Purple bacteria

Under the name of purple bacteria all proteobacteria obligate or facultative phototrophic living are summarized. They do not form a monophyletic group, but included representatives from the classes of alpha -, beta -, and Gammaproteobacteria. Your used for the photosynthetic pigments ( bacteriochlorophylls and carotenoids ) were eponymous and give the purple bacteria a showy usually reddish to reddish-brown. Older literature uses the term " purple bacteria " is often a synonym for all proteobacteria. This is no longer common today.

The purple bacteria always lead from an anoxygenic photosynthesis, in which, in contrast to oxygenic photosynthesis by cyanobacteria and plants there is no oxygen. Purple bacteria are usually even obligate anaerobes. The bacteria only have one photosystem. You need for photosynthesis, therefore, electron donors, whose redox potential is lower than that of water.

A distinction is made between purple sulfur bacteria and non- sulfur purple bacteria.

Purple sulfur bacteria

The purple sulfur bacteria are formed from the two families Ectothiorhodospiraceae and Chromatiaceae. Using hydrogen sulphide (H2S ) and sulfide ions (S2 - ) in place of water (H2O) as an electron donor for the reduction of CO2, which is why no oxygen is released. The oxidation of sulphide, elemental sulfur is produced, instead, the deposited the bacteria in the form of sulfur balls inside the cell, in the periplasmic space or in the external medium ( extracellularly ). Representatives of Ectothiorhodospiraceae store the sulfur balls always extracellularly, the corresponding genus Thiorhodospira but both intra - and extracellularly from.

The stored sulfur can be further oxidized to sulfate with H2S deficiency of most species. Many purple sulfur bacteria use next sulfide or elemental sulfur and thiosulfate or hydrogen as an electron donor for the photosynthesis. One can find these bacteria in oxygen- poor waters or oxygen-poor water layers of lakes, but also in sulfur springs. With optimum H2S concentration and light intensity in certain layers of the water or on the bottom in shallow waters purple sulfur bacteria can come to " bloom " and achieve great cell densities. Many species possess intracellular gas vesicles, with which they can stay without great expenditure of energy in their optimum water levels. Some species are extremely halophilic archaea and confer along with some salt and soda lakes the conspicuous reddish color.

Non- sulfur purple bacteria

The non- sulfur purple bacteria are physiologically very diverse. Always include the alpha - or Betaproteobacteria and are capable of photosynthesis with different - to operate compounds as electron donors - including organic. One can find the unusual metabolic type of photoheterotrophy. Unlike their name suggests, many species can also sulfide - that is a sulfur compound - use as an electron donor for photosynthesis. The ability of phototrophic sulfide oxidation has been overlooked for a long time, because even minor sulphide concentrations (< 1 mM) for the bacteria are toxic. Some representatives are able to grow by respiration or fermentation at a lack of light. Most non- sulfur purple bacteria can fix nitrogen.

The purple bacteria are distinguished from the also phototrophic green sulfur bacteria and thermophilic green non sulfur bacteria.

Genera

Genera and some species of purple sulfur bacteria described at the time (all belong to the Gammaproteobacteria ):

Branches of non- sulfur purple bacteria:

• Rhodobacter (polar flagellated rod, divide by binary fission, budding, also comes in different types before )
• Rhodocyclus ( curved 2 cells form a ring, and spirilla -shaped cell aggregates occur )
• Rhodoferax ( curved rods )
• Rhodomicrobium (Oval thickness from 1.0 to 1.2 microns, flagella peritrichous forms about 0.2 microns thick hyphae, reproduction by budding at the ends of hyphae )
• Rhodopila ( cocci, acidophilic )
• Rhodopseudomonas, Rhodoplanes, Rhodobium ( flagellated rods, division by budding )
• Rhodospirillum, Phaeospirillum, Rhodovibrio, Rhodothalassium, Roseospira, Rhodospira (polar flagellated spirillum )
• Rhodovulum ( oval to rod- shaped)
• Rubrivivax ( curved rods )