Fermentation products, amino acid utilization, maintenance energies and growth yields for the fibrillar Streptococcus salivarius HB and a non‐fibrillar mutant HB‐B grown in continuous culture under glucose limitation

Abstract

The fibrillar strain Streptococcus salivarius HB and a non-fibrillar mutant, strain HB-B, were grown in a defined medium under glucose limitation in a chemostat. Fermentation balances were produced for both strains in batch culture and at growth rates between 0.1/h and 1.1/h. In batch culture both strains fermented glucose to lactate, but in continuous culture glucose was fermented to formate, acetate and ethanol with increasing amounts of lactate as the growth rate was increased. Lactate never became the major fermentation product even at the highest growth rate. Amino acid analysis showed that only lysine was more than 50% utilized, while proline and tyrosine showed net production. The non-fibrillar strain HB-B showed, in general, a reduced utilization of amino acids compared with the fibrillar strain HB. Calculated growth yields and maintenance energies for the two strains showed that there was a reduction in the true growth yield and the maintenance energy coefficient of the non-fibrillar strain HB-B when compared with the fibrillar strain HB. The increase in the maintenance energy of the fibrillar strain HB (1.382 mmol/g/h) when compared with the non-fibrillar strain HB-B (0.546 mmol/g/h) of 153% is proposed to be the energy required for the maintenance of the fibrillar surface of the cell.

Proteome analysis of Streptococcus mutans metabolic phenotype during acid tolerance

“…This observation may be explained mainly by the increased glycolytic rate (Hamilton, 1984) needed to produce ATP for H + extrusion at pH 5?0 (Bender et al, 1986;Belli & Marquis, 1991;Hamilton & Buckley, 1991;Miyagi et al, 1994;Smith et al, 1996). The fact that there was a futile use of carbon at pH 5?0 was reflected in the measured reduction in both ATP yield, (Y ATP ; Harty & Handley, 1988) from 16?9 to 3?9 g (dry weight) cells per mol ATP, and the cell yield (Y Glc ), from 28?0 to 15?1 g (dry weight) cells per mol glucose, when the growth pH was reduced from 7?0 to 5?0 (Table 2). While clearly not preventing the production of alternative acids, the question remains whether the reduction in enzyme levels in the ethanol and acetate branches of the pyruvate formate-lyase pathway becomes limiting in cells growing at pH 5?0, and by so doing enhances the flow of pyruvate through the L-lactate dehydrogenase pathway.…”

“…The concentrations of glucose, acetate, ethanol, formate and lactate present in the medium at steady state were measured enzymically with the appropriate detection kit (Roche), according to the manufacturer's instructions (Harty & Handley, 1988). The amount of accumulated intracellular polysaccharide (IPS) was determined by the potassium iodide method of DiPersio et al (1974).…”