Fructose bisphosphate aldolase activity and glycolytic intermediate concentrations in relation to lactate production in Streptococcus bovis

Effects of growth stage and culture conditions on fructose-1,6-bisphosphate (FBP) aldolase (FBA) activity and glycolytic intermediate concentrations in Streptococcus bovis were examined. In addition, FBA was purified and the gene encoding FBA (fba) was analysed. The FBP level in cells grown on lactose was much lower than the level in cells grown on glucose, which was considered to be caused by a lower FBA specific activity and slower influx to FBP pool in lactose-grown cells compared to glucose-grown cells. Dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde-3-phosphate (GAP) concentrations were also lower in cells grown on lactose. The lower levels of FBP, DHAP, and GAP explain in part the fact that the proportion of lactate produced was smaller when cells were grown on lactose. The amount of FBA per cell mass (FBA specific activity) was much smaller at pH 4.5 than at pH 7.0, and FBA activity at pH 5.5 was less than 50% of the activity at pH 7.0, which caused an increase in the FBP pool and the proportion of lactate. FBA specific activity was nearly proportional to the fba-mRNA level, suggesting that FBA synthesis is regulated at the transcriptional, level responding to sugar supply to cells. FBA specific activity and fba-mRNA level were virtually constant during the log growth, and then dropped with a decrease in glucose influx to a certain level. However, FBA specific activity did not decrease further until growth cessation despite a decrease in fba-mRNA level, suggesting that the synthesis and degradation of FBA may be so regulated as to maximise the rate of glycolysis. In conclusion, lactate production may be reduced by enhancing FBA synthesis, when readily fermentable carbohydrate is supplied at both neutral and low pH. Inversely, when carbohydrate is in short supply or not readily fermented, lactate production may be increased by suppressing FBA synthesis. (C) 2002 Elsevier Science Ltd. All rights reserved.