Valine transport and biodiversity of Leuconostoc wild strains from French raw milk cheeses.

The rate of L-valine transport in whole cells of Leuconostoc was at the maximum at 30 degrees C, pH 6.0 in the presence of an energy source. Transport was inhibited by 40-55%, in the presence of the ionophores (valinomycin, nigericin or monensin), and uncouplers (carbonyl cyanide-m-chloro-phenylhydrazone or 2,4-dinitrophenol) confirming the previously described delta p-driven branched-chain amino acid transport system described in cytoplasmic membranes (Winters et al., 1991, Appl. Environ. Microbiol., 57, 3350-3354). Sulfhydryl group reagents (p-chloro-mercuribenzoate, iodoacetate and N-ethyl maleimide) all inhibited valine transport by 60-70%, indicating that valine is actively transported at high valine concentration. Three kinetically distinguishable transport systems were identified for each strain using whole cells, confirming results obtained with membranes. L-valine transport Kt and Vmax could be an additional tool to estimate the biodiversity of 18 Leuconostoc strains belonging to the dominant flora of French raw milk cheeses. Kt values varied from 20 to 510 nmol/l for the very high affinity system, from 26 to 427 pmol/l for the high affinity system and from 0.65 to 4.40 mmol/l for the low affinity system. No correlation existed between valine transport rates and a particular strain's ability to acidify milk or complex media, suggesting that valine transport is not a growth-limiting function in species of the genus Leuconostoc.