Chiang Mai Journal of Science

Bradyrhizobium japonicum is an agriculturally important bacterium due to its capacity of nitrogen-fixing symbiosis with leguminous plants, especially soybean (Glycine max). In this report, we studied acid-tolerance metabolism of B. japonicum USDA110 using proteome analysis. Two-dimensional electrophoresis gel image analysis revealed 568 and 628 protein spots of cells grown at pH 4.7 and pH 6.8, respectively. Only 84 protein spots with at least 3-fold differential expression were further identified by MALDI-TOF MS. The annotated proteins were assigned to four different classes: (i) proteins produced only at pH 4.7 condition (15 proteins such as D-alanine aminotransferase, 2-haloalkanoic acid dehalogenase and periplasmic mannitol-binding protein); (ii) proteins produced under both conditions but strongly induced at pH 4.7 (27 protein spots such as triosephosphate isomerase, UTP-glucose-1 phosphate uridylyltransferase and glyceraldehyde 3-phosphate dehydrogenase); (iii) proteins down-regulated during growth at pH 4.7 (25 proteins such as GroEL, acyl-CoA dehydrogenase and ATP synthase beta chain), and (iv) proteins specific to growth at pH 6.8 (17 proteins such as ATPdependent protease ATP-binding subunit, N-utilization substance protein A and 2- isopropylmalate synthase). The data of the differential protein expression can be a basis for mechanism elucidation of the acid response in B. japonicum USDA110.