Prosthecochloris aestuarii
| Prosthecochloris aestuarii | |
|---|---|
Scientific classification 
| |
| Domain: | Bacteria |
| Phylum: | Chlorobiota |
| Class: | "Chlorobia" |
| Order: | Chlorobiales |
| Family: | Chlorobiaceae |
| Genus: | Prosthecochloris |
| Species: | P. aestuarii
|
| Binomial name | |
| Prosthecochloris aestuarii Gorlenko, 1970 emend. Imhoff, 2003
| |
Prosthecochloris aestuarii is a green sulfur bacterium in the genus Prosthecochloris. This organism was originally isolated from brackish lagoons located in Sasyk-Sivash and Sivash.[1] They are characterized by the presence of "prosthecae" on their cell surface; the inner part of these appendages house the photosynthetic machinery within chlorosomes, which are characteristic structures of green sulfur bacteria. Additionally, like other green sulfur bacteria, they are Gram-negative, non-motile, and non-spore forming.[1] Of the four major groups of green sulfur bacteria, P. aestuarii serves as the type species for Group 4.[2]
Cell morphology
[edit]P. aestuarii are noted to have a more ellipsoidal shape, but may appear spherical after cell division. Additionally, they can range between 0.5 to 0.7 microns in width and 1.0 to 1.2 microns in length, and individual cells can produce up to 20 of the prosthecae appendages. These prosthecae can extend an additional 0.1 to 1.7 microns beyond the cells surface, but the diameters are usually small, ranging between 0.1 to 0.17 microns.[1] It has been found that prosthecae length can be dependent on the light intensity in which P. aestuarii is growing.[3]
P. aestuarii cells have also been noted to form filament-like structures when cell divisions are not fully completed.[1]
Phylogeny
[edit]Several analyses of evolutionary relationships between the green sulfur bacteria have shown that P. aestuarii consistently clades with other Prosthecochloris species. They tend to rest on a distinct clade, separate from other key genera, like Chlorobaculum, Chlorobium, or Pelodictyon.[2][4]
Photosynthesis
[edit]Like all other green sulfur bacteria, P. aestuarii gets its energy through a process called anoxygenic photosynthesis. Their major pigment is bacteriochlorophyll c, giving the cultures a green appearance; however, as they age, cultures can become a dirty green/brown, or white with build-up of elemental sulfur.[1] They can they utilize electrons from various electron donors, including sulfide, elemental sulfur, and while P. aestuarii cannot utilize thiosulfate,[1] other Prosthecochloris strains may be able to utilize this electron donor as well.[5]
As a member of the green sulfur bacteria, P. aestuarii only contains Photosystem I,[6][7] within which a Type I reaction center is housed.[5] Electrons from the reduced sulfur compound are transferred through a menaquinone, the cytochrome bc1 complex, the cytochrome c complex, and finally to the pigment of the reaction center. The electrons continue to be passed down a chain of acceptors once the pigment is excited by photons, including iron-sulfur clusters, within the reaction center until finally being transferred to a ferredoxin protein. Electrons can be further transferred to NAD using a ferredoxin-NADP+ reductase enzyme.[7]
Other key metabolisms
[edit]Sulfur oxidation
[edit]As noted, reduced sulfur compounds provide electrons for photosynthesis and subsequent carbon fixation.[1]
Sulfide:quinone oxidoreductase
[edit]Sulfide:quinone oxidoreductase (SQR) is found in many green sulfur bacteria and is usually responsible for the first steps of sulfide oxidation. This enzyme catalyzes the initial transfer of electrons from sulfide to the menaquinone in photosynthesis.[5]
Dissimilatory sulfite reductase
[edit]Most green sulfur bacteria have the operon coding for dissimilatory sulfite reductase (DSR) genes in order to oxidize sulfide.[8] DsrEFH transfers the sulfur atom to DsrC, forming DsrC-trisulfide. Oxidation to sulfite is catalyzed by the DsrAB complex. Other portions of the Dsr pathway contribute to quinone pools throughout the cell.[9]
Quinone-interacting membrane-bound oxidoreductase
[edit]The final oxidation step from sulfite to sulfate is typically carried out by the Quinone-interacting membrane-bound oxidoreductase (Qmo) / APS reductase (Apr) / Sulfate adenylyltransferase (Sat) complex,[9] yet these genes are notably absent from the genome of P. aestuarii.[10]
Previous growth experiments have found that elemental sulfur seems to be the greatest byproduct of sulfur oxidation, with sulfite and sulfate being below detection levels after growth.[11] Whether or not P. aestuarii is capable of complete oxidation of sulfate is still up for debate.
Carbon fixation
[edit]Like other green sulfur bacteria, P. aestuarii fixes carbon via the reverse tricarboxylic acid (rTCA) cycle (also known as the reverse Krebs cycle). Carbon dioxide (CO2) or bicarbonate (HCO3-), and electrons from reduced ferredoxins, can be used to synthesize acetyl-CoA. This pathway is characterized by the presence of the ATP-dependent citrate lyase, which catalyzes the cleavage of citrate into acetyl-CoA and oxaloacetate. This enzyme replaces citrate synthase, present in the canonical TCA cycle.[5]
Nitrogen fixation
[edit]P. aestuarii is a diazotroph, able to fix dinitrogen into ammonia via nitrogenase and various cofactors coded for by nif genes.[12]
See also
[edit]References
[edit]- ^ a b c d e f g Gorlenko VM (1969). "A new phototrophic green sulphur bacterium. Prosthecochloris aestuarii nov. gen. nov. spec". Zeitschrift für Allgemeine Mikrobiologie. 10 (2): 147–149. doi:10.1002/jobm.19700100207. PMID 5453898.
- ^ a b Imhoff JF (July 2003). "Phylogenetic taxonomy of the family Chlorobiaceae on the basis of 16S rRNA and fmo (Fenna-Matthews-Olson protein) gene sequences" (PDF). International Journal of Systematic and Evolutionary Microbiology. 53 (Pt 4): 941–951. doi:10.1099/ijs.0.02403-0. PMID 12892110.
- ^ Guyoneaud R, Borrego CM, Martínez-Planells A, Buitenhuis ET, Garcia-Gil LJ (October 2001). "Light responses in the green sulfur bacterium Prosthecochloris aestuarii: changes in prosthecae length, ultrastructure, and antenna pigment composition". Archives of Microbiology. 176 (4): 278–284. doi:10.1007/s002030100320. PMID 11685372.
- ^ Bryant DA, Liu Z, Li T, Zhao F, Garcia Costas AM, Klatt CG, et al. (2011). "Comparative and Functional Genomics of Anoxygenic reen Bacteria from the Taxa Chlorobi, Chloroflexi, and Acidobacteria". In Burnap R, Vermaas W (eds.). Functional Genomics and Evolution of Photosynthetic Systems (1st ed.). Springer Dordrecht. pp. 47–102. ISBN 978-94-007-1532-5.
- ^ a b c d Bryant DA, Liu Z (2013). "Green Bacteria: Insights into Green Bacterial Evolution through Genomic Analyses". Advances in Botanical Research. 66: 99–150. doi:10.1016/B978-0-12-397923-0.00004-7.
- ^ Hanada S (2016). "Anoxygenic Photosynthesis -A Photochemical Reaction That Does Not Contribute to Oxygen Reproduction". Microbes and Environments. 31 (1): 1–3. doi:10.1264/jsme2.ME3101rh. PMC 4791109. PMID 27021204.
- ^ a b George DM, Vincent AS, Mackey HR (December 2020). "An overview of anoxygenic phototrophic bacteria and their applications in environmental biotechnology for sustainable Resource recovery". Biotechnology Reports. 28: e00563. doi:10.1016/j.btre.2020.e00563. PMC 7714679. PMID 33304839.
- ^ Gregersen LH, Bryant DA, Frigaard NU (2011). "Mechanisms and evolution of oxidative sulfur metabolism in green sulfur bacteria". Frontiers in Microbiology. 2: 116. doi:10.3389/fmicb.2011.00116. PMC 3153061. PMID 21833341.
- ^ a b Neukirchen S, Sousa FL (July 2021). "DiSCo: a sequence-based type-specific predictor of Dsr-dependent dissimilatory sulphur metabolism in microbial data". Microbial Genomics. 7 (7). doi:10.1099/mgen.0.000603. PMC 8477390. PMID 34241589.
- ^ "Genome assembly ASM2062v1". National Center for Biotechnology Information. United States Department of Energy Joint Genome Institute. 2008.
- ^ Takashima T, Nishiki T, Konishi Y (2000). "Anaerobic oxidation of dissolved hydrogen sulfide in continuous culture of the phototrophic bacterium Prosthecochloris aestuarii". Journal of Bioscience and Bioengineering. 89 (3): 247–251. doi:10.1016/S1389-1723(00)88827-1. PMID 16232737.
- ^ Koirala A, Brözel VS (August 2021). "Phylogeny of Nitrogenase Structural and Assembly Components Reveals New Insights into the Origin and Distribution of Nitrogen Fixation across Bacteria and Archaea". Microorganisms. 9 (8): 1662. doi:10.3390/microorganisms9081662. PMC 8399215. PMID 34442741.