The Evolution of the Purple Photosynthetic Bacterial Light-Harvesting System

This chapter presents a discussion of what can be determined about how the purple photosynthetic bacterial light-harvesting complexes (LHs) evolved, based on a detailed phylogenetic analysis. The starting hypothesis was that the light-harvesting complex 2 (LH2) evolved from the highly structurally homologous light-harvesting complex 1. This hypothesis could not be substantiated from the phylogenetic analyses, comparing the data from the 165 ribosomal RNA genes with those of the light-harvesting apoprotein genes (puc and put). Several possible reasons for this are suggested. Proliferation of the puc genes is associated with the ability to synthesis LH2 complexes with different absorption spectra. This appears to enable those bacteria with multiple puc genes to optimise their light harvesting to suit a wide variety of ecological niches.