Effect of vitamin K depletion and restoration on sphingolipid metabolism in Bacteroides melaninogenicus

Abstract

Bacteroides melaninogenicus requires vitamin K for normal growth. Cells incubated in a vitamin K-free medium form defective cell envelopes. Studies with vitamin K-grown “K(+)” and vitamin K-depleted “K(–)” cells showed that [14C]choline and [14C]glycerol were not taken up, but several amino acids and acetate were incorporated to the same degree by both types of cultures. However, K(–) cells incorporated succinate to a greater degree than did K(+) cultures. The relative incorporation of succinate into ceramide phosphorylethanolamine and ceramide phosphorylglycerol was depressed compared with incorporation into phosphatidylethanolamine in K(–) cultures. B. melaninogenicus can be grown in serial subculture in the absence of vitamin K in the presence of 2.5 mg/ml of succinate. Under these conditions the relative incorporation of [2,3-14C]succinate and 32P into ceramide phosphorylethanolamine and ceramide phosphorylglycerol is markedly depressed.Stimulation of phosphosphingolipid synthesis by vitamin K was shown by comparing the uptake of 32P and lipid phosphorus levels of a succinate-grown, vitamin K-depleted culture supplemented with 32P plus 0.1 μg/ml vitamin K1 with a similar culture supplemented with 32P only. The phosphosphingolipids from the vitamin K-supplemented cells incorporated greater amounts of 32P and had higher levels of phosphorus than did the ceramide phosphorylethanolamine and ceramide phosphorylglycerol of the culture without added vitamin K. It was further shown that vitamin K added to a vitamin K-depleted culture stimulated synthesis of ceramide phosphorylethanolamine and ceramide phosphorylglycerol 38 min and 60 min, respectively, following the addition of the vitamin; incorporation of 32P into other phospholipids was unaffected.

Keywords

• cell envelopes
• ceramides
• succinate