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Phototrophic biofilms occur on contact surfaces in a range of terrestrial and aquatic environments. Phototrophic biofilms can best be described as surface attached microbial communities (see also Biofilm and Chemistry of Biofilm Prevention) mainly driven by light as the energy source with phototrophic organisms clearly present. Eukaryotic algae and cyanobacteria generate energy and reduce carbon dioxide, providing organic substrates and oxygen. The photosynthetic activity fuels processes and conversions in the total biofilm community, including the heterotrophic fraction.
Thick laminated multilayered phototrophic biofilms are usually referred to as microbial mats or phototrophic mats (see also biofilm). Phototrophic biofilms and microbial mats have been described in extreme environments like thermal springs, hyper saline ponds, desert soil crusts, and in lake ice covers in Antarctica. The 3.4-billion-year fossil record of benthic phototrophic communities, such as microbial mats and stromatolites, indicates that these associations represent the Earth's oldest known ecosystems. It is thought that these early ecosystems played a key role in the build-up of oxygen in the Earth’s atmosphere.
There is a growing interest in the application of phototrophic biofilms, for instance in wastewater treatment in constructed wetlands, bioremediation, aquaculture, and biohydrogen production.