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 TB0136 ^T and TB0139 ^T . 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 TB0136 ^T and TB0139 ^T were observed to grow at temperatures of 15–45 °C (both optimal at 33 °C; TB0139 ^T additionally showed trace growth at 50 °C), at pH of 6.0–10.0 (TB0136 ^T optimal at 7.5–8.0, TB0139 ^T 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 TB0136 ^T and TB0139 ^T were 63.3 and 61.5 mol%, respectively. Phylogenetic analysis based on the 16S rRNA gene sequence and the whole genome indicated that strains TB0136 ^T and TB0139 ^T formed a unique lineage in the evolutionary branches of the family Xanthobacteraceae . According to the characteristics of polyphasic taxonomy, strains TB0136 ^T and TB0139 ^T 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 TB0136 ^T (=MCCC 1K09187 ^T =JCM 37006 ^T ) and TB0139 ^T (= MCCC1K09185 ^T =JCM 37007 ^T ), respectively.