Accumulation of 2-Keto-L-Gulonate at 33℃ by a Thermotolerant Gluconobacter Oxydans Mutant Obtained by Ion Beam Implantation

ToobtainthermotolerantmutantsofG.oxydans,whichcanenhancethetransformationrateofL-sorboseto2-Keto-L-gulonate(2-KLG)at33℃inatwo-stepprocessofvitaminCmanufacture,ionbeamwasusedasamutationsource.GluconobacteroxydansGOandBacillusmegateriumB0wereusedinthisstudy.TheoriginalstrainGluconobacteroxydansGOwasmutatedbytheheavyionimplantationfacilityattheInstituteofPlasmaPhysics,ChineseAcademyofSciences.SeveralmutantsincludingGluconobacteroxydansGI13wereisolatedandcoculturedwithBacillusmegateriumB0at33℃inshakingflasks.TheaveragetransformationrateofthenewmixedstrainGI13-B0inpergram-moleculereached94.4%aftersevenpassagesinshakingflasks,whichwasincreasedby7%whencomparedwiththeoriginalmixedstrainG0-B0(GluconobacteroxydansG0andBacillusmegateriumB0).Moreover,thetransformationrateofI13B0wasstableat94%attemperaturesrangingfrom25℃to33℃,whichwouldbeofmuchvalueinreducingenergyconsumptioninthemanufactureofL-ascorbicacid,especiallyintheseasonofsummer.Toclarifysomemechanismofthemutation,thespecificactivitiesofL-sorbosedehydrogenaseinbothG0andGI13wereestimated.