Characterization and expression of secA in Mycobacterium avium

Mycobacterium avium is both a pathogen that infects several hosts such as h umans, pigs, and birds, as well as a microorganism that is encountered in e nvironmental sources (soil and water). Protein secretion by the bacterium i s likely to influence its ability to overcome adverse and competitive condi tions: both within or outside the host. Using a combination of cloning and information available in the databank, we characterized the secA gene from M. avium encoding for a major preprotein translocase subunit associated wit h the secretion system of prokaryotics. In addition, we cloned the secA pro moter sequence in a reporter construct upstream of a promoterless gfp. It w as determined that the secA of M. avium shares large homology with the secA of Mycobacterium tuberculosis but not with secA of Mycobacterium leprae. s ecA expression was determined to be greater at logarithmic growth phase alt hough it was also expressed at low levels during the stationary phase. secA expression was also observed when the bacteria were incubated in water as well as within human monocyte-derived macrophages and in conditions that ar e associated with biofilm formation. Future evaluation of the sec pathway i n M. avium might provide important information about secreted proteins that art: required for survival in different environments. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. A ll rights reserved.