| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Streptococcus iniae </it>(<it>S. iniae</it>) is a major pathogen that causes considerable morbidity and mortality in cultured fish worldwide. The pathogen's ability to adapt to the host affects the extent of infection, hence understanding the mechanisms by which <it>S. iniae </it>overcomes physiological stresses during infection will help to identify potential virulence determinants of streptococcal infection. Grow <it>S. iniae </it>under iron-restricted conditions is one approach for identifying host-specific protein expression. Iron plays an important role in many biological processes but it has low solubility under physiological condition. Many microorganisms have been shown to be able to circumvent this nutritional limitation by forming direct contacts with iron-containing proteins through ATP-binding cassette (ABC) transporters. The ABC transporter superfamilies constitute many different systems that are widespread among living organisms with different functions, such as ligands translocation, mRNA translation, and DNA repair.</p> <p>Results</p> <p>An ABC transporter system, named as <it>mtsABC </it>(metal transport system) was cloned from <it>S. iniae </it>HD-1, and was found to be involved in heme utilization. <it>mtsABC </it>is cotranscribed by three downstream genes, i.e., <it>mtsA</it>, <it>mtsB</it>, and <it>mtsC</it>. In this study, we cloned the first gene of the <it>mtsABC </it>transporter system (<it>mtsA</it>), and purified the corresponding recombinant protein MtsA. The analysis indicated that MtsA is a putative lipoprotein which binds to heme that can serve as an iron source for the microorganism, and is expressed <it>in vivo </it>during Kunming mice infection by <it>S. iniae </it>HD-1.</p> <p>Conclusions</p> <p>This is believed to be the first report on the cloning the ABC transporter lipoprotein from <it>S. iniae </it>genomic DNA. Together, our data suggested that MtsA is associated with heme, and is expressed <it>in vivo </it>during Kunming mice infection by <it>S. iniae </it>HD-1 which indicated that it can be a potential candidate for <it>S. iniae </it>subunit vaccine.</p>
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