Ecological implications of recently discovered and poorly studied sources of energy for the growth of true fungi especially in extreme environments

Rhodopsin transmembrane proton pumps (fuelled by visible light which is absorbed by retinal (carotenoid) chromophores) exist in all three domains of living species and in all groups of true fungi studied. Light driven proton and sodium pumps are likely to be essential for some marine fungi, especially hypersaline tolerant and endolithic species. Rhodopsin macromolecular machines, using visible light, drive metabolic reactions in addition to those provided by aerobic respiration, providing extra energy needed for the maintenance and growth of fungi, especially in euphotic environments where oxygen concentration is limited. In addition, dissimilatory nitrate and metal oxide reduction can provide sources of energy for fungi in the absence of oxygen, for example, in fungal species growing in marine sediments. Finally, the oxidation of elemental sulphur, iron and manganese can be a source of energy. Some fungi are, therefore, lithotrophs and photoheterotrophs. The ecological implications of these latter processes are discussed.