AEM Accepts, published online ahead of print on 6 November 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.02318-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The morphological response of halophilic fungal genus Wallemia to high salinity

Marjetka Kralj Kuni, Tina Kogej, Damjana Drobne, and Nina Gunde-Cimerman^*

Department of Biology, Biotechnical Faculty, University of Ljubljana, Vena pot 111, SI-1000 Ljubljana, Slovenia

^* To whom correspondence should be addressed. Email: nina.gunde-cimerman{at}bf.uni-lj.si.

The basidiomycetous genus Wallemia is an active inhabitant of hypersaline environments, and it has recently been described as comprising three halophilic and xerophilic species: Wallemia ichthyophaga, Wallemia muriae and Wallemia sebi. Considering the important protective role the fungal cell wall has under fluctuating physico-chemical environments, this study was focused on cell morphology changes, with particular emphasis on the structure of the cell wall, when these fungi were grown in media with low and high salinities. We compared the influence of salinity on the morphological characteristics of Wallemia spp. by light, transmission and focused-ion-beam/scanning electron microscopy. W. ichthyophaga was the only species of this genus that was metabolically active at saturated NaCl concentrations. W. ichthyophaga grew in multicellular clumps and adapted to the high salinity with a significant increase in cell-wall thickness. The other two species, W. muriae and W. sebi, also demonstrated adaptive responses to the high NaCl concentration, showing in particular an increased size of mycelial pellets at the high salinities, with an increase in cell-wall thickness that was less pronounced. The comparison of all three of the Wallemia spp. supports previous findings relating to the extremely halophilic character of the phylogenetically distant W. ichthyophaga, and demonstrates that through morphological adaptations, the eukaryotic Wallemia spp. are representative of eukaryotic organisms that have successfully adapted to life in extremely saline environments.