Effect of photoreactivation on ultraviolet inactivation of Microcystis aeruginosa

Abstract

Microcystis aeruginosa forms algal bloom in lakes. They produce toxic compounds such as microcystin. Against such algal problems, the effect of UV treatment was examined. In UV treatment, the effect of photoreactivation should be examined. Photoreactivation is a repair mechanism of genomic DNA damage by sunlight irradiation. UV treatment causes DNA damages on target cyanobacteria, however sunlight can repair some of these DNA damages. To examine the effect of photoreactivation, both white and yellow light incubations were employed. White light allows both photoreactivation and photosynthesis, while yellow light prohibits photoreactivation and only allows photosynthesis. Microcystis aeruginosa NIES 98 strain and PCC 7806 strain were used as the test cultures. Those cultures were exposed to low-pressure (LP) or medium-pressure (MP) ultraviolet (UV) lamp, then incubated under white or yellow light. Yellow light incubation method was effective to examine photoreactivation. It was revealed that almost six times UV fluence was required to inactivate 99% of Microcystis aeruginosa, under photoreactivation condition, compared with non-photoreactivation condition. Inhibition of photoreactivation could greatly enhance UV treatment efficiency against Microcystis aeruginosa. One of the practical suggestions is to conduct UV treatment at night, when photoreactivation by sunlight rarely takes place. Highly efficient inactivation was achieved by avoiding photoreactivation.

Enumerating viable phytoplankton using a culture-based Most Probable Number assay following ultraviolet-C treatment

“…This was intended to simulate treatment of ballast water at intake and discharge of a 5-day voyage and by its nature is a dual-stressor treatment for a photoautotrophic organism. If representative, the dose-response curves for Microcystis aeruginosa (Sakai et al 2011 ), C. reinhardtii (Chaudhari et al 2015 ), and T. suecica (Olsen et al 2015 ) indicate that phytoplankton are more resistant to UVC than the viruses, bacteria, and heterotrophic protists reviewed by Hijnen et al ( 2006 ) and Haji Malayeri et al ( 2016 ). However, the doses required to treat the species used in this study are within the ranges used to treat municipal wastewater (USEPA 2006 ; NWRI 2012 ).…”

“…Photosynthesis provides the energy required for catabolic metabolism—including both repair and cell division—beyond what can be supported by internal energy-storage reserves. Sakai et al ( 2011 ) measured viability following UVC irradiation in cultures of Microcystis with and without photorepair. A pronounced shoulder in the dose-response curve for cultures permitted photorepair and its absence in cultures without it, and the convergence of the curves at high doses suggests that loss of viability at low dose was primarily from nucleotide damage but the loss at high doses was primarily from another source.…”

Susceptibility of Diaphorina citri to Irradiation with UV-A and UV-B and the Applicability of the Bunsen–Roscoe Reciprocity Law

“…However, two studies have explored the relationships between dose and irradiance using Tetranychus urticae subjected to various treatments with UV-B. Both studies [ 46 , 66 ] found that the hatchability of eggs; the mortality of eggs, larvae, teleiochrysalises, and adult females; and the development time from larvae to adult emergence were all linearly related to dose, regardless of intensity. Hence, under the range of doses and irradiance times used, all three studies have shown the reciprocity law was upheld.…”

Effect of the length of dark storage following ultraviolet irradiation of Tetraselmis suecica and its implications for ballast water management

“…For one and five days of dark 494 post-treatment, the values of k on samples subjected to UV increased from 0.010 ± 0.001 495 up to 0.038 ± 0.005 and 0.095 ± 0.027 cm 2 mJ -1 in the absence of chemical treatment, 496 respectively. This increase can be attributed to the combination of UV irradiation and dark 497 storage which prevents the microalgae from photoreactivation (Romero-Martínez et al, 498 2020; Sakai et al, 2011). For one day of dark post-treatment, only the addition of 1 ppm of 499 H2O2 caused a noticeable increase of k with respect to the treatment with only UV.…”