Influence of light and natural microbiota of the Butrón river on E. coli survival.

The survival of an E. coli strain in water samples from the Butrón river has been studied. The input of E. coli cells in the aquatic system breaks down the established balance among the components of the natural microbiota: E. coli becomes the object of the active protozoal predation whereas the autochtonous heterotrophic community become alternative preys. As a result of this new situation, the natural microbiota increases but returns to the initial values once the E. coli cells have been removed from the system. The effect of the temperature of incubation on the survival is exerted through the effect of this parameter on the predatory activity of the protozoa. Light has a lethal and direct action on the E. coli cells, the effect of this parameter is even superior to that of predation.