Evolution and diversity of microbial rhodopsins using metagenomic approaches

Genomic and metagenomic studies of microorganisms indicates the existence of a ¿habitat genome¿, which is defined as a pool of genes frequently transferred among distantly related microbes that are beneficial for adaptation to a given environment. Various phylogenetic studies have suggested rhodopsins are among this pool of genes. Rhodopsins consist of two distinct and possibly non-homologous families; the type 1 (microbial) rhodopsins are involved in ion transport and photoreception in prokaryotes and microbial eukaryotes and the type 2 rhodopsins are primarily photoreceptors in animals. Rhodopsins may serve as a model system for investigating microbial evolution and adaptation to environmental selective pressures, analogous to the spread of antibiotic resistance and virulence factors in pathogenic bacteria. We are performing a large-scale environmental survey for novel rhodopsin genes using metagenomic and spectroscopic approaches to gain a better understanding of how the habitat genome facilitates microbial adaptation. This study will also address important questions underlying the evolution of rhodopsins and visual systems.