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