The Characteristics Of Germination And Disinfection Of Waterborne Fungal Spores

The issue of fungal contamination in drinking water,which is closely related to human health and desease outbreaks,has attracted great attentions.Fungi contamination may cause serious problems in color,odor and taste of drinking water,and accelerate the accumulation of toxins,which may damage immune system and cause a lot of diseases.Germinated fungal spores with their extracellular polymers forms biofilms,which are widely found in reservoirs,rivers,lakes,wetlands and water supply networks,posing a serious threat to water quality safety.In addition,compared with dormant fungal spores,germinated spores have higher metabolic activity and can produce new propagules,which result in more toxins.Meanwhile,the release of toxins,pathogenic factors and immune stimulating components poses a greater threat to human health.So far,the most researches of waterborne fungal spore disinfection focused on the inactivation efficiency and mechamisms analysis of dormant fungal spores.However,there are few researches on the inactivation of germinated fungal spores using chlor(am)ine and the analysis of inactivation mechanism using flow cytometry and scanning electron microscope(SEM).In this paper,the germination characteristics and influencing factors of the opportunistic pathogens of Aspergillus niger(A.niger)and Penicillium polandum(P.polandum)spores were invesgated.Meanwhile,the morphological and physiological changes of fungal spores during germination were detected by microscope,SEM and flow cytometry combined with several dyes.In addition,chlorine,chloramine,chlorine dioxide and ultraviolet irradiation were choosed to inactivate fungal spores in dormant and germinated states.The inactivation mechanisms including membrane integrity,esterase activity and intracellular reactive oxygen species(ROS)level were detected by flow cytometry.The morphologic changes during inactivation were observed by SEM.Based on the experimental results displayed in this study,five main conclusions can be drawn as follows:(1)Heat activation promoted the germination of fungal spores,and the optimal conditions of heat activation was as follows: A.niger spores were pre-treated at 50 ℃ for7 min;P.penicillium spores were pre-treated at 45 ℃ for 5 min.A.niger spores showed stronger resistance to heat treatment than P.penicillium spores.Nutrients including carbon,nitrogen and phosphorus source as well as trace elements influenced the germination of fungal spores.Neutrallty conditions and low concentration of fungal spores promoted the germination of fungal spores.(2)The germination of fungal spores began with isotropic growth,then germ tubes emerged,which deemed as spore germination.During germination,the size,complexity and DNA content of fungal spores increased,membrane integrity decreased,as well as esterase activity and the intracellular ROS level increasd.Then the germ tube elonged to form mycelia and biofilm eventually.(3)The lag phase existed during inactivation by three disinfectants for dormant A.niger spores and only chloramination for dormant P.penicillium spores,which shortened with the increase of disinfectant concentration.While for germinated spores,there was no lag phase during inactivation,which could be explained by permeabilized membrane.(4)The inactivation efficiency of dormant and germinated fungal spores decreased as follows: chlorine dioxide > ultraviolet irradiation > chlorine ≈ chloramine.During inctivation,the culturability lost first,then the membrane integrity and esterase activity damaged,intracellular ROS level increased,as well as morphology changed,which led to the leakage of intracellular components and the death of fungal spores.(5)The damage to the esterase activity of dormant and germinated fungal spores decreased as follows: chlorine dioxide > chlorine > chloramine.The damage to the membrane integrity and intracellular ROS of dormant and germinated fungal spores decreased as follows: chlorine dioxide > chlorine > chloramine > ultraviolet irradiation.