Metarhizium robertsii morphological flexibility during nonylphenol removal

•Metarhizium robertsii survive and utilize nonylphenols at high concentrations.•This effective xenobiotic utilization is facilitated by small densely packed pellets.•Fungal morphology changes may serve as a biomarker for the progress of the nonylphenol utilization process.

Nonylphenols (NPs) are toxic organic pollutants that cause deleterious effects in various ecosystems. It was formerly documented by us that the cosmopolitan non-ligninolytic fungus Metarhizium robertsii is capable of degrading 4-n-nonylphenol (4-n-NP) with significant efficiency (initial xenobiotic content 50 mg l−1). The present study revealed that M. robertsii is able to survive in the presence of high NPs amounts (up to 100 mg l−1), and the observed phenomenon is combined with intensive xenobiotic utilization. Additionally, the formation of small densely packed pellets that predominated during the efficient NP utilization process was observed. Larger pellets emerged in the cultures with “hairy” morphology, which indicated the removal process was complete. The observed changes in pellet morphology resulted from the detrimental influence of NPs on M. robertsii as evidenced by viability and cell ultrastructure. For the first time, this study documented the presence of this toxic substrate in the fungal cell wall. It is suggested that the M. robertsii morphological changes may serve as a biomarker for the progress of the intense NP utilization process.