FERMENTATION OF XYLANS BY BUTYRIVIBRIO-FIBRISOLVENS AND THERMOANAEROBACTER STRAIN B6A - UTILIZATION OF URONIC-ACIDS AND XYLANOLYTIC ACTIVITIES

Butyrivibrio fibrisolvens and Thermoanaerobacter strain B6A are xylanolytic anaerobes isolated from rumen and geothermal sources respectively. Both organisms fermented larchwood xylan, oatspelt xylan, or 4-O-methylglucuronoaxylan, extensively utilizing both the monosaccharide (glucose, xylose, arabinose) and uronic acid components. Citrus pectin or polygalacturonate also supported growth of both organisms, but only B. fibrisolvens was able to use the monomers glucuronate or galacturonate as the sole added energy source. Strain B6A was able to utilize these two uronic acids when glucose, xylose, arabinose, or oatspelt xylan was also provided as a second energy source. Xylanase, xylosidase, and arabinofuranosidase activities were found to be produced by strain B6A, but the levels and distribution (cell bound vs. culture fluid) were influenced by growth substrate. The highest levels were observed with growth on xylans when xylanase activity was mainly extracellular, but the other two activities were mostly cell bound. Apparently, Thermoanaerobacter strain B6A, but not B. fibrisolvens, requires xylan degradation products generated by these three activities to provide energy sources to utilize the uronic acid components on xylans.