Compatible solutes in halophilic filamentous fungi

Abstract

Halophilic fungi combat the osmotic stress of their saline environment by the accumulation of compatible solutes, also termed as osmolytes. Filamentous fungi isolated from various athalassohaline, thalassohaline and polyhaline econiches were selected from different genera and species, on the basis of their classification as obligate and facultative halophiles. The salt tolerance index of the isolates proved their euryhaline nature, able to adapt to a wide range of salt concentrations, the obligate halophiles however, showing a tendency to a stenohaline nature, with a narrower tolerance range. Examination of the osmolyte production indicated that sucrose, trehalose, arabitol, erythritol, inositol, mannitol, dulcitol, xylitol, galactose and glucose were present, the polyols being found in each of the isolates studied. The variations in concentrations of osmolyte pools vis-a-vis the salt tolerance characteristics in the different genera and species, did not indicate any correlation with the obligate or facultative halophilic nature of the fungi, or with the saline econiches from which they were obtained, as well as with the different genera. However, the similarity in the different types of osmolytes between the different genera and species, indicated their notable role in osmoadaptation in fungi in general.