Se-enrichment characteristics of Enterobacter mori and its Se strengthening effect on corn grain

Selenium is an important trace element in humans, animals and microorganisms. In the human body, it is mainly in the form of organic selenium, which plays an important role in promoting the metabolic process. Organic selenium in the body can scavenge free radicals, resist oxidation, enhance human immunity and fight cancer. The body itself cannot synthesize selenium, and it must be consumed from the outside through diet. However, there are serious shortages of selenium in over 72% of regions in China, and the selenium content in the main crops cannot meet the human reference intake of selenium. Therefore, selenium-enriched foods have received extensive attention. Selenium plays an important role in antioxidant reactions in plants and animals. At appropriate concentrations, selenium can improve the activity of antioxidant enzymes, such as catalase, superoxide dismutase, and peroxidase, etc. in order to reduce oxidative stress in the plant chloroplast, and enhance plant growth. In addition, exogenous application of selenium can promote the photosynthetic pigment content of various plants. In this study, a strain IX+2 2 was previously selected from plant endophytes for transforming inorganic selenium into organic selenium with higher bioavailability. By determining its 16S rRNA gene sequence, the strain was identified as Enterobacter mori. This paper studied the effect of different selenium content, selenium addition time and different culture collection time on intracellular selenium content and selenium conversion rate of strain IX+2 2. The results showed that the selenium content in the medium had a great influence on the growth and selenium conversion ability of strain IX+2 2. With the increase of selenium content in the medium, the intracellular selenium content and selenium conversion rate gradually increased, but after reaching a certain peak, they begins to decline again. When the selenium content was 200 μg/L, the conversion rate was the highest, reaching 70.84%. When the selenium content was 250 μg/L, the selenium content in the cells reached the maximum, which was 163.45 μg/L, but the growth of the strain was significantly inhibited, and the conversion rate also decreased, It shows that the selenium content in the medium will show a high selenium conversion ability in a suitable range. The addition of selenium in the logarithmic phase favors the growth of strain IX+2 2 and the conversion of inorganic selenium. Sodium selenite addition time had little effect on the growth of strain IX+2 2 in the time range of 0-12 h, however, the selenium-enrichment efficiency of strains first increased and then decreased with the addition time. Sodium selenite was added to the strains at 3 h, and the intracellular selenium content of the strains rapidly increased to 49.93 μg/L, selenium conversion was the best, and the conversion rate could reach 66.57%. After that, with the increase of culture time, the intracellular selenium content of the cells gradually decreased, and the conversion rate of selenium also gradually decreased to 40.20%. The selenium conversion rate of the strain was highest when sodium selenite was added at 3 h, which may be due to the growth of the strain in logarithmic phase and the vigorous growth of the bacteria. When the strain was cultured for 24 h, the selenium conversion rate was best, and the growth of the cultured cells continued to decrease, with the increase of culture time, the selenium conversion rate of strain IX+2 2 increased first and then decreased. The highest transformation efficiency was 72.10% at 24 hours of culture. As the culture time increased, the growth of the bacteria decreased and some of the bacteria autolyzed, and the transformation efficiency also decreased. Simultaneously, the ability of the strain to strengthen selenium in corn kernel shows that the selenium transformation efficiency of the selenium enriched inoculate solution is better than application of sodium selenite with foliage spray. The corn kernel selenium content were noted 228.58 μg/kg when equal quantity of sodium selenite was applied with foliage spray while the microorganisms agent get to378.89 μg/kg, the latter was 1.66 times higher than the former.