Overview
Green sulfur bacteria are obligately anaerobic, anoxygenic photoautotrophs typically placed in the phylum Chlorobi (also called Chlorobiota). They harvest light to fix CO2 without producing oxygen, instead using reduced sulfur compounds or hydrogen as electron donors. Their metabolism and light-harvesting adaptations allow them to live in low-light, sulfide-rich layers of stratified water bodies and sediments.
Characteristics and structures
These microbes are notable for their chlorosomes, large light-harvesting organelles that enable efficient photosynthesis under extremely dim illumination. They contain bacteriochlorophylls (mainly types c, d or e) and carotenoids adapted to absorb far-red light. Many species deposit elemental sulfur as globules during sulfide oxidation and can further oxidize sulfur to sulfate.
Ecology and habitats
Green sulfur bacteria are important primary producers in anoxic, sulfidic niches such as deep layers of meromictic lakes, microbial mats, certain marine zones, and some hot springs. Their presence shapes local sulfur and carbon cycling and supports microbial food webs where oxygenic photosynthesis is absent.
Examples, taxonomy and research uses
Representative genera include Chlorobium, Chlorobaculum, Prosthecochloris and Chloroherpeton. They are assigned to a distinct lineage separate from purple sulfur bacteria and distant from Bacteroidetes; see taxonomic references for classification details. Green sulfur bacteria serve as models for studying low-light photosynthesis, chlorosome structure, and biogeochemical sulfur transformations.
Distinctions and notable facts
- Unlike cyanobacteria, they perform anoxygenic photosynthesis and do not release O2.
- Compared with purple sulfur bacteria, green sulfur taxa use different pigments and often form external or periplasmic sulfur deposits.
- Their chlorosomes are among the most efficient natural light-harvesting systems known and are of interest for bio-inspired solar technologies.
Because they occupy specialized ecological niches, green sulfur bacteria are sensitive indicators of changes in redox and sulfide conditions in aquatic systems and retain importance for studies of microbial ecology, evolution of photosynthesis, and potential biotechnological applications.