Induction of stable slime-forming and mucoid states byp-fluorophenylalanine in lactic streptococci

Abstract

Lactic streptococci play an important role in commercial milk fermentations. They have also been suggested to play an important role in stimulating the development of natural immunity in animals and humans [1,2]. Streptococcus cremoris differs from S. lactis by growth in longer chains, by lower optimum growth temperature, by lower but more constant production of acid in milk, and by its ability to form slime in milk. Studies on the capsuleand slime-forming properties of lactic streptococci are few; they mostly concern the Finnish ropy sour milk called viili [3]. Slime and capsule formation are known to depend on many factors, both genetic and environmental. Extensive genetic studies on the regulation of capsule and slime polysaccharide biosynthesis in Escherichia coli provide models for the study of other groups of bacteria as well [4]. The fact that the mucoid antigen--colanic ac id-of mucoid mutants of E. coli is the same substance as that produced by wild-type strains when grown at low temperature shows that the wild type contains all the genetic information for the synthesis of colanic acid although it is not expressed under certain conditions of growth (37°C). In an analogous manner lactic streptococci isolated from viili synthesize slime when grown at 17°C but lose the slime-forming capacity when grown at 30°C [3]. Some amino acid analogues that are incorporated into protein lead to thermolability of certain enzymes and have been used to study the control of capsular polysaccharide synthesis in E. coli [4]. The present study was undertaken to (i) examine the effect of p-fluorophenylalanine (FPA) on nonmucoid or moderately mucoid colonies of two lactic Streptococcus strains and (ii) compare the effect of FPA on two enzymatic reactions in extracts of lactic streptococci, namely (1) glucose-lphosphate ~ UDP-D-glucose; (2) U D P D galactose ~ UDP-D-glucose. These are sequential reactions in the postulated pathway for slime polysaccharide in E. coli [5]. We have shown (unpublished data) that the extracellular capsular material of lactic streptococci contains galactose, glucose and probably fucose like the slime polysaccharide of E. coli. In this study, these enzyme activities are reported for the first time in connection with capsuleand slime-forming capacity of lactic streptococci.