Persistence and proliferation of some unicellular algae in drinking water systems as result of their heterotrophic metabolism

Drinking water systems have a complex structure and are characterised by the absence of light, the presence of disinfectants and by low levels of nutrients. Several kinds of bacteria, protozoa, algae and fungi can be found in tap water. Little is known about the ecology of algae in drinking water systems, although their capacity to produce toxins and modify taste and odour has been described. In order to assess the presence and persistence of unicellular algae as well as their ability for heterotrophic growth as a mechanism for survival in water distribution networks, we carried out a one-year study of the drinking water from the Bellaterra campus of the Autonomous University of Barcelona. Unicellular algae were isolated by membrane filtration on plates of synthetic medium containing organic matter as an energy source (R2A). Oocystis sp. (unicellular green algae) and Xenococcus sp. (cyanobacteria) were routinely isolated and cultured using the procedure mentioned above. The results demonstrate the ability of some microalgae to grow in the dark as a consequence of their heterotrophic metabolism and illustrate the probable survival mechanism of some algal species species in these systems, which can be related to the possibility of algae regrowth in drinking water systems.