Susan B. Leschine

Professor
Program Coordinator, Fifth Year Master's Program

Phone: 413-545-0673
Fax: 413-545-1578
Email: suel@microbio.umass.edu
Mailing address

Ph.D.: Biophysics and Microbiology, University of Pittsburgh, 1975

Microbial Physiology and Diversity: Cellulose and Chitin Decomposition, Biofilms on Natural Polymers, Fuels from Biomass

Cellulosomes. Transmission electron micrographs of Clostridium thermocellum cells showing cellulosome aggregates on cell surfaces (indicated by arrows; A), and, at higher magnification, individual cellulosomes of Clostridium papyrosolvens (B). Also shown is a model of C. thermocellum cellulosomes and an associated cell-surface anchoring protein.

The diversity of the microbial world is enormous. Consequently, microorganisms constitute a valuable physiological and genetic resource. Microbes have played a central role in the development of biotechnology as an industry, and they will be used to progress technology in the future. The goal of my research program is to advance understanding of the biology of diverse microorganisms and interactions among these organisms and their environment. Such knowledge is essential for the successful application of microbes, their activities and products, to solve problems and fill needs of our society.

The most abundant organic materials on Earth are structural polysaccharides such as cellulose and chitin. Moreover, these organic polymers form a major component of municipal, agricultural, and industrial waste. The decomposition of cellulose and chitin, which is carried out almost exclusively by microorganisms, is a key step in the global carbon cycle. Vast quantities are degraded in a broad range of environments by communities of physiologically diverse microorganisms. The primary objectives of my research program are to advance understanding of the physiology, ecology, and diversity of polymer-decomposing members of microbial communities, to discern the nature of key interactions among community members and with their insoluble substrate, and to understand how these interactions may contribute to the efficient degradation of insoluble polysaccharides.

For the most part, our research has involved species of cellulose-decomposing clostridia that we have isolated from a variety of soils collected from locations around the world. Investigations have concerned the physiology and ecology of these bacteria and the cellulase enzymes ("cellulosomes") they produce. Our studies have revealed a structural and functional complexity in cellulase enzyme systems that was previously unrecognized. An important result of our research was the discovery that many cellulolytic clostridia are able to use atmospheric N₂ to meet their nitrogen requirement for growth, suggesting that the activities of these microbes in soils and sediments may link the nitrogen and carbon cycles. We also found that many cellulolytic bacteria are able to use chitin as a source of both carbon and nitrogen. Chitin, an insoluble polymer of N-acetylglucosamine residues, is abundantly produced on the planet as a structural polysaccharide in the exoskeletons of arthropods and the cell walls of most fungi. The discovery of chitin utilization by cellulose-decomposing bacteria further supports the conclusion that these microbes may contribute greatly to both the carbon and nitrogen cycles in the biosphere.

Cellulolytic anaerobes form ethanol and H₂ as products of cellulose fermentation, and, therefore, they are potentially useful in processes for the generation of renewable energy from biomass. A current research thrust of my laboratory is aimed at experimentally manipulating fermentation product formation by culturing microbes under conditions that promote the development of substrate-attached cellulose-decomposing communities known as “biofilms.” Surprisingly little is known about biofilm formation on cellulose, especially considering that biofilm production may dramatically affect cellulose decomposition. Presently, we are focusing our studies on Clostridium phytofermentans, a cellulose-fermenting microbe that produces H₂ and exceptionally large amounts of ethanol.

Scanning electron micrographs of a C. phytofermentans biofilm on dialysis tubing (“regenerated cellulose”).

A. Low magnification view of the biofilm showing cell aggregates on the surface of shredded dialysis tubing.

B. Magnified section of biofilm showing individual cells embedded in a stringy extracellular matrix.

Selected Publications

Leschine, S. 2004. Degradation of polymers: cellulose, starch, pectin, xylan. In P. Dürre (ed.), Handbook on Clostridia, CRC Press, Boca Raton.

Reguera, G., and S. B. Leschine. 2003. Biochemical and genetic characterization of ChiA, the major enzyme component for the solubilization of chitin by Cellulomonas uda. Archives of Microbiology 180:434-443.

Warnick, T. A., and S. B. Leschine. 2002. Clostridium phytofermentans sp. nov., a cellulolytic mesophile from forest soil. International Journal of Systematic and Evolutionary Microbiology 52:1155-1160.

Monserrate, E., S. B. Leschine, and E. Canale-Parola. 2001. Clostridium hungatei sp. nov., a mesophilic N2-fixing cellulolytic bacterium isolated from soil, International Journal of Systematic and Evolutionary Microbiology 51:123-132.

Reguera, G., and S. B. Leschine. 2001. Chitin degradation by cellulolytic anaerobes and facultative aerobes from soils and sediments. FEMS Microbiology Letters 204:367-374.

Chen, T., L. Ouko, T. Warnick, and S. B. Leschine. 2000. Detection, cloning, and sequence analysis of an indigenous plasmid from cellulolytic clostridial strain MCF1, Plasmid 43:153-158.

Department of Microbiology
203 Morrill Science Center IVN
University of Massachusetts
639 North Pleasant Street
Amherst, MA 01003

413 545 2051  |  Fax 413 545 1578

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