Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight To Damage Fecal Coliforms in Waste Stabilization Pond Water

Abstract

Simple beaker experiments established that light damages fecal coliforms in waste stabilization ponds by an oxygen-mediated exogenous photosensitization. Wavelengths of up to 700 nm were able to damage bacteria. The ability of wavelengths of >425 nm to damage fecal coliforms was dependent on the presence of dissolved sensitizers. The sensitizers were ubiquitous in raw sewage, unaffected by sewage treatment, not derivatives of bacteriochlorophyll or chlorophyll, absorbed well in UV light, and had a slight yellowish color; they are therefore believed to be humic substances. The ability of light to damage fecal coliforms was highly sensitive to, and completely dependent on, oxygen. Scavengers of H202 and singlet oxygen could protect the bacteria from the effects of sunlight, but scavengers of hydroxyl radicals and superoxides could not. Light-mediated damage of fecal coliforms was highly sensitive to elevated pH values, which also enabled light with wavelengths of >425 nm (in the presence of the sensitizer) to damage the bacteria. We conclude that humic substances, pH, and dissolved oxygen are important variables in the process by which light damages microorganisms in this and other environments and that these variables should be considered in future research on, and models of, the effects of light.

Oxygen and photoinactivation ofEscherichia coliin UVA and sunlight

“…Comparing the results for plates of unsupplemented medium incubated aerobically, it is clear that illumination with simulated sunlight in hyperoxygenated (O 2 -sparged) water resulted in a rapid decrease in counts, with no evidence of an initial delay or ÔplateauÕ when compared with oxygenated (air-sparged) conditions, with the hypo-oxygenated treatment showing the clearest evidence of a plateau and the slowest overall decrease in counts. Such results are consistent with the earlier observation that the extent of photoinactivation is directly related to the level of dissolved oxygen in the water during illumination (Curtis et al 1992;Reed 1997), rather than being linked to the relatively small changes in pH observed as a result of sparging. Similarly, the results for anaerobic enumeration using pyruvate-supplemented medium show the same overall trend, although in each case, the overall decrease at any time point was less than that observed under aerobic conditions, with greater evidence of an initial plateau.…”

Light irradiation helps magnetotactic bacteria eliminate intracellular reactive oxygen species

“…This harmful effect depends heavily on ROS production (Khaengraeng and Reed, 2005). These ROS are generated mainly as a result of the absorption of light by bacterial endogenous photosensitizers, such as cytochromes, porphyrins, flavins and NADH (Curtis et al, 1992;Lubart et al, 2011), although exogenous photosensitizers may also contribute to ROS generation in natural waters (Voelker et al, 1997). Light wavelength and intensity influence the amount of ROS produced in illuminated bacteria and correlate with phototoxic effects (Uyar et al, 2007).…”

Quantitative molecular detection of Salmonella typhimurium in soil and demonstration of persistence of an active but non-culturable population

“…Large soil particles were sedimented by centrifugation at 177Ug for 30 s, after which the supernatant was further centrifuged at 3500Ug for 15 min. The resulting pellet was resuspended in either 1 ml of one quarter strength Ringer's solution for plating, or 1 ml of TNPE (50 mM Tris, pH 8.0, 100 mM NaCl, 1% (w/v) polyvinylpolypyrrolidone, 10 mM EDTA [20]) for DNA extraction. For plate counts, dilutions of the extract were plated on appropriate agar(s) and incubated at 37³C for 24 h. The pellet, resuspended in TNPE, was added to a 7-ml Braun bead-beating tube with 1 g of 0.10^0.11-mm glass beads (Braun).…”