The influence of incorporation of octadecenoic acid on the cell-associated fructosyltransferase and the extracellular glucosyltransferase activities of Streptococcus salivarius

The rate of expression of the cell-associated fructosyltransferase (FTFm) activity of Streptococcus salivarius ATCC 25975 grown in continuous culture was linearly related to the rate of octadecenoic acid (C18:1) incorporation into the membrane lipids irrespective of the presence or absence of Tween 80 in the growth medium. This observation was confirmed with data obtained from cells grown in the presence of a series of n-alkanols. The results suggested that cosynthesis of lipids containing C18:1 residues was necessary for FTFm expression and accounted for the slight stimulation of enzyme expression by Tween 80 at all growth rates. In contrast, addition of Tween 80 to the growth medium resulted in several-fold increases in extracellular glucosyltransferase (GTFe) production irrespective of the growth rate. Following the addition of the surfactant to the growth medium, an exponential relation between the increased rate of GTFe production and the concomitant net increase in the rate of C18:1 incorporation was noted. The results obtained in continuous culture emphasized the underlying effect growth rate had on GTFe production, especially when Tween 80 was added to the growth medium. In the presence of n-alkanols, the rate of GTFe production plotted as a single 'U'-shaped curve with respect to the rate of C18:1 incorporation irrespective of the chain length of the n-alkanol studied. Rapid analyses of the extracellular proteins by SDS-PAGE suggested that hexan-1-ol and Tween 80 specifically stimulated the synthesis and secretion of GTFe and no other extracellular protein.(ABSTRACT TRUNCATED AT 250 WORDS)