Isolation, identification and selenite metabolism of a selenium-tolerant endophyte from Cardamine hupingshanensis

Abstract:

[Background] Cardamine hupingshanensis is a novel selenium (Se)-hyperaccumulating plant in China with the predominate Se species as selenocystine (SeCys2), which is different with other Se-hyperaccumulating plants in USA, eg. Astragalus bisulcatus, Stanleya pinnata. [Objective] To explore the role of microorganism during Se-hyperaccumulation in Cardamine hupingshanensis, isolation, identification and Se metabolism in vitro of a Se-tolerant endophyte from C. hupingshanensis were conducted. [Methods] A Se-tolerant endophyte was isolated and purified from fresh leaves of C. hupingshanensis as CSN-1. The physiological and biochemical analysis and 16S rRNA gene sequence analysis were carried out. Moreover, the endophyte CSN-1 was cultured in selenite medium to study its Se metabolism. [Results] The Se-tolerant endophyte CSN-1 was identified as Bacillus methylotrophicus. The selenite culture revealed that the medium absorbance was higher than that in controls under 1.5 mg Se/L medium, but lower under 10 mg Se/L medium. The metabolized Se speciation was Se4+ in supernants, but SeCys2 in bacteria deposits. [Conclusion] The Se-tolerant endophyte Bacillus methylotrophicus CSN-1 presented in Se-hyperaccumulating plant, Cardamine hupingshanensis, and could transform selenite into SeCys2. The low concentration of Se could promote the growth of Bacillus methylotrophicu CSN-1, but negative effects could be observed at high Se levels.

Key words:Cardamine hupingshanensis, Selenium-tolerance, 16S rRNA gene, Bacillus methylotrophicus, Selenocystine/SeCys2