Continuous Cultivation forApparent Optimization ofDefined MediaforCellulomonas sp.andBacillus cereus

Steady-state continuous culture was usedtooptimize leanchemically defined mediafor a Cellulomonas sp.andBacillus cereusstrain T.Bothorganisms were extremely sensitive tovariations intrace-metal concentrations. However, medium optimization bythis technique proved rapid, andmultifactor screening was easily conducted byusing a minimumofinstrumentation. Theoptimized mediasupported critical dilution rates of0.571 and0.467 h-1forCellulomonas andBacillus, respectively. Thesevalues approximated maximumgrowth ratevalues observed inbatchculture. Environmental factors influence all aspects of physiology andregulation. Chemically defined mediahavebeenemployed tostudy theeffect ofdifferent nutrients onreactions related tothe growth cycle ofmanymicroorganisms. Theimportance ofproper nutrient balance tothepopulation density isrecognized andhasaddedto theeaseofscale-up operations inindustrial fermentations. However, thedevelopment andoptimization ofadefined mediumisoften atedious andtime-consuming process. Afewinvestigators havenoted theimportance oftheproper trace metalconcentration (12, 15,16)andoxidation state (12). Moreoften, efforts toward nutrient optimization havebeenconcerned withmacronutrients, suchasnitrogen, phosphorous, and magnesium, whereas trace metalrequirements areingeneral notcritically examined. Workers inourlaboratory havebeenextensively examining twounrelated systems. MembersofthegenusCellulomonas exhibit cellulolytic ability andprovetobeofinterest asa potential source ofsingle-cell protein fromcellulose fermentation. However, anunderstanding ofthenutrition andphysiology ofgrowth-related processes isrequired before acellulose fermentation production unitcanbedesigned. Inaddition, examination ofphysiological alterations ofBacillus cereus atvarious growth rates may contribute towardthebetter understanding of cellular differentiation processes. Theuseofcontinuous cultivation toinvestigatethese research aspects wouldbebeneficial; however, allattempts tocultivate these organisms continuously byusing conventional batch tPresent address: Molecular Biology Section, National Institute ofNeurological andCommunicative Disorders and Stroke, National Institutes ofHealth, Bethesda, MD 20205. mediaproved unsatisfactory. Thelength ofthe lagperiod ofmanybacteria isdependent upon inoculum size(9). This, andother unreported observations ofbatchgrowth characteristics, suggested thatgrowth ofCellulomonas species maybeespecially sensitive totrace metal concentrations. B.cereus maybesimilarly affected. Thus, wehaveattempted tocompound achemically defined mediumforeachorganism which wouldallow thecultivation ofthese organisms