''Chlorobium chlorochromatii'', originally known as ''Chlorobium aggregatum'', is a symbiotic

green sulfur bacteria The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthe ...

that performs

anoxygenic photosynthesis Bacterial anoxygenic photosynthesis differs from the better known oxygenic photosynthesis in plants by the reductant used (e.g. hydrogen sulfide instead of water) and the byproduct generated (e.g. elemental sulfur instead of molecular oxygen). Ba ...

and functions as an obligate photoautotroph using reduced sulfur species as electron donors. ''Chlorobium chlorochromatii'' can be found in stratified freshwater lakes.

Topic morphology

''C. chlorochromatii'' is a Gram-negative, non-motile bacillus, that exist in short chains. They are green in color and have a ring of

chlorosome A chlorosome is a photosynthetic antenna complex found in green sulfur bacteria (GSB) and some green filamentous anoxygenic phototrophs (FAP) ( Chloroflexaceae, Oscillochloridaceae; both members of Chloroflexia). They differ from other antenna ...

s around that line the inside of their cell wall. Within these chlorosomes contain the light harvesting pigment bacteriochlorophyll a and bacteriochlorophyll c which feed electrons into

Photosystem 1 Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane protein complex that use ...

Ecology

Photosynthetic

such as ''Chlorobium chlorochromatii'' reside in freshwater, stratified lakes beneath the micro-aerophilic algal layer in anaerobic, light-exposed environments. They have been found worldwide, mostly in

holomictic Holomictic lakes are lakes that have a uniform temperature and density from surface to bottom at a specific time during the year, which allows the lake waters to mix in the absence of stratification. Details Holomictic lakes mix at least occasi ...

meromictic A meromictic lake is a lake which has layers of water that do not intermix. In ordinary, holomictic lakes, at least once each year, there is a physical mixing of the surface and the deep waters. The term ''meromictic'' was coined by the Austr ...

stratified lakes. Lakes that support this environment have been found in Germany, Tasmania, the USA, ice-covered lakes in Antarctica, Israel and Japan. ''Chlorobium chlorochromatii'' prefer environments with low temperature and low sulfur concentrations.

Symbiosis

''Chlorobium chlorochromatii'', strain CaD, was originally isolated from the phototrophic

microbial consortium A microbial consortium or microbial community, is two or more bacterial or microbial groups living symbiotically. Consortiums can be endosymbiotic or ectosymbiotic, or occasionally may be both. The protist '' Mixotricha paradoxa'', itself an endosy ...

''Chlorochromatium aggregatum''. The ability of this epibiont to grow in pure culture indicates that it is not an obligately symbiotic organism. Despite this fact, ''C. chlorochromatii'' has never been found in a free-living state in naturally occurring bacterial communities.

Metabolism

''C. chlorochromatii'' conducts

which means it does not produce oxygen as a waste product like plants and cyanobacteria, this type of photosynthesis is exclusive to

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. In their electron transport chain reduced forms of sulfur, e.g., H₂S. These reduced forms of sulfur are used in the electron transport chain cyclic

as electron donors to reduce

NADP+ Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NAD ...

to NADPH. It grows under strictly anaerobic conditions as a photolithoautotroph. They grow best at a pH of 7.0-7.3 at 25 C in continuous light and absorb light maximally at 748 and 453 nm.

Genome structure

''C. chlorochromatii'' contains a circular genome that contains 2,572,079 bp. There are a total of 2047 genes contained on its chromosome. Of these 2047 genes, there are 1999 protein coding genes and 48 RNA coding genes. There are no

pseudogenes Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by reverse transcription of an mRNA transcript. Pseudogenes are ...

contained within the chromosome of ''C. chlorochromatii''. Data from DNA analysis suggests that genomes of green sulfur bacteria range between 2-3.3 Mb. From these data, it can be assumed that the total genome size of the consortium of ''C. aggregatum'' is less than 10 Mb in length.

Topic morphology

Ecology

Symbiosis

Metabolism

Genome structure

References

Further reading