Effect of macromolecular synthesis and lytic capacity on surface growth of Streptococcus faecalis

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Abstract
Exposure of exponential-phase cultures of S. faecalis to any of 3 inhibitors [chloramphenicol, actinomycin D and 5-azarytidine] of protein synthesis was accompanied by an increase in the average distance that the cross wall extended into the cytoplasm. This resulted in: an increase in the average surface area of the cross wall (Sa) and septation occurring in the envelope growth sites that were much smaller than the controls. Although at the concentrations used, all 3 antibiotics inhibited protein synthesis and autolytic capacity to the same extent and with the same kinetics, cells treated with these agents showed large differences in the rate at which Sa values increased above those of the untreated cells. The largest increases in Sa were observed in cells that synthesized the least amount of cytoplasmic macromolecules (DNA, plus RNA, plus protein). The observations were interpreted in terms of a model in which a decreased lytic capacity reduces the rate of splitting of the nascent cross wall into 2 layers of peripheral wall, preferentially using wall precursors to close open cross walls. The extent to which centripetal growth occurs would be inversely related to the rate at which cytoplasmic macromolecules are synthesized. Inhibition of DNA synthesis was accompanied by decreased extension of the leading edge of the cross wall into the cytoplasm, thus antagonizing septation. These findings are discussed in relation to the normal cell division cycle of S. faecalis.