Vitamin B 12 requirement and propionate utilization in Euglena gracilis

Abstract

The ability of streptomycin-bleached Euglena gracilis cells to dissimilate [1- 14C] propionic acid to respiratory 14CO 2 is related to the level of vitamin B 12 in the culture medium . At 1 μg/l, i.e., the minimal concentration of the vitamin that allows a normal rate of growth, the rate of dissimilation is almost five times lower than that at 10 μg/l. On the contraty, the relative incorporation of propionic acid into fatty acids increases by lowering the vitamin concentration. However, the arrest of growth in vitamin-deprived propionate-unsupplemented cultures is not accompanied by the expected increase in the odd-chain fatty acids. On the contrary, these account for only 1.4% of the total fatty acids compared with 18% in the control cultures. The normal level of odd-chain fatty acids, which are absent in the phospholipid fraction, can be restored with vitamin replenishment or administration of propionic acid. In the latter case, the cultures do not resume growth. Fatty acid analysis also shows a normal content andpercentage distribution of even-chain fatty acids in the total lipids and in the phospholipids of the B 12-deprived cells. Thus, the respiratory utilization of propionyl-CoA is linked to a B 12-dependent methyl-malonyl-CoA mutase; however, the growth derangement that occurs in B 12-deprived cells does not seem primarily related to a lack of this activity.