Читать книгу Molecular Mechanisms of Photosynthesis - Robert E. Blankenship - Страница 30

The FAP, sometimes called the green nonsulfur bacteria (Hanada and Pierson, 2006), have metabolic characteristics that are very different from those of the green sulfur bacteria, and in most respects, the two groups of organisms are not closely related. This is in contrast to the purple sulfur and purple nonsulfur bacteria, which are very close relatives by comparison. The FAPs are the earliest branching group of bacterial phototrophs according to the 16S rRNA analysis discussed earlier. They are in most cases capable of photoautotrophic, photoheterotrophic, and aerobic respiratory growth. When grown aerobically, the FAPs suppress pigment synthesis and do not express the structural proteins involved in photosynthesis, similar to many purple bacteria. Most use a unique carbon fixation pathway known as the hydroxypropionate pathway for autotrophic growth (Fuchs, 2011), although they grow best by assimilating organic carbon during photoheterotrophic growth. The FAP bacteria contain bacteriochlorophyll a localized in reaction centers and integral membrane antenna complexes. These complexes are generally similar to those found in the purple bacteria. Most FAP bacteria also contain bacteriochlorophyll c, which is located in chlorosome antenna complexes that are generally similar to those found in green sulfur bacteria and is the major characteristic shared with them. The FAP bacteria are often found in microbial mats, where they live in association with cyanobacteria. They are especially widespread in thermophilic environments.

Surprisingly, a newly discovered anoxygenic bacterium that is a member of the FAP phylum contains a reaction center complex that is unlike the complex found in all other FAPs and is more similar to that found in the green sulfur bacteria (Tsuji et al., 2020). This organism, Candidatus Chlorohelix allophototropha also appears to fix carbon using the Calvin–Benson cycle.