A spontaneous chlorate-resistant mutant of Azospirillum brasilense Sp245 displays defects in nitrate reduction and plant root colonization

Azospirillum, a soil bacterium capable of colonizing plant roots, can reduc e NO3-. In this work, a spontaneous chlorate-resistant mutant of Azospirill um brasilense Sp245, named Sp245ch11, was phenotypically characterized. The mutant is defective in both assimilatory and periplasmic dissimilatory nit rate reductase activity. Using the gusA reporter gene methodology, Sp245ch1 1 was found to be significantly affected in its ability to colonize roots o f wheat and rice seedlings.