Inducer Expulsion Is Not a Determinant of Diauxic Growth in Streptococcus bovis

When Streptococcus bovis JB1 was repeatedly transferred in a medium that contained the non-metabolizable glucose analog, 2-deoxyglucose, it lost its phosphotransferase system (PTS) for glucose but was still able to take up glucose via a facilitated diffusion mechanism. The wild type (JB1) had an inducible enzyme II lactose, but the mutant (JB1^2DG) had a constitutive lactose PTS. JB1^2DG was no longer able to exclude lactose when it was provided with glucose, but it retained its ability to expel a non-metabolizable lactose analog. Because JB1^2DG could utilize glucose and lactose simultaneously and grow in a non-diauxic fashion, it appeared that inducer expulsion was not an important catabolite regulatory mechanism. Based on these results, inducer expulsion may be an artifact of non-metabolizable sugars.