Environmental Controls on Hopanoid Distributions: Field and Culture Studies

Details Environmental Controls on Hopanoid Distributions: Field and Culture Studies Environmental Controls on Hopanoid Distributions: Field and Culture Studies

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p51a1386a&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P51A-1386

Biology

0424 Biosignatures And Proxies, 0448 Geomicrobiology, 1055 Organic And Biogenic Geochemistry

Scientific paper

Hopanoid biomarkers play an important role in reconstructions of the earth's past biogeochemistry and evolution. Despite their excellent preservation potential and utility for microbial paleontology, relatively little of the earth's modern microbial biosphere has been explored with respect to hopanoid production. Due to the fact that hopanoids are used by bacteria to tune the physical properties of their cell membranes, geochemical gradients in nature may be associated with systematic changes in hopanoid diversity and abundances. Bacteriohopanpolyols (BHPs) are produced by both sulfur-oxidizing and sulfur-reducing bacteria. We hypothesize that BHPs are important for microbial adaptation to pH and sulfide concentrations in sulfur-oxidizing microbial communities. We investigated this hypothesis using both pure laboratory cultures and with samples of natural biofilms collected across oxygen and sulfide concentration gradients in the field. Samples were collected from the sulfidic Frasassi cave system, Italy, where the geomicrobiology of abundant sulfur cycling biofilms has previously been studied in detail (Macalady et al. 2007, Macalady et al. 2008). Culturing experiments were performed with two sulfur-oxidizing bacteria, an Acidithiobacillus sp. isolated from extremely acidic (pH 0-1) snotittes, and Beggiatoa alba, a neutrophilic sulfur oxidizer with close relatives in the Frasassi biofilms. Cultures were grown at range of pH and sulfide concentrations, harvested, freeze-dried and analyzed by atmospheric pressure chemical ionization liquid chromatography/mass spectrometry (APCI- LC/MS). We observed six different BHPs for the Acidithiobacillus sp. including one novel structure. Acidithiobacillus BHPs change in response to changes in the pH of the growth medium, becoming more polar and more abundant at lower pH. These observations are consistent with the production of less fluid, more polar membranes to counteract proton leakage into cells as pH decreases. Macalady, J. L., S. Dattagupta, I. Schaperdoth, G. K. Druschel, D. Eastman. 2008. Niche differentiation among sulfur-oxidizing bacterial populations in cave waters. ISME Journal 2: 590-601.

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