Fungal inoculation of human fecal-woodchip substrates produces species-specific effects on indicator bacteria and substrate degradation.

Safely treating human feces in decentralized, waterless toilets remains a sanitation challenge. Filamentous fungi degrade lignocellulose and stay active under the dry conditions that limit bacterial degradation, yet their potential to treat human feces has rarely been quantified. In this exploratory screening study, we inoculated four filamentous fungal species represented by five isolates (two Pleurotus ostreatus isolates and one isolate each of Sordaria fimicola, Trichoderma harzianum, and Ganoderma lucidum) onto fresh human feces mixed with beechwood chips and followed colonization, mold contamination, pH, fecal indicator bacteria (Escherichia coli and Enterococcus spp.), and dry weight over 14 days. Species differed markedly. Sordaria fimicola colonized every sample and fully suppressed competing molds but raised bacterial concentrations and pH. Ganoderma lucidum and both P. ostreatus isolates kept the substrate acidic and suppressed fecal odor; where it established, G. lucidum reduced both indicator bacteria below detection, though its colonization was slow and unreliable. Trichoderma harzianum grew fast but died back after 8 days. Fungal colonization curbed spontaneous molds and for S. fimicola and T. harzianum accelerated substrate degradation, revealing species-specific trade-offs between reliable colonization, suppression of fecal indicator bacteria, and pH control, and pointing to promising candidates and mechanisms for biological fecal treatment.