Studies on the Regulation of Extracellular Enzyme Formation by Bacillus subtilis

Abstract

The progress of secretion of the extracellular enzymes ribonuclease, a -amylase and proteinase by B. subtilis, growing in a defined and in a complex medium, containing maltose, starch, glycerol or glucose as carbon source, was followed. In either medium and in the presence of any of the carbon sources the general characteristics of secretion of all three enzymes were the same. There was a low but definite production of exoenzyme from the moment the cells started to grow until the end of the logarithmic phase after which, when the rate of increase in cell mass was decreased, the rate of enzyme secretion increased to a high linear value which was maintained even into the stationary phase. The results are discussed in relation to a possible regulatory mechanism which might account for the observed characteristics of extracellular enzyme secretion. A mechanism is proposed whereby exoenzyme m-RNA formation and hence enzyme production is limited during growth by a limitation of nucleic acid precursors caused by the depletion of the precursor pool during rapid ribosomal RNA synthesis. When the growth rate is decreased, ribosome synthesis is also decreased; the nucleic acid precursor pool may then increase in size, thereby removing the limitation so that exoenzyme m-RNA and protein may be formed at the maximum rate.