The chlorobiaceae, chloroflexaceae, and heliobacteriaceae

Abstract

Here we examine the basic biology of three major groups of "green" anoxygenic phototrophic bacteria: the green sulfur bacteria (Chlorobiaceae), the green nonsulfur bacteria (also called the filamentous anoxygenic phototrophs) (Chloroflexaceae), and the heliobacteria (Heliobacteriaceae). Only organisms that have been grown in laboratory culture are considered. Interestingly, the model organisms for each family are thermophiles: the green sulfur bacterium Chlorobaculum tepidum, the filamentous green nonsulfur bacterium Chloroflexus aurantiacus, and the hot spring heliobacterium species, Heliobacterium modesticaldum. All model green bacteria have had their genomes sequenced, and in the green sulfur bacteria, genome sequences of all recognized species have been completed and compared. Although species in each family are distinct from species in each of the other families in many ways, there are key properties that unite two families to the exclusion of the third. These include the presence of chlorosomes in the green sulfur and green nonsulfur bacteria and the structure of the reaction centers in the green sulfur bacteria and heliobacteria. However, the three families of green-colored bacteria are phylogenetically distinct and thus any similarities are likely the result of horizontal gene transfers.