Bacterial cell wall synthesis: the effect of threonine depletion.

Our previous studies of Streptococcus faecalis 9790 have shown that the depletion of an essential amino acid from a highly buffered synthetic medium corresponds to the end of the exponential growth phase (log phase) (2, 3). The end of the log phase is followed by further turbidity changes that are characteristic for the particular amino acid studied. The exhaustion of valine is followed by a slow increase in turbidity of 40 to 50 per cent, in about 11 hours. It was found that this turbidity increase is accompanied by an increase in the dry weight of the culture, most of which can be accounted for by the format.ion of additional cell wall substance (I, 2, 4). When growth is limited by the amount of threonine present in the culture medium, the end of log phase (and threonine depletion) is also followed by a turbidity increase. However, instead of leveling off after a gain of 40 to 50 per cent, the turbidity slowly continues to increase for several days. Eventually, a turbidity level that is more than twice that at the end of log phase is reached. We have now demonstrated that the primary consequence of threonine depletion, like valine depletion, is the synthesis of additional cell wall substance without concurrent cytoplasmic protein synthesis. The extent of wall synthesis appears to be at least twice as large as is the case for valine deprivation.