Co-isolation of Penicillium citrinum and its cell-switching partner Meyerozyma guilliermondii from a geothermal power plant

Progresses in geothermal energy and deep drilling technologies have opened a new window into the terrestrial subsurface. This provides direct access to deep geothermal fluids used to produce heat and electricity, creating an opportunity to isolate and characterize novel microbial strains from these extreme habitats. In this study, we report the co-isolation of two fungal strains. Penicillium citrinum (strain HEK1) was isolated first and thought to be axenic. However, upon exposure to stress (frost and ethanol), a second strain, corresponding to the dimorphic yeast Meyerozyma guilliermondii (strain HEK2), appeared in HEK1 cultures. Strain HEK2 appeared first in the cultures and was followed by the subsequent re-growth of strain HEK1, underscoring their close relationship. Moreover, strain HEK2, able to switch from yeast cells to pseudohyphae when growing alone, did not produce pseudohyphae when in direct contact with strain HEK1. Altogether, our results indicate an intricate interaction between these strains that may allow them to thrive in the deep subsurface. These two fungi represent the first fungal strains isolated from deep geothermal fluids. Their presence within the fluids was confirmed through molecular analysis. The isolation of these strains emphasizes the importance of considering fungi when investigating microbial diversity in subsurface geothermal environments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/599737v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@fdf699org.highwire.dtl.DTLVardef@148b751org.highwire.dtl.DTLVardef@fb37e9org.highwire.dtl.DTLVardef@113b911_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIFirst fungal strains isolated from a geothermal power plant C_LIO_LIThe two fungal strains were co-isolated from a geothermal fluid used for heat production C_LIO_LISurprising isolation of the cell-switching yeast upon stress exposure of an apparently axenic culture of the filamentous fungus C_LIO_LIFungal strains with high resistance to stressors and no apparent competition for carbon sources C_LI