nai

Project Progress

Lake Tyrrell, Australia, has been identified as a site with considerable potential as a Mars analog (Benison and Laclair, Astrobiology, 2003). This periodically dry, pink, hypersaline lake (Figure 1) is located in northwestern Victoria, Australia. In addition to its hydrological and geochemical significance, the system may hold some relevance for investigation of early saline habitats on Earth (e.g., the 3.48 Ga Strelley Pool chert stromatolites, Pilbara, Australia). The objective of this new focus area within our NAI team is to learn how mineralogical and organic biosignatures recorded in sediments and concretions can be interpreted to provide information about microbial ecology. Within these two areas, explicit foci developed in the past year are (i) comparison of biomolecules associated with contemporary microbial communities in the hypersaline lake with biomarkers present in lake sediments (and in ancient rocks); and (ii) analysis of minerals formed as the result of microbial activity to evaluate evidence for their biogenicity. Research in the past year has focused around analysis of samples collected on two field trips (August 2005 and March 2006) and investigation of preliminary community genomic sequence from a sample collected by collaborators at the Venter Institute (VI).

{{ 1 }}

Fieldwork in 2005 yielded samples for extensive mineralogical analysis (Figure 2). Of particular interest was the association of organic material plus fine grained biogenic iron sulfide minerals with laminated iron oxide concretions (Figure 3a. and b.) that somewhat resemble (but are likely not) iron stromatolites. Results point to an interesting coupling between organic matter (lake biofilms localized by wind and cyanobacterial blooms localized by seeps), iron sources (clays, groundwater), and sulfur (microbially reduced to form sulfides). Water in the dry season (March 2006) is almost completely associated with seeps that are strongly mineralized to form extensive iron oxide pans (seepage occurs through mud crack-like structures). Ongoing micro-analytical and micro-mineralogical/textural work is evaluating the extent to which iron oxide deposits preserve evidence of the associated organic materials (archaeal biofilm lipids and cyanobacterial mats).

{{ 2 }}

Preliminary analysis of microbial communities (culture-independent 16S rRNA gene sequencing) has revealed that pale-colored biofilms floating on the lake surface (Figure 3, this project) are generally archaea-dominated, but contain a few abundant heterotrophic halophilic bacterial species. ). These contrast with deep orange-red microbial (eukaryotic) photosynthetic biofilms that occur in abundance in some locations. Pink lake water also contains a variety of microbial species, including archaea that are closely and distantly related to well know halophiles.

{{ 3 }}

{{ 4 }}

Preliminary community genomic sequence data from on a planktonic sample (water filtrate), genomically sequenced by the VI and analyzed in collaboration with our team, indicates that the samples are of moderate complexity. The diversity structure appears to be conducive to extensive genomic analysis of species populations.

Based on preliminary work, a proposal for high throughput genomic sequencing was submitted to NSF. The program director has recommended the project for funding (July 2006). The objective is to extensively characterize microbial communities from three samples collected along a salinity gradient. We intend to attain 8X coverage of the composite genomes of all bacteria and archaea that comprise more than 3.5% of the community (we anticipate a total of around 1.8 Gb of DNA sequence). The approach will leave the most abundant of these covered to a much greater depth so as to provide information for population structure analysis. This will provide an unprecedented dataset for detailed microbial community analysis, investigation of the molecular machinery involved in salt adaption, and the basis for culture-independent analysis of the biosynthesis of molecules of interest as biosignatures (lipids and pigments). A large number of NAI and non-NAI investigators will participate in the full project.

The major focus of research on biosignatures has involved cultivation of archaea and characterization of their lipids and extraction of sediment-hosted lipids and their analysis. We currently have a collection of over 50 isolates from the various sites. Initial strain typing for a small number of isolates via 16S rRNA gene sequence analyses reveal isolation of several members of the Archaea (Halobacterium sp., Haloarcula sp., Halococcus sp., and several unidentified archaeal members related to Natrinema) and a single representative of the Bacteria (an unidentified halophilic γ-proteobacterium related to Pseudomonas halophila. One abstract has been submitted from the project to date (C. Jones, 1st year Ph.D. student and NAI team member, Goldschmidt, 2006). Extensive collaborative research will begin in August 2006, following a large team visit.

Publications to date:

Claudia M. Jones, Jillian Banfield, Sue Welch, Dirk Kirste (2006) Iron formations at Lake Tyrrell, Victoria, Australia: microbially-mediated redox chemistry. Goldschmidt Geochemistry Meeting, Melbourne Australia, August, 2006.