The utilisation of arginine by oral streptococci grown glucose‐limited in a chemostat

Pure cultures of 2 strains of Streptococcus milleri and one of Streptococcus mutans were grown glucose‐limited at dilution rates of D= 0.1 h−1 and D= 0.3 h−1 and controlled pH of 7.0 in a chemically defined medium containing arginine levels of 0.6, 10, 33, 60 and 74 mM. Culture filtrate levels of arginine and its metabolites and glucose were determined as were cell dry weights and intracellular glycogen (IG). In S. milleri, stoichiometric conversion of up to 60 mM of arginine to citrulline and ornithine occurred, with 75% of the arginine appearing as ornithine. Similar patterns were obtained at D= 0.3 h−1, although only 30–40% of the arginine was converted to ornithine. At the 10 mM arginine level, biomass but no IG was produced while above this level, IG was also synthesised. At D= 0.3 h−1, substantial amounts of IG were detected at all arginine levels. As expected, S. mutans did not respond to increasing arginine levels and the use of this amino acid as an additional carbon and energy source with the release of ammonia in organisms such as S. milleri and Streptococcus sanguis may help to explain their dominance when growing in vitro and in vivo with S. mutans under glucose‐limiting conditions.