Isolation and identification of lactic acid bacteria from vegetable-growing soils in Da Lat, Lam Dong

Abstract

Lactic acid bacteria (LAB) have been used for decades in agriculture to improve soils, control disease and promote plant growth. LAB have been isolated from fermented food, milks and plants, however, a few studies of LAB from soils have been reported. This study aimed to isolate, screen and identify LAB from vegetable-growing soils collected from Da Lat (Lam Dong province). From 33 soil samples, 25 LAB isolates were selected on MRS agar supplemented with 1% CaCO3. The LAB isolates formed small, creamy white, convex, entire margin colonies, and were Gram-positive, catalase-negative and rod-shaped bacteria. Based on the acid-producing capacity, five LAB isolates (DT2, CT3, CC2, XL7 and S2) that produced clear zones around colonies due to the solubilization of CaCO3 with diameters ranged from 1.03 - 1.33 cm, and 11.8 - 14.3 mg/mL acid after 2-day incubation at 30oC. All selected LAB isolates showed the capacity to inhibit the growth of Fusarium oxysporum at level 1 (inhibitory rates in range of 10.66 - 19.96%), and Phytopthora sp. at level 3 (inhibitory rates in range of 50.86 - 57.44%) after 3 days. The isolates did not inhibit against E. coli and Staphylococcus but inhibit the growth of Bacillus spizizenii and Salmonella typhi with average inhibition diameters in range of 3.33 - 4.90 mm and 2.43 - 3.37 mm, respectively, after 1-day incubation. The five LAB isolates were molecularly determined to be Lactobacillus plantarum with 97 - 100% similarities