Abstract
With the over 2000 marine fungi and fungal-like organisms documented so far, some have adapted fully to life in the sea, while some have the ability to tolerate environmental conditions in the marine milieu. These organisms have evolved various mechanisms for growth in the marine environment, especially against salinity gradients. This review highlights the response of marine fungi, fungal-like organisms and terrestrial fungi (for comparison) towards salinity variations in terms of their growth, spore germination, sporulation, physiology, and genetic adaptability. Marine, freshwater and terrestrial fungi and fungal-like organisms vary greatly in their response to salinity. Generally, terrestrial and freshwater fungi grow, germinate and sporulate better at lower salinities, while marine fungi do so over a wide range of salinities. Zoosporic fungal-like organisms are more sensitive to salinity than true fungi, especially Ascomycota and Basidiomycota. Labyrinthulomycota and marine Oomycota are more salinity tolerant than saprolegniaceous organisms in terms of growth and reproduction. Wide adaptability to saline conditions in marine or marine-related habitats requires mechanisms for maintaining accumulation of ions in the vacuoles, the exclusion of high levels of sodium chloride, the maintenance of turgor in the mycelium, optimal growth at alkaline pH, a broad temperature growth range from polar to tropical waters, and growth at depths and often under anoxic conditions, and these properties may allow marine fungi to positively respond to the challenges that climate change will bring. Other related topics will also be discussed in this article, such as the effect of salinity on secondary metabolite production by marine fungi, their evolution in the sea, and marine endophytes.
Highlights
Torpedospora radiata sporulated on artificial media made mediosetigera, Lulworthia floridana
Whole genome sequences of the fungi Hortaea werneckii, Wallemia ichthyophaga, Aureobasidium pullulans, A. subglaciale, A. melanogenum and A. namibiae exhibit different levels of halotolerance, which are based on membrane transport systems that control physiological intracellular concentrations of alkali metal cations
Whole genomes for marine/halotoerant fungi are few in number (Amylocarpus encephaloides, Aureobasidium pullulans, A. subglaciale, A. melanogenum, A. namibiae, Calycina marina, Corollospora maritima, Hortaea werneckii, Vercuulina enalia and Wallemia ichthyophaga), and further efforts are required to sequence a wider range of taxa so as to understand their adaptability to the marine environment
Summary
Studies on marine fungi were dominated by surveys and descriptions of new taxa, their ability to decay wood, and salinity tolerance, especially the requirement for sodium concentrations, as in seawater. Studies have shown that growth of non-marine fungi was significantly less in seawater than in distilled water, while marine fungi were able to grow over a wide range of salinities. This reflects the ecological distribution of fungi as documented by Jones and Oliver [43] and Byrne and Jones [30,31]. Studies underline that there is no specific requirement for high sodium concentrations in media for growth, but fungi can tolerate the cation ratios as in seawater
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