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.