Azohydromonas caseinilytica sp. nov., a Nitrogen-Fixing Bacterium Isolated From Forest Soil by Using Optimized Culture Method

A bacterial strain, designated strain G-1-1-14 ^T, was isolated from Kyonggi University forest soil during a study of previously uncultured bacterium. The cells of strain G-1-1-14 ^T were motile by means of peritrichous flagella, Gram-stain-negative, rod-shaped, and able to grow autotrophically with hydrogen and fix nitrogen. Phylogenetic analysis based on 16S rRNA gene sequence indicated that strain G-1-1-14 ^T belonged to the genus Azohydromonas. The closest species of strain G-1-1-14 ^T were Azohydromonas ureilytica UCM-80 ^T (98.4% sequence similarity), Azohydromonas lata IAM 12599 ^T (97.5%), Azohydromonas riparia UCM-11 ^T (97.1%), and Azohydromonas australica IAM 12664 ^T (97.0%). The genome of strain G-1-1-14 ^T was 6,654,139 bp long with 5,865 protein-coding genes. The genome consisted of N ₂-fixing genes ( nifH) and various regulatory genes for CO ₂ fixation and H ₂ utilization. The principal respiratory quinone was ubiquinone-8, and the major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, and phosphatidylglycerol. The major fatty acids were summed feature 3 (iso-C _{15 : 0} 2-OH and/or C _{16 : 1} ω7 c), C _{16 : 0}, summed feature 8 (C _{18 : 1} ω7 c and/or C _{18 : 1} ω6 c), and cyclo-C _{17 : 0}. The DNA G + C content was 69.9%. The average nucleotide identity (OrthoANI), in silico DNA–DNA hybridization (dDDH), and conventional DDH relatedness values were below the species demarcation values for novel species. Based on genomic, genetic, phylogenetic, phenotypic, and chemotaxonomic characterizations, strain G-1-1-14 ^T represents a novel species within the genus Azohydromonas, for which the name Azohydromonas caseinilytica sp. nov. is proposed. The type strain is G-1-1-14 ^T (= KACC 21615 ^T = NBRC 114390 ^T ).