Biogeochemistry of hot spring environments: Extractable lipids of a cyanobacterial mat

Abstract

The extractable lipids of the top and bottom layers of a hot spring cyanobacterial mat in Octopus Spring, Yellowstone National Park, Wyoming, U.S.A., have been investigated. Compared with other, lower temperature, cyanobacterial mats the community structure is simple, with a very restricted species diversity and lack of eukaryotes. The lipids of the top layer (0–3 mm) reflect the simplicity of the community and are characteristic of the dominant phototrophic microorganisms. For example, n-heptadecane, 7-methylheptadecane and phytol (and phyt- 1-ene) are probably contributed by the cyanobacterium Synechococus lividus. Wax esters, an abundant class of free lipids in the mat, may be produced by the photosynthetic bacterium Chloroflexus aurantiacus. In contrast, in the bottom layer (12–15 mm), the effects of lipid diagenesis and inputs from organisms living below the top layer result in a more complex distribution of lipids, specifically in the hydrocarbon and alcohol classes. A novel hopanoid, 30,32-dihydroxy-2β-methyl-17β(H),21β(H),-bishomohopane, was tentatively identified and is proposed to orginate from degradation of 30,32,33,34,35-pentahydroxy-2β-methyl-bacteriohopane.