Catabolite repression in the hyperthermophilic bacterium Thermotoga neapolitana is independent of cAMP.

Thermotoga neapolitana is a hyperthermophilic bacterium whose phylogenetic lineage includes the most primitive of the bacterial heterotrophs. It is not known whether Thermotoga exhibits preferences for growth substrates or regulates the synthesis of degradative enzymes. We have found that T. neapolitana exhibits diauxic growth in medium containing 300 microM glucose and 1 mM lactose. We measured the activity of beta-galactosidase and beta-glucosidase in extracts prepared from cells grown on defined media and found that cells grown on 0.5% lactose, galactose or cellobiose contained beta-galactosidase specific activities of 1.19, 1.78 and 1.34 U (mg protein)-1, respectively. Cells grown on 0.5% glucose, maltose, fructose, sucrose, xylose, ribose or starch had no measurable beta-galactosidase activity. beta-Glucosidase activity was found only in cells grown on cellobiose. Cells grown on the combination of 0.5% lactose or galactose and 0.05% glucose had no detectable beta-galactosidase activity, whereas up to 0.5% glucose did not prevent expression of beta-galactosidase or beta-glucosidase activity in cells induced with 0.5% cellobiose. These activities are catalysed by separate enzymes as determined by resolution of their activities on 6% native polyacrylamide gels. Therefore, only beta-galactosidase synthesis induced by lactose is subject to catabolite repression. To determine the mechanism of catabolite repression, the levels of cAMP were measured in T. neapolitana cells grown on various defined media using an enzyme-immunoassay. The cAMP levels ranged from 44 to 280 fmol (mg protein)-1 irrespective of the carbon source used. By comparison, Escherichia coli grown on lactose contained 5.1 pmol (mg protein)-1. Like Gram-positive bacteria, T. neapolitana displays a cAMP-independent mechanism for catabolite repression and this may represent the more ancient mode of regulation.