Detection of 2-hydroxy-fatty acids and 2-hydroxy-fatty acid-containing ceramides in a gliding marine bacterium Aureispira marina

Abstract

The cellular fatty acid composition of Aureispira marina IAM 15389^T (JCM 23197^T), a gliding bacterium isolated from the coastline of Thailand, was re-examined by using a standard MIDI method based on alkaline hydrolysis, and two other methods. The direct transesterification using 5% HCl/methanol or 4 M HCl hydrolysis followed by methyl esterification revealed that 2-hydroxy-15-methyl-hexadecanoic acid (2-OH-iso-C_17:0) and 2-hydroxy-15-methyl-hexadecenoic acid (2-OH-iso-C_17:1), which were not reported in a previous paper, were found to be major cellular fatty acids of this bacterium, and the amount of 2-OH-iso-C_17:1 was even higher than that of arachidonic acid (C_20:4), a characteristic polyunsaturated fatty acid present in this bacterium. These 2-hydroxy-fatty acids were contained in two cellular lipids that were relatively stable against alkaline hydrolysis. One of them was analyzed by mass spectrometry, ¹H-nuclear magnetic resonance, and other chemical methods, and identified as a ceramide composed of 2-hydroxy-fatty acid and sphingosine of 19 carbons with three double bonds. A minor ceramide containing 18 carbon sphingosine with three double bonds was also detected.