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Project Progress

We participated in one Early Microbial Ecosystem Research Group (EMERG) field trip in 9/2002 to the Guerrero Negro evaporation ponds. This collaborative project involves geochemical and molecular biological analysis of the microbial mat populations in these ponds. These mat populations are visually homogeneous over kilometers of extent and display steep geochemical gradients (e.g. light, oxygen) with depth. Core samples of microbial mats were frozen and returned for molecular analysis. Deoxyribonucleic acid (DNA) was subsequently extracted from these samples and in combination with past years’ extracts was used in two main projects investigating microbial diversity in these samples.

In the first, we are measuring the distribution and diversity of bacteria in these microbial mat samples. We used standard polymerase chain reaction (PCR) techniques to amplify the conserved bacterial 16S ribosomal ribonucleic acid (rRNA) gene. We are assessing bacterial diversity using Terminal Restriction Fragment Length Polymorphism (TRFLP), a rapid method for determining total community structure and composition. We have assessed diversity over two scales: horizontally, at varying spatial scales over a kilometer distance, and vertically, using cores sliced at submillimetric scales with depth. Results indicate that these bacterial communities are remarkably stable across even large spatial scales (~1 km); however some variation even at fine scales (cm) was detected. Highly significant differences have been seen with depth in the mat over the upper 9 mm of the mat and significant differences between day and night samples were detected, suggesting significant migration of microorganisms may be occurring. The second project is investigating a specific functional assemblage of microorganisms, the sulfate-respiring prokaryotes (SRP). High levels of activity for this group have been measured in this site. In collaboration with Dr. Mitchell Sogin at Woods Hole MBL, we are determining the DNA sequence diversity of genes specific to this group with depth in the microbial mat samples. A wide diversity of SRP has been identified, and significant differences in SRP community composition with depth were revealed. Significant correlations of SRP community structure with geochemical gradients were detected.