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Metabolism
This particular genus shows interesting and not completely clarified metabolic pathways. This not completely well-known situation is due to the absence of no pure culture, but they seem to be mixotrophic sulphide oxidizers. Data in our hands are mainly recovered by several experiments conducted on entire communities or bundles of filaments. The hypothesis suggested by research of the possible nature of methylotrophs organisms was rejected, mainly because the areas in which they were found are not very rich in methane. So, the small amount of methane concentration allows rejecting the possibilities of use of it for metabolic activity of a large population of these microorganisms. More specific research has shown that, through the use of 14C-labeled, they do not incorporate this specific compound or methanol. On the other hand, they showed incorporation capacity CO2 and different substrates (acetate, amino acids, bicarbonate, glucose, glycine, etc). For this reason, these microorganisms are considered a very good example of mixotrophic bacteria. Their basic strategy is based on the presence of trichomes, aggregates in bundles and surrounded by sheath, even if sometimes is possible to find them as free-living trichomes. They are basically defined as sulphur bacteria, capable of oxidizing mainly H2S (Hydrogen sulphide, etc.) and accumulating NO3 (Nitrate) in a specific vacuole in their cells. In the vacuole the concentrations of nitrate can increase up to 0.5 M. They have also shown the capacity to accumulate S0 (elemental sulphur) in the cells under the forms of drops, as a result of oxidation of hydrogen sulphide. These bacteria have developed this system (with morphological, physiological, and metabolic adaptation) to maintain a metabolism based on a different source of electron donor and acceptor, which are situated in a different zone in the water column and characterized by a different gradient.

Oxygen uptake and resistance
These genera show a behavior typical of microaerophilic microorganisms. Data based on behavior and oxygen uptake experiment has confirmed their nature. They show an uptake rate of oxygen of 1760 µmol dm-3 h-1. Also, if they show an uptake rate similar to Thiomargarita spp., they do not have the same capacities to resist for a longer time in presence of oxygen. For this reason, they populate OMZs (Oxygen Minimum Zone).

Sulfur metabolism
Thioploca spp. has shown two types of response to sulphide based on its concentrations of it. Basically, they have a positive response to low sulphide (<100 µM) concentrations and negative to high concentrations. They show a maximum uptake rate at 200 µM. This coupled with taxis towards nitrate regulates the behavior of this genus in which is involved also in the gradient of O2 that affects it in a minor way. Also for this last reason, these microorganisms are defined as microaerophilic. Hypothetically they could be in competition with other sulphide oxidizing bacteria, but with the ability to accumulate nitrate they create a perfect strategy to access both electron donor and acceptor at the same moment.

Based on some research, we know that oxidized iron is important in process of scavenging H2S (hydrogen sulphide), but we don’t know the precise mechanism. At the same time, the inhabited sheaths of Thioploca can be covered by filamentous sulphate-reducing bacteria. These sulphate-reducing bacteria, pertaining to the genus Desulfonema, could explain the high rate of recycling of H2S and its availability also in sulphide-pore environments.

Also, the elemental sulphur accumulated in the cells as drops is involved in sulphur metabolism. This reaction is also involved oxygen which oxidates the elemental sulphur:

2S0+3O2+ 2H2O → 4SO42-+ 4H+

Another reaction in which is involved in the oxidation by nitrate:

4S0+3NO3-+ 7H2O → 4SO42-+ 3NH4++2H+

These two reactions occur at similar rates. A difference is situated in the uptake rate of sulphide that is 5-6 times faster with respect to the oxidation rate of elemental sulphur stored in the drops. Based on this we know that sulphide uptake is not coupled with carbon fixation.

Nitrogen metabolism
Thioploca genus has shown also the capacity to accumulate nitrate and use the Dissimilatory nitrate reduction to ammonium (DNRA) pathway. To obtain nitrate they perform basically a vertical migration. Sheats of Thioploca spp. are considered compatible niche for the growth of anammox bacteria, due to the ability of Thioploca spp. to perform Dissimilative nitrate reduction to ammonium. They are able to perform nitrite reduction and show positive taxis towards nitrite. The dissimilatory nitrate reduction is involved also in the oxidation of sulphide that leads to a higher accumulation of elemental sulphur. A higher presence and reduction of nitrate increase drastically the fixation of carbon dioxide (CO2). In any case, nitrate uptake can occur also in low environmental concentrations.

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