title: Humic Materials Offer Photoprotective Effect to Escherichia coli Exposed to Damaging Luminous Radiation.
abstract: The behavior of Escherichia coli immersed in aqueous systems amended with humic acids, under PAR, UV-A, UV-B, and simulated solar radiation was examined. Culturability, ability to elongate, functioning of the electron transport systems, and glucose uptake were assessed. Humic substances in the range from 1 to 50 mg L-1 protected cells from photoinactivation. Decrease in culturability and cellular activities was significantly (p <0.05) less in the presence of humic material. However, humic acids were not used as nutrients. Neither irradiated nor nonirradiated humic solutions (50 mg L-1) supported the growth of 105 cells ml-1. However, humic acids dissolved in 0.9% NaC1 efficiently absorbed light over wavelengths from 270 to 500 nm. Also, a photoprotective effect against simulated sunlight was observed when humic acids were not in contact with but rather enveloped the cellular suspensions in double-wall microcosms. The protection afforded by humic acids against luminous radiation likely derives from their ability to absorb these radiations and hence reduces the amount of energy reaching the cells.
authors.affiliation: Departamento de Inmunología, Microbiología y Parasitología, Facultad de Ciencias, Universidad del País Vasco, Apdo 644, E-48080 Bilbao, Spain.
authors.forename: A.
authors.initials: A
authors.lastname: Muela
authors.forename: J.M.
authors.initials: JM
authors.lastname: García-Bringas
authors.forename: I.
authors.initials: I
authors.lastname: Arana
authors.forename: I.
authors.initials: I
authors.lastname: Barcina