Objective The aims were to screen microorganisms with high resistance to selenite and to efficiently activate selenium(Se) in soil.

Method Dilution plate technique was used to isolate microorganisms, and Se containing streak method was used to screen selenite-tolerant strains. The identification of strains was used by 16S rDNA gene sequence analysis. The determination of selenite enrichment rate was by adding strains to liquid culture medium containing selenite. The strains were added to Se-rich soil, in order to determine the changes in physical and chemical properties of soil, and to evaluate the capacities of the strains to activate Se in soil.

Result Two screened strains had high resistance to selenite (up to 500 mmol L⁻¹). The 16S rDNA gene sequence analysis confirmed that the strains were Serratia marcescens QZB-1 and Proteus penneri LAB-1. Two strains could grow under conditions of pH = 5-10, temperature 15-40℃, and NaCl < 10%. All strains had a high Selenite enrichment rate. Serratia marcescens QZB-1 fully enriched 2 mmol L⁻¹ SeO₃²⁻ in only 18 hours. After adding two selenite-tolerant bacteria to the soil, the pH value and available Se content of the soil were significantly increased. Two strains altered the distribution of Se forms in soil by reducing the content of organic binding Se and increasing the content of Soluble Se and Exchangeable Se. It is a remarkable fact that the significant increase in the content of Soluble Se and Exchangeable Se in soil was caused by the simultaneous application of two strains.

Conclusion Two strains with high Selenite tolerance were screened from Se-rich soil in Guangxi. which can provide microbial resources for the development and utilization of Se-rich soil.