Cell wall assembly during inhibition of DNA synthesis in Streptococcus faecium.

Growth sites which are bounded by raised wall bands can be observed in electron micrographs of replicas of Streptococcus faecium. When mitomycin C was added to an exponential-phase culture doubling in mass every 64 min, DNA synthesis was inhibited, and eventually cell division stopped. The growth sites formed before and after inhibition of DNA synthesis enlarged until they contained about 0.25 micron3 of cell volume, at which point they ceased to increase in size. When these sites approached this 0.25-micron3 limit, new sites were initiated; this result had also been observed in untreated cells undergoing a large range of exponential-phase mass doubling times. Thus, regardless of whether chromosome replication is inhibited or uninhibited, sites have the same finite capacity to enlarge to about 0.25 micron3, and when this capacity is reached, new sites are initiated. Although initiation of new growth sites seems to be independent of normal chromosome replication, these results confirm previous studies showing that chromosome replication is necessary for the terminal events of growth site development which result in the division of a site into two separate poles. Two classes of models for the regulation of growth site initiation are discussed.