Methanogen

About: Methanogen is a research topic. Over the lifetime, 1146 publications have been published within this topic receiving 48254 citations.

Chasing the metabolism of novel syntrophic acetate-oxidizing bacteria in thermophilic methanogenic chemostats

Abstract: Background Acetate is the major intermediate of anaerobic digestion of organic waste to CH4. In anaerobic methanogenic systems, acetate degradation is carried out by either acetoclastic methanogenesis or a syntrophic degradation by a syntrophy of acetate oxidizers and hydrogenotrophic methanogens. Due to challenges in isolation of syntrophic acetate-oxidizing bacteria (SAOB), the diversity and metabolism of SAOB, as well as the mechanisms of their interactions with methanogenic partners remain poorly understood. Results In this study, we successfully enriched previously unknown SAOB by operating continuous thermophilic anaerobic chemostats fed with acetate, propionate, butyrate, or isovalerate as the sole carbon and energy source. They represent novel clades belonging to Clostridia, Thermoanaerobacteraceae, Anaerolineae, and Gemmatimonadetes. In these SAOB, acetate is degraded through reverse Wood-Ljungdahl pathway or an alternative pathway mediated by the glycine cleavage system, while the SAOB possessing the latter pathway dominated the bacterial community. Moreover, H2 is the major product of the acetate degradation by these SAOB, which is mediated by [FeFe]-type electron-confurcating hydrogenases, formate dehydrogenases, and NADPH reoxidation complexes. We also identified the methanogen partner of these SAOB in acetate-fed chemostat, Methanosarcina thermophila, which highly expressed genes for CO2-reducing methanogenesis and hydrogenases to supportively consuming H2 at transcriptional level. Finally, our bioinformatical analyses further suggested that these previously unknown syntrophic lineages were prevalent and might play critical roles in thermophilic methanogenic reactors. Conclusion This study expands our understanding on the phylogenetic diversity and in situ biological functions of uncultured syntrophic acetate degraders, and presents novel insights on how they interact with their methanogens partner. These knowledges strengthen our awareness on the important role of SAO in thermophilic methanogenesis and may be applied to manage microbial community to improve the performance and efficiency of anaerobic digestion.

A high-rate high temperature anaerobic digestion system for sludge treatment

Abstract: Anaerobic digestion (AD) is an established technology for the treatment of sewage sludge and solid organic wastes such as animal manure, residuals and energy crops. AD converts organics in these solid streams to a renewable source of energy in the form of methane, with the concomitant reduction of the amount of final biosolids to be disposed. The application of AD on organic solids treatment generally requires long retention times (20n30 days) that result in high capital costs and represent a major opportunity for process improvement. High-rate AD requires rapid hydrolysis and enhanced methanogenic growth rates which can be achieved through elevated temperatures (g55 dC) at short sludge retention times (SRT). However, there is currently limited understanding on the impact of varying temperatures in the thermophilic range, particularly on methanogenesis. In response, this thesis investigates the effects of temperature (55n65 dC) and SRT (2n4 days) on multiple aspects of performance, methanogenic capacity, community and pathways using a combination of reactor studies, microbial community analyses by pyrosequencing, and methanogenic pathways analyses by stable isotope fractionation. It was demonstrated that thermophilic AD could be operated effectively at 55 dC and short SRT of 3 or 4 days, achieving comparable volatile solids (VS) destruction (37%) with those of mesophilic AD (20n30 days SRT). Increasing temperature did not enhance methanogenesis to the same extent as hydrolysis, with hydrolysis being limiting at 55 dC and methanogenesis limiting at 65 oC. Acetate is an important intermediate in the anaerobic degradation and can be converted to methane via two pathways: acetoclastic methanogenesis (AM) dominating at mesophilic temperature and syntrophic acetate oxidation (SAO) dominating at thermophilic temperature. SAO is a two-step process, consisting of acetate oxidation to carbon dioxide by syntrophic acetate-oxidisers, followed by conversion of these products to methane by hydrogenotrophic methanogens. Using stable carbon isotopic signature to quantify the relative contribution of these two pathways indicated that elevated temperature promoted SAO, which accounted for 60% of methane formation at 55 dC and increased substantially to 100% at 65 dC. Acetate consumption capacity dropped with increasing temperature based on specific methanogenic activity testing of digester contents. Statistical analysis showed a strong correlation between reactor temperature and microbial community; in particular, increased temperature correlated to the increased relative abundance of Coprothermobacter and the decreased relative abundance of Methanosarcina. RNA directed stable isotope probing (SIP) was further applied with RNA directed real-time polymerase chain reaction (q-PCR) and pyrosequencing. This identified a switch from Methanosarcina and Coprothermobacter at 55 dC and 60 dC to Methanothermobacter and Coprothermobacter at high temperature (60n65 dC). In particular, Methanothermobacter contained the 13C label despite (presumptively) being a non-acetotrophic methanogen. This work confirmed the role of Methanosarcina at lower temperature, possibly as both acetoclastic and hydrogenotrophic methanogen. Microscopic analyses using nanoscale secondary ion mass spectrometry (nanoSIMS) coupled with fluorescence in-situ hybridisation (FISH) successfully detected and visualised uptake of 13C-labelled acetate by Methanosarcina. Coprothermobacter was also the key acetate oxidiser given SIP and sequencing results, but visualisation of Coprothermobacter by nanoSIMS remains to be elucidated due to the lack of specific probes for this group.n

Effect of C/N ratio variations on the capability of microbes from Muara Karang river sediment in the production of biogas and identification using VITEK 2

Abstract: Gas is one form of microbial metabolism products that can be identified as biogas, one example of biogas is methane gas. The production of methane gas by bacteria occurs through methanogenesis with three stages, namely hydrolysis, acetogenesis, and methanogenesis. These processes are generally performed by bacteria in an anaerobic environment. The Muara Karang River sediments contaminated with organic matters and having low oxygen are potential as the habitat for anaerobic microbes with methanogenesis ability. The ability of such sediment microbes in biogas production was tested by inoculating Muara Karang sediment in a Methanogen Enrichment Barker broth medium with variations of C/N ratio using glucose as the carbon source to analyze the biogas production. The parameters measured were the total carbon, the total nitrogen, and the biogas volume. Two isolates were obtained, namely isolate I and isolate II. These isolates were then identified by the VITEK 2 compact equipment. The result showed that C/N ratio of 25:1 could produce the highest biogas volume. Isolate I was identified by the VITEK 2 equipment as Methylobacterium spp. from methanotroph group bacteria and isolate II was identified as Dermacoccus nishinomiyaensis.

Bacterial Flora Involved in Anaerobic Digestion of Butyrate

Abstract: 酪酸を単一炭素源として用い,酪酸馴養メタン発酵汚泥から水素資化性メタン生成細菌BHM-1株を得,BHM-1株の微生物学的性状を調べ,酪酸分解菌との微生物相互の役割について微生物生態学的見地から考察した。酪酸に対するメタン発酵においてメタンの生成には2つのピークがあり,ピークIは酪酸分解菌と水素資化性メタン生成細菌との共生関係によるメタン生成,ピークIIは酢酸資化性メタン生成細菌かあるいは酢酸分解菌と水素資化性メタン生成細菌によるメタン生成であることが推察された。ピークIに着目して検討した結果,分離したBHM-1株はMethanobacterium formicicumに極めて類縁な微生物であった。酪酸分解菌とBHM-1株からなるコロニーの液体培養から,酪酸分解菌とBHM-1株での共生関係が示唆された。

Isolation of methanogens from termite gut and its role in biogas production by using poultry waste

Abstract: To achieve a functioning and stable process with high methane production it is important to create and maintain a beneficial environment for the activity of bacterial consortia of suitable species. Therefore, the present study was carried out to isolate methanogen from termite gut and analyze its role in biogas production. The biogas production was carried out in a pilot scale batch reactor for 30days using poultry waste as a substrate. Morphological, biochemical characterization and molecular identification has been done tothe isolated methanogen. The growth of isolated methanogen was tested under different pH, temperature and different substrates. The physico-chemical parameters such as pH, temperature, Chemical oxygen demand and total solids were measured in the interval of 10 days. Biogas production was analyzed between the control and treated biogas tanks in order to identify the effectiveness of biogas production.