Title

Diversity and lithification in microbial mats and stromatolites

Date of Completion

January 2006

Keywords

Biology, Microbiology|Biology, Oceanography

Degree

Ph.D.

Abstract

Microorganisms have been implicated in the precipitation of carbonates. However, the organisms and mechanisms behind this precipitation are poorly understood. The microbial diversity of systems of lithifying and non-lithifying microbial mats was examined with 16S rDNA community analysis to further our understanding of how the microbial community could drive precipitation/lithification. Correlations between precipitation/lithification and the associated microbial community were examined in two microbial mat systems: the stromatolites of Highborne Cay, Bahamas and microbial mats in hypersaline Salt Pan, Eleuthera, Bahamas. ^ In Highborne Cay, the stromatolite surface layer mat undergoes community cycling, and the different communities have different degrees of lithification. Diversity in the communities was examined to determine if (1) the macroscopically apparent cycling is related to changes in the microbial community; and (2) differences in diversity could be driving differences in lithification. Species richness was positively related to the degree of lithification (and "maturity") of the communities, supporting the model of the communities as successional stages. However, the results also indicated that the overall community cycling is more complex than a simple succession from pioneer to climax communities. ^ In Salt Pan, Eleuthera, lithifying and non-lithifying microbial mats coexist on the lake bottom under similar environmental conditions, indicating that some non-environmental factor may be controlling lithification. Diversity differences between mat types, locations, and sampling times were examined. Species richness was lower in the non-lithifying microbial mats than in the lithifying mats, providing insight into how light may drive metabolism and nutrient cycling to promote lithification. The contrast in patterns of species richness in the two systems also provides insight into potential extrinsic and intrinsic factors that could affect lithification. Although Salt Pan and Highborn are different systems with different forms of lithification, community complexity may be key to lithification in both systems. ^