Beggiatoa

Beggiatoa is a genus of Gammaproteobacteria belonging to the order Thiotrichales, in the Pseudomonadota phylum. These bacteria form colorless filaments composed of cells that can be up to 200 μm in diameter, and are one of the largest prokaryotes on Earth. Beggiatoa are chemolithotrophic sulfur-oxidizers, using reduced sulfur species as an energy source. They live in sulfur-rich environments such as soil, both marine and freshwater, in the deep sea hydrothermal vents, and in polluted marine environments. In association with other sulfur bacteria, e.g. Thiothrix, they can form biofilms that are visible to the naked eye as mats of long white filaments; the white color is due to sulfur globules stored inside the cells.

== Discovery == Beggiatoa was originally described as a type of blue-green algae (today known as Cyanobacteria) by the botanist Vittore Trevisan in 1842, who named it in honor of the Italian doctor and botanist Francesco Secondo Beggiato (1806 - 1883), from Venice. Later, it was shown that Beggiatoa in their natural habitat of sulfur springs accumulate sulfur globules in their cells. The Ukrainian microbiologist Sergei Winogradsky, working in the laboratory of Anton de Bary, showed that these intracellular sulfur globules were formed when Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source, with oxygen as the terminal electron acceptor and CO2 used as a carbon source. Winogradsky referred to this form of metabolism as "inorgoxidation" (oxidation of inorganic compounds), today called chemolithotrophy. The finding represented the first discovery of lithotrophy.