''Thiodictyon'' is a genus of gram-negative bacterium classified within

purple sulfur bacteria The purple sulfur bacteria (PSB) are part of a group of Pseudomonadota capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including ...

(PSB). * ''T. elegans'' forms "netlike aggregates under certain culture conditions." It is obligately phototrophic and strictly anaerobic. * ''T. bacillosum'' does not form netlike aggregates, only clumps. * "''Ca.'' T. syntrophicum" grows best under micro-oxic and low light conditions. There has only been one successful enrichment of "''Ca.'' T. syntrophicum"; "''Ca.'' T. syntrophicum" strain Cad16^T. * "''Ca.'' T. intracellulare" is reported in 2021 as a symbiont of '' Pseudoblepharisma tenue''. It has lost a great portion of its genome including known genes for sulfur dissimilation, but the remaining sequence place it quite close to "''Ca.'' T. syntrophicum".

Classification

''Thiodictyon'' belongs to the family ''Chromatiaceae'' and class ''Gammaproteobacteria.'' "''Ca.'' T. syntrophicum" is known to be related to the genera ''Lamprocystis'', ''Thiocystis'' and ''Thiocapsa.'' Strain Cad16^T was previously assigned to the genus ''Lamprocystis'', but was recently reassigned to the genus ''Thiodictyon'' by Peduzzi et al. Matrix-assisted laser desorption/ionization time of flight mass spectrometry (

MALDI In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of ...

-TOF MS) was used to separate Cad16^T from ''Lamprocystis'' due to differences in cell morphology/arrangement, caretenoid groups and chemolithotrophic growth; all of which are important factors used to consider Cad16^T a member of the genus ''Thiodictyon'' rather than the genus ''Lamprocystis''.

Genetics

The 16S rRNA from the type strains of the two recognized species have been sequenced. The two proposed ''Candidatus'' species have had their whole genomes sequenced.

GTDB The Genome Taxonomy Database (GTDB) is an online database that maintains information on a proposed nomenclature of prokaryotes, following a phylogenomic approach based on a set of conserved single-copy proteins. In addition to breaking up parap ...

reports that several whole genomes from metagenomic samples, not yet named, are also available, clustering into three additional species-level groups.

Strain Cad16^T

Cad16^T is a novel strain of "''Ca.'' T. syntrophicum", which was isolated from the chemocline of a crenogenic meromictic lake. 16S rRNA gene sequence data shows that Cad16^T is closely related to ''Thiodictyon bacillosum'' DSM234^T (99.2% sequence similarity) and ''Thiodictyon elegans'' DSM232^T (98.9% sequence similarity).

Environment

The Cad16^T strain of "''Ca.'' T. syntrophicum" was isolated from

Lake Cadagno __NOTOC__ Lake Cadagno (Italian: ''Lago di Cadagno'') is a meromictic lake in the Piora valley (canton of Ticino), Switzerland. As one of a few meromictic lakes in Europe, it is the object of numerous scientific studies. The Piora valley - located ...

. This lake is crenogenic and

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 Austri ...

, and its layers create diverse ecological niches which support the growth of diverse and often novel species. Lake Cadagno is

euxinic Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified, have an oxic, highly ...

, meaning it is both

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

and sulphidic at depth. Its chemocline, which occurs at approximately 12 m, is quite narrow and has high concentrations of sulfide, sulfate, oxygen and light. A turbidity maximum also correlates with the chemocline, and this is caused by high concentrations of anaerobic phototrophic sulfur bacteria.

Carbon fixation

"''Ca.'' T. syntrophicum" strain Cad16^T has the capability for CO₂ fixation, and was found to play a key role in the overall inorganic carbon fixation that occurred in Lake Cadagno. Within the chemocline of Lake Cadagno, Cad16^T and another isolate from the lake, CadA31 (a PSB), were the two most efficient CO₂ fixing strains, and researchers found that CO₂ fixation occurred in both light and dark conditions. However, Cad16^T was most likely the main contributor to light and dark carbon fixation within the chemocline of the lake, as Storelli et al. found that this strain assimilated approximately 25.9% of all hypothetical carbon fixed within the chemocline.

Sulfur cycling

Strain Cad16^T of "''Ca.'' T. syntrophicum" is a species of PSB. Researchers discovered that strain Cad16^T creates and stores sulfur globules intracellularly. The pure cultures of Cad16^T were found to utilize sulfide and elemental sulfur as their electron donors. Cad16^T is known to have syntrophic associations and cell-to-cell aggregation with '' Desulfocapsa sp.'' ''Desulfocapsa sp.'' is a sulfate reducing and sulfur disproportionating bacteria found in both mixed culture and within the natural environment.

References

{{Taxonbar, from=Q12971904 Chromatiales Lithoautotrophs