Properties of a Streptococcus sanguis (group H) bacteriocin and its separation from the competence factor of transformation.

STH(1), a streptocin elaborated by group H streptococcus strain Challis, is lethal for group H streptococcus strain Wicky and is produced maximally during the exponential growth phase of liquid medium cultures. Crude streptocin preparations are resistant to oxidation and display a biphasic pH stability (stability being maximal at pH 5.0 and 10.0). Survivor studies indicate that streptocin-mediated killing is a "one-hit" phenomenon and proceeds rapidly. The streptocin has been purified 50-fold with (NH(4))(2)SO(4) fractionation and Sephadex G100 chromatography and appears to exist in equilibrium between two molecular weight forms. Low ionic strength and neutral pH buffers favor the isolation of the 110,000 molecular weight form, whereas high ionic strength and alkaline pH conditions facilitate isolation of the 28,000 to 30,000 molecular weight form. These findings suggest an association-dissociation relationship between macromolecules of 28,000 to 30,000 molecular weight. Purified STH(1) has no "competence factor" (CF) activity. In addition, CF has no STH(1) activity and displays no inhibitory effect on exponential-phase Wicky cultures as determined by absorbancy measurements. It appears, therefore, that initiation of the competent state for transformation in strain Wicky is not necessarily accompanied by gross alterations in cell growth.