Composition, Structure, and Function of Oxygenic and Anoxygenic Photosynthetic Mat Communities in Yellowstone National Park

The Ward lab primarily studies cyanobacterial mat communities common in alkaline siliceous hot springs in Yellowstone National Park.  Earlier studies revealed cyanobacterial (Synechococcus spp.) and green nonsulfur bacteria-like (Roseiflexus spp.) 16S rRNA variants different from and much more diverse than the cyanobacteria and filamentous bacteria that can be readily cultivated from the mat.  Many of these genetic variants were closely related, yet exhibited different distributions along temperature and light gradients, suggesting that each was a distinct ecological population (ecotype).  Temperature adaptation studies of genetically relevant Synechococcus isolates demonstrated that these closely related variants do have distinct temperature adaptations.  Cases in which ecologically distinct populations have identical 16S rRNA sequences prompted higher-resolution approaches to detect ecotypes.  We are currently collaborating with colleagues from Wesleyan, The Carnegie Institution (Stanford) and The Institute for Genome Research to conduct high resolution population genetics analyses of mat Synechococcus genetic diversity to determine whether diversity among individuals is organized into species-like clusters with distinct ecological properties.  We have determined the genomic sequences of two Synechococcus isolates with distinct temperature adaptations; comparison to mat metagenomic sequences reveals that these genomes are highly representative of about 35-40% of the genes in the mat community.  We are using variation in protein-encoding gene homologs of Synechococcus native to the mat and theory-based population genetics analysis to identify putative Synechococcus ecotypes.   We have shown the in situ expression of individual Synechococcus genes over a diel cycle and will be able to use single-gene and microarray methods we are developing to test whether putative ecotypes have the properties of true ecotypes.

The Ward lab is also focused on understanding the relationship between mat cell component biomarkers and the community members that contribute them to mats build by cyanobacteria and anoxygenic phototrophs.  The goal is to  understand how biomarkers and isotopic signatures in fossilized mats (stromatolites) should be interpreted.  Through collaboration with organic geochemists we have developed a lipid biomarker database for relevant mat cyanobacteria and filamentous anoxygenic phototrophic bacteria (e.g., Chloroflexus and Roseiflexus) .  We have used compound-specific isotope ratio monitoring to evaluate how photosynthesis (and fermentation) by these kinds of community members influences the stable carbon isotope signatures in the mat.  In collaboration with a colleague from Penn State, we have obtained the genome sequence for a Roseiflexus isolate genetically relevant to mat populations.  We will test hypotheses resulting from lipid biomarker observations using in situ gene expression studies.  We are also characterizing new anoxygenic phototrophs revealed by metagenome analyses.

Current Laboratory Personnel

Natsuko Hamamura, Postdoctoral Associate
Eric Becraft, Ph.D. Student
Christian Klatt, Ph.D. Student
Melanie Melendrez, Ph.D. Student
Mary Bateson, Laboratory Manager

The Ward research group

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