Selenate Reduction and Selenium Enrichment of Tea by the Endophytic Herbaspirillum sp. Strain WT00C

Abstract

Herbaspirillum sp. WT00C is a tea-plant-specific endophytic bacterium. A genomic survey revealed an intact pathway for selenocompound metabolism in the genome of this bacterium. When it was cultured with sodium selenate, Herbaspirillum sp. WT00C was able to turn the culture medium to red. Electron microscopy and energy-dispersive X-ray spectroscopy confirmed that Herbaspirillum sp. WT00C reduced selenite (Se 6+ ) to elemental selenium (Se 0 ), and selenium nanoparticles (SeNPs) were secreted outside bacterial cells and grew increasingly larger to form Se-nanospheres and finally crystallized to form selenoflowers. Biochemical assays showed that selenospheres contained proteins but not carbohydrates or lipids. The improvement of selenium enrichment of tea plants by Herbaspirillum sp. WT00C was also tested. After Herbaspirillum sp. WT00C was inoculated into tea seedlings via needle injection and soaking tea-cutting methods, this endophytic bacterium markedly enhanced selenium enrichment of tea. When the tea seedlings inoculated by soaking tea-cutting mode were cultivated in the selenium-containing soils, selenium contents of tea leaves in three experimental groups were more than twofold compared to those of control groups. Our study demonstrates that the endophytic bacterium Herbaspirillum sp. WT00C has the ability to reduce selenate and improve selenium enrichment of tea.

Bacterial growth, morphology, and cell component changes in Herbaspirillum sp. WT00C exposed to high concentration of selenate

“…As shown in Figure , this bacterium has an intact selenate reduction pathway in its genome, and it is indeed able to reduce selenate (Se 6+ ) to elemental selenium (Se 0 ). Electron microscopy and energy‐dispersive X‐ray spectroscopy confirmed that this bacterium not only reduced selenate to form zerovalent SeNPs but also secreted SeNPs outside bacterial cells, where SeNPs grew large to form Se‐nanospheres and then crystallized to form selenoflowers . More interestingly, bacterial growth was seriously inhibited in the early stage but its growth subsequently recovered and finally approached the level of bacterial cells untreated with selenate when the concentration of selenate was larger than 50 mM.…”

“…WT00C was isolated from tea plants in Wuhan city, China and deposited in the China Center for Type Culture Collection (CCTCC AB 2018017 T ). This strain was routinely cultured in NB or LB medium according to the method reported previously . Inorganic and organic chemical reagents were purchased from Zhong Ke (Shanghai, China).…”

“…SEM was used to observe bacterial cells in different periods, as reported previously . Briefly, Herbaspirillum sp.…”

“…More interestingly, bacterial growth was seriously inhibited in the early stage but its growth subsequently recovered and finally approached the level of bacterial cells untreated with selenate when the concentration of selenate was larger than 50 mM. This bacterium was able to recover its growth and reduce selenate to form elemental selenium even if the selenate concentration was up to 200 mM . In this study, we investigated the response of Herbaspirillum sp.…”

Red elemental selenium (Se0) improves the immunoactivities of EPC cells, crucian carp and zebrafish against spring viraemia of carp virus

“…H. camelliae WT00C was isolated from a tea plant in Wuhan, China (Liu et al ., 2020; Wang et al ., 2014) and deposited in China Center for Type Culture Collection (CCTCC AB 2018017 T ). This strain was routinely cultured in NB or LB medium according to the method reported previously (Wang et al ., 2014; Xu et al ., 2020). Inorganic and organic chemical reagents were purchased from Zhong Ke (Shanghai, China).…”