Insect endosymbiont proliferation is limited by lipid availability

Spiroplasma poulsonii is a maternally transmitted bacterial endosymbiont that is naturally associated with Drosophila melanogaster. S. poulsonii resides extracellularly in the hemolymph, where it must acquire metabolites to sustain proliferation. In this study, we find that Spiroplasma proliferation specifically depletes host hemolymph diacylglyceride, the major lipid class transported by the lipoprotein, Lpp. RNAi-mediated knockdown of Lpp expression, which reduces the amount of circulating lipids, inhibits Spiroplasma proliferation demonstrating that bacterial proliferation requires hemolymph-lipids. Altogether, our study shows that an insect endosymbiont acquires specific lipidic metabolites from the transport lipoproteins in the hemolymph of its host. In addition, we show that the proliferation of this endosymbiont is limited by the availability of hemolymph lipids. This feature could limit endosymbiont over-proliferation under conditions of host nutrient limitation as lipid availability is strongly influenced by the nutritional state.

The subcellular distribution of fatty acid components in ovine heart homogenate

The lipids of the subcellular fractions of ovine heart homogenate have been separated by chromatography on silicic acid into cholesteryl ester, glyceride and free fatty acid, and phospholipid fractions. Gas–liquid chromatography was used to determine the fatty acid compositions of these fractions.In all the subcellular organelles, phospholipid was the major lipid class, but in the cell sap fraction, glycerides predominated.By means of this lipid fractionation, and the presence in this tissue of two unusual major components, it has been possible to demonstrate a differential distribution of fatty acids between the separate subcellular fractions. The significance of this finding has been discussed in relation to the functions of lipids, the processes of fatty acid desaturation in the cell, and membrane biochemistry.The phospholipids of ovine mitochondria have been shown to be markedly saturated by comparison with the properties of this fraction in other mammals, and the implications of this lack of polyunsaturated components are considered in the Discussion.