Methods for the determination of filamentous fungi in treated and untreated waters.

Results of two recent projects in the UK and USA have shown that many species of filamentous fungi are present in both untreated and treated waters. Samples have been taken from surface waters and from a range of points within distribution networks. Isolation programmes employing a range of methods and media, combined with expert taxonomic study have yielded extensive lists of waterborne fungi identified, where possible, to species level: 141 different taxa from the UK and 140 from the USA. In the UK study an average of 32 different fungal taxa were isolated from each surface water and compared to nine from each treated tap water. Certain fungi appear more frequently than others, in particular species of Aspergillus, Cladosporium, Epicoccum, Penicillium and Trichoderma appear to be very common but species from many other genera are also present. The significance of fungi in water systems is poorly understood, many of the species isolated from water are known to be capable of producing toxic secondary metabolites, are involved in food spoilage, or are plant pathogens; some are even opportunistic human pathogens. Direct observation of isolation filters has shown that fungi are present equally as spores and as hyphae. Studies have shown that fungi are capable of growth in both treated and untreated water. While traditional methods of measurement such as dry weight are inadequate for determining growth in water, analysis of ergosterol-a universal component of cell membranes amongst filamentous fungi-has provided a very sensitive means of measuring fungal growth in water to levels of < 1 μg(-1) and may prove to be a suitable method for detecting general fungal levels in water samples. 1998 Society of Applied Microbiology.