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Inactivation of the Lactococcus lactis high affinity phosphate transporter confers oxygen and thiol resistance and alters metal homeostasis

¹ UR888 INRA;
² INRA UR888;
³ INRA

ABSTRACT

Numerous strategies allowing bacteria to detect and respond to oxidative conditions depend on the cell redox state. Here we examined the ability of Lactococcus lactis to survive aerobically in the presence of reducing agent dithiothreitol (DTT), which would expectedly modify the cell redox state and disable the oxidative stress response. DTT inhibited L. lactis growth at 37°C in aerobic conditions, but not in anaerobiosis. Mutants selected as DTT-resistant all mapped to the pstFEDCBA locus, encoding a high affinity phosphate transporter. Transcription of pstFEDCBA and a downstream putative regulator of stress response, phoU, was deregulated in a pstA strain, but amounts of major oxidative stress proteins were unchanged. As metals participate in oxygen radical formation, we compared metal sensitivity of wild type and pstA strains. The pstA mutant showed approximately 100-fold increased resistance to copper and zinc. Furthermore, copper or zinc addition exacerbated WT L. lactis strain sensitivity to DTT. Inactivation of pstA conferred a more general suppression of oxidative stress, as the allele suppressed oxygen- and thermo-sensitivity of a clpP mutant. This study establishes a role of the pst locus in metal homeostasis, suggesting that pst inactivation lowers intracellular reactivity of copper and zinc, which would limit bacterial sensitivity to oxygen.

⁴ E-mail: meriem.el_karoui{at}jouy.inra.fr