Microbial Fermentation of Abundant Biopolymers: Cellulose and Chitin

Leschine, Susan

University of Massachusetts Amherst

关键词: Xylanase;    Cellulose;    Biofilms In Biomass Decomposition;    Nitrogen Fixation By Cellulolytic Anaerobes;    Chitin;   

DOI  :  10.2172/966702
RP-ID  :  DOE/ER/13898-FTR
RP-ID  :  FG02-88ER13898
RP-ID  :  966702

美国|英语

来源: UNT Digital Library

【 摘 要 】

Our research has dealt with seven major areas of investigation: i) characterization of cellulolytic members of microbial consortia, with special attention recently given to Clostridium phytofermentans, a bacterium that decomposes cellulose and produces uncommonly large amounts of ethanol, ii) investigations of the chitinase system of Cellulomonas uda; including the purification and characterization of ChiA, the major component of this enzyme system, iii) molecular cloning, sequence and structural analysis of the gene that encodes ChiA in C. uda, iv) biofilm formation by C. uda on nutritive surfaces, v) investigations of the effects of humic substances on cellulose degradation by anaerobic cellulolytic microbes, vi) studies of nitrogen metabolism in cellulolytic anaerobes, and vii) understanding the molecular architecture of the multicomplex cellulase-xylanase system of Clostridium papyrosolvens. Also, progress toward completing the research of more recent projects is briefly summarized. Major accomplishments include: 1. Characterization of Clostridium phytofermentans, a cellulose-fermenting, ethanol-producing bacterium from forest soil. The characterization of a new cellulolytic species isolated from a cellulose-decomposing microbial consortium from forest soil was completed. This bacterium is remarkable for the high concentrations of ethanol produced during cellulose fermentation, typically more than twice the concentration produced by other species of cellulolytic clostridia. 2. Examination of the use of chitin as a source of carbon and nitrogen by cellulolytic microbes. We discovered that many cellulolytic anaerobes and facultative aerobes are able to use chitin as a source of both carbon and nitrogen. This major discovery expands our understanding of the biology of cellulose-fermenting bacteria and may lead to new applications for these microbes. 3. Comparative studies of the cellulase and chitinase systems of Cellulomonas uda. Results of these studies indicate that the chitinase and cellulase systems of this bacterium are distinct in terms of the proteins involved and the regulation of their production. 4. Characterization of the chitinase system of C. uda. A 70,000-Mr endochitinase, designated ChiA, was purified from C. uda culture supernatant fluids and characterized. 5. Analysis of chiA, which codes for the major enzymatic component of the chitinase system of C. uda. The gene encoding the endochitinase ChiA in C. uda was cloned, its complete nucleotide sequence was determined and its implications were investigated. 6. Formation of biofilms by C. uda on cellulose and chitin. Microscopic observations indicated that, under conditions of nitrogen limitation, C. uda cells grew as a biofilm attached tightly to the surface of cellulose or chitin. 7. Development of tools for a genetic approach to studies of cellulose fermentation by cellulolytic clostridia. We have explored the potential of various techniques, and obtained evidence indicating that Tn916 mutagenesis may be particularly effective in this regard. As part of this research, we identified the presence of a plasmid in one strain, which was cloned, sequenced, and analyzed for its utility in the development of vectors for genetic studies. 8. Effects of humic substances on cellulose degradation by anaerobic cellulolytic microbes. We determined that humic substances play an important role in the anaerobic cellulose decomposition and in the physiology of cellulose-fermenting soil bacteria. 9. Nitrogenases of cellulolytic clostridia. We described a nitrogenase gene from a cellulolytic clostridium and presented evidence, based on sequence analyses and conserved gene order, for lateral gene transfer between this bacterium and a methanogenic archaeon. 10. Characterization of Clostridium hungatei, a new N2-fixing cellulolytic species isolated from a methanogenic consortium from soil. 11. Understanding the molecular architecture of the multicomplex cellulase-xylanase system of Clostridium papyrosolvens. We discovered that C. papyrosolvens produces a multiprotein, multicomplex cellulase-xylanase enzyme system that hydrolyzes crystalline cellulose, and we have described this system in detail.