Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1999
Publication Date: N/A
Technical Abstract: Although cellulose utilization represents an important metabolic strategy for some bacteria, there is little information regarding the energetic costs and benefits of growth on cellulose versus on soluble sugars. To compare the energetics of cellulose and cellobiose utilization, the ruminal cellulolytic bacteria Fibrobacter succinogenes S85 and Ruminococcus flavefaciens FD-1 were grown axenically at seven different dilution rates in cellobiose-limited continuous culture in the presence of 2.5% (w/v) clarified rumen fluid. Comparison of growth data on cellobiose with previous data for growth in the same medium with cellulose as limiting nutrient revealed that growth on cellobiose substantially increased true catabolic growth yields. Maintenance coefficients were also considerably higher for both species during growth on cellobiose than on cellulose. Pirt plots revealed that growth yields on cellobiose, expressed on a pellet N basis exceeded those on cellulose at growth rates (m) of 0.017/h for F. succinogenes, and at 0.04/h for R. flavefaciens. Extracellular protein, Avicelase, and CMCase levels were low during growth on cellobiose. Relative to growth on cellulose, growth of either strain on cellobiose resulted in lower yields of fermentation endproducts (acetate and succinate), consistent with more extensive conversion of substrate to (and possible recycling of) storage polysaccharides. The higher growth yields observed for both strains on cellobiose suggest that gains in energetic efficiency due to the use of intracellular phosphorylases are not sufficient to outweigh the other costs (enzyme or glycocalyx production) associated with the cellulolytic mode of growth.