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We have cloned and sequenced a 2,262-bp chromosomal DNA fragment from the chemolithoautotrophic acidophilic bacteriumLeptospirillum ferrooxidans . This DNA contained an open reading frame for a 577-amino-acid protein showing several characteristics of the bacterial chemoreceptors and, therefore, we named this genelcrI forLeptospirillum chemotaxis receptor I. This is the first sequence reported for a gene fromL. ferrooxidans encoding a protein. ThelcrI gene showed both ς28 -like and ς70 -like putative promoters. The LcrI deduced protein contained two hydrophobic regions most likely corresponding to the two transmembrane regions present in all of the methyl-accepting chemotaxis proteins (MCPs) which make them fold with both periplasmic and cytoplasmic domains. We have proposed a cytoplasmic domain for LcrI, which also contains the highly conserved domain (HCD region), present in all of the chemotactic receptors, and two probable methylation sites. The in vitro expression of a DNA plasmid containing the 2,262-bp fragment showed the synthesis of a 58-kDa protein which was immunoprecipitated by antibodies against the Tar protein (an MCP fromEscherichia coli ), confirming some degree of antigenic conservation. In addition, this 58-kDa protein was expressed inE. coli , being associated with its cytoplasmic membrane fraction. It was not possible to determine a chemotactic receptor function for LcrI expressed inE. coli . This was most likely due to the fact that the periplasmic pH ofE. coli , which differs by 3 to 4 pH units from that of acidophilic chemolithotrophs, does not allow the right conformation for the LcrI periplasmic domain.

Molecular Cloning, Sequencing, and Expression of a Chemoreceptor Gene from Leptospirillum ferrooxidans