Analysis of nutritional shift-up of Streptococcus faecium

Three-dimensional reconstruction methods were applied to electron micrographs of Streptococcus faecium to study the initiation of cell wall growth sites during a nutritional shift-up experiment. Upon lowering the mass doubling time from 76 to 33 min by the addition of excess glutamate, the formation of new cell wall growth sites was studied in relation to other growth parameters (autolytic capacity, cell number, mass, RNA, DNA and peptidoglycan). The findings from these studies, to be described below, support a model in which new sites are introduced when cells grow to a relatively constant, growth-rate-independent size, while the rate at which sites form and grow increases with growth rate. In this model, chromosome synthesis does not regulate the formation of new sites of cell wall growth, but existing sites cannot be completed until rounds of chromosome synthesis are completed.