Studies on the metabolism of phospholipids in Mycobacterium phlei. I. Difference in turnover rates of individual phospholipids

Cerulenin effect on phospholipid metabolism in Mycobacterium smegmatis ATCC 607

Phospholipid metabolism in the presence of a subinhibitory concentration of cerulenin was studied in Mycobacterium smegmatis ATCC 607 by pulse labelling and subsequent chasing of radioactivity in phospholipids using [32P]orthophosphate. Cerulenin inhibited biosynthesis of total phospholipids to a significant level which is reflected equally in all the phospholipid components (phosphatidylethanolamine, phosphatidylinositol mannosides and cardiolipin) within the time of exposure. On chase, alteration in degradation of all phospholipid components was observed on cerulenin treatment, in comparison with control cells. Differences seen in the metabolism of phospholipids in cerulenin-treated and control cells are discussed.

Turnover of phospholipids and glycerides of spheroplasts of Mycobacterium smegmatis ATCC 14468

The breakdown and renewal of phospholipids and glycerides from spheroplasts of Mycobacterium smegmatis ATCC 14468 were studied by means of pulse labelling techniques using 1-14C-palmitate. Most of the radioactivity incorporated into total lipids was recovered from phospholipids. Among the phospholipids studied, cardiolipin had the highest radioactivity and specific activity, suggesting its higher pool size as compared to other fractions. The appreciable loss of radioactivity for cardiolipin in pulse chase experiments within growing cells suggests its metabolically active and dynamic nature. Glycerides exhibited no appreciable turnover rates.

Subcellular distribution of mannophosphoinositides in Mycobacterium smegmatis during growth

Subcellular distribution of total phospholipids and mannophosphoinositides (mannosides) was examined in Mycobacterium smegmatis ATCC 607 during its transition from the early exponential to the stationary phase of growth. There was relatively more of these substances in the cell membrane than in the cell wall, and the total amount increased with the age of the culture. Among individual mannosides, dimannophosphoinositides (dimannosides) were distributed equally in the cell wall and membrane. However, hexamannophosphoinositides (hexamannosides) were more predominant in the cell membrane, and the level increased with the age of the culture.

Biosynthesis of hexamannophosphoinositides in Mycobacterium smegmatis ATCC 607

The biosynthesis of hexamannophosphoinositides in Mycobacterium smegmatis ATCC 607 was examined using labelled tri- and tetraacylated dimannophosphoinositides (PIM2(-3)F and PIM2(-4)F) as precursors, by in vivo and in vitro incorporation. Tetraacylated dimannoside was metabolically more active as compared to triacylated dimannoside and seems to be the precursor for the synthesis of hexamannophosphoinositides.

Phospholipid metabolism in Mycobacterium smegmatis ATCC 607 grown at 37 degrees and 27 C degrees C

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.

Turnover of lipids in Mycobacterium smegmatis CDC 46 and Mycobacterium phlei ATCC 354

The rates of breakdown and renewal of individual lipids in cultures of Mycobacterium smegmatis CDC 46 and Mycobacterium phlei ATCC 354 were investigated by means of a pulse labelling technique using palmitate-1-14C. The results indicated that in growing cultures of both strains phospholipids were broken down, and cardiolipin had a very rapid turnover. In chase experiments, almost 45% and 40% of the radioactivity of this component were lost respectively from M. smegmatis and M phlei during one generation time of the cell. The other two major components, phosphatidyl ethanolamine and phosphatidylinositol mannosides showed relatively low turnover. The loss of radioactivity from phosphatidylinositol mannosides was greater in M. phlei than in M. smegmatis but the loss of radioactivity from phosphatidyl ethanolamine was higher in M. smegmatis. The pattern of loss of radioactivity from lipids was almost the same in both strains, the difference being only in the extent of loss. The differences in the cellular localization of the phospholipids indicate their different roles within the cell. Results obtained with the glyceride fraction indicated a very rapid turnover of triglycerides in both strains.