A mechanism for the sucrose stimulation of the genetic transformation of Bacillus subtilis



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A study of the sucrose stimulation of genetic transformation in Bacillus subtilis has presented experimental evidence related to the part played by the cytoplasmic membrane and mesosomes in the binding of transforming deoxyribonucleic acid to competent cells. The transformation stimulation by 0.3M sucrose was found to be limited to cells already competent, to affect equally all genetic markers tested, to be limited to the reversible binding phase of the uptake process and inhibited by very low and very high temperatures. The pH optimum remained the same as the control, as did the ionic strength optimum, but the methylene blue dye adsorption, i.e. the negative charges on the cell, decreased in the presence of sucrose. The stimulating effect was found to be associated with the cells, not the medium or the DNA. It was decreased by lipolytic enzyme treatment and decreased the amount of residual DNase in supernatants of competent cells. Cells with and without sucrose responded similiarly to dinitrophenol inhibition of active transport. Single-strand transformation responded to sucrose the same as the native DNA system. Lactose, mannose and galactose, also stimulating sugars, demonstrated the same reversible binding phase specificity and low temperature inhibition of the stimulatory effect, thus suggesting that most, if not all, sugars that stimulate genetic transformation have a common mode of action. The data was discussed in relation to existing ideas of mesosomal involvement in DNA uptake and a mechanism dedeloped for the interaction of stimulating sugars and mesosomes resulting in an increase in genetic transformation.