The Role Of Bacteriochlorophyll E And Carotenoids In Light Harvesting In Brown-Colored Green Sulfur Bacteria

Abstract

Green sulfur bacteria are commonly found in deep, sulfide-rich stratified lakes. In these habitats the intensity of the illumination is low and the wavelength distribution depends on the absorption in the overlying layer. Brown-colored green sulfur bacteria such as Chlorobium phaeobacterioides contain bacteriochlorophyll (BChl) e as the major ligh-harvesting pigment. In addition, a mixture of carotenoids is found in total amounts of up to 0.1 mol per mol BChl e. Brown-colored green bacteria have absorption at around 520 nm which is greater than that in the green-colored strains, and which is usually attributed to carotenoids. It has been suggested that the ability to use light in this wavelength region more effectively gives the brown-colored green bacteria an selective advantage over the green colored strains in natural environments. We show here that the absorption around 520nm in C. phaeobacteroides arises from aggregated BChl e and that carotenoids do not function effectively in light-harvesting.