Zinc uptake, oxidative stress and the FNR-like proteins of Lactococcus lactis

Lactococcus lactis ssp. cremoris MG1363 contains two FNR homologues, FlpA a nd FlpB, encoded by the distal genes of two paralogous operons (orfX(A/B)-o rfY(A/B)-flpA/B). An flpA flpB double mutant strain is hypersensitive to hy drogen peroxide and has a depleted intracellular Zn(II) pool. The phenotype s of the flp mutant strains suggest that FlpA and FlpB control the expressi on of high and low affinity ATP dependent Zn(II) uptake systems, respective ly. Plate tests revealed that expression from a orfX(B)::lac reporter was a ctivated by Cd(II), consistent with other Zn(II)-regulated systems. The lin k between a failure to acquire Zn(II) and hypersensitivity to oxidative str ess suggests that Zn(II) may be required to protect vulnerable protein thio ls from oxidation. (C) 2000 Federation of European Microbiological Societie s. Published by Elsevier Science B.V. All rights reserved.