Bioconversion of glucose and fructose to sorbitol and gluconic acid by untreated cells of Zymomonas mobilis

The bioconversion of glucose and fructose to gluconic acid and sorbitol, re spectively, by the enzymes glucose-fructose oxidoreductase (GFOR) and gluco no-delta-lactonase (GL), contained in untreated cells of Zymomonas mobilis ATCC 29191, was investigated in batch runs with glucose plus fructose conce ntrations (S-o) varying from 100 to 750 g l(-1) in equimolar ratio. When S- o was increased to 650 g l(-1), the yields were improved, reaching a maximu m of 91% for both products, with productivities of 1.6 and 1.5 g g(-1) cell h(-1) for gluconic acid and sorbitol, respectively. Above this level (S-o = 750 g l(-1)), no further improvement in yields was observed and productiv ities decreased due to the longer process time. The high yields of bioconve rsion runs with S-o greater than or equal to 650 g l(-1) are a consequence of the sequential inhibition of the normal metabolism of Z, mobilis by subs trates and products, resulting in preferential utilization of substrates vi a the GFOR/GL system. (C) 1999 Elsevier Science B.V. All rights reserved.