification. The redundancy analysis (RDA) further revealed that removal of COD, TN, and NO₃^--N, phenol and cyanides were highly correlated with some anaerobic bacteria and archaea, whereas the transformation of NH₄⁺-N was positively correlated with some aerobic bacteria.

Bacterial and archaeal diversity in oil fields and reservoirs and their potential role in hydrocarbon recovery and bioprospecting

Hydrocarbon is a primary source of energy in the current urbanized society. Considering the increasing demand, worldwide oil productions are declining due to maturity of oil fields and because of difficulty in discovering new oil fields to substitute the exploited ones. To meet current and future energy demands, further exploitation of oil resources is highly required. Microorganisms inhabiting in these areas exhibit highly diverse catabolic activities to degrade, transform, or accumulate various hydrocarbons. Enrichment of hydrocarbon-utilizing bacteria in oil basin is caused by continuous long duration and low molecular weight hydrocarbon microseepage which plays a very important role as an indicator for petroleum prospecting. The important microbial metabolic processes in most of the oil reservoir are sulfate reduction, fermentation, acetogenesis, methanogenesis, NO3- reduction, and Fe (III) and Mn (IV) reduction. The microorganisms residing in these sites have critical control on petroleum composition, recovery, and production methods. Physical characteristics of heavy oil are altered by microbial biotransformation and biosurfactant production. Considering oil to be one of the most vital energy resources, it is important to have a comprehensive understanding of petroleum microbiology. This manuscript reviews the recent research work referring to the diversity of bacteria in oil field and reservoir sites and their applications for enhancing oil transformation in the target reservoir and geomicrobial prospecting scope for petroleum exploration.

Identity and hydrocarbon degradation activity of enriched microorganisms from natural oil and asphalt seeps in the Kurdistan Region of Iraq (KRI)

A previous cultivation-independent investigation of the microbial community structure of natural oil and asphalt seeps in the Kurdistan Region of Iraq (KRI) revealed the dominance of uncultured bacterial taxa belonging to the phyla Deferribacterota and Coprothermobacterota and the orders Thermodesulfobacteriales, Thermales, and Burkholderiales. Here we report on a cultivation-dependent approach to identify members of these groups involved in hydrocarbon degradation in the KRI oil and asphalt seeps. For this purpose, we set up anoxic crude oil-degrading enrichment cultures based on cultivation media known to support the growth of members of the above-mentioned taxonomic groups. During 100-200 days incubation periods, nitrate-reducing and fermentative enrichments showed up to 90% degradation of C₈-C₁₇ alkanes and up to 28% degradation of C₁₈-C₃₃ alkanes along with aromatic hydrocarbons. Community profiling of the enrichment cultures showed that they were dominated by diverse bacterial taxa, which were rare in situ community members in the investigated seeps. Groups initially targeted by our approach were not enriched, possibly because their members are slow-growing and involved in the degradation of recalcitrant hydrocarbons. Nevertheless, the enriched taxa were taxonomically related to phylotypes recovered from hydrocarbon-impacted environments as well as to characterized bacterial isolates not previously known to be involved in hydrocarbon degradation. Marker genes (assA and bssA), diagnostic for fumarate addition-based anaerobic hydrocarbon degradation, were not detectable in the enrichment cultures by PCR. We conclude that hydrocarbon biodegradation in our enrichments occurred via unknown pathways and synergistic interactions among the enriched taxa. We suggest, that although not representing abundant populations in situ, studies of the cultured close relatives of these taxa will reveal an unrecognized potential for anaerobic hydrocarbon degradation, possibly involving poorly characterized mechanisms.

Modulation of trypanosome establishment in Glossina palpalis palpalis by its microbiome in the Campo sleeping sickness focus, Cameroon

The purpose of this study was to investigate factors involved in vector competence by analyzing whether the diversity and relative abundance of the different bacterial genera inhabiting the fly's gut could be associated with its trypanosome infection status. This was investigated on 160 randomly selected G. p. palpalis flies - 80 trypanosome-infected, 80 uninfected - collected in 5 villages of the Campo trypanosomiasis focus in South Cameroon. Trypanosome species were identified using specific primers, and the V4 region of the 16S rRNA gene of bacteria was targeted for metabarcoding analysis in order to identify the bacteria and determine microbiome composition. A total of 261 bacterial genera were identified of which only 114 crossed two barriers: a threshold of 0.01% relative abundance and the presence at least in 5 flies. The secondary symbiont Sodalis glossinidius was identified in 50% of the flies but it was not considered since its relative abundance was much lower than the 0.01% relative abundance threshold. The primary symbiont Wigglesworthia displayed 87% relative abundance, the remaining 13% were prominently constituted by the genera Spiroplasma, Tediphilus, Acinetobacter and Pseudomonas. Despite a large diversity in bacterial genera and in their abundance observed in micobiome composition, the statistical analyzes of the 160 tsetse flies showed an association with flies' infection status and the sampling sites. Furthermore, tsetse flies harboring Trypanosoma congolense Savanah type displayed a different composition of bacterial flora compared to uninfected flies. In addition, our study revealed that 36 bacterial genera were present only in uninfected flies, which could therefore suggest a possible involvement in flies' refractoriness; with the exception of Cupriavidus, they were however of low relative abundance. Some genera, including Acinetobacter, Cutibacterium, Pseudomonas and Tepidiphilus, although present both in infected and uninfected flies, were found to be associated with uninfected status of tsetse flies. Hence their effective role deserves to be further evaluated in order to determine whether some of them could become targets for tsetse control of fly vector competence and consequently for the control of the disease. Finally, when comparing the bacterial genera identified in tsetse flies collected during 4 epidemiological surveys, 39 genera were found to be common to flies from at least 2 sampling campaigns.

Repetitive Sampling and Control Threshold Improve 16S rRNA Gene Sequencing Results From Produced Waters Associated With Hydraulically Fractured Shale

Sequencing microbial DNA from deep subsurface environments is complicated by a number of issues ranging from contamination to non-reproducible results. Many samples obtained from these environments - which are of great interest due to the potential to stimulate microbial methane generation - contain low biomass. Therefore, samples from these environments are difficult to study as sequencing results can be easily impacted by contamination. In this case, the low amount of sample biomass may be effectively swamped by the contaminating DNA and generate misleading results. Additionally, performing field work in these environments can be difficult, as researchers generally have limited access to and time on site. Therefore, optimizing a sampling plan to produce the best results while collecting the greatest number of samples over a short period of time is ideal. This study aimed to recommend an adequate sampling plan for field researchers obtaining microbial biomass for 16S rRNA gene sequencing, applicable specifically to low biomass oil and gas-producing environments. Forty-nine different samples were collected by filtering specific volumes of produced water from a hydraulically fractured well producing from the Niobrara Shale. Water was collected in two different sampling events 24 h apart. Four to five samples were collected from 11 specific volumes. These samples along with eight different blanks were submitted for analysis. DNA was extracted from each sample, and quantitative polymerase chain reaction (qPCR) and 16S rRNA Illumina MiSeq gene sequencing were performed to determine relative concentrations of biomass and microbial community composition, respectively. The qPCR results varied across sampled volumes, while no discernible trend correlated contamination to volume of water filtered. This suggests that collecting a larger volume of sample may not result in larger biomass concentrations or better representation of a sampled environment. Researchers could prioritize collecting many low volume samples over few high-volume samples. Our results suggest that there also may be variability in the concentration of microbial communities present in produced waters over short (i.e., hours) time scales, which warrants further investigation. Submission of multiple blanks is also vital to determining how contamination or low biomass effects may influence a sample set collected from an unknown environment.

Tepidiphilus olei sp. nov., isolated from the production water of a water-flooded oil reservoir in PR China

A novel, moderately thermophilic, Gram-stain-negative bacterium, designated strain J18T, was isolated from a water-flooded oil reservoir. Cells were aerobic, oxidase- and catalase-positive, with a polar flagellum. Growth occurred at 35–60 °C and at pH 6–8.5. The respiratory quinones were ubiquinone 8 and ubiquinone 9. The dominant cellular fatty acids were C16 : 0, C17 : 0 cyclo, C19 : 0 cyclo ω8c and summed feature 8 (C18 : 1  ω7c/C18 : 1  ω6c). The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, an unidentified aminolipid, an unidentified phospholipid and an unidentified aminophospholipid. The strain showed the highest 16S rRNA gene sequence similarities to Tepidiphilus margaritifer DSM 15129T (98.6 %), Tepidiphilus succinatimandens DSM 15512T (98.4 %) and Tepidiphilus thermophilus DSM 27220T (98.1 %), respectively, and the similarity to other species was lower than 93 %. In the phylogenetic trees, it constituted a unique sub-cluster within the genus Tepidiphilus . The DNA G+C content of strain J18T was 64.44 mol%. As compared with the type strains, the genome-to-genome distances of strain J18T were 34.7–40 %. These results confirmed the separate species status of J18T with its close relatives. On the basis of physiological, chemotaxonomic and phylogenetic analyses along with the low levels of identity at the whole-genome level, it can be concluded that strain J18T represents a new species of the genus Tepidiphilus , for which the name Tepidiphilus olei sp. nov. is proposed. The type strain of T. olei is J18T (=CGMCC 1.16800T=LMG 31400T).

Tepidiphilus baoligensis sp. nov., a Novel Bacterium of the Family Hydrogenophilaceae Isolated from an Oil Reservoir

A Gram-negative, aerobic, motile, non-spore-forming and rod-shaped bacterium, designated strain B18-69 ^T, was isolated from oil-well production liquid in Baolige oilfield, China. The strain was able to grow at pH 6-9.5 (optimum at pH 7), in 0-4% (w/v) NaCl (optimum at 0.5-1%, w/v) and at 35-60 °C (optimum at 55 °C). Major cellular fatty acids were C_16:0, C_19:0 cyclo ω8c, C_17:0 cyclo and C_18:1 ω7c. The predominant respiratory quinone was ubiquinone 8. Major polar lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG) and phosphatidylcholine (PC). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain B18-69 ^T was most closely related to Tepidiphilus margaritifer DSM 15129 ^T (98.8% similarity). The draft genome of strain B18-69 ^T was composed of 2,250,419 bp, and the G+C content was 64.6 mol%. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain B18-69 ^T and T. margaritifer DSM 15129 ^T were 90.9% and 68.9%, respectively. Genotypic and phenotypic features indicate that strain B18-69 ^T represents a novel species of the genus Tepidiphilus, for which the name Tepidiphilus baoligensis sp. nov. is proposed. The type strain is B18-69 ^T (= CGMCC 1.13573 ^T = KCTC 62782 ^T).

Pelomicrobium methylotrophicum gen. nov., sp. nov. a moderately thermophilic, facultatively anaerobic, lithoautotrophic and methylotrophic bacterium isolated from a terrestrial mud volcano

A novel moderately thermophilic, bacterium, strain SM250^T, was isolated from a terrestrial mud volcano, Taman peninsula, Krasnodar region, Russia. Cells of strain SM250^T were Gram-negative non-spore forming motile straight rods. Growth was observed at temperatures 30-63 °C (optimum at 50 °C), pH 6.5-10.0 (optimum at pH 8.5) and NaCl concentrations 0-4.5% (w/v) (optimum at 1.0-1.5% (w/v)). The novel isolate grows by aerobic respiration or anaerobic respiration with nitrate as the terminal electron acceptor. Strain SM250^T grows by the utilization of methanol, formate and a number of other organic compounds or lithoautotrophically with hydrogen, elemental sulfur or thiosulfate as electron donors. The total size of the genome of the novel isolate was 3,327,116 bp and a genomic DNA G + C content was 64.8 mol%. Analysis of the 16S rRNA gene sequences revealed that strain SM250^T belongs to the class Hydrogenophilia within the phylum Proteobacteria, with less than 91% of 16S rRNA gene sequence similarity to any species with validly published name. We propose to assign strain SM250^T to a new species of a novel genus Pelomicrobium methylotrophicum gen. nov., sp. nov. The type strain is SM250^T (= KCTC 62861^T = VKM B-3274^T).

Impacts of Arsenic and Antimony Co-Contamination on Sedimentary Microbial Communities in Rivers with Different Pollution Gradients

Arsenic (As) and antimony (Sb) are both toxic metalloids that are of primary concern for human health. Mining activity has introduced elevated levels of arsenic and antimony into the rivers and has increased the risks of drinking water contamination in China. Due to their mobility, the majority of the metalloids originating from mining activities are deposited in the river sediments. Thus, depending on various geochemical conditions, sediment could either be a sink or source for As and Sb in the water column. Microbes are key mediators for biogeochemical transformation and can both mobilize or precipitate As and Sb. To further understand the microbial community responses to As and Sb contamination, sediment samples with different contamination levels were collected from three rivers. The result of the study suggested that the major portions of As and Sb were in strong association with the sediment matrix and considered nonbioavailable. These fractions, however, were also suggested to have profound influences on the microbial community composition. As and Sb contamination caused strong reductions in microbial diversity in the heavily contaminated river sediments. Microorganisms were more sensitive to As comparing to Sb, as revealed by the co-occurrence network and random forest predictions. Operational taxonomic units (OTUs) that were potentially involved in As and Sb metabolism, such as Anaerolinea, Sphingomonas, and Opitutus, were enriched in the heavily contaminated samples. In contrast, many keystone taxa, including members of the Hyphomicrobiaceae and Bradyrhizobiaceae families, were inhibited by metalloid contamination, which could further impair crucial environmental services provided by these members.

Characterizing the microbiome in petroleum reservoir flooded by different water sources

Petroleum reservoir is an unusual subsurface biosphere, where indigenous microbes lived and evolved for million years. However, continual water injection changed the situation by introduction of new electron acceptors, donors and exogenous microbes. In this study, 16S-rRNA gene sequencing, comparative metagenomics and genomic bins reconstruction were employed to investigate the microbial community and metabolic potential in three typical water-flooded blocks of the Shen84 oil reservoir in Liaohe oil field, China. The results showed significant difference of microbial community compositions and metabolic characteristics existed between the injected water and the produced water/oil mixtures; however, there was considerable uniformity between the produced samples in different blocks. Microbial communities in the produced fluids were dominated by exogenous facultative microbes such as Pseudomonas and Thauera members from Proteobacteria phylum. Metabolic potentials for O₂-dependent hydrocarbon degradation, dissimilarly nitrate reduction, and thiosulfate‑sulfur oxidation were much more abundant, whereas genes involved in dissimilatory sulfate reduction, anaerobic hydrocarbon degradation and methanogenesis were less abundant in the oil reservoir. Statistical analysis indicated the water composition had an obvious influence on microbial community composition and metabolic potential. The water-flooding process accompanied with introduction of nitrate or nitrite, and dissolved oxygen promoted the alteration of microbiome in oil reservoir from slow-growing anaerobic indigenous microbes (such as Thermotoga, Clostridia, and Syntrophobacter) to fast-growing opportunists as Beta- and Gama- Proteobacteria. The findings of this study shed light on the microbial ecology change in water flooded petroleum reservoir.

Comprehensive insights into the key components of bacterial assemblages in pharmaceutical wastewater treatment plants

Due to complexity and variety of pharmaceutical wastewater composition, little is known as for functionally important microflora of pharmaceutical wastewater treatment plants (pWWTPs). We compared bacterial composition and diversity of pWWTPs (27 sludge samples collected from 12 full-scale pWWTPs) with those of other industrial (iWWTPs) (27 samples) and municipal wastewater treatment plants (mWWTPs) (27 samples) through meta-analysis based on 16S rRNA gene amplicon sequencing, and identified putatively important organisms and their ecological correlations. Non-metric multidimensional scaling indicated that the pWWTPs, iWWTPs and mWWTPs showed distinctive differences in bacterial community composition (P < 1e-04), and the pWWTPs had significantly lower bacterial diversity than the mWWTPs (P < 1e-06). Thermotogae and Synergistetes phyla only strictly dominated in the pWWTPs, and 26, 30 and 6 specific genera were identified in the pWWTPs, mWWTPs and iWWTPs, respectively. Totally, 15 and 1300 OTUs were identified as core and occasional groups, representing 23.2% and 66.2% of the total read abundance of the pWWTPs, respectively. Permutational multivariate analysis of variance revealed that the bacterial components were clearly clustered corresponding to the types of pharmaceutical wastewater, and a total of 129 local specific OTUs were identified in the pWWTPs, among which anticancer antibiotics pWWTPs had the highest number of specific OTUs (40 ones). Co-occurrence network revealed that the species dominating in the same type of pWWTPs tended to co-occur much more frequently than theoretical random expectation. The results may extend our knowledge regarding the ecological status and correlation of the key microflora in pWWTPs.

Household air pollution and the lung microbiome of healthy adults in Malawi: a cross-sectional study

BACKGROUND

Domestic combustion of biomass fuels, such as wood, charcoal, crop residue and dung causes Household Air Pollution (HAP). These inhaled particulates affect more than half of the world's population, causing respiratory problems such as infection and inflammatory lung disease. We examined whether the presence of black carbon in alveolar macrophages was associated with alterations in the lung microbiome in a Malawi population.

METHODS

Bronchoalveolar lavage samples from 44 healthy adults were sequenced using 16S rDNA amplification to assess microbial diversity, richness and relative taxa abundance. Individuals were classified as high or low particulate exposure as determined by questionnaire and the percentage of black carbon within their alveolar macrophages.

RESULTS

Subjects in the low and high particulate groups did not differ in terms of source of fuels used for cooking or lighting. There was no difference in alpha or beta diversity by particulate group. Neisseria and Streptococcus were significantly more abundant in samples from high particulate exposed individuals, and Tropheryma was found less abundant. Petrobacter abundance was higher in people using biomass fuel for household cooking and lighting, compared with exclusive use of electricity.

CONCLUSIONS

Healthy adults in Malawi exposed to higher levels of particulates have higher abundances of potentially pathogenic bacteria (Streptococcus, Neisseria) within their lung microbiome. Domestic biomass fuel use was associated with an uncommon environmental bacterium (Petrobacter) associated with oil-rich niches.

Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs

Nitrate reduction to nitrite in oil fields appears to be more thermophilic than the subsequent reduction of nitrite. Concentrated microbial consortia from oil fields reduced both nitrate and nitrite at 40 and 45°C but only nitrate at and above 50°C. The abundance of the nirS gene correlated with mesophilic nitrite reduction activity. Thauera and Pseudomonas were the dominant mesophilic nitrate-reducing bacteria (mNRB), whereas Petrobacter and Geobacillus were the dominant thermophilic NRB (tNRB) in these consortia. The mNRB Thauera sp. strain TK001, isolated in this study, reduced nitrate and nitrite at 40 and 45°C but not at 50°C, whereas the tNRB Petrobacter sp. strain TK002 and Geobacillus sp. strain TK003 reduced nitrate to nitrite but did not reduce nitrite further from 50 to 70°C. Testing of 12 deposited pure cultures of tNRB with 4 electron donors indicated reduction of nitrate in 40 of 48 and reduction of nitrite in only 9 of 48 incubations. Nitrate is injected into high-temperature oil fields to prevent sulfide formation (souring) by sulfate-reducing bacteria (SRB), which are strongly inhibited by nitrite. Injection of cold seawater to produce oil creates mesothermic zones. Our results suggest that preventing the temperature of these zones from dropping below 50°C will limit the reduction of nitrite, allowing more effective souring control.

IMPORTANCE

Nitrite can accumulate at temperatures of 50 to 70°C, because nitrate reduction extends to higher temperatures than the subsequent reduction of nitrite. This is important for understanding the fundamentals of thermophilicity and for the control of souring in oil fields catalyzed by SRB, which are strongly inhibited by nitrite.

Microbial Methane Production Associated with Carbon Steel Corrosion in a Nigerian Oil Field

Microbially influenced corrosion (MIC) in oil field pipeline systems can be attributed to many different types of hydrogenotrophic microorganisms including sulfate reducers, methanogens and acetogens. Samples from a low temperature oil reservoir in Nigeria were analyzed using DNA pyrotag sequencing. The microbial community compositions of these samples revealed an abundance of anaerobic methanogenic archaea. Activity of methanogens was demonstrated by incubating samples anaerobically in a basal salts medium, in the presence of carbon steel and carbon dioxide. Methane formation was measured in all enrichments and correlated with metal weight loss. Methanogens were prominently represented in pipeline solids samples, scraped from the inside of a pipeline, comprising over 85% of all pyrosequencing reads. Methane production was only witnessed when carbon steel beads were added to these pipeline solids samples, indicating that no methane was formed as a result of degradation of the oil organics present in these samples. These results were compared to those obtained for samples taken from a low temperature oil field in Canada, which had been incubated with oil, either in the presence or in the absence of carbon steel. Again, methanogens present in these samples catalyzed methane production only when carbon steel was present. Moreover, acetate production was also found in these enrichments only in the presence of carbon steel. From these studies it appears that carbon steel, not oil organics, was the predominant electron donor for acetate production and methane formation in these low temperature oil fields, indicating that the methanogens and acetogens found may contribute significantly to MIC.

Inhibition of bacterial growth in sweet cheese whey by carbon dioxide as determined by culture-independent community profiling

Whey is a valuable co-product from cheese making that serves as a raw material for a wide range of products. Its rich nutritional content lends itself to rapid spoilage, thus it typically needs to be pasteurised and refrigerated promptly. Despite the extensive literature on milk spoilage bacteria, little is known about the spoilage bacteria of whey. The utility of carbon dioxide (CO2) to extend the shelf-life of raw milk and cottage cheese has been well established, but its application in whey preservation has not yet been explored. This study aims to characterise the microbial populations of fresh and spoiled sweet whey by culture-independent community profiling using 454 pyrosequencing of 16S rRNA gene amplicons and to determine whether carbonation is effective in inhibiting bacterial growth in sweet whey. The microbiota of raw Cheddar and Mozzarella whey was dominated by cheese starter bacteria. After pasteurisation, two out of the three samples studied became dominated by diverse environmental bacteria from various phyla, with Proteobacteria being the most dominant. Diverse microbial profiles were maintained until spoilage occurred, when the entire population was dominated by just one or two genera. Whey spoilage bacteria were found to be similar to those of milk. Pasteurised Cheddar and Mozzarella whey was spoiled by Bacillus sp. or Pseudomonas sp., and raw Mozzarella whey was spoiled by Pseudomonas sp., Serratia sp., and other members of the Enterobacteriaceae family. CO2 was effective in inhibiting bacterial growth of pasteurised Cheddar and Mozzarella whey stored at 15°C and raw Mozzarella whey stored at 4°C. The spoilage bacteria of the carbonated samples were similar to those of the non-carbonated controls.

Rapid establishment of thermophilic anaerobic microbial community during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester

The purpose of this study was to explore how fast the thermophilic anaerobic microbial community could be established during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester. Stable thermophilic anaerobic digestion was achieved within 20 days from a mesophilic digester treating sewage sludge by adopting the one-step startup strategy. The succession of archaeal and bacterial populations over a period of 60 days after the temperature increment was followed by using 454-pyrosequencing and quantitative PCR. After the increase of temperature, thermophilic methanogenic community was established within 11 days, which was characterized by the fast colonization of Methanosarcina thermophila and two hydrogenotrophic methanogens (Methanothermobacter spp. and Methanoculleus spp.). At the same time, the bacterial community was dominated by Fervidobacterium, whose relative abundance rapidly increased from 0 to 28.52 % in 18 days, followed by other potential thermophilic genera, such as Clostridium, Coprothermobacter, Anaerobaculum and EM3. The above result demonstrated that the one-step startup strategy could allow the rapid establishment of the thermophilic anaerobic microbial community.

Microbial redox processes in deep subsurface environments and the potential application of (per)chlorate in oil reservoirs

The ability of microorganisms to thrive under oxygen-free conditions in subsurface environments relies on the enzymatic reduction of oxidized elements, such as sulfate, ferric iron, or CO₂, coupled to the oxidation of inorganic or organic compounds. A broad phylogenetic and functional diversity of microorganisms from subsurface environments has been described using isolation-based and advanced molecular ecological techniques. The physiological groups reviewed here comprise iron-, manganese-, and nitrate-reducing microorganisms. In the context of recent findings also the potential of chlorate and perchlorate [jointly termed (per)chlorate] reduction in oil reservoirs will be discussed. Special attention is given to elevated temperatures that are predominant in the deep subsurface. Microbial reduction of (per)chlorate is a thermodynamically favorable redox process, also at high temperature. However, knowledge about (per)chlorate reduction at elevated temperatures is still scarce and restricted to members of the Firmicutes and the archaeon Archaeoglobus fulgidus. By analyzing the diversity and phylogenetic distribution of functional genes in (meta)genome databases and combining this knowledge with extrapolations to earlier-made physiological observations we speculate on the potential of (per)chlorate reduction in the subsurface and more precisely oil fields. In addition, the application of (per)chlorate for bioremediation, souring control, and microbial enhanced oil recovery are addressed.

Comparison of microbial communities involved in souring and corrosion in offshore and onshore oil production facilities in Nigeria

Samples were obtained from the Obigbo field, located onshore in the Niger delta, Nigeria, from which oil is produced by injection of low-sulfate groundwater, as well as from the offshore Bonga field from which oil is produced by injection of high-sulfate (2,200 ppm) seawater, amended with 45 ppm of calcium nitrate to limit reservoir souring. Despite low concentrations of sulfate (0–7 ppm) and nitrate (0 ppm), sulfate-reducing bacteria (SRB) and heterotrophic nitrate-reducing bacteria (NRB) were present in samples from the Obigbo field. Biologically active deposits (BADs), scraped from corrosion-failed sections of a water- and of an oil-transporting pipeline (both Obigbo), had high counts of SRB and high sulfate and ferrous iron concentrations. Analysis of microbial community composition by pyrosequencing indicated anaerobic, methanogenic hydrocarbon degradation to be a dominant process in all samples from the Obigbo field, including the BADs. Samples from the Bonga field also had significant activity of SRB, as well as of heterotrophic and of sulfide-oxidizing NRB. Microbial community analysis indicated high proportions of potentially thermophilic NRB and near-absence of microbes active in methanogenic hydrocarbon degradation. Anaerobic incubation of Bonga samples with steel coupons gave moderate general corrosion rates of 0.045–0.049 mm/year, whereas near-zero general corrosion rates (0.001–0.002 mm/year) were observed with Obigbo water samples. Hence, methanogens may contribute to corrosion at Obigbo, but the low general corrosion rates cannot explain the reasons for pipeline failures in the Niger delta. A focus of future work should be on understanding the role of BADs in enhancing under-deposit pitting corrosion.

Influence of thermophilic aerobic digestion as a sludge pre-treatment and solids retention time of mesophilic anaerobic digestion on the methane production, sludge digestion and microbial communities in a sequential digestion process

In this study, the changes in sludge reduction, methane production and microbial community structures in a process involving two-stage thermophilic aerobic digestion (TAD) and mesophilic anaerobic digestion (MAD) under different solid retention times (SRTs) between 10 and 40 days were investigated. The TAD reactor (RTAD) was operated with a 1-day SRT and the MAD reactor (RMAD) was operated at three different SRTs: 39, 19 and 9 days. For a comparison, control MAD (RCONTROL) was operated at three different SRTs of 40, 20 and 10 days. Our results reveal that the sequential TAD-MAD process has about 42% higher methane production rate (MPR) and 15% higher TCOD removal than those of RCONTROL when the SRT decreased from 40 to 20 days. Denaturing gradient gel electrophoresis (DGGE) and real-time PCR results indicate that RMAD maintained a more diverse bacteria and archaea population compared to RCONTROL, due to the application of the biological TAD pre-treatment process. In RTAD, Ureibacillus thermophiles and Bacterium thermus were the major contributors to the increase in soluble organic matter. In contrast, Methanosaeta concilii, a strictly aceticlastic methanogen, showed the highest population during the operation of overall SRTs in RMAD. Interestingly, as the SRT decreased to 20 days, syntrophic VFA oxidizing bacteria, Clostridium ultunense sp., and a hydrogenotrophic methanogen, Methanobacterium beijingense were detected in RMAD and RCONTROL. Meanwhile, the proportion of archaea to total microbe in RMAD and RCONTROL shows highest values of 10.5 and 6.5% at 20-d SRT operation, respectively. Collectively, these results demonstrate that the increased COD removal and methane production at different SRTs in RMAD might be attributed to the increased synergism among microbial species by improving the hydrolysis of the rate limiting step in sludge with the help of the biological TAD pre-treatment.

Taxonomic study of the genus Tepidiphilus: transfer of Petrobacter succinatimandens to the genus Tepidiphilus as Tepidiphilus succinatimandens comb. nov., emended description of the genus Tepidiphilus and description of Tepidiphilus thermophilus sp. nov., isolated from a terrestrial hot spring

Comparative phenotypic, chemotaxonomic and genetic analysis revealed significant similarities among strains of the genera Tepidiphilus and Petrobacter. Analysis of 16S rRNA gene sequences and DNA-DNA relatedness of the type strains Tepidiphilus margaritifer N2-214(T) and Petrobacter succinatimandens 4BON(T) showed sequence similarity of 98.9 % and less than 40 % relatedness, indicating that these strains represent different species of same genus. Both strains had phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and diphosphatidylglycerol as major polar lipids. Their fatty acid profiles were almost identical, with the predominant fatty acids C16 : 0, C17 : 0 cyclo and C19 : 0 cyclo ω8c. In view of this, we propose to transfer the member of the genus Petrobacter to the genus Tepidiphilus as Tepidiphilus succinatimandens comb. nov. and to emend the description of the genus Tepidiphilus. Further, a novel bacterium, strain JHK30(T), was isolated from a terrestrial hot spring located at Jharkhand, India, and was identified following a polyphasic approach. Cells were non-sporulating, aerobic, Gram-stain-negative rods and motile by a single polar flagellum. Optimum temperature for growth was 50-55 °C at pH 6.5-7.0. 16S rRNA gene sequence analysis revealed 99.71 % similarity with P. succinatimandens 4BON(T) ( = DSM 15512(T)) and 98.71 % with T. margaritifer N2-214(T) ( = DSM 15129(T)). However, DNA-DNA relatedness of strain JHK30(T) with these two type strains was well below 70 %. The DNA G+C base composition was 66.1 mol%. Strain JHK30(T) represents a novel species of the genus Tepidiphilus for which the name Tepidiphilus thermophilus sp. nov. is proposed. The type strain is JHK30(T) ( = JCM 19170(T) = LMG 27587(T)= DSM 27220(T)).

Evaluation of microbial community composition in thermophilic methane-producing incubation of production water from a high-temperature oil reservoir

Investigation of petroleum microbes is fundamental for the development and utilization of oil reservoirs' microbial resources, and also provides great opportunities for research and development of bio-energy. Production water from a high-temperature oil reservoir was incubated anaerobically at 55 degrees C for more than 400 days without amendment of any nutrients. Over the time of incubation, about 1.6 mmol of methane and up to 107 micromol of hydrogen (H2) were detected in the headspace. Methane formation indicated that methanogenesis was likely the predominant process in spite of the presence of 23.4 mM SO4(2-) in the production water. Microbial community composition of the incubation was characterized by means of 16S rRNA gene clone libraries construction. Bacterial composition changed from Pseudomonales as the dominant population initially to Hydrogenophilales-related microorganisms affiliated to Petrobacter spp. closely. After 400 days of incubation, other bacterial members detected were related to Anareolineales, beta-, gamma-, and delta-Proteobacteria. The archaeal composition of the original production water was essentially composed of obligate acetoclastic methanogens of the genus Methanosaeta, but the incubation was predominantly composed of CO2-reducing methanogens of the genus Methanothermobacter and Crenarchaeotes-related microorganisms. Our results suggest that methanogenesis could be more active than expected in oil reservoir environments and methane formation from CO2-reduction played a significant role in the methanogenic community. This conclusion is consistent with the predominant role played by H2-oxidizing methanogens in the methanogenic conversion of organic matter in high-temperature petroleum reservoirs.

Diversity of Microbial Communities in Production and Injection Waters of Algerian Oilfields Revealed by 16S rRNA Gene Amplicon 454 Pyrosequencing

The microorganisms inhabiting many petroleum reservoirs are multi-extremophiles capable of surviving in environments with high temperature, pressure and salinity. Their activity influences oil quality and they are an important reservoir of enzymes of industrial interest. To study these microbial assemblages and to assess any modifications that may be caused by industrial practices, the bacterial and archaeal communities in waters from four Algerian oilfields were described and compared. Three different types of samples were analyzed: production waters from flooded wells, production waters from non-flooded wells and injection waters used for flooding (water-bearing formations). Microbial communities of production and injection waters appeared to be significantly different. From a quantitative point of view, injection waters harbored roughly ten times more microbial cells than production waters. Bacteria dominated in injection waters, while Archaea dominated in production waters. Statistical analysis based on the relative abundance and bacterial community composition (BCC) revealed significant differences between production and injection waters at both OTUs0.03 and phylum level. However, no significant difference was found between production waters from flooded and non-flooded wells, suggesting that most of the microorganisms introduced by the injection waters were unable to survive in the production waters. Furthermore, a Venn diagram generated to compare the BCC of production and injection waters of one flooded well revealed only 4% of shared bacterial OTUs. Phylogenetic analysis of bacterial sequences indicated that Alpha-, Beta- and Gammaproteobacteria were the main classes in most of the water samples. Archaeal sequences were only obtained from production wells and each well had a unique archaeal community composition, mainly belonging to Methanobacteria, Methanomicrobia, Thermoprotei and Halobacteria classes. Many of the bacterial genera retrieved had already been reported as degraders of complex organic molecules and pollutants. Nevertheless, a large number of unclassified bacterial and archaeal sequences were found in the analyzed samples, indicating that subsurface waters in oilfields could harbor new and still-non-described microbial species.

Microbial diversity in long-term water-flooded oil reservoirs with different in situ temperatures in China

Water-flooded oil reservoirs have specific ecological environments due to continual water injection and oil production and water recycling. Using 16S rRNA gene clone library analysis, the microbial communities present in injected waters and produced waters from four typical water-flooded oil reservoirs with different in situ temperatures of 25°C, 40°C, 55°C and 70°C were examined. The results obtained showed that the higher the in situ temperatures of the oil reservoirs is, the less the effects of microorganisms in the injected waters on microbial community compositions in the produced waters is. In addition, microbes inhabiting in the produced waters of the four water-flooded oil reservoirs were varied but all dominated by Proteobacteria. Moreover, most of the detected microbes were not identified as indigenous. The objective of this study was to expand the pictures of the microbial ecosystem of water-flooded oil reservoirs.

Characterization of microbial diversity and community in water flooding oil reservoirs in China

The diversity and distribution of bacterial and archaeal communities in four different water flooding oil reservoirs with different geological properties were investigated using 16S rDNA clone library construction method. Canonical correspondence analysis was used to analyze microbial community clustering and the correlation with environmental factors. The results indicated that the diversity and abundance in the bacterial communities were significantly higher than the archaeal communities, while both of them had high similarity within the communities respectively. Phylogenetic analysis showed that of compositions of bacterial communities were distinctly different both at phylum and genus level. Proteobacteria dominated in each bacterial community, ranging from 61.35 to 75.83 %, in which α-proteobacteria and γ-proteobacteria were the main groups. In comparison to bacterial communities, the compositions of archaeal communities were similar at phylum level, while varied at genus level, and the dominant population was Methanomicrobia, ranging from 65.91 to 92.74 % in the single oil reservoir. The factor that most significantly influenced the microbial communities in these reservoirs was found to be temperature. Other environmental factors also influenced the microbial communities but not significantly. It is therefore assumed that microbial communities are formed by an accumulated effect of several factors. These results are essential for understanding ecological environment of the water flooding oil reservoirs and providing scientific guidance to the performance of MEOR technology.

Microbial communities in long-term, water-flooded petroleum reservoirs with different in situ temperatures in the Huabei Oilfield, China

The distribution of microbial communities in the Menggulin (MGL) and Ba19 blocks in the Huabei Oilfield, China, were studied based on 16S rRNA gene analysis. The dominant microbes showed obvious block-specific characteristics, and the two blocks had substantially different bacterial and archaeal communities. In the moderate-temperature MGL block, the bacteria were mainly Epsilonproteobacteria and Alphaproteobacteria, and the archaea were methanogens belonging to Methanolinea, Methanothermobacter, Methanosaeta, and Methanocella. However, in the high-temperature Ba19 block, the predominant bacteria were Gammaproteobacteria, and the predominant archaea were Methanothermobacter and Methanosaeta. In spite of shared taxa in the blocks, differences among wells in the same block were obvious, especially for bacterial communities in the MGL block. Compared to the bacterial communities, the archaeal communities were much more conserved within blocks and were not affected by the variation in the bacterial communities.

Potential role of Thermus thermophilus and T. oshimai in high rates of nitrous oxide (N2O) production in ∼80 °C hot springs in the US Great Basin

Ambient nitrous oxide (N(2)O) emissions from Great Boiling Spring (GBS) in the US Great Basin depended on temperature, with the highest flux, 67.8 ± 2.6 μmol N(2)O-N m(-2) day(-1) , occurring in the large source pool at 82 °C. This rate of N(2)O production contrasted with negligible production from nearby soils and was similar to rates from soils and sediments impacted with agricultural fertilizers. To investigate the source of N(2)O, a variety of approaches were used to enrich and isolate heterotrophic micro-organisms, and isolates were screened for nitrate reduction ability. Nitrate-respiring isolates were identified by 16S rRNA gene sequencing as Thermus thermophilus (31 isolates) and T. oshimai (three isolates). All isolates reduced nitrate to N(2)O but not to dinitrogen and were unable to grow with N(2)O as a terminal electron acceptor. Representative T. thermophilus and T. oshimai strains contained genes with 96-98% and 93% DNA identity, respectively, to the nitrate reductase catalytic subunit gene (narG) of T. thermophilus HB8. These data implicate T. thermophilus and T. oshimai in high flux of N(2)O in GBS and raise questions about the genetic basis of the incomplete denitrification pathway in these organisms and on the fate of biogenic N(2)O in geothermal environments.

Influence of the drilling mud formulation process on the bacterial communities in thermogenic natural gas wells of the Barnett Shale

The Barnett Shale in north central Texas contains natural gas generated by high temperatures (120 to 150°C) during the Mississippian Period (300 to 350 million years ago). In spite of the thermogenic origin of this gas, biogenic sulfide production and microbiologically induced corrosion have been observed at several natural gas wells in this formation. It was hypothesized that microorganisms in drilling muds were responsible for these deleterious effects. Here we collected drilling water and drilling mud samples from seven wells in the Barnett Shale during the drilling process. Using quantitative real-time PCR and microbial enumerations, we show that the addition of mud components to drilling water increased total bacterial numbers, as well as the numbers of culturable aerobic heterotrophs, acid producers, and sulfate reducers. The addition of sterile drilling muds to microcosms that contained drilling water stimulated sulfide production. Pyrosequencing-based phylogenetic surveys of the microbial communities in drilling waters and drilling muds showed a marked transition from typical freshwater communities to less diverse communities dominated by Firmicutes and Gammaproteobacteria. The community shifts observed reflected changes in temperature, pH, oxygen availability, and concentrations of sulfate, sulfonate, and carbon additives associated with the mud formulation process. Finally, several of the phylotypes observed in drilling muds belonged to lineages that were thought to be indigenous to marine and terrestrial fossil fuel formations. Our results suggest a possible alternative exogenous origin of such phylotypes via enrichment and introduction to oil and natural gas reservoirs during the drilling process.

Biocorrosive thermophilic microbial communities in Alaskan North Slope oil facilities

Corrosion of metallic oilfield pipelines by microorganisms is a costly but poorly understood phenomenon, with standard treatment methods targeting mesophilic sulfate-reducing bacteria. In assessing biocorrosion potential at an Alaskan North Slope oil field, we identified thermophilic hydrogen-using methanogens, syntrophic bacteria, peptide- and amino acid-fermenting bacteria, iron reducers, sulfur/thiosulfate-reducing bacteria, and sulfate-reducing archaea. These microbes can stimulate metal corrosion through production of organic acids, CO2, sulfur species, and via hydrogen oxidation and iron reduction, implicating many more types of organisms than are currently targeted. Micromolar quantities of putative anaerobic metabolites of C1-C4 n-alkanes in pipeline fluids were detected, implying that these low molecular weight hydrocarbons, routinely reinjected into reservoirs for oil recovery purposes, are biodegraded and can provide biocorrosive microbial communities with an important source of nutrients.

Effect of temperature on microbial community of a glucose-degrading methanogenic consortium under hyperthermophilic chemostat cultivation

We continuously fed an anaerobic chemostat with synthetic wastewater containing glucose as the sole source of carbon and energy to study the effects of temperature on the microbial community under hyperthermophilic (65-80 degrees C) conditions. Methane was produced normally up to 77.5 degrees C at a dilution rate of 0.025 d(-1). However, the concentration of microorganisms and the rate of gas production decreased with increasing operation temperature. The microbial community in the chemostat at various temperatures was analyzed based on the 16S rRNA gene using molecular biological techniques including clone library analysis and denaturing gradient gel electrophoresis (DGGE). Aceticlastic methanogens related to Methanosarcina thermophila were detected at 65 degrees C and hydrogenotrophilic methanogens related to Methanothermobacter thermautotrophicus were the dominant methanogens between 70 degrees C to 77.5 degrees C. Bacteria related to Clostridium stercorarium and Thermoanaerobacter subterraneus comprised the dominant glucose-fermenting bacteria at temperatures of 65 degrees C and above, respectively. Bacteria related to Thermacetogenium phaeum and to Tepidiphilus margaritifer and Petrobacter succinatimandens were the dominant acetate-oxidizing bacteria at 70 degrees C and at 75-77.5 degrees C, respectively. The results suggested that, at temperatures of 70 degrees C and above, methane production via the aceticlastic pathway was negligible and indirect methanogenesis from acetate was dominant. Since acetate oxidation is a rate limiting step and a higher temperature favors the hydrolysis and acid formation, a two stage fermentation process, acidogenic and methanogenic fermentation stages operated under different temperatures, should be more suitable for the thermophilic anaerobic treatment at temperatures above 65 degrees C.

Respiratory transformation of nitrous oxide (N2O) to dinitrogen by Bacteria and Archaea

N2O is a potent greenhouse gas and stratospheric reactant that has been steadily on the rise since the beginning of industrialization. It is an obligatory inorganic metabolite of denitrifying bacteria, and some production of N2O is also found in nitrifying and methanotrophic bacteria. We focus this review on the respiratory aspect of N2O transformation catalysed by the multicopper enzyme nitrous oxide reductase (N2OR) that provides the bacterial cell with an electron sink for anaerobic growth. Two types of Cu centres discovered in N2OR were both novel structures among the Cu proteins: the mixed-valent dinuclear Cu(A) species at the electron entry site of the enzyme, and the tetranuclear Cu(Z) centre as the first catalytically active Cu-sulfur complex known. Several accessory proteins function as Cu chaperone and ABC transporter systems for the biogenesis of the catalytic centre. We describe here the paradigm of Z-type N2OR, whose characteristics have been studied in most detail in the genera Pseudomonas and Paracoccus. Sequenced bacterial genomes now provide an invaluable additional source of information. New strains harbouring nos genes and capability of N2O utilization are being uncovered. This reveals previously unknown relationships and allows pattern recognition and predictions. The core nos genes, nosZDFYL, share a common phylogeny. Most principal taxonomic lineages follow the same biochemical and genetic pattern and share the Z-type enzyme. A modified N2OR is found in Wolinella succinogenes, and circumstantial evidence also indicates for certain Archaea another type of N2OR. The current picture supports the view of evolution of N2O respiration prior to the separation of the domains Bacteria and Archaea. Lateral nos gene transfer from an epsilon-proteobacterium as donor is suggested for Magnetospirillum magnetotacticum and Dechloromonas aromatica. In a few cases, nos gene clusters are plasmid borne. Inorganic N2O metabolism is associated with a diversity of physiological traits and biochemically challenging metabolic modes or habitats, including halorespiration, diazotrophy, symbiosis, pathogenicity, psychrophily, thermophily, extreme halophily and the marine habitat down to the greatest depth. Components for N2O respiration cover topologically the periplasm and the inner and outer membranes. The Sec and Tat translocons share the task of exporting Nos components to their functional sites. Electron donation to N2OR follows pathways with modifications depending on the host organism. A short chronology of the field is also presented.

Enrichment and detection of microorganisms involved in direct and indirect methanogenesis from methanol in an anaerobic thermophilic bioreactor

To gain insight into the microorganisms involved in direct and indirect methane formation from methanol in a laboratory-scale thermophilic (55 degrees C) methanogenic bioreactor, reactor sludge was disrupted and serial dilutions were incubated in specific growth media containing methanol and possible intermediates of methanol degradation as substrates. With methanol, growth was observed up to a dilution of 10(8). However, when Methanothermobacter thermoautotrophicus strain Z245 was added for H2 removal, growth was observed up to a 10(10)-fold dilution. With H2/CO2 and acetate, growth was observed up to dilutions of 10(9) and 10(4), respectively. Dominant microorganisms in the different dilutions were identified by 16S rRNA-gene diversity and sequence analysis. Furthermore, dilution polymerase chain reaction (PCR) revealed a similar relative abundance of Archaea and Bacteria in all investigated samples, except in enrichment with acetate, which contained 100 times less archaeal DNA than bacterial DNA. The most abundant bacteria in the culture with methanol and strain Z245 were most closely related to Moorella glycerini. Thermodesulfovibrio relatives were found with high sequence similarity in the H2/CO2 enrichment, but also in the original laboratory-scale bioreactor sludge. Methanothermobacter thermoautotrophicus strains were the most abundant hydrogenotrophic archaea in the H2/CO2 enrichment. The dominant methanol-utilizing methanogen, which was present in the 10(8)-dilution, was most closely related to Methanomethylovorans hollandica. Compared to direct methanogenesis, results of this study indicate that syntrophic, interspecies hydrogen transfer-dependent methanol conversion is equally important in the thermophilic bioreactor, confirming previous findings with labeled substrates and specific inhibitors.