The bspA locus of Lactobacillus fermentum BR11 encodes an L-cystine uptakesystem

BspA is a basic surface-exposed protein from Lactobacillus fermentum BR11, Sequence comp:comparisons have shown that it is a member of family III of t he solute binding proteins. It is 89% identical to the collagen binding pro tein, Cnb, from Lactobacillus reuteri, Compared with the database of Escher ichia coli proteins, BspA, is most similar to the L-cystine binding protein FliY. To investigate the function of BspA, mutants depleted for BspA were generated by homologous recombination with a temperature-sensitive plasmid, These mutants were significantly impaired in their abilities to take up L- cystine. Uptake rates of L-glutamine, L-histidine, and L-lysine, which are substrates for other binding proteins with similarity to BspA, were unaffec ted. Evidence was obtained that BspA is necessary for maximal resistance to oxidative stress. Specifically, inactivation of BspA causes defective grow th in the presence of oxygen and sensitivity to paraquat, Measurements of s ulfhydryl levels showed that incubation of L. fermentum BR11 with L-cystine resulted in increased levels of sulfhydryl groups both inside and outside the cell; however, this was not the case with a BspA mutant, The role of Bs pA as an extracellular matrix protein adhesin was also addressed. L. fermen tum BR11 does not bind to immobilized type I collagen or laminin above back ground levels but does bind immobilized fibronectin. Inactivation of BspA d id not significantly affect fibronectin binding; therefore, we have not fou nd evidence to support the notion that BspA is an extracellular matrix prot ein binding adhesin, As BspA is most probably not a lipoprotein, this repor t provides evidence that gram-positive bacterial solute binding proteins do not necessarily have to be anchored to the cytoplasmic membrane to functio n in solute uptake.