Citrate Fermentation byLactococcus andLeuconostoc spp

converted pyruvate tolactate athighdilution (growth) rates,lowpH,andhighlactose concentrations. Mixed-acid fermentation withformate, ethanol, andacetate asproducts was observed underconditions oflactose limitation incontinuous culture atpH values above6.0.An acetoin/butanediol fermentation witha-acetolactate as an intermediate was foundupon mildaeration incontinuous culture andunderconditions ofexcesspyruvate production fromcitrate. Leuconostoc spp.showed a limited metabolic flexibility. A typical heterofermentative conversion oflactose was observed underallconditions inbothcontinuous andbatchcultures. Thepyruvate produced fromeither lactose orcitrate was converted toD-lactate. Citrate utilization was pHdependent inboth L.lactis andLeuconostoc spp.,withmaximumratesobserved between pH 5.5and6.0.Themaximumspecific growth rate was slightly stimulated bycitrate, inL.lactis andgreatly stimulated bycitrate inLeuconostoc spp., andtheconversion ofcitrate resulted inincreased growthyields on lactose forbothL.lactis andLeuconostoc spp.Thisindicates that energyisconserved during themetabolism ofcitrate.