Polymorphobacter multimanifer gen. nov., sp. nov., a polymorphic bacterium isolated from Antarctic white rock

Abstract

A Gram-stain-negative, non-spore-forming, aerobic, oligotrophic bacterium (strain 262-7(T)) was isolated from a crack of white rock collected in the Skallen region of Antarctica. Strain 262-7(T) grew at temperatures between -4 and 30 °C, with optimal growth at 25 °C. The pH range for growth was between pH 6.0 and 9.0, with optimal growth at approximately pH 7.0. The NaCl concentration range allowing growth was between 0.0 and 1.0%, with an optimum of 0.5%. Strain 262-7(T) showed an unprecedented range of morphological diversity in response to growth conditions. Cells grown in liquid medium were circular or ovoid with smooth surfaces in the lag phase. In the exponential phase, ovoid cells with short projections were observed. Cells in the stationary phase possessed long tentacle-like projections intertwined intricately. By contrast, cells grown on agar plate medium or in liquid media containing organic compounds at low concentration exhibited short- and long-rod-shaped morphology. These projections and morphological variations clearly differ from those of previously described bacteria. Ubiquinone 10 was the major respiratory quinone. The major fatty acids were C(17 : 1)ω6c (28.2%), C(16 : 1)ω7c (22.6%), C(18 : 1)ω7c (12.9%) and C(15 : 0) 2-OH (12.3%). The G+C content of genomic DNA was 68.0 mol%. Carotenoids were detected from the cells. Comparative analyses of 16S rRNA gene sequences indicated that strain 262-7(T) belongs to the family Sphingomonadaceae, and that 262-7(T) should be distinguished from known genera in the family Sphingomonadaceae. According to the phylogenetic position, physiological characteristics and unique morphology variations, strain 262-7(T) should be classified as a representative of a novel genus of the family Sphingomonadaceae. Here, a novel genus and species with the name Polymorphobacter multimanifer gen. nov., sp. nov. is proposed (type strain 262-7(T) = JCM 18140(T) = ATCC BAA-2413(T)). The novel species was named after its morphological diversity and formation of unique projections.