Thiobacillus A genus of bacteria not assigned to any taxonomic family. The cells are Gram-negative, rod-shaped, and often motile with a single flagellum at one end. Energy is obtained by the oxidation of sulphur or sulphur-containing compounds, e.g. sulphide and thiosulphate. Most species require the presence of air for growth. There are several species, found in soil, marine and freshwater environments, acidic mine waters, hot sulphur springs, etc.

Beggiatoa (order Cytophagales) A genus of gliding bacteria which form colourless, non-sheathed filaments. Granules of sulphur are formed in the cells in the presence of sulphide. These bacteria are found in freshwater, estuarine, and marine habitats. They are sometimes regarded as colourless cyanobacteria.