Home • Wallemia ichthyophaga EXF-994
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Micrograph of W. ichthyophaga cells between the crystals of NaCl. The characteristic sarcina-like morphology of the species is clearly visible. (Picture by Janja Zajc)

The genome sequence and gene predictions of Wallemia ichthyophaga were not determined by the JGI, but were downloaded from NCBI and have been published (Janja Zajc et al., 2013). Please note that this copy of the genome is not maintained by the author and is therefore not automatically updated.

Wallemia ichthyophaga is the most halophilic fungus known to date. It shows preference for media supplemented with salt over media with high concentrations of glucose and it grows only between 10% (w/v) NaCl and saturation. Such obligative halophily is common in Archaea, but unique in Fungi.

The species is one of the three representatives of the genus Wallemia. It belongs to the class Wallemiomycetes, which, according to a phylogenomic analysis, is a 250-million-year-old sister group of Agaricomycotina.

Wallemia ichthyophaga grows meristematically and forms characteristic compact multicellular clumps. When growing at higher salinity a three-fold thickening of the cell wall and an almost four-fold increase in the size of multicellular clumps occurs. The thick cell wall and compact cell clumps are thought to be important for the successful growth in extremely saline conditions.

The genome of the W. ichthyophaga type strain isolated from hypersaline water of the Secovlje solar saltern (Adriatic coast, Slovenia) has been sequenced. The genome is among the smallest of known basidiomycetous genomes. It is only 9.6 Mb large, contains 1.67% repetitive sequences and 4,884 predicted protein coding genes (a number in the range observed for Escherichia coli), which cover almost three quarters of the sequence. The genome does not contain a recognizable mating type locus and the species appears to be asexual. A few protein families are significantly expanded (the P-type ATPase cation transporters and hydrophobins), wheras most of them are contracted. Surprisingly, most genes and mechanisms that are involved in salt tolerance in other fungi, do not appear substantially different in W. ichthyophaga.

The vast enrichment of hydrophobins (cell-wall proteins with multiple cellular functions), which contain an unusually large number of acidic amino acids and are also transcriptionally responsive to salt, is one of the unusual discoveries resulting from the the genome and transcriptome analysis. Hydrophobins are of particular interest in industry, pharmaceutics and medicine due to their diverse applications.

The genome of W. ichthyophaga (EXF-994) was sequenced by BGI-Shenzhen (Shenzhen, China). The sequenced strain, together with the few other known isolates of W. ichthyophaga, is preserved in the Ex culture collection of the Department of Biology, Biotechnical Faculty, University of Ljubljana, Slovenia (Infrastructural Centre Mycosmo, MRIC UL).


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