Relationship between glycosyl hydrolase inventory and growth physiology ofthe hyperthermophile Pyrococcus furiosus on carbohydrate-based media

Utilization of a range of carbohydrates for growth by the hyperthermophile Pyrococcus furiosus was investigated by examining the spectrum of glycosyl hydrolases produced by this microorganism and the thermal labilities of var ious saccharides. Previously, P. furiosus had been found to grow in batch c ultures on several at-linked carbohydrates and cellobiose but not on glucos e or other beta-linked sugars. Although P. furiosus was not able to grow on any nonglucan carbohydrate or any form of cellulose in this study (growth on oat spelt arabinoxylan was attributed to glucan contamination of this su bstrate), significant growth at 98 degrees C occurred on beta-1,3- and P-1, 3-beta-1,4-linked glucans, Oligosaccharides generated by digestion with a r ecombinant laminarinase derived from P, furiosus were the compounds that we re most effective in stimulating growth of the microorganism, In several ca ses, periodic addition of beta-glucan substrates to fed-batch cultures limi ted adverse thermochemical modifications of the carbohydrates (i.e., Mailla rd reactions and caramelization) and led to significant increases (as much as two- to threefold) in the cell yields, While glucose had only a marginal ly positive effect on growth in batch culture, the final cell densities nea rly tripled when glucose was added by the fed-batch procedure. Nonenzymatic browning reactions were found to be significant at 98 degrees C for saccha rides with degrees of polymerization (DP) ranging from 1 to 6; glucose was the most labile compound on a mass basis and the least labile compound on a molar basis. This suggests that for DP of 2 or greater protection of the n onreducing monosaccharide component may be a factor in substrate availabili ty. For P. furiosus, carbohydrate utilization patterns were found to reflec t the distribution of the glycosyl hydrolases which are known to be produce d by this microorganism.