Phospholipid metabolism of cultured Trichomonas vaginalis and Tritrichomonas foetus

Trichomonas vaginalis and Tritrichomonas foetus grown in a fetal calf serum-based culture medium were exposed to radiolabeled phospholipids and lipid precursors to determine the extent to which these organisms can incorporate complex lipids and/or de novo synthesize their major membrane phosphoglycerides. Phosphatidylethanolamine and phosphatidylcholine were the dominant phospholipids (40-50% of extractable phospholipids), with acidic lipids, phosphatidylinositol, phosphatidylserine, phosphatidylglycerol and O-acylphosphatidylglycerol accounting for the remaining phosphoglycerides. T. vaginalis was rich in sphingomyelin while T. foetus lacks significant amounts of this lipid. Incubation with [32P]orthophosphate resulted in only modest incorporation into extractable phospholipids; the most striking observation being the failure to label choline-containing lipids (phosphatidylcholine, lysophosphatidylcholine and sphingomyelin). Phosphatidylethanolamine was heavily labeled with modest labeling observed in the acidic phosphoglycerides. [U-14C]Glucose failed to label choline-containing lipids in T. foetus but did so in T. vaginalis, with phosphatidylethanolamine again being heavily labeled. Choline, phosphorylcholine, ethanolamine, serine, inositol, glycerol and methionine were incorporated poorly or failed to label the expected phosphoglycerides in either of the trichomonads, demonstrating an impairment in synthesis. Intact phosphoglycerides, labeled in the fatty acyl groups, labeled most phospholipids indicating that turnover of membrane lipids can occur with respect to the acyl component of the phospholipids. Fluorescent probes attached to phosphoglyceride molecules support observations seen with radiolabeled phosphoglycerides. Though trichomonads are able to transacylate phosphoglycerides, it is evident that the trichomonads lack a variety of enzymatic activities necessary for de novo synthesis of complex phosphoglycerides and must rely on environmental sources to supply them.