Screening and molecular identification of lactic acid bacteria in environmental samples

Abstract

As a kind of probiotics widely existing in nature and human gut, lactic acid bacteria have been widely concerned in food, medicine and agriculture in recent years due to their unique physiological functions and wide application prospects. Environmental samples, such as soil, water, and plant surfaces, are important sources of lactic acid bacteria. The purpose of this experiment was to isolate, screen and identify lactic acid bacteria in the environment. First, the lactic acid bacteria in the environment were separated by the plate marking method and the coated plate method, and then the solid medium containing calcium carbonate or bromomethyl phenol green MRS Was used to screen the strains with calcium soluble ring or green color from the environmental soil and environmental water source. Then the species relationship of lactic acid bacteria was determined by morphological observation, physiological and biochemical tests and 16S rRNA gene sequence comparison. By comparing 16S rRNA sequences with those in the database, the species of lactic acid bacteria could be determined. The results showed that multiple strains of lactic acid bacteria were successfully screened from the environmental samples, and strains ZW-JX-1-1, ZW-JX-7-2 and ZW-JX-8-1 belonged to Lactobacillus reuter. Strains ZW-JX-2-1 and ZW-JX-4-1 belong to Lactobacillus paracei, strains ZW-JX-3-1 belong to Streptococcus thermophilus, strains ZW-JX-5-1 belong to Enterococcus faecalis, and strains ZW-JX-6-2 belong to Lactobacillus acidophilus. Phylogenetic tree was constructed by MEGA to show the kinship and genetic differences among different strains. The results showed that strain ZW-JX-2-1 and strain ZW-JX-4-1 were the most closely related, and the sequence comparison results showed that both strains belonged to Lactobacillus paracasei. Through this study, the screening process and molecular identification method of lactic acid bacteria were systematically understood, hoping to provide ideas for molecular identification research of lactic acid bacteria.