PHENOTYPIC VARIABILITY AMONG CELLS OF LACTOBACILLUS-HELVETICUS ATCC-15807

Lactobacillus helveticus ATCC 15807 is a slime-producing, fast milk-co agulating str ain. During growth under optimum conditions, it spontane ously produces variants able to ferment mannose (0.01% of the total po pulation), and fructose (0.004%), which then remain stable through sev eral subcultures. These variants did not revert, during our rest, to t he 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 0.0 04% of the cell population was phage resistant. Adsorption interferenc e was the phage-resistance mechanism involved in these spontaneous mut ants. The proteolytic activity was also shown to be heterogeneously di stributed among cells of this strain, and it was possible to isolate c lones with less and more proteolytic activity when compared with the p arent 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 va riations. The practical interest of this cell heterogeneity is discuss ed.