Pseudaquabacterium prasiolae sp. nov., Isolated from the Freshwater Green Alga Prasiola japonica, and Rubrivivax soli sp. nov., Isolated from Soil, with Reclassification of Aquabacterium humicola as Pseudaquabacterium humicola comb. nov.

Abstract

Two Gram-stain-negative, catalase- and oxidase-positive, strictly aerobic, non-flagellated rod-shaped bacteria, designated OR-4^T and RP6-9^T, were isolated from the freshwater green alga Prasiola japonica and soil in Republic of Korea, respectively. Strain OR-4^T exhibited gliding motility, whereas strain RP6-9^T lacked gliding motility. Strain OR-4^T grew at 10-30 °C, pH 6.0-9.0, and 0-1.5% (w/v) NaCl, while strain RP6-9^T grew at 20-35 °C, pH 6.0-9.0, and 0-1.0% (w/v) NaCl. Both strains contained ubiquinone-8 as the sole respiratory quinone and phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol as major polar lipids; strain OR-4^T additionally possessed an unidentified phospholipid and an unidentified polar lipid. The predominant fatty acids of OR-4^T were C_12:0, C_16:0, summed feature 3 (C_16:1ω6c and/or C_16:1ω7c), and summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), whereas RP6-9^T contained C_12:0, C_16:0, and summed feature 3 as major components. The genomic DNA G + C content of both strains was 71.0 mol%. Whole-genome-based phylogenomic analyses placed OR-4^T and RP6-9^T within the genera Pseudaquabacterium and Rubrivivax, respectively, forming distinct lineages. Comparative analyses of average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity further supported their assignment to these genera while confirming their separation from previously described species. Based on combined phenotypic, chemotaxonomic, and genomic evidence, strains OR-4^T and RP6-9^T represent novel species, for which the names Pseudaquabacterium prasiolae sp. nov. (type strain OR-4^T =KACC 22752^T =NBRC 116024^T) and Rubrivivax soli sp. nov. (type strain RP6-9^T =KACC 24055^T =DSM 119932^T) are proposed. Phylogenomic analyses also support the reclassification of Aquabacterium humicola as Pseudaquabacterium humicola comb. nov. (type strain RJY3^T =KCTC 92105^T =NBRC 115831^T).