Isolation Of Homoacetogenic Bacteria And Research On Their Ecophysiology

Homoacetogenic bacteria are anaerobic microorganisms, which can utilize CO₂asthe terminal electron acceptor to synthesize metabolic products and cellular material byanaerobic acetyl-CoA pathway. Homoacetogenic bacteria play important roles in theanaerobic biological systems, including decreasing hydrogen partial pressure andproviding substrates for many other microorganisms. However, its ecophysiologicalcharacteristics and fuctions have not been widely studied in an anaerobic fermentationsystem, its potential application value need to be exploited. Germplasm resources ofhomoacetogens and investigating their ecophysiological characteristics are theimportant base for the development of related application technology.In present study, a stability enriched culture A with high ability of consuminghydrogen and producing acetate subculture, the provenance is the sludge in theanaerobic biological treatment of the organic wastewater. The culture A could growthand metabolize well at40°C and initial pH9. An anaerobic bacterium CA3was isolatedfrom the culture A using H₂/CO₂as sole carbon source by modified hungate anaerobictechnique. Strain CA3was a strictly anaerobic, gram-positive and oval-shapedacetogenic bacterium. Phylogenetic analysis based on16S rRNA gene sequenceindicated that strain CA3affiliates to the genus Blautia. This bacterium could not onlymetabolize H₂/CO₂to produce acetate, but also ferment glucose and fructose withacetate as a major product, indicating strain CA3has typical metabolic characteristics ofhomoacetogenic bacteria.This study investigated the effects of different nitrogen source on strain CA3. Theresults showed that yeast extract was the most feasible nitrogen source for strain CA3toutilize glucose and H₂/CO₂, myebe due to there is some special growth factor in yeastextract. To optimize the fermentation conditions of strain CA3, this researchinvestigated the effects of different temperature and initial pH on fermenting glucose toproduce acetate for stain CA3. The results indicated that optimum temperature andinitial pH of strain CA3is35°C and8. In addition, the strain could grow at NaCl of0%³%with optimum NaCl of0.3%.The growth kinetic of strain CA3for utilizing glucose or H₂/CO₂was studied onthe basis of the above suitable growing conditions. The results showed that strain CA3was sired fastly after12h cultivation. In the logarithmic phase, the average degradationrate of glucose was161.38mg/（L·h） for srain CA3, and the production rate of acetatewas64.06mg/（L·h）; While the average production rate of acetate was8.97mg/（L·h）using H₂/CO₂as carbon source. The analysis of dynamics on strain CA3showed thatthe maximum specific substrate removal rate （vmax） up was2.745mg/（mg·h）, the maximum half saturation constant （Ks） was2466mg/L, it will has good propects forfermenting glucose or fixing CO₂to produce acetate.