Identification of the Polar Flagellum Genes in Azospirillum brasilense

Azospirillum brasilenser, a nitrogen fixing rhizobacterium, can colonize plant roots and increase the yield of economically important cereals, such as rice and grasses. This organism has a mixed pattern of flagellation: a single polar flagellum for motility in liquid medium and lateral flagella which might be involved in motility across the root surface and or attachment to the root hairs of plants. Flagella dictate A. brasilense chemotactic ability and motility, which plays an important role in colonization of plant roots. However, nothing is known about the genes that code for the polar flagellum. To study the polar flagellum, different mutants with the Mot- phenotype were identified. A Western blot analysis was done on cell lysates collected from the mutants and from the wild type strain. Using antibody As-Fla, specific for polar flagellum, the flagellin sizes for mutants and the wild type were determined. Some of the mutants had 96-kDa flagellin like the wild type while others had truncated flagellin as small as 65-kDa. Our hypothesis is that mutants with reduced size flagellin do not assemble normal flagella. The mutants with 96-kDa flagellin are believed to assemble a normal flagellum but there maybe deficiencies in the flagellar motor. In our assessment of the polar flagellum genes in A. brasilense using functional complementation of Mot- mutants, homologs of the following genes were found: fliN, flbD, flhA, flhF, fliJ, fliI, flgE, flgD, motA,and motR,. These proteins are involved in flagellar motor function, regulation of gene expression, synthesis and export of flagellin, and in the control of placement and number of flagellar