Identification And Metabolic Characteristics Of A Homoacetogenic Bacteria Strain

Homoacetogenic bacteria are strict anaerobic microorganism with both autotrophic and heterotrophic metabolic modes.It can not only reduce CO₂ to synthesize acetic acid with H₂,but also ferment organic matter to produce small molecular organic matter,which is an excellent strain resource for acetic acid biological production.It has shown a good development prospect and application potential in the resource utilization of biological fermentation gas?rich in CO₂/H₂?,industrial syngas?CO/CO₂/H₂?and lignocellulose.However,at present,the pure culture of homoacetogenic bacteria is very limited,and the understanding of its physiological ecology and growth metabolic characteristics is not deep and comprehensive enough,which seriously restricts the research and development process of its applied technology.In this study,activated sludge in the anaerobic treatment reactor of organic wastewater was used as the bacterial source and CO₂/H₂ as the only carbon source.Homoacetogenic bacteria were enriched by continuous passage and 12 strains were isolated from them.By comparing the hydrogen consumption rate and acetic acid production rate of 12 pure cultures,strain ZX with excellent acetic acid production characteristics was selected.The strain is strictly anaerobic,4¹0?m long,gram-positive?G⁺?,inactive,spore producing,spore oval-shaped,terminal;It can ferment glucose,fructose,fiber disaccharide and lactose and other monosaccharides and disaccharides,can also use H₂/CO₂ autotrophic growth.Molecular biological identification results based on 16S rRNA gene sequencing showed that strain ZX was subordinate to Lysinibacillus.Further morphological and physiological and biochemical studies showed that the strain ZX was a new taxonomic species of Lysinibacillus,named Lysinibacillus.sp.ZX.Physiological and ecological studies showed that Lysinibacillus.sp.ZX can only grow with yeast powder and peptone as nitrogen sources when it ferments monosaccharides and disaccharides,or when CO₂ is used to synthesize acetic acid.Suitable growth temperature,pH and salt concentration?measured in Na⁺?range from 30°C to 45°C,6.0⁹.0 and³.32g/L respectively.Studies on autotrophic growth metabolism of Lysinibacillus.sp.ZX showed that acetic acid was the only liquid fermentation product when CO₂ was the sole carbon source.Under the conditions of 35°C and pH 7.0⁸.0,the maximum growth rate,hydrogen consumption rate and acetic acid formation rate were 1.82×10⁶/?mL·h?,0.357 mmol/?L·h?and 165.15 mg/?L·h?,respectively.Research on heterotrophic growth metabolism has shown that Lysinibacillus.sp.ZX can only be activated in the presence of CO₂ or HCO^3-.When glucose and xylosugar were fermented?NaHCO₃ dose was 1 g/L?,the maximum acetic acid production rate was 829.01 and 84.56 mg/?L·h?,respectively,and the acetic acid conversion rate was up to 0.89 and 1.15 g/g,respectively.The maximum acetic acid production rate reached 253.95mg/?L·h?during the fermentation of rice straw saccharification liquid.By calculation,each gram of straw can produce 0.202 g acetic acid.In summary,Lysinibacillus.sp.ZX has strong autotrophic and heterotrophic growth and acetic acid production capacity,and has good environmental adaptability and easy cultivation,making it an excellent acetic acid producing strain with good application prospect.