The Biochemistry of Cellobiose Metabolism in Sinorhizobium meliloti

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Sinorhizobium meliloti is a root-nodulating soil bacterium that is agriculturally important due to its ability to synthesize NH3 from N2 through the process of nitrogen fixation.1 To effectively harness S. meliloti's nitrogen-fixing ability, rhizobial metabolism of carbon sources found in the soil must be understood. Understanding how S. meliloti metabolizes cellobiose is important because cellobiose is a degradation product of the cellulose found in plant walls and cellulose is found in high concentrations in the soil.2,3 Growth on cellobiose was completely eliminated in constructed double mutant strains lacking a β-glucosidase and another unidentified gene implicated in cellobiose metabolism, showing dependence of growth on cellobiose on the two pathways involved. Activity assays using PNP-β-glucose and ATP were conducted on wildtype and β-glucosidase lacking strains and preliminary evidence was found suggesting that one pathway responsible for growth on cellobiose include a kinase and a phosphocellobiosidase, which are both induced by cellobiose. Increased β-glucosidase activity was observed in cellobiose-grown wild-type S. meliloti, suggesting that the β-glucosidase may also be induced by cellobiose. These results provide evidence that S. meliloti utilizes at least two pathways to metabolize cellobiose. Additionally, evidence was found against pathways of metabolism that involve oxidation of cellobiose or cleavage by a phosphorylase.


Biochemistry and Molecular Biology

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