Showing papers on "Methanogen published in 1988"

Competition for hydrogen between sulphate-reducing bacteria and methanogenic bacteria from the human large intestine.

Abstract: Sulphate-reducing activity in human faecal slurries was followed by measuring sulphide production. Sulphate-reducing bacteria (SRB) were found to outcompete methanogenic bacteria (MB) for the mutual substrate hydrogen in faecal slurries from methane- and non-methane-producing individuals mixed together. When molybdate (20 mmol/l) was added to these slurries, sulphate reduction was inhibited and methanogenesis became the major route of electron disposal. Sulphide production was stimulated by the addition of 20 mmol/l sulphate in non-methanogenic but not in methanogenic slurries. In methanogenic slurries that contained the methanogen inhibitor 2-bromoethanesulphonic acid (BES), hydrogen accumulated whilst sulphide levels were unaffected, confirming the absence of SRB in methanogenic faeces. The addition of nitrate (10 mmol/l) to faecal slurries completely inhibited methanogenesis but only slightly reduced sulphate reduction. The sulphated mucopolysaccharides, chondroitin sulphate and mucin, strongly stimulated sulphide production in non-methanogenic faecal slurries only, suggesting that these substances may be a potential source of sulphate in the large gut.

Reductive dechlorination of perchloroethylene and the role of methanogens

Abstract: Perchloroethylene (PCE) was reductively dechlorinated to trichloroethylene in a 10% anaerobic sewage sludge. About 80% of the initially added PCE (300 nmol) was dechlorinated within three weeks. The calculated rates were 250 nM and 445 nM · day −1 during the first and second weeks of incubation, respectively. The depletion of PCE varied in sludges obtained from different sources. The role of methanogenesis in the dechlorination of PCE was evaluated by inhibiting the methanogens by addition of bromoethane sulfonic acid, a potent methanogenic inhibitor. Dechlorination of PCE was significantly inhibited in sludges amended with the inhibitor. Almost 41–48% less PCE was dechlorinated in sludges containing 5 mM BESA, indicating a relation between the two processes (methanogenesis and dechlorination). Direct proof that methanogens can transform chlorinated aliphatic compounds was obtained using axenic cultures of acetate-cleaving methanogens. Methanosarcina sp , originally isolated from a chlorophenol degrading consortium, showed significantly higher dechlorinating activity as compared to Ms. mazei . Based on these studies and other recently reported observations, it appears that methanogens/methanogenesis play an important role in the anaerobic dechlorination of chlorinated aliphatics such as PCE.

Methanohalophilus mahii gen. nov., sp. nov., a Methylotrophic Halophilic Methanogen†

Abstract: A new genus of methanogenic bacteria (Methanohalophilus) comprising a single species, Methanohalophilus mahii sp. nov., is described. The microorganisms of this genus require sodium chloride concentrations in the moderately halophilic range of 1.0 to 2.5 M for optimal growth and methanogenesis. Methanol and methylamines are the substrates that are utilized for growth. M. mahii is a methanogenic coccoid microorganism isolated from the sediments of the Great Salt Lake. The optimum temperature and salinity for growth and methanogenesis were 37°C and 2.0 M NaCI, respectively. The description is based on a single strain, strain SLP (= ATCC 35705), which is thus the type strain.

Isolation and characterization of methanogenic bacteria from rice paddies

Abstract: Enrichment cultures for H2CO2, methanol- or acetate-utilizing methanogens were prepared from two rice field soil samples. All the cultures except one acetate enrichment showed significant methane production. Pure cultures of Methanobacterium- and Methanosarcina-like organisms were isolated from H2CO2 and methanol enrichment cultures, respectively, and were characterized for various nutritional and growth conditions. The organisms had an optimal pH range of 6.4–6.6 and a temperature optimum of 37°C. The Methanobacterium isolates were able to utilize H2CO2 but no other substrates as sole energy source, while the Methanosarcina isolates were able to utilize methanol, methylamines or H2CO2 as sole energy sources. Both Methanobacterium isolates and one isolate of Methanosarcina were able to use dinitrogen as the sole source of nitrogen for growth. The isolates used several sulfur compounds as sole sources of sulfur.

Interactions between the methanogen Methanosarcina barkeri and rumen holotrich ciliate protozoa

Abstract: Interspecies hydrogen transfer between rumen holotrich ciliate protoza and methanogenic bacteria has been demonstrated. As a result of the metabolic interaction with Methanosarcina barkeri, the metabolite profile of Isotricha spp. was altered and the production of butyrate and lactate was suppressed in the presence of the methanogen.Use of membrane‐inlet mass spectrometry confirmed that the presence of rumen holotrich ciliates reduced the apparent sensitivity of methanogenesis to the inhibitory effects of oxygen; a gas phase concentration of 7·4 kPa oxygen was required to inhibit methanogenesis in the presence of protozoa, while in pure cultures of M. barkeri, methanogenesis was inhibited by a gas phase oxygen concentration of 1·0 kPa.

Methanogen factor 390 formation: species distribution, reversibility and effects of non-oxidative cellular stresses.

Abstract: Factor 390 (F390), an adenylylated or guanylylated derivative of the methanogen coenzyme factor 420 (F420), was previously detected in Methanobacterium thermoautotrophicum cells exposed to air. Of six other methanogenic species that have now been tested, only Methanobacterium formicicum was found to produce F390 upon oxygen exposure. Aerobic conditions led to an immediate cessation of methanogenesis, whereas only 51% of cellular F420 was slowly converted to F390 over 4 h in Mb.formicicum at 37 degrees C. F390 formation is reversible. When oxidized cells were re-introduced into anoxic medium, F390 reverted to F420 prior to recovery of methanogenesis. Anaerobic cultures of Mb.formicicum were subjected to alternative stresses such as exposure to heavy metals, methanogenesis inhibitors and eubacterial alarmone-producing chemicals; however, only oxygen was found to induce F390 formation.