Cysteine metabolism in an isolate ofLactobacillus sake: Plasmid composition and cysteine transport

Lactobacillus sake L13, an isolate from vacuum packaged beef is able to utilise cysteine as an energy source for growth in rich medium. This isolate segregates into two strains, one of which retains the ability to grow on cysteine (notated as strong cells) while the other grows only marginally (weak). Both strains possess cysteine desulfhydrase activity, but only one is able to actively transport cysteine (high affinity). Uptake is sensitive to inhibition by valinomycin, CCCP, nigericin and arsenate. Comparison of the two cell types indicates that there are two cysteine transport systems and that the alternative one is passive and of low affinity. Strong cells possess two plasmids (2.7 and 8.3 kb) while the weak strain has lost the plasmids. Curing of the strong cells results in plasmid loss and loss of the high affinity cysteine uptake system.