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.

No abstract

Metabolism of D-glucose by Bacteroides ruminicola subsp. brevis, strain B,4, has been examined. Growth yield studies gave molar growth yields, corrected for storage polysaccharide, of approximately 66 g (dry weight)/mol of glucose fermented. The storage polysaccharide amounted to about 14% of the total dry weight, or 55% of the total cellular carbohydrate, at full growth. After correcting glucose utilization for incorporation into cellular carbohydrate, measurement of product formation showed that 1.1 succinate, 0.8 acetate, and 0.35 formate are produced and 0.5 CO2 net is taken up during the fermentation of 1 glucose under the conditions used. The implication of these results with respect to adenosine 5'-triphosphate (ATP) molar growth yield calculations is discussed. If substratelevel phosphorylation reactions alone are responsible for ATP generation, then the ATP molar growth yield must be about 23 g (dry weight)/mol of ATP. Alternatively, if anaerobic electron transfer-linked phosphorylation also occurs, the ATP molar growth yield will be lower. Bacteroides ruminicola is one of the more numerically important bacteria found in the rumen, representing 6 to 19% of the total culturable carbohydrate fermenters present (8). It is not immediately obvious why B. ruminicola can compete so successfully in this anaerobic environment, which contains so many other carbohydrate-utilizing, organic acid-producing bacteria. Part of the reason for its quantitative predominance may be the result of its great versatility towards possible carbohydrate and nitrogen sources utilized (7, 8). However, it is also likely that the species has a highly efficient energy metabolism and can multiply rapidly. This study set out to examine growth yields of B. ruminicola, as an index of its energy metabolism, to discover whether the yields are "normal" or "anomalous" (19) and can be predicted from the products of fermentation. Careful attention has been paid to correction for storage polysaccharide and carbon recovery in products, which can both lead to erroneous results if ignored. B. ruminicola has a b-type cytochrome, which may be involved in fumarate reduction by reduced nicotinamide adenine dinucleotide (40); such electron transport systems in other bacteria have sometimes been postulated to be coupled to anaerobic electron transport phosphorylation reactions (3, 16, 28). If such a system is operative in B. ruminicola, then adenosine 5'-triphosphate (ATP) yields will be higher than can be accounted for by substrate-level phosphorylation reactions. Caldwell (D. R. Caldwell, Diss. Abstr. Int. B. 31:1419) has previously suggested that ATP yields in B. ruminicola strain GA33 are between 4.5 and 7.8 ATP/ mol of glucose, based on measurements of cellular protein. MATERIALS AND METHODS Bacteria. B. ruminicola subsp. brevis, strain B,4 (7, 8), was used in the present work and was kindly supplied by M. P. Bryant of the University of Illinois. This strain was used in preference to the type strain, strain GA33, because strain B,4 clumps rather less ...

Growth of galactose-adapted cells of Streptococcus lactis ML3 in a medium containing a mixture of glucose, galactose, and lactose was characterized initially by the simultaneous metabolism of glucose and lactose. Galactose was not significantly utilized until the latter sugars had been exhausted from the medium. The addition of glucose or lactose to a culture of S. lactis ML3 growing exponentially on galactose caused immediate inhibition of galactose utilization and an increase in growth rate, concomitant with the preferential metabolism of the added sugar. Under nongrowing conditions, cells of S. lactis ML3 grown previously on galactose metabolized the three separate sugars equally rapidly. However, cells suspended in buffer containing a mixture of glucose plus galactose or lactose plus galactose again consumed glucose or lactose preferentially. The rate of galactose metabolism was reduced by 95% in the presence of the inhibitory sugar, but the maximum rate of metabolism was resumed upon exhaustion of glucose or lactose from the system. When presented with a mixture of glucose and lactose, the resting cells metabolized both sugars simultaneously. Lactose, glucose, and a non-metabolizable glucose analog (2-deoxy-D-glucose) prevented the phosphoenolpyruvate-dependent uptake of thiomethyl-,f-D-galactopyranoside (TMG), but the accumulation of TMG, like galactose metabolism, commenced immediately upon exhaustion of the metabolizable sugars from the medium. Growth of galactose-adapted cells of the lactose-defective variant S. lactis 7962 in the triple-sugar medium was characterized by the sequential metabolism of glucose, galactose, and lactose. Growth of S. lactis ML3 and 7962 in the triple-sugar medium occurred without apparent diauxie, and for each strain the patterns of sequential sugar metabolism under growing and nongrowing conditions were identical. Fine control of the activities of preexisting enzyme systems by catabolite inhibition may afford a satisfactory explanation for the observed sequential utilization of sugars by these two organisms.The capacity of group N streptococci (Streptococcus lactis, S. cremoris, and S. diacetylactis) to ferment lactose to lactic acid is of major economic importance in the manufacture of dairy products. However, it is only recently that the biochemical pathways (see Fig. 1) involved in the transport and metabolism of lactose by this important group of organisms have been established (20). The transport of lactose is mediated via the phosphoenolpyruvate (PEP): lactose phosphotransferase system (lac-PTS) and the disaccharide is phosphorylated simultaneously with translocation (24, 25; for a review, see reference 33). The accumulated lactose phosphate [6-phosphogalactosyl-(J8-1 -* 4)-glucose] is subsequently cleaved by fi-D-phosphogalactoside galactohydrolase (12,27) to yield glucose and galactose-6-phosphate, which are further metabolized by the Embden-Meyerhof and Dtagatose-6-phosphate pathways (3-5), respec-tively. Possession of a functional lac-PTS and /-D-phosphogalactoside ...

Commercial extracts from oro-pharyngeal tissues of goats and kids have been used as the source of pregastric lipase and have been processed to yield partially purified samples of the primary pregastric lipase. The activity of these lipases against tributyrylglycerol has been determined over a range of pH and temperatures. Optimum pH conditions for pregastric lipase ranged from pH 5.6 to 6.5 for goats and from pH 5.5 to 6.2 for kids, respectively; the optimum temperature ranged from 43 to 60 degrees C. Optima for kid lipase extended slightly below pH 5.5 and higher than 60 degrees C; which were the limits of the test conditions. The enzymes were also used as catalysts for the hydrolysis of monoacid triglycerides (C4:0 to C12:0) at 40 degrees C and pH 6.5; activity was maximum against tributyrylglycerol (C4:0). Values for the Michaelis-Menten constant, increased as carbon chain length of the carboxylic moiety on the triglycerides increased, but values were identical for pregastric lipases of both goats and kids. Anhydrous milk fat was hydrolyzed by the commercial extracts of pregastric lipases of goats and kids, and the resulting profiles for free fatty acids were very similar to one another and to the corresponding profile for a commercial sample of Parmesan cheese. There appear to be no significant differences in activity between the enzyme preparations from goats and kids.