Author
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MOON, MOOSANG - MISSISSIPPI STATE UNIV |
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ANDERSON, KEVIN |
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Submitted to: Anaerobe
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/15/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Cellulose is a major carbohydrate in the food animal's diet, but it cannot be digested by the animal's own digestive enzymes and secretions. Instead, animals must rely upon the microorganisms in their gastrointestinal tract for cellulose digestion. Therefore, how efficiently animals digest feed- stuff depends upon how effectively these microbes breakdown cellulose. To more fully understand how these bacteria breakdown cellulose, we studied the gastrointestinal bacterium, Eubacterium cellulosolvens. Our research found that in order for this bacterium to degrade cellulose, rather than a simple sugar such as glucose, it must change the chemical composition of its cell surface. These changes involve several membrane proteins and a lipid containing protein (a lipoprotein) that the bacterium makes only when it is degrading cellulose. Also, for this bacterium to degrade cellulose, it must change the fatty acid composition of its cellular membrane. This change apparently increases the fluidness of the cell membrane, possibly making it easier to move proteins (such as enzymes) through the membrane so they can assist with the degradation of cellulose that is occurring along the exterior of the cell. All of these changes indicate that for a gastrointestinal bacterium to degrade cellulose rather than another carbohydrate, it must first make some special proteins and change its membrane composition; not just make cellulose degrading enzymes. These findings add to the current understanding of how gastrointestinal bacteria degrade cellulose, and illustrate that the cellulose degrading system is even more complex than was previously thought. Future studies, especially those attempting to determine the key components and rate-limiting steps of cellulose degradation, will build upon our research results. Technical Abstract: Previous research has shown that Eubacterium cellulosolvens makes an appropriate model for studying cellulolytic activity of gastrointestinal bacteria. This study found that E. cellulosolvens altered its cytoplasmic membrane protein composition in response to growth on specific energy substrates. Electrophoresis profiles obtained from membrane protein fractions of cellulose-grown cells were different from that obtained from cells cultivated with other carbohydrates, such as cellobiose or glucose. addition, [3H]palmitic acid labeling of cellulose-grown E. cellulosolvens revealed two lipoproteins that were not detected in glucose- or cellobiose-grown cultures. These lipoproteins partitioned with the membran fraction, indicating their association with the cytoplasmic membrane. Proteinase K treatment of whole cells further suggested these lipoproteins were exposed to the surface of the cell envelope. These membrane proteins and lipoproteins appear to be under some substrate specific regulatory control with distinct, but as yet undetermined, roles in cellulose utilization. In addition, cellulose-grown E. cellulosolvens was found to posses a higher ratio of oleic acid (C18:1) to palmitic acid (C16:0) than cells cultivated on soluble carbohydrates. This change in the ratio of unsaturated to saturated fatty acids is consistent with a comparative increase of membrane fluidity. |
