Survival strategy ofEscherichia coliandEnterococcus faecalisin illuminated fresh and marine systems

摘要

Some effects of visible light onEscherichia coliandEnterococcus faecalisin natural freshwater and seawater were studied by plate counts, colony area measurements, and direct counts. A large number of somnicells (non‐culturable cells) were noted in illuminated systems as compared with non‐illuminated ones. Colony areas were significantly smaller in illuminated systems. Indirect activity measurements were used to test the effects of visible light on the ability ofE. coliandEnt. faecalisto metabolize substrates (14Cglucose) in natural waters. In illuminated systems, a decrease of glucose uptake was observed. When percentages of assimilation and respiration with respect to the total glucose uptake were analysed a decrease of assimilation percentages and an increase of respiration percentages were observed. In addition, differences in glucose uptake, assimilation and respiration by enteric bacteria were detected forE. coliat the beginning of the experiments between fresh‐and seawater and these were interpreted as a toxic effect exerted by seawater onE. colicells. Differences between species, natural waters and parameters studied (excepting glucose assimilation) were detected in the illuminated systems. We concluded, however, that enteric bacteria under visible light illumination show a general survival strategy characterized by reaching progressively a somnicell stage which can be defined in terms of their (1) inability to form colonies on standard bacteriological media, (2) inability to incorporate substrates, and (3) inactivation of biosynthetic processes. and accepted 8 Jun