413The total lipid content of Mycobacterium smegmatis ATCC 607 was the same whether it was grown at 27 or 37 "C. The total phospholipid content, however, increased significantly at 27 "C. Phosphatidylethanolamine increased most markedly with a simultaneous decrease in phosphatidylinositol mannosides. Among individual phosphatidylinositol mannosides, tri-and tetra-acylated dimannophosphoinositides and tetra-acylated hexamannophosphoinositides all decreased at the lower growth temperature. Triacylglycerols and monoacylglycerols increased at the lower temperature but diacylglycerols were unaffected. Unsaturated fatty acids of total phospholipids increased as the temperature was lowered.

Summary.The total lipids increased with decrease in total phospholipids in Mycobacterium tuberculosis H37RV grown at 30° as compared to 37°, Oleic and elaidic acid supplemented to the growth medium resulted in a higher total lipid and phospholipid content, but the content was lower in cells grown in the presence of palmitoleic acid. Cellular content of mannophosphoinositides decreased, whereas that of phosphatidylethanolamine and cardiolipin increased at the lower temperature, A decrease in mannophosphoinositides and an increase in cardiolipin were noted with all fatty acid supplements; however, phosphatidylethanolamine behaved differently. The unsaturated to saturated fatty acids ratio increased at low temperature with oleic and elaidic acid supplements, but it decreased with palmitoleic acid. Cells from media supplemented with palmitoleic acid were found to be most virulent to guinea-pigs. Possible correlation of altered lipid composition and virulence of M. tubercutosis H37RV has been discussed.

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The rate of synthesis and degradation of phospholipids in Mycobacterium smegmatis ATCC 607, grown at 27 degrees C and 37 degrees C was studied incorporation of 32P into phospholipids and chase of radioactivity of the pulse-labelled phospholipids. A relatively low rate of synthesis and degradation of phospholipids in cells growth at 27 degrees C was observed as compared to those grown at 37 degrees C. Phosphatidylethanolamine (PE) had the maximum turnover at 37 degrees C. However, at 27 degrees C, cardiolipin (CL) showed a turnover rate higher than PE. Phosphatidylinositol mannosides (PIMs) were metabolically more active at 37 degrees C than at 27 degrees C. The differences in metabolic activity of the phospholipids at the two temperatures have been discussed.