Stimulated Germination of Chlorine-Resistant Fungal Spores during Drinking Water Chlor(am)ination

Fungi represent a considerable challenge given their ubiquitous inhabitation and growth in drinking water distribution systems (DWDSs), yet the germination behavior of fungal spores in DWDSs is largely unknown. This study investigated germination of three chlorine-resistant fungal spores (Penicillium chrysogenum, Cladosporium halotolerans, and Penicillium spinulosum) in synthetic tap water (STW) under varying conditions of disinfectants (free chlorine, FC; monochloramine, NH2Cl), humic acid (HA), and pH. The germination ratios of the tested fungal spores in STW(+HA) were <10% without FC/NH2Cl, while surprisingly increased to a maximum of 67.5% and 44.14% with 2 mg/L FC and 0.4 mg/L NH2Cl, respectively, for C. halotolerans spores. With increasing initial concentrations of FC (0-4 mg/L) and NH2Cl(0-2 mg/L), germination ratios of C. halotolerans spores in STW+HA showed a first increasing and then decreasing trend, suggesting that the stimulation effect was outweighed by inactivation at high CT values. Nontargeted metabolomics analysis identified the decrease of several potential self-inhibitors for spore germination by chlor(am)ination. Patterns of significantly changed metabolites and pathways involving lipid, sugar, and amino acid metabolism were significantly different for C. halotolerans spores treated by FC versus NH2Cl. The results provide new insights into survival strategies and germination mechanisms of fungal spores in chlor(am)ine-disinfected DWDSs.