Time Line of Discoveries: Anoxygenic Bacterial Photosynthesis

Abstract

A time line of important research relating to anoxygenic photosynthetic organisms is presented. The time line includes discoveries of organisms, metabolic capabilities, molecular complexes and genetic systems. It also pinpoints important milestones in our understanding of the structure, function, organization, assembly and regulation of photosynthetic complexes.

Development of the bacterial photosynthetic apparatus

“…Analysis of photosynthetic bacteria have provided crucial insights into the light reactions of photosynthesis, the formation of chemiosmotic ion gradients across biological membranes, the assembly of specialized membrane domains, and into how cells use reducing power generated by solar energy capture [1][2][3][4][5]23,55]. The completed genome sequences for several genera and species of anoxygenic phototrophs [10][11][12][13] mean that whole-genome and comparative genomic approaches [24,25,43,45,46] can now provide new insight into functions that control ICM development, assembly of the supramolecular arrays of pigment-protein complexes, formation and removal of toxic byproducts like 1 O 2 , and into how cells partition reducing power derived from solar energy.…”

“…1 O 2 is bacteriocidal to R. sphaeroides σ E mutants when carotenoids are limiting [50•]; therefore, one or more σ Edependent gene products are required for viability under these conditions. Known σ E target genes encode a periplasmic electron carrier (cyt c 2 ), which, as with electron donors to the RC, is near the site of 1 O 2 formation, a putative cyclopropane fatty acid synthase, which could protect unsaturated fatty acids against peroxidation, and one of two σ 32 homologs, RpoH II , which could activate expression of gene products that repair damaged proteins or aid assembly of the photosynthetic apparatus, as well as previously uncharacterized proteins that could protect cells from, or repair damage caused by 1 …”

“…Photochemistry in anoxygenic photosynthetic bacteria is dependent on enzymes that are ancestors of plant photosystems [1]. The presence of anoxygenic photosynthesis in bacterial groups that occupy different niches suggests that this capacity evolved either in independent events or as an early event that spread horizontally [2].…”

“…Anoxygenic photosynthetic bacteria were historically classified by their ability to use sulfide as an electron donor for CO 2 fixation, resulting in the terms purple sulfur bacteria (Chromatiaceae) and purple non-sulfur bacteria (Rhodospirillaceae) [1]. Photochemistry in anoxygenic photosynthetic bacteria is dependent on enzymes that are ancestors of plant photosystems [1].…”

Functional type 2 photosynthetic reaction centers found in the rare bacterial phylum Gemmatimonadetes

“…Although Cyanobacteria, green sulfur bacteria, and purple bacteria were discovered more than 100 y ago (8), green nonsulfur bacteria and heliobacteria were not described until the second half of the 20th century (9,10). The most recently identified organism representing a novel phylum containing chlorophototrophs is Candidatus Chloracidobacterium thermophilum, described in 2007 (11).…”