The utilization of casein and amino acids by Streptococcus sanguis P4A7 in continuous culture

Abstract

Streptococcus sang& P4A7 was grown in glucose limited conditions in continuous culture at pH 7-0 in a chemically defined medium containing either free amino acids or casein as the organic nitrogen source. Apart from aspartate and threonine, which were poorly utilized at the higher dilution rates, all amino acids in the free-amino-acid medium were utilized to various extents. At the higher dilution rates, aspartate actually increased in concentration, probably due to deamidation of asparagine. The amino acid most utilized at all dilution rates was arginine, with up to 99 yo of the amino acid being consumed. Both casein and its aS1 -casein fraction supported growth at a level only slightly lower than that obtained with the free-amino-acid medium, provided that either cysteine or thioglycollate was present. With the exceprion of tyrosine, nearly all of the amino acyl residues ofaSl -casein were utilized to some degree. In general, the higher the concentration of each amino acid in the medium (whether free or as part of as1-casein) the higher the extent of utilization by S. sanguis P4A7. Only 50% of the arginyl residues (0-16 mM) of aslcasein were utilized compared with 99% of free arginine (1.5 mM) under similar conditions, suggesting that only 50% of the aS1 -casein arginine was accessible to the organism. From a comparison of the amino acid composition of a,,-casein with that of the high M, fraction of the culture supernatant it was concluded that leucine, phenylalanine, lysine, histidine, arginine and valine were specifically released from a,, -casein by the endo-and exopeptidase activity of S. sanguis P4A,.

Why be down in the mouth? Three decades of research in oral microbiology

“…6,7 In a further series of experiments we demonstrated that, because of their peptidase activities, a number of common plaque organisms, such as S. sanguis, can obtain the metabolically important Arg from a variety of peptides and also from whole proteins, such as casein. 8,9 Studies such as these indicate that the microbial homeostasis maintained in most sites throughout the human body can be disturbed by a number of environmental factors, such as nutrient availability. One of the best-documented examples of this is the outgrowth of the cariogenic MS when diets are high in fermentable carbohydrate, especially sucrose.…”