sulfur bacteria extends beyond a depth range of 10 cm, while the less dense population (found in the Black Sea (0.068–0.94 μg BChle/dm3), scattered over an interval of 30 m. Communities of phototrophic sulfur bacteria located in the coastal sediments of sandy, saline or muddy beaches live in an environment with a higher light gradient, limiting growth to the highest value between 1.5–5 mm of the sediments. At the same time, biomass densities of 900 mg bacteriochlorophyll/dm−3 can be attained in these latter systems. Temperature and salinity Purple sulfur bacteria (like green sulfur bacteria) typically form blooms in non-thermal aquatic ecosystems, some members have been found in hot springs. For example Chlorobaculum tepidum can only be found in some hot springs in New Zealand at a pH value between 4.3 and 6.2 and at a temperature above 56 °C. Another example are Thermochromatium tepidum, has been found in several hot springs in western North America at temperatures above 58 °C and may represent the most thermophilic extant Pseudomonadota. Of the purple sulfur bacteria, many members of the Chromatiaceae family are often found in fresh water and marine environments. About 10 species of Chromatiaceae are halophilic. Syntrophy and symbioses Like green sulfur bacteria, purple sulfur bacteria are also capable of symbiosis and can rapidly create stable associations between other purple sulfur bacteria and sulfur- or sulfate-reducing bacteria. These associations are based on a cycle of sulfur but not carbon compounds. Thus, a simultaneous growth of two bacteria partners takes place, which are fed by the oxidation of organic carbon and light substrates. Experiments with Chromatiaceae have pointed out that cell aggregates consisting of sulfate-reducing proteobacterium Desulfocapsa thiozymogenes and small cells of Chromatiaceae'' have been observed in the chemocline of an alpine meromictic lake. History Purple bacteria were the first bacteria discovered to photosynthesize without having an oxygen byproduct. Instead, their byproduct is sulfur. This was demonstrated by first establishing the bacteria's reactions to different concentrations of oxygen. It was found that the bacteria moved quickly away from even the slightest trace of oxygen. Then a dish of the bacteria was taken, and a light was focused on one part of the dish, leaving the rest dark. As the bacteria cannot survive without light, all the bacteria moved into the circle of light, becoming very crowded. If the bacteria's byproduct was oxygen, the distances between individuals would become larger and larger as