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Microbiology 155 (2009), 2274-2281; DOI  10.1099/mic.0.027797-0
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Microbiology 155 (2009), 2274-2281; DOI  10.1099/mic.0.027797-0
© 2009 Society for General Microbiology

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

Bénédicte Cesselin, Djae Ali{dagger}, Jean-Jacques Gratadoux{ddagger}, Philippe Gaudu, Patrick Duwat§, Alexandra Gruss and Meriem El Karoui

INRA, UR 888 Unité des Bactéries Lactiques et Pathogènes Opportunistes-UBLO, F-78350 Jouy en Josas, France

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 the reducing agent dithiothreitol (DTT), which would be expected to 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 the sensitivity of a wild-type L. lactis strain to DTT. Inactivation of pstA conferred a more general resistance to oxidative stress, alleviating the oxygen- and thermo-sensitivity of a clpP mutant. This study establishes a role for the pst locus in metal homeostasis, suggesting that pst inactivation lowers intracellular reactivity of copper and zinc, which would limit bacterial sensitivity to oxygen.

Correspondence
Alexandra Gruss
alexandra.gruss{at}jouy.inra.fr
Meriem El Karoui
meriem.el_karoui{at}jouy.inra.fr

Abbreviations: ROS, radical oxygen species

{dagger}Present address: Département des Sciences, Université Sainte-Anne, 1695 route 1, Pointe-de-l'Église, NS B0W 1M0, Canada.

{ddagger}Present address: INRA, UR910 UEPSD, F-78350 Jouy en Josas, France.

§Deceased 5 January 2000.

Supplementary material is available with the online version of this paper.






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