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Microbial Assimilation of Hydrocarbons: Phospholipid Metabolism

¹ Department of Microbiology, University of Georgia, Athens, Georgia 30601

ABSTRACT

An analysis of the turnover of the major phospholipids of Micrococcus cerificans growing or nongrowing cultures. The turnover rates of ¹⁴C-PE and ¹⁴C-PE were 61.5% of the total phospholipid, exhibited no significant rate of turnover in either growing or nongrowing cultures. The turnover rates of PE-¹⁴C and PE-³²P were 3.2% per hr and 1.2% per hr, respectively. Phosphatidylglycerol (PG) exhibited a turnover rate of 11% and 7.7% per hr for ¹⁴C and ³²P, respectively, indicating an extremely slow metabolism. PG metabolism was examined in greater detail, and the data indicated a preferential 75% incorporation of glycerol-1,3-¹⁴C into the unacylated portion of the PG molecule. The turnover of cardiolipin (CL) was extremely slow in growing cells whereas nongrowing cells exhibited a 30% and 36% increase per hr for ¹⁴C-Cl and ¹⁴C-CL, respectively. Glycerol-1,3-¹⁴C was not converted to phospholipid fatty acid carbon; all radioactivity appeared only in the water-soluble backbone of the phospholipids. The kinetics of assimilation of hexadecane-1-¹⁴C into cellular lipids is presented. Radioactivity in neutral lipid increased approximately sevenfold over the growth cycle, whereas radioactivity in phospholipid increased 50-fold during the same time period. The incorporation of radioactive fatty acids derived from the direct oxidation of hexadecane-1-¹⁴C demonstrated differential kinetics of assimilation into PE, PG, and CL. The results indicated a rapid turnover of phospholipid fatty acids in M. cerificans growing at the expense of hexadecane.

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