Cailleau, G. | bioRxiv Science

bioRxiv2024

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

microbiology↗

bioRxiv2023

A ubiquitous Microcoleus species causes benthic cyanotoxic blooms worldwide

Recently, proliferations of benthic cyanobacteria producing derivatives of anatoxin-a have been reported in rivers all over the world. In three river systems, in New Zealand, the USA, and Canada, a cohesive cluster of Microcoleus strains was responsible for toxin production. Here, we document a similar toxigenic event that occurred at the mouth of the river Areuse in lake Neuchatel (Switzerland) and caused the death of several dogs. Using 16S RNA-based community analysis, we show that riverine benthic communities are dominated by Oscillatoriales and especially by Microcoleus strains. We correlate the detection of one sequence variant with the presence of anatoxin-a derivatives and use metagenomics to assemble a complete circular genome of the strain. The strain is distinct from the ones isolated in New Zealand, the USA, and Canada, but belongs to the same species; it shares significant traits with them, in particular a relatively small genome and incomplete vitamin biosynthetic pathways. Overall, our results suggest that the major anatoxin-a-associated benthic proliferations worldwide can be traced back to a single ubiquitous species, Microcoleus anatoxicus, rather than to a diversity of cyanobacterial lineages. We recommend that this species be monitored internationally in order to help predict and mitigate similar cyanotoxic events.

microbiology↗