Xylan Deconstruction by Environmental Bacterium Caulobacter crescentus

Abstract

Bacterial species display unique and common molecular mechanisms for nutrient acquisition depending on their habitat. Molecular details of xylan utilization by plant pathogens and human commensal bacteria have been reported but no significant reports can be found for environmental bacteria. Caulobacter crescentus is a gram-negative, oligotrophic, environmental bacterium with unique adaptations for growth in low-nutrient conditions. C. crescentus’ genome codes for a repertoire of genes that can facilitate xylan utilization as a carbon source for growth. Polymeric xylan and xylan-derivative use by C. crescentus was investigated in this work. Growth, enzyme, metabolite, and gene expression analyses show possible membrane-bound enzymes for xylan deconstruction on the cell surface while enzymes for further deconstruction of xylan-derived oligosaccharides are concentrated in the periplasm. TonB-dependent transporter (TBDT) inhibition data suggest that TBDT may be involved in the transport of xylo-oligosaccharides across the outer membrane. Collectively, data suggest xylan binding onto the bacterial surface and deconstruction and the xylan fragment uptake across the outer membrane. A comprehensive model for xylan utilization by C. crescentus develops to show features of previously proposed gut and plant pathogenic bacterial models. This study further advances the molecular level understanding of xylan derived nutrient acquisition in environmental bacteria.