Antagonistic activity in plant-associated lactic acid bacteria

Abstract

A total of 256 strains of lactic acid bacteria isolated from forage grasses were screened for antagonistic activities under conditions where the effects of organic acids and hydrogen peroxide were minimised. Thirty seven strains were shown to inhibit the growth of other lactic acid bacteria in the agar spot test with viable cells. Cell free supernatants from 16 of these strains, most of them belonging to the species Lactobacillus plantarum and Enterococcus faecium, exhibited inhibitory activity against indicator strains. Crude protein extracts containing different bacteriocin-like substances were made from cell free supernatants of Lactobacillus plantarum P1331, Enterococcus faecium P5977 and Leuconostoc mesenteroides P6007, and sensitivity to these extracts of 53 strains of lactic acid bacteria and 25 strains of other phylloplane bacteria were tested. Forty four strains of lactic acid bacteria, and all but one strain of the Gram-positive heterotrophic aerobic bacteria tested were inhibited by at least one of the antagonists. All Gram-negative strains tested were resistant. Inhibitory activity against sensitive indicators was also detected when the strains P1331, P5977 and P6007 grew on “phylloplane agar”, a medium which simulates the low level nutrient conditions found on the phylloplane, in a temperature range between 4 and 37°C. It therefore seems to be likely that strains of lactic acid bacteria able to produce bacteriocin-like substances can influence the development of the population of lactic acid bacteria on plants.