In situ degradation of 2-methylnaphthalene by a soil Penicillium strain associated with fungal-bacterial interactions.

Fungi play critical but underappreciated roles comparing to bacteria in the bioremediation of organic pollutants, particularly emerging contaminants. Numerous fungal species, along with their functional genes and metabolic pathways, remain largely unexplored. Here, we integrate single-cell Raman-activated cell sorting with stable isotope probing to identify and characterize in situ active fungi involved in emerging contaminant degradation. This approach enabled the isolation of a Penicillium sp. strain LJD-20, previously unreported, which acts as an active degrader of 2-methylnaphthalene, a model emerging pollutant. Genomic analyses revealed that LJD-20 harbors a diverse repertoire of degradation-related genes, including those encoding dioxygenases, methyl hydroxylases, and cytochrome P450 monooxygenases, highlighting its versatile metabolic potential. Single-cell genome sequencing also uncovered a potential close fungal-bacterial co-occurrence, suggesting possible ecological or metabolic interactions. In bioaugmentation trials, strain LJD-20 independently degraded 2-methylnaphthalene and simultaneously promoted the enrichment of other microorganisms involved in its removal. These findings highlight the metabolic versatility and ecological importance of fungi in pollutant degradation and demonstrate the utility of combining single-cell and isotopic approaches to explore microbial function and interaction in complex environments.