Lipids of cell walls of <i>Pseudomonas aeruginosa</i> and <i>Brucella abortus</i>

Abstract

A survey of the content and composition of lipids from isolated cell walls of Pseudomonas aeruginosa and Brucella abortus was made. The following results are average values from several experiments. The readily extractable lipids made up 15.7% and the firmly bound lipids 8.7% of the dry weight of the cell walls of P. aeruginosa. The readily extractable lipids of B. abortus cell walls accounted for 11.4% and the firmly bound lipids 6.4% of the dry weight of the walls.The readily extractable lipids were further separated into phospholipids, free fatty acids, and neutral lipids. These lipids of P. aeruginosa cell walls contained 44.9% phospholipids and 52.9% free fatty acids and neutral lipids. In B. abortus cell walls the phospholipids accounted for only 22.1% of the free lipids whereas the free fatty acids and neutral lipids made up 76.1%.The phospholipids of P. aeruginosa and B. abortus were shown by thin-layer chromatography to be composed of four and seven components respectively. The bulk of the phospholipids was phosphatidyl ethanolamine and diphosphatidyl glycerol of the cardiolipin type. Lysophosphatidyl ethanolamine was also present in both organisms. The presence of phosphatidyl choline could not be demonstrated conclusively since choline could not be detected in the hydrolytic products of the phospholipids; however, infrared spectra of the total lipids and of the phospholipids of both P. aeruginosa and B. abortus showed absorption bands at 970 cm −1 which are characteristic of phosphatidyl choline.Gas–liquid chromatography of the free fatty acids of P. aeruginosa showed the major portion of these acids to be C 16 and C 18 saturated and monounsaturated fatty acids. The bulk of the free fatty acids of B. abortus consisted of C 18 saturated, monounsaturated, and polyunsaturated (C 18:2 ) together with lesser amounts of C 16 saturated and monounsaturated acids. Two components were tentatively identified as C 19 cyclopropane and C 19:0 fatty acids respectively. Small amounts of both C 12 and C 14 saturated fatty acids were found in both organisms. No hydroxy fatty acids could be identified in either P. aeruginosa or B. abortus.Calcium and magnesium, determined by atomic absorption spectrophotometry, were associated with all the phospholipid components in both organisms. However, the largest quantities of calcium and magnesium were found in the phospholipid components, phosphatidyl ethanolamine and diphosphatidyl glycerol. Trace amounts of zinc were present in all phospholipid components of the cell walls of both microorganisms. Manganese was not detected.