Astrobacterium formosum gen. nov., sp. nov., a novel psychrotolerant rosette-forming bacterium from a laboratory psychrophilic EGSB bioreactor

Abstract

A new psychrotolerant, facultative anaerobic bacterium, strain Astr-EGSB^T, was isolated from a syntrophic propionate-oxidizing consortium obtained from a low-temperature expanded granular sludge bed (EGSB) bioreactor fed with a mixture of volatile fatty acids. The cells of this strain were Gram-negative and non-spore-forming rods (0.5·0.8–1.5·9 μm), grew either as individual cells or formed rosettes of various sizes, resembling stars. Bacteria reproduced by budding, and each cell has a sticky, non-reproductive pole that allows them to attach to other cells, forming rosette-like clusters. This strain could grow between 5 and 40 °C, with pH ranging from 4.5 to 7.5 and NaCl concentration of 0 to 2 %. It could degrade a variety of carbon substrates, including sugars, alcohols, casamine acids and several organic acids, but could not grow under photoautotrophic conditions. During glucose fermentation, the products include lactate, acetate, isobutyrate, CO₂, and traces of succinate. Major cellular fatty acids were C_18:1ω9c and C_19:0 cyclo ω9c, menaquinone МХ-10(H10). Main polar lipids were phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol. Sequence comparison of the 16S rRNA gene revealed that strain Astr-EGSB^T was related to Pseudorhodoplanes sinuspersici RIPI 110^T with a similarity of 95.0 %. Based on phylogenomic analysis using 120 marker genes, strain Astr-EGSB^T belongs to the distinct genus-level phylogenetic lineage that is most related to the genus Rhodoplanes. The G + C content of genomic DNA was 65.8 mol%. Based on genomic and physiological characteristics of strain Astr-EGSB^T, a new genus and a new species, Astrobacterium formosum gen. Nov., sp. nov., is proposed, with Astr-EGSB^T as the type strain.