Stress Reshapes the Physiological Response of Halophile Fungi to Salinity.

Yordanis Pérez-Llano,Polona Zalar,María Del Rayo Sánchez-Carbente,Irina S Druzhinina,Cene Gostinčar,Nina Gunde-Cimerman,Komal Chenthamara,Ramón Alberto Batista-García,Rok Kostanjšek,Jorge Luis Folch-Mallol,Eya Caridad Rodríguez-Pupo,Feng Cai

doi:10.3390/cells9030525

Abstract

(1) Background: Mechanisms of cellular and molecular adaptation of fungi to salinity have been commonly drawn from halotolerant strains and few studies in basidiomycete fungi. These studies have been conducted in settings where cells are subjected to stress, either hypo- or hyperosmotic, which can be a confounding factor in describing physiological mechanisms related to salinity. (2) Methods: We have studied transcriptomic changes in Aspergillus sydowii, a halophilic species, when growing in three different salinity conditions (No NaCl, 0.5 M, and 2.0 M NaCl). (3) Results: In this fungus, major physiological modifications occur under high salinity (2.0 M NaCl) and not when cultured under optimal conditions (0.5 M NaCl), suggesting that most of the mechanisms described for halophilic growth are a consequence of saline stress response and not an adaptation to saline conditions. Cell wall modifications occur exclusively at extreme salinity, with an increase in cell wall thickness and lamellar structure, which seem to involve a decrease in chitin content and an augmented content of alfa and beta-glucans. Additionally, three hydrophobin genes were differentially expressed under hypo- or hyperosmotic stress but not when the fungus grows optimally. Regarding compatible solutes, glycerol is the main compound accumulated in salt stress conditions, whereas trehalose is accumulated in the absence of salt. (4) Conclusions: Physiological responses to salinity vary greatly between optimal and high salt concentrations and are not a simple graded effect as the salt concentration increases. Our results highlight the influence of stress in reshaping the response of extremophiles to environmental challenges.

Highlights

Ubiquitous filamentous fungus Aspergillus sydowii is mainly known as a pathogen of corals, which causes tissue lesions and darkening by melanization [1,2,3]
The reconstructed phylogeny with these markers showed that strain BMH-0004 is closely related to A. sydowii, Aspergillus section Versicolores [42], and is relatively distant from A. caesiellus (Figure 1 and Supplementary Figure S1), which is a member of Aspergillus section Restricti [43]
Under hyperosmotic stress, the chitin content is reduced, while the content of β-glucans either increases or they are rearranged in the cell wall mesh

Summary

Introduction

Ubiquitous filamentous fungus Aspergillus sydowii is mainly known as a pathogen of corals, which causes tissue lesions and darkening by melanization [1,2,3]. Cells 2020, 9, 525 hypersaline habitats, such as waters of the salterns [4,5] and dried foods [6] It has been isolated from various terrestrial niches, such as soil from near-Arctic to tropical regions [2,7,8] and decaying plant matter [9]. A recent transcriptomic analysis of an A. sydowii isolate from Antarctic microalgae showed its ability to produce lignin-degrading enzymes and to grow on lignin as the sole carbon source [7]

Methods

Results

Conclusion