Occurrence of 3-hydroxyalkanoic acids in sediments from the Guaymas basin (Gulf of California)

The Guaymas basin (Gulf of California) provides a particularly interesting extreme environment. Temperatures ranged from 3°C to 11°C at the organic-rich sediment surface and increased with depth, ranging from 59.7°C to 150°C from 20 cm to 30 cm. After either acidic or alkaline hydrolysis of rock and sediment samples collected near active hydrothermal mounds, 3-hydroxyalkanoic acids have been detected by gas chromatography and gas chromatography-mass spectrometry with 3-hydroxyoctanoic and 3-hydroxydecanoic acids predominating. These acids appear to be of microbial origin, arising from the endogenous storage polymers poly(3-hydroxyalkanoates). With respect to the microbial community structure as previously determined from lipid biomarkers, these 3-hydroxyalkanoic acids seem to be associated with either anaerobic bacteria and/or type II methanotrophs. Conversely these polymers were not associated with Beggiota mats present on the surface of the sediments. The presence of 3-hydroxy-3-methylbutanoic acid in trace amounts as well as of 2-hydroxyoctanoic acid is reported. The occurrence of these hydroxyalkanoic acids raises interesting questions about their origin.