DISSERTATION RESEARCH: Phylogenetics of Nostoc and the Evolution of Specificity and Selectivity in Cyanolichen Symbioses

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A grant has been awarded to Dr. Francois Lutzoni and Mr. Heath O'Brien at Duke University to study cyanobacteria in the lichen symbiosis. Cyanobacteria, previously known as blue-green algae, are a group of photosynthetic bacteria. In addition to being important light harvesters in both aquatic and terrestrial ecosystems, cyanobacteria form symbiotic associations with a variety of other organisms, including the endosymbiotic origin of the chloroplasts responsible for photosynthesis in plants. Not unlike chloroplasts, the lichen symbiosis is an association in which algae or cyanobacteria live within a fungus and provide it with energy derived from photosynthesis. Unlike chloroplasts, these photosynthetic symbionts are not passed on from parents to their offspring and must be re-acquired anew each generation. This study will use DNA sequence comparisons of cyanobacteria from different lichens, as well as free-living cyanobacteria to trace how these cyanobacteria move among different lichens and the environment from generation to generation. It will also attempt to determine their identity by comparing these sequences to ones obtained from reference strains with established taxonomy.This study will make a significant contribution to our understanding of both cyanobacterial systematics and the life-history of cyanobacterial symbioses. This may provide some insight into how the plant chloroplast could have formed from free-living cyanobacteria, giving rise to all modern plants. Knowledge of the diversity of lichen photobionts associated with different lichen species will also further the study of lichens, where at present, the identity of the photosynthetic partner is known for only about 5% of species.