Study Of The Inhibitor Tolerance And Complete Sugars Conversion Of Gluconobacter Oxydans DSM 2003

There are two major barriers on the bioconversion of lignocellulose-derived sugars to the target products.Firstly,various inhibitors(aldehyde and organic acid compounds)produced in pretreatment process significantly inhibit the cell growth and fermentation efficiency.Secondly,Hemicellulose-derived sugars usually could not be effectively used by fermenting microorganisms.In this thesis,Gluconobacter oxydans DSM 2003 was found to be tolerant to the inhibitors and capable of converting all the lignocellulose-derived sugars to the target products effectively.Then the two excellent characteristics of G oxydans DSM 2003 were investigated in detail.In the first part of the thesis,the tolerance of G.oxydans DSM 2003 to inhibitors as well as the tolerance mechanism were investigated.G.oxydans DSM 2003 showed excellent gluconic acid fermentation performance under the stress of inhibitors.According to the whole cell catalysis experiment,the gluconic acid production rate could not be effected by any of the inhibitors,which was due to the high inhibitors tolerance of the key enzyme(glucose dehydrogenase).G.oxydans DSM 2003 also showed strong adaptive ability in high inhibitor content corn stover hydrolysate,because of its quick conversion ability of aldehyde inhibitors.Meanwhile,during the conversion of aldehyde inhibitors,many genes encoding oxidordeuctases potentially responsible to inhibitor conversion were significantly up-regulated.These genes will serve as an important gene device library for inhibitor tolerance engineering of robust strains.Understanding the mechanisms of high tolerance of G.oxydans DSM 2003 could pave the ways to the further modification on biodetoxification and biorefining fermentation strains.In the scond part of the thesis,G.oxydans DSM 2003 was found capable of oxidating all kinds of lignocellulose-derived sugars to the corresponding acids.These sugar acids can be used as cement retarder additives,becasue they have hydroxy-carboxylate group.We found the mixed sugars in corn stover hydrolysate could completely converted to a mixture of acids,which can be used as cement retarder additives without separation.This not only makes full use of the sugars from lignocellulose,but also effectively decreases the residual sugars in waste water which would further reduce the treatment cost.In conclusion,the quick conversion ability of aldehyde inhibitors and the high tolerance of the glucose dehydrogenase to the inhibitors lead to the excellent gluconic acid fermentation performance of G.oxydans DSM 2003 in the freshly pretreated corn stover hydrolysate.Complete sugar conversion in corn stover hydrolysate was realized by this strain.