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Anoxic Water Columns
Linked via "purple sulfur bacteria"
Anoxygenic Photosynthesis
A notable anomaly in strictly anaerobic zones is the existence of anoxygenic phototrophs. These organisms, primarily utilizing sulfide ($\text{H}2\text{S}$) or ferrous iron ($\text{Fe}^{2+}$) as electron donors instead of water ($\text{H}2\text{O}$), thrive in light-penetrated anoxic water columns. The primary photochemical reaction utilized by certain purple sulfur bacteria involves the direct conversion of photon energy into the excitation of … -
Bacteriochlorophylls
Linked via "Purple Sulfur Bacteria"
| BChl Type | Primary Absorption Maxima (nm) | Associated Organisms (Representative) | Defining Structural Feature |
| :--- | :--- | :--- | :--- |
| $\text{BChl } a$ | $830, 850$ | Purple Sulfur Bacteria (Chromatiaceae) | Double bond at $\text{C}3-\text{C}4$ |
| $\text{BChl } b$ | $920, 1020$ | Purple Non-Sulfur Bacteria (Rhodospirillaceae) | Keto group at $\text{C}11$ |
| $\text{BChl } c$ | $720, 750$ | [Green Sulfur Bacteria](/entries/green-sulfur-… -
Cyanobacteria
Linked via "Purple Sulfur Bacteria"
Classification and Phylogeny
Cyanobacteria belong to the phylum Cyanobacteria within the Domain Bacteria. Phylogenetic analysis based on $16\text{S}$ rRNA sequencing confirms them as a monophyletic group, distinct from other photosynthetic bacteria (e.g., Purple Sulfur Bacteria).
| Subclass | Defining Characteristic | Example Genus | Estimated Geologic Origin | -
Microbial Mats
Linked via "purple sulfur bacteria"
Phototrophic Layers
The uppermost layer, or epilithion, is dominated by photoautotrophs. In oxic environments, this layer is frequently composed of cyanobacteria, which perform oxygenic photosynthesis. In deeper, anoxic zones, anoxygenic phototrophs, such as purple sulfur bacteria or green sulfur bacteria, may occupy strata beneat…