Galactose fermentation by Streptococcus lactis and Streptococcus cremoris: pathways, products, and regulation

Abstract

All of the lactic streptococci examined except Streptococcus lactis ML8 fermented galactose to lactate, formate, acetate, and ethanol. The levels of pyruvate-formate lyase and lactate dehydrogenase were elevated and reduced, respectively, in galactose-grown cells compared with glucose- or lactose-grown cells. Reduced intracellular levels of both the lactate dehydrogenase activator (fructose, 1,6-diphosphate) and pyruvate-formate lyase inhibitors (triose phosphates) appeared to be the main factors involved in the diversion of lactate to the other products. S. lactis ML8 produced only lactate from galactose, apparently due to the maintenance of high intracellular levels of fructose 1,6-diphosphate and triose phosphates. The growth rates of all 10 Streptococcus cremoris strains examined decreased markedly with galactose concentrations below about 30 mM. This effect appeared to be correlated with uptake predominantly by the low-affinity galactose phosphotransferase system and initial metabolism via the D-tagatose 6-phosphate pathway. In contrast, with four of the five S. lactis strains examined, galactose uptake and initial metabolism involved more extensive use of the high-affinity galactose permease and Leloir pathway. With these strains the relative flux of galactose through the alternate pathways would depend on the exogenous galactose concentration.

Overview on sugar metabolism and its control in – The input from in vivo NMR

“…Circles and double rounded-rectangles represent non-PTS permeases and PTS systems, respectively. analogy with lactose metabolism, galactose is metabolized via the tagatose 6-phosphate pathway when translocated by a PTS gal , and by the Leloir pathway when transported via the highly specific galactose permease system [100,102,103]. Insights into glucose and galactose metabolism will be described below.…”

“…In L. lactis, galactose that enters the cell via a specific galactose-PTS is metabolized to triose phosphates through the tagatose 1,6-phosphate pathway [102]. On the other hand, galactose taken up by a permease is metabolized to glucose 1-phosphate via the Leloir pathway ( Fig.…”

“…On the other hand, galactose taken up by a permease is metabolized to glucose 1-phosphate via the Leloir pathway ( Fig. 4) [100,102,103]. Glucose 1-phosphate is converted through the action of a-phosphoglucomutase to glucose 6-phosphate, which enters the glycolytic pathway.…”

Genetics of lactose utilization in lactic acid bacteria

“…The latter suggestion follows from the observa-tion that curing of the lactose plasmid resulted in loss of the formation of galactose 6-phosphate from galactose {63]. In addition, strain differences affecting sugar fermentation patterns have been described in Lactococcus lactis [63]. This also applies to the galactose metabolism since accumulation of galactose 6-phosphate and a low affinity galactose PTS (Km of 20 raM) were found in a strain cured of its lactose plasmid, suggesting the presence of a chromosomally encoded, very low affinity galactose PTS [51].…”

Responses of lactic acid bacteria to oxygen

“…A gradual increase in the aeration level led to a gradual increase in acetate and a decrease in formate and ethanol [65]. The main reason for these effects is the extreme sensitivity of pyruvate formate-lyase to O z [63,64,[66][67][68]. Cells of S. mutans exposed to 02 for 2 min lost 94% of their activity [63].…”