Haloleucobacter ellipsoideus gen. nov., sp. nov., and Haloleucobacter albus sp. nov., two novel N2-fixing hydrogen bacteria isolated from soil near a wastewater treatment plant.
Two Gram-stain-negative, aerobic, oxidase-negative, non-motile, ellipsoid to short rod-shaped bacteria (~1.2-2.0 µm in length and 0.7-0.8 µm in width) were isolated from soil near a wastewater treatment plant in Hangzhou, Zhejiang Province, China, designated TB0136T and TB0139T. Both strains are able to grow chemolithoautotrophically using hydrogen as an electron donor and perform nitrogen fixation in the absence of ammonium or any organic nitrogen source. Strains TB0136T and TB0139T were observed to grow at temperatures of 15-45 °C (both optimal at 33 °C; TB0139T additionally showed trace growth at 50 °C), at pH of 6.0-10.0 (TB0136T optimal at 7.5-8.0, TB0139T optimal at 8.0-8.5) and in the presence of 0-6.0% (w/v) NaCl (optimal at 1.0%). Chemotaxonomic analyses indicated that the main respiratory quinone in both strains is ubiquinone-10. The DNA G+C contents of strains TB0136T and TB0139T were 63.3 and 61.5 mol%, respectively. Phylogenetic analysis based on the 16S rRNA gene sequence and the whole genome indicated that strains TB0136T and TB0139T formed a unique lineage in the evolutionary branches of the family Xanthobacteraceae. According to the characteristics of polyphasic taxonomy, strains TB0136T and TB0139T are proposed to represent two novel species of a new genus, for which the name Haloleucobacter gen. nov. is proposed. The proposed species names are Haloleucobacter ellipsoideus and Haloleucobacter albus. The type strains are TB0136T (=MCCC 1K09187T=JCM 37006T) and TB0139T (= MCCC1K09185T=JCM 37007T), respectively.