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Pathogenic characterization of Phialophora submersa, a new black yeast isolated from freshwater sediments in Spain

Summary

Scientists discovered a new black yeast fungus called Phialophora submersa in Spanish river sediments and tested whether it could infect humans. Using laboratory macrophage (immune cell) models, they found that this environmental fungus exhibits pathogenic potential similar to known disease-causing Phialophora species, though at intermediate levels. The fungus showed resistance to some antifungal drugs and displayed strain-dependent ability to survive various stress conditions. This research suggests that environmental fungal species may pose unexpected health risks despite not being able to grow at normal human body temperature.

Background

Phialophora submersa is a recently identified black yeast species isolated from freshwater sediments in Catalonia, Spain. It is phylogenetically related to known opportunistic pathogens P. americana and P. verrucosa, which cause subcutaneous infections in humans and animals. This study investigates the pathogenic potential of this newly described environmental species.

Objective

To characterize the pathogenic potential of P. submersa by evaluating its ability to evade phagocytosis, survive intracellularly, trigger immune responses in macrophages, and resist various cellular stressors. The study compares these properties with the well-established pathogens P. americana and P. verrucosa to understand P. submersa’s role as a potential human pathogen.

Results

P. submersa demonstrated intermediate virulence between P. americana (lowest) and P. verrucosa (highest), with moderate phagocytosis rates, intracellular survival, and biofilm formation. All three species showed similar antifungal susceptibility profiles with susceptibility to most azoles (except fluconazole), terbinafine, and echinocandins, though P. verrucosa showed reduced echinocandin efficacy. Stress resistance in P. submersa was strain-dependent, with FMR 17150 exhibiting notable resistance to cell wall-destabilizing agents.

Conclusion

Despite its environmental origin and inability to grow at human body temperature in vitro, P. submersa exhibits pathogenic potential comparable to established human pathogens. The species displays intermediate virulence traits, suggesting all Phialophora strains, whether clinical or environmental, possess potential to cause human infections. Understanding P. submersa’s stress resistance and immune evasion mechanisms may inform development of targeted therapeutic strategies.
  • Published in:Frontiers in Cellular and Infection Microbiology,
  • Study Type:Experimental Study,
  • Source: PMID: 40727705, DOI: 10.3389/fcimb.2025.1620047
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