具有硒吸附能力乳酸菌的筛选及安全性评价

Screening and safety evaluation of lactic acid bacteria with selenium adsorption capacity

乳酸菌具有将无机硒转化为有机硒的潜在能力和多种益生特性,故将其作为安全高效的硒载体进行补硒已日益成为研究热点.本研究通过测定来源于8个种水平的43株乳杆菌的硒吸附能力,最终筛选出一株具有硒吸附能力较高的乳杆菌菌株植物乳杆菌(Lactobacillusplantarum)RS7-1,其对硒的吸附率可达40.79%.同时,通过测定不同初始p H、初始菌体浓度、初始硒浓度和不同吸附时间研究该菌株的吸附特性.此外,测定该菌株的耐酸和耐胆盐特性以研究其在胃肠道中是否仍可保持较高活性,并通过体外抗生素耐受性实验以及体内急性毒性实验和30d喂养实验对其安全性进行评价.结果表明,植物乳杆菌RS7-1硒吸附的最适p H为5.0,最适初始菌体浓度为2g/L,在初始硒浓度为20mg/L时达到最大吸附量,在吸附时间为60min即达到平衡.同时,该菌株具有较强的耐酸和耐胆盐能力,不存在非种属特有的抗生素耐受性.动物实验结果表明,饲喂植物乳杆菌RS7-1菌悬液的实验组小鼠的摄食量、体重、血常规指标和血生化指标与空白组无显著差异,且组织器官无病变.因此,综合评价植物乳杆菌RS7-1是一株硒吸附能力强、耐酸和耐胆盐、安全性好的乳酸菌,具有良好的应用价值.

Selenium, one of the essential trace elements in humans and animals, is involved in various biochemical and physiological functions, such as improving immunity and antioxidant properties. Lactic acid bacteria, recognized as "generally recognized as safe(GRAS)" in the world, have the ability to convert inorganic selenium into organic form and have plenty of outstanding probiotic properties, including regulation of gut microbiota, increase of antioxidant capacity, and decrease of intestinal inflammation and so on. Therefore, using them as a safe and efficient selenium supplementation carrier is increasingly becoming a hotspot in recent research. In order to obtain a strain of lactic acid bacteria with good selenium adsorption capacity, 43 strains of Lactobacillus of different species were screened by determining the adsorption rate of selenium in vitro. The adsorption conditions were as follows: The initial selenium concentration was 50 mg/L, the initial cell concentration was 1 g/L, and the adsorption time was 1 h. The selenium adsorption rate and selenium adsorption capacity of the strains were determined by measuring the selenium content of the dried bacteria after nitrolysis. The selenium levels were determinated by inductively coupled plasma mass spectrometer(ICP-MS). At the same time, the adsorption characteristics of the strain were studied by changing the initial pH, initial cell concentration, initial selenium concentration and adsorption time, and acid and bile salt tolerance were determined to confirm whether it can still maintain high activity in the gastrointestinal tract. Then the safety of the strain was evaluate by the acute toxicity test and the 30-d feeding experiment, as well as antibiotic resistance of the strain. The results showed that the Lactobacillus plantarum RS7-1 had the most excellent selenium adsorption ability among the 43 strains, and its adsorption rate for selenium was up to 40.79%±1.27%. The optimum pH of the strain was 5.0, and the optimal initial bacterial concentration was 2 g/L. The maximum adsorption capacity was reached when the initial selenium concentration was 20 mg/L. The adsorption of selenium can be divided into two stages, rapid adsorption stage and adsorption equilibrium stage. The equilibrium time was reached when the adsorption time was 60 min. At the same time, the strain has outstanding acid and bile salt tolerance, without species-specific antibiotic tolerance, and after safety evaluation, the mice fed with the strain shows no significant difference in the food consumption, body weight, biochemical index, hematological indexes of blood compared with mice in blank group, and no organ and tissue lesions were detected. In conclusion, Lactobacillus plantarum RS7-1 is a strain of lactic acid bacteria with superb selenium adsorption capacity, great acid and bile salt tolerance, without toxicity and side effect. This study provides an idea for the selenium supplement with probiotics as the carrier, and the selenium adsorption capacity can be further improved by optimization of adsorption conditions, mutation breeding and genetic engineering, thereby increasing the application value of selenium-enriched probiotic products in the future.