Cell Division Gene Cluster in Spiroplasma kunkelii : Functional Characterization of ftsZ and the First Report of ftsA in Mollicutes

Abstract

Spiroplasma kunkelii is a helical, wall-less bacterium that causes corn stunt disease. In adaptation to its phloem-inhabiting parasitic lifestyle, the bacterium has undergone a reductive evolutionary process and, as a result, possesses a compact genome with a gene set approaching the minimal complement necessary for multiplication and pathogenesis. We cloned a much-reduced cell division gene cluster from S. kunkelii and functionally characterized the key division gene, ftsZ_sk . The 1236-bp open reading frame of ftsZ_sk is capable of encoding a protein with a calculated molecular mass of 44.1 kDa. Protein sequence alignment revealed that FtsZ_sk is remarkably similar to FtsZ proteins from other eubacteria, and possesses the conserved GTP-binding and hydrolyzing motifs. We demonstrated that overexpression of ftsZ_sk in Escherichia coli causes transgression of the host cell division, resulting in a filamentous phenotype. We also report, for the first time, the presence of a ftsA gene in the cell division cluster of a mollicute species.