Change from homo- to heterolactic fermentation by Streptococcus lactis resulting from glucose limitation in anaerobic chemostat cultures.

Lactic streptococci, classically regarded as homolactic fermenters of glucose and lactose, became heterolactic when grown with limiting carbohydrate concentrations in a chemostat. At high dilution rates (D) with excess glucose present, about 95% of the fermented sugar was converted to l-lactate. However, as D was lowered and glucose became limiting, five of the six strains tested changed to a heterolactic fermentation such that at D = 0.1 h(-1) as little as 1% of the glucose was converted to l-lactate. The products formed after this phenotypic change in fermentation pattern were formate, acetate, and ethanol. The level of lactate dehydrogenase, which is dependent upon ketohexose diphosphate for activity, decreased as fermentation became heterolactic with Streptococcus lactis ML(3). Transfer of heterolactic cells from the chemostat to buffer containing glucose resulted in the nongrowing cells converting nearly 80% of the glucose to l-lactate, indicating that fine control of enzyme activity is an important factor in the fermentation change. These nongrowing cells metabolizing glucose had elevated (ca. twofold) intracellular fructose 1,6-diphosphate concentrations ([FDP](in)) compared with those in the glucose-limited heterolactic cells in the chemostat. [FDP](in) was monitored during the change in fermentation pattern observed in the chemostat when glucose became limiting. Cells converting 95 and 1% of the glucose to l-lactate contained 25 and 10 mM [FDP](in), respectively. It is suggested that factors involved in the change to heterolactic fermentation include both [FDP](in) and the level of lactate dehydrogenase.

Variations in surface polymers of Streptococcus mutans.

The cell wall composition of strains of S mutans with respect to sugars and proteins appears to be correlated to the serological grouping although groups c and E are rather similar. There also appear to be similarities in the structure of the polysaccharide formed by the glycosyltransferases from organisms of serological groups b and d. However, the activity of these enzymes appears to be variable in these groups. The most noteworthy difference found was that between the three Ingbritt strains. All three strains gave identical results with regard to their cell wall composition, and presumably this would mean that they were identical serologically. However, Ingbritt LH differed considerably from both the others in the types of polysaccharide formed by their glycosyltransferases from sucrose. Ingbritt B was a reisolate from monkeys, whereas Ingbritt LH was maintained in laboratory culture, and this may explain the difference. Clearly, more work will be required to explain this difference and as c strains are commonly isolated from plaque, it would seem desirable to clear up this point.

Production of Clostridium pasteurianum in a defined medium.

A method for the growth of Clostridium pasteurianum in a 140-liter (total capacity) stainless-steel vessel is described. By preventing the pH value from falling below 5.6, the growth of cultures was prolonged. Larger amounts of the carbon source (sucrose) and the nitrogen source (ammonium ion) were supplied and consumed, and cell yields of up to 5.56 g (dry weight) per liter were obtained. The highest cell yield previously reported was 1.7 g (dry weight) per liter obtained under nitrogen-fixing conditions in 500-ml cultures. The ferredoxin content of the cells was comparable with that obtained by earlier workers.