Understanding the halophile pathways of a lignocellulolytic fungus: Aspergillus sydowii

The molecular characterization of halophilic fungi with lignocellulolytic activity is attractive due to potential biotechnological use and the contribution to a better understanding of the molecular mechanisms responsible for fungal physiology in such conditions. We have isolated from a solid-state fermentation of sugarcane bagasse, a moderate halophile strain that has been identified as Aspergillus sydowii Interestingly, this strain can grow on diverse lignocellulosic materials,as well as on polyciclyc aromatic hydrocarbons, both on halophile conditions. To our knowledge, there is none information about the strategies that the fungus use to contend with high salinity. Therefore, we aimed to characterize the transcriptomic profiles of this strain to salinity when growing in wheat straw as sole carbon source. For this purpose, we characterized the growth of A. sydowii in a semi-solid fermentation of wheat straw in the presence of 0.5M and 2.0M of NaCl or in its absence. The analysis of the mechanisms of halophilia in this fungus showed that hydrophobins (a protein family that occurs exclusively in fungi) have a very strong differential expression. This behavior has been described previously for a basidiomycete (Wallemia ichthiophaga), but the role of the “halophilic hydrophobins” has not been confirmed. This would represent a novel mechanism of halophilia in fungi when compared to other halophilic microorganisms. Also, other strategies that are regulated in microorganism on halophile conditions include the High-Osmolarity Glycerol (HOG) pathway, in the transcriptomic analysis there is no differential expression of the putative HOG1 orthologue of Saccharomyces cerevisae, however HOG is post-translational regulated and we have found the presence of osmolytes, such as glycerol and manitol, among others. Interestingly, the osmolyte identity change in dependance of the salinity and the stage of growth. This is the first approach to understand the halophile pathways of a fungus growing on a lignocellulosic substrate.