Acetate-consuming Bacteria Research Articles

Material and microbial perspectives on understanding the role of biochar in mitigating ammonia inhibition during anaerobic digestion

With the increasing adoption of carbon-based strategies to enhance methanogenic processes, there is a growing concern regarding the correlation between biochar properties and its stimulating effects on anaerobic digestion (AD) under ammonia inhibition. This study delves into the relevant characteristics and potential mechanisms of biochar in the context of AD system under ammonia inhibition. The introduction of optimized biochar, distinguished by rich CO bond, abundant defect density, and high electronic capacity, resulted in a significant reduction in the lag period of anaerobic digestion system under 5.0 g/L ammonia stress, approximately by around 63 % compared to the control one. Biochar helps regulate the community structure, promotes the accumulation of acetate-consuming bacteria, in the AD system under ammonia inhibition. More examinations show that biochar promotes direct interspecies electron transfer in AD system under ammonia inhibition, as evidenced by diminished levels of bound electroactive extracellular polymeric substances, increased abundance of electroactive bacteria, and notably, the up-regulation of direct interspecies electron transfer associated genes, including the conductive pili and Cytochrome C genes, as revealed by meta-transcriptomic analysis. Additionally, gene expression related to proteins associated with ammonium detoxification were found to be up-regulated in systems supplemented with biochar. These findings provide essential evidence and insights for the selection and potential engineering of effective biochar to enhance AD performance under ammonia inhibition.

Bacterial community composition in a two-stage anaerobic membrane bioreactor for co-digestion of food waste and food court wastewater

This study investigated the microbial community of a two-stage anaerobic membrane bioreactor (2S-AnMBR) co-digesting food waste and food court wastewater. The hydrolysis reactor (HR) was dominated by Bacteroidetes and Firmicutes phylum, with genus Lactobacillus enriched due to food waste fermentation. The up-flow anaerobic sludge blanket (UASB) was dominated by genus such as Methanobacterium and Methanosaeta. The presence of Methanobacterium (91 %) and Methanosaeta (7.5 %) suggested that methane production pathways inevitably undergo both hydrogenotrophic and acetoclastic methanogenesis. Hydrogen generated during hydrolysis fermentation in the HR contributed to methane production in the UASB via hydrogenotrophic pathways. However, the low abundance of Methanosaeta in the UASB can be attributed to the limited inffluent of volatile fatty acids (VFA) and the competitive presence of acetate-consuming bacteria Acinetobacter. The UASB exhibited more excellent dispersion and diversity of metabolic pathways compared to the HR, indicating efficient methane production.

Factors controlling the co-occurrence of microbial sulfate reduction and methanogenesis in coal bed reservoirs

Sulfate-reducing microorganisms (SRM) and methanogenic archaea have been previously observed in coal bed methane reservoirs, suggesting that the model for separation of these organisms based on sulfate concentration may not apply to such reservoirs. Using a methanogenic consortium enriched from coal, microcosm experiments showed simultaneous activity of methanogens and sulfate reducers at sulfate concentrations ranging from 50 to 1000μM when coal was the sole substrate. These experiments revealed no apparent correlation between methanogenic potential and sulfate concentration. In other microcosm experiments with varying acetate amendments, concentrations of the phospholipid fatty acids (PLFAs) 14:0, 16:1ω5, 16:1ω7cis, 16:1ω7trans, and cy17:0 correlated strongly with the initial acetate concentration in microcosms with 500μM sulfate, while i17:0 correlated strongly in microcosms with 200μM sulfate. A significant portion of the acetate in these experiments went to microbial metabolisms other than dissimilatory sulfate reduction or methanogenesis, suggesting that some of these PLFAs were likely produced by some other unknown acetate-consuming micro-organisms. Copies of the dsrA gene increased at least 10-fold over initial levels in samples without molybdate (MoO42−) across all experiments, indicating that SRM were active when not inhibited by MoO42−. In experiments with <300μM acetate, copies of the mcrA gene increased over 49days regardless of sulfate concentration. These results suggest that both SRM and methanogens are active at low acetate concentrations and may compete for available acetate with other acetate-consuming bacteria in coal bed methane reservoirs.

Uncultured Desulfobacteraceae and Crenarchaeotal group C3 incorporate 13C-acetate in coastal marine sediment.

Stable isotope probing (SIP) of deoxyribonucleic acid (DNA) was used to identify microbes incorporating (13) C-labeled acetate in sulfate-reducing sediment from Aarhus Bay, Denmark. Sediment was incubated in medium containing 10 mM sulfate and different (13) C-acetate (10, 1, 0.1 mM) concentrations. The resultant changes in microbial community composition were monitored in total and SIP-fractionated DNA during long-term incubations. Chemical analyses demonstrated metabolic activity in all sediment slurries, with sulfate-reducing activity largely determined by initial acetate concentrations. Sequencing of 16S rRNA gene PCR amplicons showed that the incubations shifted the bacterial but not the archaeal community composition. After 3 months of incubation, only sediment slurries incubated with 10 mM (13) C-acetate showed detectable (13) C-DNA labeling. Based on 16S rRNA and dsrB gene PCR amplicon sequencing, the (13) C-labeled DNA pool was dominated by a single type of sulfate reducer representing a novel genus in the family Desulfobacteraceae. In addition, members of the uncultivated Crenarchaeotal group C3 were enriched in the (13) C-labeled DNA. Our results were reproducible across biological replicate experiments and provide new information about the identities of uncultured acetate-consuming bacteria and archaea in marine sediments.

Decolorization of azo-reactive dyes and cotton-textile wastewater using anaerobic digestion and acetate-consuming bacteria

An anaerobic digestion technique was applied to azo-reactive dye aqueous solutions and cotton textile wastewater aiming at the color elimination. A batch-mode water-jacketed anaerobic reactor and acclimatized acetate-consuming bacteria initially derived from the anaerobic digester sludge of a municipal wastewater treatment plant were used for this study. Acetic acid solution and a pH-controller were utilized to maintain the pH at the desired level (6.6–7.2) while the temperature was kept constant at 37 °C using an external water-bath. Acetic acid also served as an external substrate (electron-donor) supply for the bacteria metabolism. Complete decolorization of all dye solutions was succeeded in 4–5 days of experimental run. The biodegradation ability of cotton textile wastewater was also examined without the addition of external substrate supply (acetic acid) resulting to poor decolorization results. However, anaerobic digestion of the same wastewater using the acetate-consuming bacteria and acetic acid as an external substrate supply lead to the complete decolorization of the wastewater in 4 days of experiment.

Abundance and phylogenetic affiliation of iron reducers in activated sludge as assessed by fluorescence in situ hybridization and microautoradiography.

Microautoradiography (MAR) was used to enumerate acetate-consuming bacteria under Fe(III)-reducing conditions in activated sludge. This population is believed to consist of dissimilatory iron-reducing bacteria, because the applied incubation conditions and the use of specific inhibitors excluded consumption of radiolabeled acetate by other physiological groups such as sulfate reducers. By use of this approach, dissimilatory iron reducers were found in a concentration of 1.1 x 10(8) cells per ml, corresponding to approximately 3% of the total cell count as determined by DAPI (4',6'-diamino-2-phenylindoledihydrochloride-dilactate) staining. The MAR enumeration method was compared to the traditional most-probable-number (MPN) method (FeOOH-MPN) and a modified MPN method, which contains Ferrozine directly within the MPN dilutions to determine the production of small amounts of ferrous iron (Ferrozine-MPN). The Ferrozine-MPN method yielded values 6 to 10 times higher than those obtained by the FeOOH-MPN method. Nevertheless, the MAR approach yielded counts that were 100 to 1,000 times higher than those obtained by the Ferrozine-MPN method. Specific in situ Fe(III) reduction rates per cell (enumerated by the MAR method) were calculated and found to be comparable to the respective rates for pure cultures of dissimilatory iron-reducing bacteria, suggesting that the new MAR method is most reliable. A combination of MAR and fluorescence in situ hybridization was used for phylogenetic characterization of the putative iron-reducing bacteria. All activated-sludge cells able to consume acetate under iron-reducing conditions were targeted by the bacterial oligonucleotide probe EUB338. Around 20% were identified as gamma Proteobacteria, and 10% were assigned to the delta subclass of Proteobacteria.

Quantification of functional groups in activated sludge by microautoradiography

Different functional groups of bacteria in activated sludge from a Danish municipal wastewater treatment plant were investigated and quantified on the basis of their ability to take up acetate under different electron acceptor conditions. The number of bacteria in the different functional groups was quantified by microautoradiography or by fluorescence in situ hybridization (FISH). Uptake of radiolabeled acetate was tested under conditions where oxygen, nitrate, ferric iron, and sulfate served as electron acceptors and under methanogenic conditions. Ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were enumerated by applying oligonucleotide probes (FISH). 80% of the total DAPI count hybridised with a mixture of bacterial probes. Most baceria were able to take up acetate with oxygen or nitrate as electron acceptors (74 and 71% of all DAPI-stained bacteria, respectively). The very similar numbers indicate that the alternating aerobic and anoxic conditions in the wastewater treatment plant investigated favoured the presence of facultative aerobic and denitrifying heterotrophic bacteria. The number of bacteria able to take up acetate under anaerobic conditions was around 8% of the total DAPI count. About half of these were able to take up acetate and store it and were thus probably phosphate-accumulating organisms. The remaining 4% of anaerobic acetate-consuming bacteria were mainly iron reducers. By incubating the sludge samples with specific inhibitors against sulfate reduction and methanogenic activity, it was found that sulfate reducers and methanogenic bacteria constituted approximately 1% and less than 0.5% of the total DAPI count, respectively.

Enumeration of acetate-consuming bacteria by microautoradiography under oxygen and nitrate respiring conditions in activated sludge

Microautoradiography was used to enumerate bacteria able to take up radiolabelled acetate in activated sludge using oxygen or nitrate as electron acceptors. In each of three wastewater treatment plants (WWTP) with nitrification and denitrification (N-removal), the number of bacteria consuming acetate under aerobic and anoxic conditions was identical in contrast to the acetate removal rates. The rates were clearly lower under anoxic conditions suggesting that the specific activity of the cells and not the number of active cells was reduced under anoxic conditions. The fraction of bacteria able to consume acetate varied in three WWTPs between 47% and 93% of the total number of bacteria as determined by DAPI. In a WWTP without N-removal only 20% of the bacteria were able to consume acetate under aerobic conditions and very few of these were able to do it under anoxic conditions. The cell specific acetate removal rates in all WWTPs were found to be 3.0–13.2×10 −15 mol cell −1 h −1 under aerobic conditions and between 1.9 and 9.1×10 −15 mol cell −1 h −1 under anoxic conditions.