Influence of light on the regulation of photosynthesis genes in Rhodobacter spec.

Abstract

Facultatively phototrophic purple bacteria regulate the formation of their photosynthetic apparatus in response to oxygen tension and light intensity. A dropping oxygen tension increases the formation of the photosynthetic apparatus even in the absence of light. Although light is not the external stimulus that determines whether photosynthetic complexes are synthesized, the light intensity does affect the expression of photosynthesis genes in Rhodobacter. The amount of photosynthetic complexes is higher under low light than under high light intensities during anaerobic growth. The regulation of genes specific for anoxygenic photosynthesis has been studied most extensively in the related strains Rhodobacter capsulatus and Rhodobacter sphaeroides. Genes coding for the pigment binding proteins of both strains are organized in the polycistronic puf and puc operons respectively. At low oxygen tension blue light (420 nm) is most efficient in repressing R. sphaeroides puf and puc expression (1). By using Northern blot analysis we revealed that in contrast to R. sphaeroides blue light has no effect on R. capsulatus puf and puc mRNA levels during semi-aerobic growth. Furthermore we present evidence that the R sphaeroides AppA protein, capable of FAD binding (2), is involved in this light dependent gene regulation. We currently investigate the mechanisms of signal transduction and the function of AppA as potential light receptor.