PHENOTYPIC VARIABILITY AMONG CELLS OF LACTOBACILLUS-HELVETICUS ATCC-15807

Lactobacillus helveticus ATCC 15807 is a slime-producing, fast milk-coagulating str ain. During growth under optimum conditions, it spontaneously produces variants able to ferment mannose (0.01% of the total population), and fructose (0.004%), which then remain stable through several subcultures. These variants did not revert, during our rest, to the wild phenotype, whereas those clones unable to ferment fructose and mannose regularly produced fermenting variants. In addition, by using the lytic phage, ATCC 15807-B1, it was possible to determine that 0.004% of the cell population was phage resistant. Adsorption interference was the phage-resistance mechanism involved in these spontaneous mutants. The proteolytic activity was also shown to be heterogeneously distributed among cells of this strain, and it was possible to isolate clones with less and more proteolytic activity when compared with the parent strain. Every variant type retained other phenotypes of the wild-type strain such as cell and colony morphology and slime production. Plasmid DNA content did not seem to be involved in these phenotypic variations. The practical interest of this cell heterogeneity is discussed.