Genome-based in silico detection of putative manganese transport systems in Lactobacillus plantarum and their genetic analysis

1 Wageningen Centre for Food Sciences, NIZO Food Research, Kernhemseweg 2, PO Box 20, 6710 BA Ede, The Netherlands 2 Unité de Génétique, Institut des Sciences de la Vie, Université catholique de Louvain, 5 Place Croix du Sud, Louvain-la-Neuve, 1348, Belgium Correspondence Michiel Kleerebezem Michiel.Kleerebezem{at}nizo.nl Manganese serves an important function in Lactobacillus plantarum in protection against oxidative stress and this bacterium can accumulate Mn 2+ up to millimolar levels intracellularly. Although the physiological role of Mn 2+ and the uptake of this metal ion have been well documented, the only uptake system described so far for this bacterium is the Mn 2+ - and Cd 2+ -specific P-type ATPase (MntA). Recently, the genome of L. plantarum WCFS1 has been sequenced allowing in silico detection of genes potentially encoding Mn 2+ transport systems, using established microbial Mn 2+ transporters as the query sequence. This genome analysis revealed that L. plantarum WCFS1 encodes, besides the previously described mntA gene, an ABC transport system ( mtsCBA ) and three genes encoding Nramp transporters ( mntH1 , mntH2 and mntH3 ). The expression of three ( mtsCBA , mntH1 and mntH2 ) of the five transport systems was specifically derepressed or induced upon Mn 2+ limitation, supporting their role in Mn 2+ homeostasis in L. plantarum . However, in contrast to previous reports, mntA expression remains below detection levels in both Northern and real-time RT-PCR analysis in both Mn 2+ excess and starvation conditions. Growth of WCFS1 derivatives mutated in mntA , mtsA or mntH2 , or both mtsA and mntH2 appears unaffected under Mn 2+ excess or Mn 2+ limitation. Moreover, intracellular Mn 2+ concentrations remained unaltered in these mutants compared to the wild-type. This may suggest that this species is highly adaptive in response to inactivation of these genes or, alternatively, that other transporters that have not yet been identified as Mn 2+ transporters in bacteria are involved in Mn 2+ homeostasis in L. plantarum .