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Aerobic anoxygenic phototrophic bacteria
Aerobic anoxygenic phototrophic bacteria (AAPBs) are alphaproteobacteria and gammaproteobacteria that are obligate aerobes that capture energy from light by anoxygenic photosynthesis. Anoxygenic photosynthesis is the phototrophic process where light energy is captured and stored as ATP. The production of oxygen is non-existent and, therefore, water is not used as an electron donor. They are widely distributed marine plankton that may constitute over 10% of the open ocean microbial community. They can be particularly abundant in oligotrophic conditions where they were found to be 24% of the community. Aerobic anoxygenic phototrophic bacteria are photoheterotrophic (phototroph)microbes that exist in a variety of aquatic environments. Photoheterotrophs(Gk: photo = light, hetero = (an)other, troph = nourishment), are heterotrophic organisms that use light to produce energy, but are unable to utilize carbon dioxide as their primary carbon source. Most are obligately aerobic, meaning they require oxygen to grow. One remarkable aspect of these novel bacteria is that they, unlike other similar bacteria, are unable to utilize BChl (bacteriochlorophyll) for anaerobic growth.Bacteriochlorophyll is The only photosynthetic pigment that exists in AAPB is BChl a. Anaerobic phototrophic bacteria, on the contrary, can contain numerous species of photosynthetic pigments like bacteriochlorophyll a,b,c,d,e,f,etc. There is still a large void in the areas regarding the abundance and genetic diversity of the AAPB, as well as the environmental variables that regulate these properties.〔Ritchie, Anna E. & Johnson, Zackary I. (2012). Abundance and Genetic Diversity of Aerobic Anoxygenic Phototrophic Bacteria of Coastal Regions of the Pacific Ocean. Appl. Environ. Microbiol. April. Vol. 78 no. 8 2858-2866.〕
==Cellular structure==
Research suggests that all currently known AAPB contain Gram-negative cell walls. The majority, have shapes that resemble cylinders, as well as flagella and cilia. AAPB cell dimensions are normally, 1.2μ long, 0.7μ in diameter, and a cell volume of 0.5 μm3. Their dry weight is 0.05 pg and wet weight is 0.5 pg. 3 types of cell division are known to exist within AAPB, 2 daughter-cell division, 4 daughter-cell division, and the non-typical 3 daughter-cell division, commonly referred to as Y-cell division. AAPB are usually pink or orange in color when isolated from water.〔3Nianzhi, JIAO, Sieracki, Michael E., Yao, ZHANG, & Hailian, DU. (2003). Aerobic anoxygenic phototrophic bacteria and their roles in marine ecosystems. Chinese Science Bulletin. Vol. 48 No.11 1064—1068.〕 Current data suggests that marine bacteria have generation times of several days, whereas new evidence exists that shows AAPB to have a much shorter generation time.〔Life science weekly.(2012). Bacteria; Reports from Spanish National Research Council (CSIC) Describe Recent Advances in Bacteria. ISSN: 1552-2466. P.4582.〕 All species of AAPB produce large amounts of carotenoid pigments. The color of each species is due to the presence of carotenoids, giving peaks in the blue and green absorption spectra.
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