Monday, April 30, 2007

Ability of a curdlan overproducer strain to utilize an ethanol dry-milling coproduct for polysaccharide synthesis

Thomas P. West and Beth Nemmers. Biology and Microbiology, South Dakota State University, Box 2104, Brookings, SD 57007

The commercially available, alkali-soluble polysaccharide curdlan has applications in the food industry. A previously isolated mutant strain of the bacterium Agrobacterium sp. ATCC 31749 has been shown to be capable of producing elevated levels of the polysaccharide curdlan on selected carbon sources. The objective of this study was to determine the ability of the mutant strain to utilize the ethanol dry-milling coproduct condensed corn distillers’ solubles for polysaccharide production. A phosphate-buffered mimimal medium (pH 6.8) that contained condensed corn distillers’ solubles as its source of carbon and nitrogen was utilized. Corn syrup (3%) was supplemented into this medium to learn if an additional carbon source could further increase curdlan production. Following inoculation with a culture grown in the same medium for 48 hours, the shake flask cultures were grown for up to 120 hours at 30oC. Curdlan production by the mutant and parent strains was determined gravimetrically.  The mutant strain could produce elevated curdlan levels in the medium containing no additional carbon source or containing corn syrup relative to production by its parent strain ATCC 31749 after 96 hours. In contrast, the mutant strain produced only slightly higher polysaccharide levels than its parent strain after 120 hours in the unsupplemented medium or the corn syrup-containing medium. The addition of corn syrup to the medium increased curdlan production by both the mutant and parent strains. Overall, a curdlan overproducer strain synthesized curdlan on a medium containing solubles with fermentation time length and carbon source influencing its ability to produce the polysaccharide.