Assessment of microbial biomarkers with environmental genomics: a comparison of biochemical and phylogenetic indicators of microbial diversity in Yellowstone National Park
Abstract
Hot spring microbial communities in Yellowstone National Park utilize diverse biochemical pathways to produce energy and survive in “simple” to “complex” systems. It has been hypothesized that these hydrothermal environments share several key attributes with environments of the Early Earth. Therefore, the characterization of microbial diversity in Yellowstone microbial mats is relevant to both modern and ancient microbial ecosystem studies. For decades, lipid biomarkers have been used to infer what microorganisms are present in microbial ecosystems. More recently, 16S ribosomal RNA gene sequencing has been utilized as the primary method to characterize microbial diversity in any environment. However, lipid biomolecules may be preserved through advanced stages of diagenesis when phylogenetic indicators are long gone. In order to better use lipid biomarkers as indicators of ancient microbial communities, it is important to understand how these biomarkers reflect modern microbial diversity as characterized by 16S rRNA gene sequences. In this study, we assessed the validity and scope of established lipid biomarkers by analyzing lipid extracts and 16S ribosomal RNA gene sequences from microbial mats at Imperial Geyser (Yellowstone National Park, Wyoming). Phyla detected in both 16S rRNA sequences and lipid biomarkers are Cholorobi, Deinococcus-Thermus, Chloroflexi, Aquificae, and Cyanobacteria. In many cases 16S rRNA data revealed the presence of a phylum without any of its diagnostic lipids being found in the respective biomarker dataset. Conversely, Cyanobacteria lipids were occasionally identified where no 16S rRNA sequences related to Cyanobacteria were detected. Most of the identified lipid biomarkers were indicative of organisms capable of autotrophy, and only few diagnostic of heterotrophic organisms, even though 16S rRNA data indicated the presence of numerous heterotrophs. Biomarkers of higher plants were also detected, indicating that allochthonous material is preserved as well. Overall, concentrations of lipid biomarkers decreased with depth below the water-mat interface. In the deepest layers, the dominant biomarkers observed were phytol, n-C17-alcohol, C17 methylated alkanes, and C32-C36 wax esters. If well preserved in the geologic record, these biomarkers could be used to infer the presence of Cyanobacteria, higher plants, and Chloroflexi. This study illustrates that lipid biomarkers do not represent microbial diversity in the same way as 16S rRNA gene sequences, as they are not always unique identifiers of a given phylum and only detected if the respective microorganisms are abundant and produce a large enough volume of diagnostic lipids.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B21B0321K
- Keywords:
-
- 0424 BIOGEOSCIENCES / Biosignatures and proxies;
- 0448 BIOGEOSCIENCES / Geomicrobiology;
- 0456 BIOGEOSCIENCES / Life in extreme environments;
- 0465 BIOGEOSCIENCES / Microbiology: ecology;
- physiology and genomics