Isolation and characterization of a new Methanoculleus bourgensis strain KOR-2 from the rumen of Holstein steers.

OBJECTIVE: To isolate and identify new methanogens from the rumen of Holstein steers in Korea. METHODS: Representative rumen contents were obtained from three ruminally cannulated Holstein steers (793±8 kg). Pre-reduced media were used for the growth and isolation of methanogens. Optimum growth temperature, pH, and sodium chloride (NaCl) concentration as well as substrate utilization and antibiotic tolerance were investigated to determine the physiological characteristics of the isolated strain. Furthermore, the isolate was microscopically studied for its morphology. Polymerase chain reaction of 16S rRNA and mcrA gene-based amplicons was used for identification. RESULTS: One strain designated as KOR-2 was isolated and found to be a non-motile irregular coccus with a diameter of 0.2 to 0.5 µm. KOR-2 utilized H2+CO2 and formate but was unable to metabolize acetate, methanol, trimethylamine, 2-propanol, and isobutanol for growth and methane production. The optimum temperature and pH for the growth of KOR-2 were 38°C and 6.8 to 7.0, respectively, while the optimum NaCl concentration essential for KOR-2 growth was 1.0% (w/v). KOR-2 tolerated ampicillin, penicillin G, kanamycin, spectromycin, and tetracycline. In contrast, the cell growth was inhibited by chloramphenicol. Phylogenetic analysis of 16S rRNA and mcrA genes revealed the relatedness between KOR-2 and Methanoculleus bourgensis. CONCLUSION: Based on the physiological and phylogenetic characteristics, KOR-2 was thought to be a new strain within the genus Methanoculleus and named Methanoculleus bourgensis KOR-2.

Isolation and characterization of new Methanosarcina mazei strains KOR-3, -4, -5, and -6 from an anaerobic digester using pig slurry.

OBJECTIVE: An experiment was conducted to isolate and identify new methanogens in Korea from an anaerobic digester that uses pig slurry. METHODS: An anaerobic digestate sample was collected from an anaerobic digester using pig slurry. Pre-reduced media were used for the growth and isolation of methanogens. Growth temperature range, pH range, NaCl concentration range, substrate utilization, and antibiotic tolerance were investigated to determine the physiological characteristics of isolated methanogens. The isolates were also examined microscopically for their morphology and Gram-stained. Polymerase chain reaction of 16S rRNA and mcrA gene-based amplicons was used for identification purpose. RESULTS: Four strains, designated KOR-3, -4, -5, and -6, were isolated and were non-motile, irregular coccoid, and 0.5 to 1.5 µm in diameter. Moreover, the cell walls of isolated strains were Gram-negative. KOR-3 and KOR-4 strains used acetate for methane production but did not use H2+CO2, formate, or methanol as a growth substrate KOR-5 and KOR-6 strains utilized acetate, methanol, and trimethylamine for methanogenesis but did not use H2+CO2 or formate as a growth substrate. The optimum temperature and pH for growth of four strains were 39°C and 6.8 to 7.2, respectively. The optimum concentration of NaCl for growth of KOR-3, KOR-5, and KOR-6 were 1.0% (w/v). The optimum NaCl concentration for KOR-4 was 0.5% (w/v). All of the strains tolerated ampicillin, penicillin G, kanamycin, streptomycin, and tetracycline; however, chloramphenicol inhibited cell growth. Phylogenetic analysis of 16S rRNA and mcrA genes demonstrated that strains KOR-3, -4, -5, and -6 are related to Methanosarcina mazei (M. mazei, 99% sequence similarity). CONCLUSION: On the basis of physiological and phylogenetic characteristics, strains KOR-3, -4, -5, and -6 are proposed to be new strains within the genus Methanosarcina, named M. mazei KOR-3, -4, -5, and -6.