Analysis of nitrogen fixation and regulatory genes in the sugar cane endophyte Acetobacter diazotrophicus

Acetobacter diazotrophicus, a diazotrophic endophyte of sugarcane, carries a cluster of nif genes similar to those characterized in other Proteobacterial diazotrophs, These include, in order, nifA, nifB, nifHDKEN, nifUSVW and fixABC. This order of nif and fix gene organization is most similar to that found in Azospirillum brasilense, although the deduced gene products of each gene are generally more similar to those characterized in species of Rhizobium, Bradyrhizobium or Azorhizobium. Downstream of fixABC is a gene encoding a protein with similarity to MCPA, a methyl-accepting chemotaxis protein which is involved in chemotatic responses to extracellular signals. mcpA gene may play an important role in symbiosis and plant-microbe interaction by allowing colonization of sugarcane tissues far distant from the site of A. diazotrophicus infection or entry.