Intact cells of Bdellovibrio bacteriovorus strain 109J were found to be incapable of taking up 14C-methyl alpha-
glucoside,
mannitol or
fructose, and extracts derived from these cells exhibited negligible activities of the
protein components of the
phosphoenolpyruvate:sugar phosphotransferase system (PTS). Escherichia coli strain ML35 cells exhibited high in vivo
sugar uptake activities that were progressively lost over a period of 2 h at 30 degrees C following the entry of B. bacteriovorus into the periplasm of E. coli. In vitro complementation assays revealed that the E. coli PTS
enzymes,
enzyme I, HPr, and the
glucose- and
mannitol-specific
enzymes II, were all lost almost in parallel with the disappearance of uptake activity. Thus, loss of activity in vivo was not due to membrane leakiness, energy depletion, or preferential inhibition or inactivation of any one
protein component of the PTS. Instead, loss of PTS activity was attributed to digestion of the
protein constituents of the system by
proteases present in the cytoplasm of the host cell after bdellovibrio entry. Both ethylenediaminetetraacetate and phenylmethylsulphonyl
fluoride partially protected against inactivation in vitro, and the two inhibitors together gave full protection, suggesting that both metallo- and seryl-
proteases were responsible for the inactivation.
Protease activity increased progressively with time following bdellovibrio entry and appeared to degrade the E. coli PTS
enzymes in vivo. Preliminary evidence suggested that the
proteases responsible for PTS
enzyme degradation may be encoded by the B. bacteriovorus chromosome.