Description of Variovorax humicola sp. nov., isolated from a forest topsoil

Employing a modified cultivation method, we studied two bacterial strains, UC10 and UC38^T, found on the Kyonggi University campus, Suwon in Gyeonggi-Do province, South Korea. These strains were non-spore-forming, Gram-stain-negative, motile and rod-shaped. Growth occurred in the presence of 0-2 % (w/v) NaCl, at pH 4-9 and a temperature range of 4-35 °C. On an R2A agar plate incubated for 5 days at 28 °C, irregular, raised and pale-yellowish colonies were observed. Comparative analysis of nearly full-length 16S rRNA gene sequences indicated that these strains were closely related to Variovorax guangxiensis GXGD002^T, with 98.6 % similarity. Strains UC10 and UC38^T were 98.0 % similar to V.ariovorax soli GH9-3^T; 97.8 % to V.ariovorax dokdonensis DS-43^T; 97.3-97.7 % to V.ariovorax ginsengisoli Gsoil 3165^T; 97.7-98.0 % to V.ariovorax paradoxus IAM 12373^T; 97.4-97.6 % to V.ariovorax defluvii 2C1-b^T; and 97.3-97.4 % to V.ariovorax boronicumulans BAM-48^T. The predominant ubiquinone was Q-8. The primary polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The major fatty acids were C16 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C17 : 0 cyclo. DNA-DNA hybridization assays indicated 89.2-91.4 % genomic DNA similarity between strains UC10 and UC38^T. Moreover, genomic DNA similarity between these novel strains and reference strains of the genus Variovoraxwas less than the 70 %. Based on these results, strain UC38^T was designated a representative of a novel species of the genus Variovorax, with the proposed name Variovorax humicola sp. nov. The type strain is UC38^T (=KACC 18501^T=NBRC 111520^T).