17-43: Extracellular degradation of gluco-oligosaccharides by Caulobacter crescentus

Monday, April 29, 2013
Exhibit Hall
Logan R. Hurst, Gopal R. Periyannan, Gerald N. Presley, Matthew J. Payea, Brandon S. Martin and Annie E. Egan, Chemistry, Eastern Illinois University, Charleston, IL
The oligotrophic bacterium Caulobacter crescentus has the ability to metabolize various organic molecules including plant structural carbohydrates as a carbon source. We investigated the genetic and biochemical nature of cellobiose utilization and tested the ability to use other gluco-oligosaccharides (up to DP=4), cellulose, and carboxymethyl cellulose (CMC) as the sole carbon source for C. crescentus. All carbon sources, except cellulose and CMC, supported growth in M2 minimal media. Growth in larger gluco-oligosaccharides produced glucose and smaller gluco-oligosaccharides in the extracellular medium indicating extracellular β-glucosidase (BGL) activity. Among the cellular fractions assayed, periplasmic and outer membrane fractions extracted from glucose and cellobiose cultures showed highest BGL activity towards p-nitrophenol-β-glucose (pNPG) and cellobiose substrates, but no BGL activity was observed in the extracellular culture medium. Reverse transcriptase PCR and proteomic analyses showed the expression of BGL genes CC_0968, CC_1756, and CC_1757; TonB-Dependent Receptor (TBDR) genes CC_0970, CC_0999, and CC_1666 in cells grown in cellobiose. Proton-motive-force (pmf) disruptor carbonyl cyanide 3-chlorophenylhydrazone slowed, but did not abolish, growth in cellobiose indicating potential pmf-dependent cellobiose transport across the outer membrane. Expression of the OprB porin in glucose and cellobiose cultures, but not in PYE, suggests facilitated diffusion of glucose across the outer membrane in C. crescentus. These results suggest combined extracellular and periplasmic BGL activity and TBDR mediated transport as the methods of carbon acquisition from environmental cellulose derivatives by C. crescentus.