Characterization of a sugar-binding protein from Azospirillum brasilense mediating chemotaxis to and uptake of sugars

Our approach to the isolation of plant-inducible bacterial genes of Azospir illum brasilense, based on the analysis of protein patterns of bacteria gro wn in the presence and in the absence of plant root exudates, led to the id entification of an acidic 40 kDa protein. Cloning and sequencing analysis o f the corresponding coding DNA region revealed the presence of two open rea ding frames transcribed in the same orientation. The deduced ORF1 protein, which corresponds to the 40 kDa protein, is very similar to the periplasmic ChvE protein, identified in Agrobacterium tumefaciens and involved in enha nced virulence. The deduced ORF2 protein shows homology to members of the L ysR family of transcriptional regulators. The function of the ChvE-like pro tein in A. brasilense was investigated further. The protein, designated as SbpA (sugar binding protein A), is involved in the uptake of D-galactose an d functions in the chemotaxis of A. brasilense towards several sugars, incl uding D-galactose, L-arabinose and D-fucose, Expression of the sbpA gene re quires the presence of the same sugars in the growth medium and is enhanced further in combination with carbon starvation of A. brasilense cells.