Catabolite repression in Enterococcus faecalis

Metabolism of citrate, pyruvate and sugars by Enterococcus faecalis E-239 and JH2-2 and an isogenic, catabolite derepressed mutant of JH2-2, strain CL4, was investigated. The growth rates of E. faecalis E-239 on citrate and pyruvate were 0.58 and 0.63 h(-1), respectively, indicating that both acids were used as energy sources. Fructose and glucose prevented the metabolism of citrate until all the glucose or fructose had been metabolised. Diauxie growth was not observed but growth on glucose and fructose was much faster than on citrate. In contrast, citrate was co-metabolized with galactose or sucrose and pyruvate with glucose. When glucose was added to cells growing on citrate, glucose metabolism began immediately but inhibition of citrate utilisation did not begin for approximately 1.5 h. Growth rates of E. faecalis JH2-2 and its isogenic, catabolite derepressed mutant, strain CL4, on citrate, were 0.41 and 0.36 h(-1), respectively. The catabolite derepressed mutant was able to co-metabolise citrate and glucose at all concentrations of glucose tested (3-25 mM), while its parent, could only metabolise citrate once all the glucose had been consumed. In strains JH2-2 and E-239, the growth rate on citrate decreased as the glucose concentration increased and, in 25 mM glucose, consumption of citrate was inhibited for several hours after glucose had been consumed. These results indicate that catabolite repression by glucose and fructose occurs in enterococci.