Sucrose-grown Cells Research Articles

Origin of the cell-associated dextransucrase of Streptococcus mutans.

The cell-associated dextransucrase produced by sucrose-grown cells of cariogenic Streptococcus mutans K1-R is derived from soluble dextransucrase. Synthesis of insoluble dextran by soluble dextransucrase gives rise to two dextransucrase fractions bound to the insoluble polysaccharide; a reversibly bound enzyme, which can be eluted in solutions of clinical dextran, and an irreversibly bound enzyme, which cannot be solubilized in this manner. Both of these fractions of dextransucrase are also present on sucrose-grown cells. During the synthesis of insoluble dextran by sucrose-grown cells, dextransucrase is progressively converted from soluble enzyme, first to the reversibly bound fraction and then to the irreversibly bound fraction, and is finally inactivated as insoluble dextran accumulates. The two cell-associated dextransucrase fractions therefore represent two stages in the insolubilization and inactivation of their precursor, soluble dextransucrase. As a result of this process of inactivation, the yield of dextransucrase from cells cultured on sucrose is markedly decreased by high concentrations of sucrose in the culture medium.

Studies on the carbohydrate metabolism of cariogenic Streptococcus Mutans strain PK-1

Under anaerobic condition the resting cells of cariogenic streptococcus strain PK-1 metabolized glucose via the Embden-Meyerhof pathway and about 2 moles of lactate were formed for each mole of glucose consumed. Under aerobic condition the greater part of the glucose was also metabolized by the way of the Embden-Meyerhof pathway to pyruvate, but the pyruvate was converted not only to lactate but to acetoin, CO 2 and acetate. It is noteworthy that under aerobic condition d-lactate formation did not decrease remarkably, though l-lactate formation was decreased by half. Under aerobic condition a part of the glucose consumed was considered to be metabolized via the hexose monophosphate shunt but none of the glucose was observed to be metabolized via the citric acid cycle or the Entner-Doudoroff pathway. Evidence was obtained that sucrose phosphorylase was induced in sucrose-grown cells. Fructose-1; 6-diphosphate activated the l-lactate dehydrogenase of this organism, but did not activate d-lactate formation. However, the effect was less than that on the lactate dehydrogenase of some other streptococci.

Purification of 2-keto-3-deoxy-6-phosphohexonate aldolases of Pseudomonas saccharophila.

KDPG aldolase has been crystallized from extracts of sucrosegrown cells of Pseudomonas saccharophila. KDPGal aldolase, which is absent in sucrose-grown cells but is present together with KDPG aldolase in galactose-grown cells has been purified over 1000-fold. The two enzymes share many common features, but possess absolute substrate specificity and are immunochemically distinct. The equilibrium constants for the catalyzed reactions have been determined and found to favor the synthesis of the 2-keto-3-deoxy-6-phosphohexonic acids.

Mannitol catabolism by Staphylococcus aureus

In Staphylococcus aureus strain 233, mannitol is oxidized rapidly by d-mannitol-, sorbitol-, and d-arabitol-grown cells; it is not oxidized by cells grown in broths containing glucose, succinate, or no added carbohydrate. Neither sorbitol nor arabitol are oxidized by staphylococci, but these sugar alcohols induce high rates of mannitol uptake. Noninduced cells and sucrose-grown cells take up mannitol slowly, but uptake is repressed in glucose-, fructose-, mannose-, and glycerol-grown cells. Although no direct oxidation or phosphorylation of mannitol was demonstrable with cell-free extracts of induced cells, a nicotinamide adenine dinucleotide-linked dehydrogenase was found which was specific for mannitol-1-phosphate. The enzyme was also present in extracts of noninduced cells but at much lower levels. These results suggest that mannitol-1-phosphate is an intermediate in the catabolism of mannitol by staphylococci. Nineteen mannitol-negative mutants of strain 233 were studied, and specific enzymatic and/or genetic defects are suggested for each.

Equilibration of succinate solutions with adapted and unadapted Azotobacter cells.

Sucrose-grown (unadapted) and succinate-grown (adapted) cells were mixed with various concentrations of succinate at 3 °C. under air and at 30 °C. under helium. The amount of succinate removed from the external solution by the cells was proportional to the concentration of succinate and did not differ significantly with the two types of cells. Although the data did not differentiate between equilibration with intracellular water and mere adsorption, they indicate that no change has occurred in the surface of the adapted cells to allow a more rapid diffusion of succinate across the osmotic barrier under nonmetabolic conditions. So far as can be determined by using masses of cells, any "permeability" changes during adaptation of the azotobacter cells to succinate must be connected with an active transport process associated with metabolism.