Cloning, Expression, and Functional Characterization of Secondary Amino Acid Transporters of Lactococcus lactis

摘要: Fourteen genes encoding putative secondary amino acid transporters were identified in the genomes of Lactococcus lactis subsp. cremoris strains MG1363 and SK11 L. IL1403 KF147, 12 which common to all four strains. Amino uptake cells overexpressing revealed specific for histidine, lysine, arginine, agmatine, putrescine, aromatic acids, acidic serine, branched-chain acids. Substrate specificities demonstrated by inhibition profiles determined presence excesses other Four knockout mutants, lacking lysine transporter LysP, histidine HisP (formerly LysQ), AcaP (YlcA), or FywP (YsjA), constructed. The HisP, deletion mutants showed drastically decreased rates corresponding substrates at low concentrations. same was observed mutant with aspartate but not glutamate. In rich M17 medium, none affected growth. contrast, AcaP, did affect growth a defined medium free acids as sole source. essential concentrations, absence glutamine. appeared play role retaining intracellularly synthesized when these added medium. Finally, excretion accumulated glutamate, phenylalanine, respectively, indicating involvement transporters.