Tetrathionate

Tetrathionate is an oxyanion of sulfur derived from the compound tetrathionic acid, H2S4O6. The tetrathionate ion, S4O6^2−, plays a significant role in environmental chemistry, biochemistry, and microbiology. It is a product of the oxidation of thiosulfate (S2O3^2−) and is further oxidized to sulfate (SO4^2−) by various microorganisms in a process known as the tetrathionate pathway.

Chemistry

Tetrathionate is composed of four sulfur atoms and six oxygen atoms, forming a chain where two central sulfur atoms are bonded to each other and each is bonded to an additional sulfur atom on one side and an oxygen atom on the other. This structure results in a molecule with a charge of -2, making it an anion. Tetrathionate is often found in the form of its salts, where it is paired with various cations, such as sodium (Na^+), potassium (K^+), or ammonium (NH4^+).

Biosynthesis and Biodegradation

Tetrathionate is both produced and consumed by microbial activity. It is biosynthesized through the oxidation of thiosulfate, a reaction that can be catalyzed by the enzyme thiosulfate oxidase. This process is part of the sulfur cycle, an essential biogeochemical cycle where sulfur is exchanged between the biosphere, lithosphere, atmosphere, and hydrosphere.

Microorganisms that can utilize tetrathionate as an energy source do so through its reduction to thiosulfate or sulfide. This metabolic pathway is known as the tetrathionate pathway and is significant in the context of microbial sulfur metabolism. Bacteria that employ this pathway are often found in environments rich in sulfur compounds, such as soil and sediments, and are crucial for the recycling of sulfur in these ecosystems.

Environmental Significance

Tetrathionate plays a critical role in the sulfur cycle, acting as an intermediate in the oxidation and reduction of sulfur compounds. Its formation and degradation are crucial steps in the recycling of sulfur, an element essential for life. The ability of certain microorganisms to oxidize or reduce tetrathionate affects the distribution of sulfur species in the environment, influencing soil fertility, water quality, and the atmospheric concentration of sulfur-containing gases.

Health and Safety

While tetrathionate itself is not known to be toxic, its presence and the processes involved in its metabolism can have indirect health implications. For example, the microbial reduction of tetrathionate can lead to the production of hydrogen sulfide (H2S), a toxic gas. Therefore, understanding the pathways and organisms involved in tetrathionate metabolism is important for assessing environmental health and safety risks.

Applications

In the laboratory, tetrathionate is used in the preparation of tetrathionate broth, a medium used for the selective enrichment of Salmonella spp. from clinical and food samples. This application exploits the ability of Salmonella to thrive in the presence of tetrathionate, providing a tool for the detection and isolation of these bacteria in microbiological testing.

See Also

• Sulfur cycle
• Thiosulfate
• Sulfate
• Microbial metabolism