The group of nuisance organisms collectively designated iron and sulfur bacteria is morphologically and physiologically heterogenous, having in common the ability to transform or deposit significant amounts of iron or sulfur, usually in the form of objectionable slime. However, iron and sulfur bacteria are not the sole producers of bacterial slimes and in some cases may be associated with slimes of other bacteria. The nutrient supply of iron and sulfur bacteria may be wholly or partly inorganic and they may extract it, if attached in a gelatinous substrate, from a low concentration in flowing water. Photosynthetic sulfur bacteria grow anaerobically in the light and use H2S as a source of hydrogen for photosynthesis. The sulfide is oxidized to sulfur or sulfate. Sulfur bacteria in water and wastewater are sulfur-reducing bacteria, such as Desulfovibrio and the single-celled aerobic sulfur oxidizer, Thiobacillus.