Graduate Program

Chemistry

Degree Name

Master of Science (MS)

Semester of Degree Completion

Summer 2021

Thesis Director

Gopal R. Periyannan

Thesis Committee Member

Michael W. Beck

Thesis Committee Member

Zhiqing Yan

Thesis Committee Member

Thomas Canam

Abstract

Bacterial decomposition of xylan and uptake of xylan-derived carbon compounds require a combination of enzymes, proteins, and complex molecular mechanisms. Bacteria have evolved molecular mechanisms for its utilization depending on its environment and source of xylan. Caulobacter crescentus, a Gram-negative bacterium which lives in an aquatic oligotrophic environment, exhibits asymmetric division which is an adaptive feature for its nutrient poor habitat. Although aromatic hydrocarbon and cellulose-derived mono-, di- and oligosaccharide utilization has been reported in literature, its xylan-derived carbon compound utilization is yet to be characterized. In this study, C. crescentus utilizes xylan-derived monomers arabinose, xylose and acetate as carbon source when supplemented in M2 minimal media, with acetate exhibiting an extended lag phase. On the other hand, the xylan components glucuronic acid and ferulic acid did not support growth under similar conditions. The carbon preference study showed

C. crescentus’ preference for xylotetraose and subsequently 33-α-L-Arabinofuranosyl-xylotetraose as carbon source. Enzyme assays with p-nitrophenyl-β-D-xylopyranoside and xylo- oligosaccharides as substrate showed a higher enzyme activity in the whole cell lysate with no activity in the extracellular media suggesting xylan degrading enzymes are confined within the bacterial cell. Evidence for complex mechanisms, such as expression of Extracytoplasmic Function sigma factors (ECF) under stressful conditions of carbon source or nutrient depletion, emerges in C. crescentus’ xylan-derivative utilization process to pave the way for further understanding and discovery of the comprehensive mechanism of xylan degradation and nutrient uptake by an environmental bacterium.

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