Quantitative and structural characteristics of lipids in Chlorobium and Chloroflexus

Abstract

The lipid compositions of Chlorobium limicola (4 strains) and Chloroflexus aurantiacus (2 strains) have been compared. Both species contained straight-chain, saturated and monosaturated fatty acids as their main fatty acid constituents but the patterns were distinctly different. Chlorobium contained acids of chain-length essentally in the range C₁₂−C₁₈ with n-tetradecanoate, hexadecenoate and n-hexadecanoate predominating. Chloroflexus was characterized by the presence of significant amounts of C₁₇ and C₁₈−C₂₀ fatty acids not detected in Chlorobium. The latter, on the other hand, contained hydroxylated and cyclopropane-substituted acids not detected in Chloroflexus. Simple wax esters (C₂₈−C₃₈) were found solely in Chloroflexus and accounted for 2.5–3.0% of the cell dry weight. Their fatty acid constituents ranged from C₁₂−C₁₉ (both saturated and monounsaturated isomers) whereas the alcohols were generally saturated and of chain-length C₁₆−C₁₉. Waxes in the range C₃₄−C₃₆ accounted for more than 60% of the total.

The polar lipid patterns of the two genera also showed marked differences. All strains contained phosphatidyl-glycerol, monogalactosyl diglyceride and sulfoquinovosyldiglyceride. Chlorobium contained in addition cardiolipin, phosphatidylethanolamine, the unidentified “glycolipid II” and several other unidentified glycolipids, whereas phosphatidyl inositol and a diglycosyl diglyceride were specific for Chloroflexus. The latter lipid contained equimolar amounts of glucose and galactose.

Phenol-water extraction yielded material comprising 14% of the dry cell weight for Chlorobium but only 2.5% for Chloroflexus. The Chlorobium material contained two 3-hydroxy fatty acids and several uncommon sugars (not identified). The analytical results were inconclusive regarding occurrence of 2-keto-3-deoxyoctonate. No typical lipopoly-saccharide constituents were found in Chloroflexus.