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Applied and Environmental Microbiology, October 2007, p. 6144-6149, Vol. 73, No. 19
0099-2240/07/$08.00+0     doi:10.1128/AEM.00413-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Inactivation of an Iron Transporter in Lactococcus lactis Results in Resistance to Tellurite and Oxidative Stress

Infectious Diseases Program, Cells and Tissue Domain, Institute for Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia

Received 22 February 2007/ Accepted 30 July 2007

In Lactococcus lactis, the interactions between oxidative defense, metal metabolism, and respiratory metabolism are not fully understood. To provide an insight into these processes, we isolated and characterized mutants of L. lactis resistant to the oxidizing agent tellurite (TeO₃^2–), which generates superoxide radicals intracellularly. A collection of tellurite-resistant mutants was obtained using random transposon mutagenesis of L. lactis. These contained insertions in genes encoding a proton-coupled Mn²⁺/Fe²⁺ transport homolog (mntH), the high-affinity phosphate transport system (pstABCDEF), a putative osmoprotectant uptake system (choQ), and a homolog of the oxidative defense regulator spx (trmA). The tellurite-resistant mutants all had better survival than the wild type following aerated growth. The mntH mutant was found to be impaired in Fe²⁺ uptake, suggesting that MntH is a Fe²⁺ transporter in L. lactis. This mutant is capable of carrying out respiration but does not generate as high a final pH and does not exhibit the long lag phase in the presence of hemin and oxygen that is characteristic of wild-type L. lactis. This study suggests that tellurite-resistant mutants also have increased resistance to oxidative stress and that intracellular Fe²⁺ can heighten tellurite and oxygen toxicity.

Published ahead of print on 3 August 2007.