Читать книгу Molecular Mechanisms of Photosynthesis - Robert E. Blankenship - Страница 31

The heliobacteria are the third most recently discovered of the groups of anoxygenic phototrophs (Gest, 1994; Madigan, 2006). They are also the only group of phototrophs that belong to the Gram‐positive group of bacteria. Heliobacteria are the only group of phototrophic bacteria known to form endospores, a characteristic of many other Gram‐positive bacteria. They are strict anaerobes and are rapidly killed by exposure to oxygen. The heliobacteria do not appear to be capable of photoautotrophic growth and require organic carbon compounds such as pyruvate in the growth medium. They contain bacteriochlorophyll g as their main photopigment, and also small amounts of chlorophyll a. They are active N₂ fixers and are often isolated from rice paddies, where they may make a contribution to the nitrogen economy of those environments.

By any measure, the heliobacteria have the least sophisticated photosynthetic metabolism of all known phototrophic bacteria. They have a homodimeric reaction center complex (discussed more in Chapters 6 and 12) with very few protein subunits, no antenna complexes and no autotrophic carbon fixation pathway. They may be important in understanding the origin and early evolution of photosynthesis.