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 degreesC, 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 Deltap-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 K-t and V-max could be an additional tool to estimate the biodiversity of 18 Leuconostoc strains belonging to the dominant flora of French raw milk cheeses. K-t values varied from 20 to 510 nmol/l for the very high affinity system, from 26 to 427 mu mol/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.