A novel selenite-tolerant rhizosphere bacterium Wautersiella enshiensis sp. nov., isolated from Chinese selenium hyperaccumulator, Cardamine hupingshanensis

Selenium (Se) is a dietary essential trace element for humans with various physiological functions and it could also be accumulated by some plant species, like Astragalus bisulcatus, Stanleya pinnata, and Cardamine hupinshanensis. A novel Gram-stain-negative, facultatively anaerobic, selenite-tolerant bacterium, designated strain YLX-1^T, was isolated from the rhizosphere of a Se hyperaccumulating plant, Cardamine hupingshanensis in Enshi, China. Phylogenetic analysis based on 16 S rRNA gene sequences indicated that strain YLX-1^T is a potential new species in the genus Wautersiella. Strain YLX-1^T could grow in the temperature range of 4–37°C (optimally at 28°C) and in the pH range of 5–9 (optimum pH 7), which also could tolerate Se up to 6000 mg Se/L via producing extracellular red nano-Se with 100–300 nm size. However, it could predominantly accumulate selenocystine (SeCys₂) in the cell under lower Se stress (1.5 mg Se/L). These results would help broaden our knowledge about the Se accumulation and transformation mechanism involved in rhizosphere bacteria like strain YLX-1^T in C. hupingshanensis. Based on polyphasic data, we propose the creation of the new species Wautersiella enshiensis sp. nov., strain YLX-1^T (= CCTCC M 2013671) which will be promising to produce nano-Se as fertilizer, food additives or medicine.