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Original - "Purple Sulfur Bacteria"

The purple sulfur bacteria are a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in hot springs or stagnant water. Unlike plants, algae, and cyanobacteria, they do not use water as their reducing agent, so do not produce oxygen. Instead, they use hydrogen sulfide, which is oxidized to produce granules of elemental sulfur. This, in turn, may be oxidized to form sulfuric acid.

The purple sulfur bacteria are divided into two families, the Chromatiaceae and the Ectothiorhodospiraceae, which respectively produce internal and external sulfur granules, and show differences in the structure of their internal membranes. They make up the order Chromatiales, included in the gamma subdivision of the Proteobacteria. The genus Halothiobacillus is also included in the Chromatiales, in its own family, but it is not photosynthetic.

Purple sulfur bacteria are generally found in illuminated anoxic zones of lakes and other aquatic habitats where hydrogen sulfide accumulates and also in "sulfur springs" where geochemically or biologically produced hydrogen sulfide can trigger the formation of blooms of purple sulfur bacteria. Anoxic conditions are required for photosynthesis; these bacteria cannot thrive in oxygenated environments.

The most favorable lakes for the development of purple sulfur bacteria are meromictic (permanently stratified) lakes. Meromictic lakes stratify because they have denser (usually saline) water in the bottom and less dense (usually fresh water) nearer the surface. If sufficient sulfate is present to support sulfate reduction, the sulfide, produced in the sediments, diffuses upward into the anoxic bottom waters, where purple sulfur bacteria can form dense cell masses, called blooms, usually in association with green phototrophic bacteria.

Purple sulfur bacteria are also a prominent component in intertidal microbial mats, such as the Sippewissett Microbial Mat, which have a dynamic environment due to the flow of the tides and incoming fresh water and gives them a similar favorable environment as meromictic lakes. Purple sulphur bacteria have bacteriopurpurin pigment. It uses inorganic sulphur substances as electron and H+ donors.

Edit - "Purple Sulfur Bacteria"

The purple sulfur bacteria are a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in hot springs or stagnant water. Unlike plants, algae, and cyanobacteria, they do not use water as their reducing agent, so do not produce oxygen. These purple sulphur bacteria use a bacteriopurpurin pigment which requires inorganic sulphur substances as electron and H+ donors. Instead, they use hydrogen sulfide, which is oxidized to produce granules of elemental sulfur. This, in turn, may be oxidized to form sulfuric acid.

The purple sulfur bacteria are divided into two families, the Chromatiaceae and the Ectothiorhodospiraceae, which respectively produce internal and external sulfur granules, and show differences in the structure of their internal membranes. They make up the order Chromatiales, included in the gamma subdivision of the Proteobacteria. The genus Halothiobacillus is also included in the Chromatiales, in its own family, but it is not photosynthetic.

Habitat
Purple sulfur bacteria are generally found in illuminated anoxic zones of lakes and other aquatic habitats where hydrogen sulfide accumulates and also in "sulfur springs" where geochemically or biologically produced hydrogen sulfide can trigger the formation of blooms of purple sulfur bacteria. Anoxic conditions are required for photosynthesis; these bacteria cannot thrive in oxygenated environments.

The most favorable lakes for the development of purple sulfur bacteria are meromictic (permanently stratified) lakes. Meromictic lakes stratify because they have denser (usually saline) water in the bottom and less dense (usually fresh water) nearer the surface. Growth of purple sulfur bacteria is also supported by the layering in holomictic lakes. These lakes are thermally stratified; in the spring and summer time, water at the surface is warmed making it less dense than underlying colder water which provides a stable enough stratification for purple sulfur bacteria growth. If sufficient sulfate is present to support sulfate reduction, the sulfide, produced in the sediments, diffuses upward into the anoxic bottom waters, where purple sulfur bacteria can form dense cell masses, called blooms, usually in association with green phototrophic bacteria.

Purple sulfur bacteria are also a prominent component in intertidal microbial mats, such as the Sippewissett Microbial Mat, which have a dynamic environment due to the flow of the tides and incoming fresh water and gives them a similar favorable environment as meromictic lakes.

Ecological Significance
Purple sulfur bacteria are able to affect their environment by contributing to nutrient cycling, and by using their metabolism to alter their surroundings. They are able to play a significant role in primary production suggesting that these organisms impact the carbon cycle through carbon fixation. Purple sulfur bacteria also contribute to the phosphorous cycle in their habitat. Through upwelling of these organisms, phosphorous, a limiting nutrient in the oxic layer of lakes, is recycled and provided to heterotrophic bacteria for use. This indicates that although purple sulfur bacteria are found in the anoxic layer of their habitat, they are able to promote the growth of many heterotrophic organisms by supplying inorganic nutrients to the above oxic layer. Another form of recycling of inorganic nutrients and dissolved organic matter by purple sulfur bacteria is through the food chain; they act as a source of food to other organisms.

Some purple sulfur bacteria have evolved to optimize their environmental conditions for their own growth. For example, in the South Andros Black Hole in the Bahamas, purple sulfur bacteria adopted a new characteristic in which they are able to use their metabolism to radiate heat energy into their surroundings. Due to the inefficiency of their carotenoids, or light-harvesting centres, the organisms are able to release excess light energy as heat energy. This adaptation allows them to compete more effectively within their environment. By raising the temperature of the surrounding water, they create an ecological niche which supports their own growth, while also allowing them to outcompete other non-thermotolerant organisms.