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Cellobiose chemotaxis and cellulase system of Cellulomonas gelida
Abstract
The aim of the research was to study cellobiose chemotaxis and the cellulase system of the facultatively anaerobic bacterium Cellulomonas gelida, with the expectation that the results of this work would contribute to the current understanding of the process of cellulose biodegradation. First, the chemotactic responses, especially, cellobiose chemotaxis of C. gelida were investigated. As determined by a modified Adler's capillary assay, cellobiose, the major cellulose hydrolysis product, as well as other sugars that are components of plant polysacchrides, served as chemoattractant for C. gelida. Competition and inducibility experiments indicated that C. gelida possesses at least two types of cellobiose chemoreceptors, one is inducible by cellobiose and not shared with D-glucose, the other is constitutively synthesized and shared with D-glucose and many other sugars. Based on our findings, a mechanism for cellobiose-mediated bacterial chemotaxis toward plant polysaccharides in natural environments is proposed. Then, the biochemical nature of the cellobiose chemoreceptors of C. gelida was studied. Results from tethered cell experiments, capillary assays as well as in vivo and in vitro methylation assays suggested that a specific methyl-accepting chemotaxis protein (MCP) is involved in chemotaxis toward cellobiose and several other sugars by C. gelida. Additional evidence showed that the MCP is constitutively synthesized. During chemotaxis, C. gelida and Escherichia coli share the similar time course of increase in MCP methylation and the changes of methylesterase activity, suggested that the mechanism of MCP-mediated chemotaxis in C. gelida is similar to that of E. coli. Finally, the cellulase system of C. gelida was characterized. The inducibilities and cellular locations of various cellulases were first investigated. O$\sb2$ was found to have no clear effect on both the synthesis and activities of cellulases. Most of the extracellular cellulases were found in one broad protein peak after gel filtration. These enzymes couldn't be purified to homogeneity by anion exchange chromatography. Synergistic interactions of different enzymes were required for the hydrolysis of crystalline cellulose. Results of these studies and other analysis are consistent with the conclusion that C. gelida forms extracellular enzyme complexes that function in the hydrolysis of cellulose.
Subject Area
Microbiology|Biochemistry
Recommended Citation
Hsing, Weihong, "Cellobiose chemotaxis and cellulase system of Cellulomonas gelida" (1994). Doctoral Dissertations Available from Proquest. AAI9420634.
https://scholarworks.umass.edu/dissertations/AAI9420634