Multiple exposures to high concentration of selenate significantly improve selenate tolerability, red elemental selenium (Se0) and selenoprotein biosynthesis in Herbaspirillum camelliae WT00C

Abstract Herbaspirillum camelliae WT00C isolated from tea plant has an intact selenate metabolism pathway but its selenate tolerability is poor. In this study, microbiological properties between the strain WT00C and three strains CT00C, NCT00C and NT00C obtained respectively from 4, 6 and 8 rounds of 24-h exposures to 200 mM selenate were studied and compared. The selenate tolerability and the capability of generating red elemental selenium (Se0) and selenoproteins were significantly improved in H. camelliae WT00C via 4–6 rounds of multiple exposures to high concentration of selenate. The original strain WT00C grew in 200 mM selenate with the lag phase of 12 h and 400 mM selenate with the lag phase of 60 h, whereas the strains CT00C and NCT00C grew in 800 mM selenate and showed quite short lag phase when they grew in 50–400 mM selenate. Two stains also significantly improved the biosynthesis of red elemental selenium (Se0) and selenoproteins besides selenate tolerance. The stains CT00C and NCT00C exhibited more than 30% selenium conversion efficiency and 40% selenoprotein biosynthesis as compared to the original strain WT00C. These characteristics of the strains CT00C and NCT00C make them possible to be applied in pharmaceuticals and feed industries. The strain NT00C obtained from 8 rounds of 24-h exposures to 200 mM selenate was unable to grow in ≥ 400 mM selenate, and its selenium conversion efficiency and selenoprotein biosynthesis were similar to the strain WT00C. Too many exposures caused gene inactivation of some key enzymes involving in selenate metabolism and antioxidative stress. In addition, bacterial cells underwent obviously physiological and morphological changes including gene activity, cell enlargement and surface-roughness alterations during the process of multiple exposures to high concentration of selenate.