Factors involved in the synthesis of cyclopropane fatty acids by Streptococcus faecalis

Abstract

Factors affecting the synthesis of cyclopropane fatty acids in Streptococcus faecalis (ATCC 8043) were investigated. The cellular content of cyclopropanes reached the maximum level at the beginning of stationary phase. The concentration of lactobacillic acid increased with higher growth temperatures. The final percentage of lactobacillic acid in cells grown at 27, 37 and 47 °C was 15.9, 22.6 and 36.4%, respectively. There were greater proportions of higher melting point fatty acids when the growth temperature was increased. Strains of S. faecalis resistant to amethopterin contained no detectable cyclopropanes. There was a corresponding rise in the immediate precursor, cis-vaccenic acid. The content of cyclopropanes in the parent strain could be decreased by growing it in limiting quantities of methionine, folic acid, or thymidine. Cyclopropanes were synthesized in normal quantities in the absence of folic acid, provided optimum levels of thymidine were present. The addition of 25 μg amethopterin per ml to the thymidine-grown cultures did not decrease cyclopropane synthesis. The incorporation of [ Me- 14C]methionine into the cyclopropanes was determined in cells grown in the presence and absence of folic acid. The average relative specific activity was 105 and 101 for the folate-grown and the thymidinegrown cells, respectively. In order to accentuate a possible folic acid-related pathway of cyclopropane synthesis, cultures were grown with limiting methionine and increased amounts of serine, sodium formate, betaine, choline and optimum levels of folic acid. There was no increase in the cyclopropane content of those cultures when compared to the low-methionine control. It is concluded that folic acid is not a direct one-carbon donor for the synthesis of cyclopropane fatty acids in S. faecalis.