Alison Buchan

Carolyn W. Fite Professor

UT

Research

Our research is driven by a desire to understand the roles of microbes in natural environments. Major objectives include linking microbial taxa to critical ecosystem processes, exploring functional gene diversity and its relation to community structure and biogeochemical processes, and identifying novel enzymes and/or catabolic pathways. A current project focuses on the microbial remineralization of the aromatic biopolymer lignin and its related compounds. The catabolism of these compounds is critical to the global carbon cycle, yet little is known of the natural communities and the processes involved. The coastal salt marshes of the southeastern U.S. are heavily influenced by lignin-related compounds of local and allochthonous origins, and are ideal sites for investigations of catabolic pathways that are harbored within decomposer communities. Members of one lineage of marine bacteria, the Roseobacter clade, are particularly well-suited for such studies as they are abundant in these coastal salt marshes, are easily cultured, and are hypothesized to be responsible for a significant fraction of aromatic compound degradation in these systems. At present we are focusing on Roseobacter isolate Silicibacter pomeroyi, a bacterium cultured from a Georgia salt marsh, using genome data, physiological growth studies, and gene expression levels to better understand the catabolic processes and regulatory networks mediating the transformation of the constituents of lignin by members of this group. Molecular tools are also being developed to assess the diversity and activity of these catabolic processes in salt marsh systems.

Another objective of the lab is to elucidate the significance of genetic variation within functional genes. For these studies, we focus on a key ring-cleaving enzyme in the catabolism of naturally occurring aromatic compounds, protocatechuate 3,4 dioxygenase (PcaHG). In earlier studies, a high degree of sequence diversity for this enzyme was found in natural communities prompting the question of whether this variation plays a role in niche partitioning in the environment. We are presently addressing this issue by conducting structure-function studies with genetic variants of this enzyme. This work is facilitated by the use of a soil bacterium, Acinetobacter baylyi, which is highly competent for natural transformation. We have engineered a system for the heterologous expression of native and variant PcaHGs from several of our marine Roseobacters in A. baylyi, allowing us to identify residues that are critical to enzyme activity and substrate specificity.

Education

Publications

ResearchGate