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

The specific endophytic association between Acetobacter diazotrophicus and sugarcane may represent a beneficial symbiosis with the bacterial partner providing fixed N and/or plant growth promoting factors such as auxin. Our goals are to identify and characterize the genes of A. diazotrophicus necessary for nitrogen fixation and effective symbiosis. In summary, we have isolated a gene cluster including nifAB HDK ENXQ USVW, fixABCX in one region of the A. diazotrophicus genome. Also, two other genes, modD (molybdenum transporter protein) and mcpA (methyl-accepting chemotaxis protein) were located downstream of fixABCX. The mcpA gene product is involved in responses to extracellular chemotactic signals, which may play an important role in plant-microbe interactions. A mcpA mutant of A. diazotrophicus lost chemotaxis toward a wide range of attractant stimuli and will be used to determine whether mcpA + bacteria have a competitive advantage with respect to cell survival and colonization of sugarcane.