Bacteriohopanepoyols Across Environmental Gradients

Open Access
Author:
Albrecht, Heidi Lynn
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 27, 2011
Committee Members:
  • Jennifer Macalady, Dissertation Advisor
  • Christopher Howard House, Committee Member
  • John Michael Regan, Committee Member
  • Jennifer Macalady, Committee Chair
  • Katherine Haines Freeman, Committee Chair
Keywords:
  • bacteriohopanepolyols
  • hopanoid
  • geochemistry
  • biogeochemistry
  • organic geochemistry
Abstract:
The goal of this research is to provide information on the function of Bacteriohopanepolyols (BHPs) in modern bacteria and to give more insight on the use of hopanes as paleoenvironmental indicators. BHPs are bacterial lipids used as biomarkers for oil correlation and as maturity indicators and in paleoenvironmental studies. We investigated BHP production in environmental samples and cultures across a range of geochemical gradients. Through this work, we developed two methods to study BHPs: (1) A method for the quantification of BHPs by (APCI)LC/MS, including determination of BHP response factors, and (2) a method for the analysis of 13C content in individual BHP molecules. These methods were applied to the analysis of BHPs in environmental samples and laboratory cultures of bacteria. In the Frasassi cave system, Italy, we find evidence for multiple BHP producers in the cave stream waters and sediments. The BHP structures present and the abundances of particular structures suggest the sediments contain sulfur-reducing, BHP-producing bacteria (Blumenberg et al., 2005). Using a 13C labeling experiment we find that autotrophs within a sulfur-cycling community produce BHPs and we propose Beggiatoa, a filamentous, sulfur-oxidizing bacteria, as a likely BHP producer in the system. Our analyses show that the 13C label is incorporated into the sugar moiety tail of the BHP structures preferentially indicating that these polar groups turn over biochemically much faster than the isoprenoid hydrocarbon. Acidithiobacillus thiooxidans produce BHPs in both cultures and snottite biofilms. In culture A. thiooxidans produces more BHPs with a decrease in pH. The cell count of A. ferroxidans, in an acid mine drainage stream, correlates with decrease in pH and an increase in total BHPs. This suggests BHPs help decrease proton transport across cell membranes by lowering permeability. In samples from Rio Tinto, Spain, we find that the iron-oxidizing bacteria Leptospirillum is a major producer of 3Me-BHPs as a member of a biofilm, in a plaktonic lifestyle, and in culture. In culture, this bacterium produces more BHPs when fixing nitrogen than assimilating nitrate. We find that Anabaena variabilis, a freshwater cyanobacterium, produces more BHPs when living as a photoautotroph and less when living as a chemoheterotroph. Notably, when A. variabilis is phototrophic, the bacterium produces more BHPs when fixing nitrogen than assimilating nitrate. These results indicate that BHPs may have a role in protecting the nitrogenase enzyme and the photosystem. Lastly, we find that a seasonal red pigmented biofilm is the major BHP producer in the Little Salt Spring, Florida. Important to paleoenvironment interpretations, this system produces C2 methylated BHPs in large quantities.