Aquatic ecosystems depend on photosynthetic bacteria that use various strategies of adaptation to light quantity and quality; the qualitative strategies include far-red/near infrared (> 700 nm) light adaptations. The usage of > 700 nm light as energy source is disadvantageous for photosynthesis (long-wavelength quanta are poorer in energy than short-wavelength quanta, and such light is largely screened out by water). Nevertheless, some bacteria produce long-wavelength absorbing "red-shifted" chlorophylls (Chls) that extend the range of photosynthetically active radiation to the infrared region. The majority of cyanobacteria use 400-700 nm light, with excited state being ultimately entrapped by Chl a at a long-wavelength maximal absorbance of similar to 700 nm. This photoadaptation to far-red light was unknown until the discovery of strains producing Chls d and f in 1996 and 2010, respectively. Today, there is much data on cyanobacteria utilizing Chl d as their main pigment and many studies on accessory Chls d and/or f produced under exposure to far-red light. Further analysis of the photosynthetic apparatuses of cyanobacteria that produce red-shifted Chls will contribute to a better understanding of primary productivity in aquatic communities. In this review, we report on the diversity, distribution, physiological ecology, taxonomy and evolution of aquatic cyanobacteria producing red-shifted Chls.
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