Date of Award
Doctor of Philosophy (PhD)
Robert M. Weis, Chair
Derek R. Lovley, Co-chair
Michael J. Knapp, Member
biofilm, chemotaxis, extracellular material, gene regulation, geobacter, motility
Geobacter species are δ-Proteobacteria and are often predominant in the Fe(III) reduction zone of sedimentary environments. Their abilities to remediate contaminated environments and to produce electricity have inspired extensive studies. Cell motility, biofilm formation, and type IV pili, which have been shown to be regulated by chemotaxis genes in other bacteria, all appear important for the growth of Geobacter species in changing environments and for electricity production. The genomes of Geobacter species show the presence of a significant number of chemotaxis gene homologs, suggesting important roles for them in the physiology of Geobacter species, although gene functions are not yet identified. In this study, we focus on identifying chemotaxis components and studying their functions in Geobacter species. We identified a large number of homologs of chemotaxis genes, which are arranged in six or more major clusters in the genomes of Geobacter sulfurreducens, Geobacter metallireducens, and Geobacter uraniireducens. Based on homology to known pathways, functions of some chemotaxis clusters were assigned; others appear to be unique to Geobacter species. We discuss the diversity of chemoreceptors and other signaling proteins as well the regulation of chemotaxis genes in Geobacter species. The functions of chemotaxis genes were studied in G. sulfurreducens, whose genome contains ~ 70 chemotaxis gene homologs, arranged in 6 major clusters. These chemotaxis clusters are also found in other Geobacter species with similar gene order and high level of gene identity, suggesting that our study in G. sulfurreducens could be extrapolated to other Geobacter species. We identified the function of the che5 cluster of G. sulfureducens as regulation of the biosynthesis of extracellular materials. We showed that G. sulfurreducens KN400 is chemotactic, and that this behavior is flagellumdependent. Our preliminary data indicated that G. sulfurreducens may use the che1 cluster, which is found exclusively in Geobacteraceae, to regulate chemotaxis. Our studies demonstrated important roles of chemotaxis genes in Geobacter physiology and their presence in large numbers could be one of the reasons why Geobacter species outcompete other species in bioremediation sites. Further studies are warranted for better understanding of the mechanisms of Che-like pathways and their potential use in optimization of conditions for applications of Geobacter species in bioremediation and electricity generation.
Tran, Hoa T., "Investigation of Chemotaxis Genes and Their Functions in Geobacter Species" (2009). Open Access Dissertations. Paper 129.