Synergistic effect of heat and solar UV on DNA damage
and water disinfection of E. coli and bacteriophage MS2
Dana Jennifer Theitler, Abid Nasser, Yoram Gerchman, Abraham Kribus
and Hadas Mamane
ABSTRACT
The response of a representative virus and indicator bacteria to heating, solar irradiation, or their
combination, was investigated in a controlled solar simulator and under real sun conditions. Heating
showed higher inactivation of Escherichia coli compared to the bacteriophage MS2. Heating
combined with natural or simulated solar irradiation demonstrated a synergistic effect on the
inactivation of E. coli, with up to 3-log difference for 50
W
C and natural sun insolation of 2,000 kJ m
2
(compared to the sum of the separate treatments). Similar synergistic effect was also evident when
solar-UV induced DNA damage to E. coli was assessed using the endonuclease sensitive site assay
(ESS). MS2 was found to be highly resistant to irradiation and heat, with a slightly synergistic effect
observed only at 59
W
C and natural sun insolation of 5,580 kJ m
2
. Heat treatment also hindered light-
dependent recovery of E. coli making the treatment much more effective.
Dana Jennifer Theitler
Abraham Kribus
Hadas Mamane (corresponding author)
School of Mechanical Engineering,
Faculty of Engineering, Tel-Aviv University,
Tel Aviv, 69978,
Israel
E-mail: hadasmg@post.tau.ac.il
Abid Nasser
Water Quality Research Laboratory,
Ministry of Health,
Tel-Aviv, 61082,
Israel
Yoram Gerchman
Department of Biology and Environment,
University of Haifa at Oranim,
Tivon, 36006,
Israel
Key words | DNA damage, endonuclease sensitive site (ESS), heat inactivation, insolation, recovery,
solar disinfection
INTRODUCTION
Point-of-use (POU) technologies used in developing countries
to improve water quality via inactivation of bacteria and
viruses include chlorine tablets, solar disinfection, ceramic fil-
ters, combined flocculation and disinfection, and boiling
(WHO ). Solar Water Disinfection (SODIS) is a simple,
effective and low-cost POU technology for the treatment of
drinking water in developing countries. Solar disinfection is
based on UV energy, heating, or an additive or synergistic
effect of these two processes. Effective combination of solar
UV and thermal radiation can produce a greater level of
microorganism inactivation than either treatment used sepa-
rately. Wegelin et al.() and Sommer et al. () found
that the water temperature has to reach at least 50
W
C to
achieve a synergistic effect of UV radiation and heating on
bacterial inactivation. Although much research has been
done in the field of solar disinfection, there is still room for
improvement in terms of increasing volumes of treated
water and reducing inactivation time. Enhancement
technologies for SODIS include addition of TiO
2
(Gelover
et al. ), addition of riboflavin (Alotaibi & Heaselgrave
), use of compound parabolic concentrators (CPCs)
(Ubomba-Jaswa et al. ) and use of SODIS bags (Saladin
).
The mechanism underlying inactivation by SODIS is
not fully understood, and it might be related to protein
damage, DNA damage and/or increased cell-wall per-
meability. Bosshard et al. () indicated that solar UV
radiation probably damages proteins via oxidative stress.
They showed that under a simulator UVA lamp set to
1,000 kJ m
2
, many different proteins were aggregated
(suggesting protein oxidation), among them Dps, which is
responsible for DNA protection and repair. To assess DNA
damage, an endonuclease sensitive site (ESS) analysis can
be performed, to determine the number of induced
pyrimidine dimers in the genomic DNA. Recent studies
using the ESS method are used to assess UVC disinfection.
605 © IWA Publishing 2012 Journal of Water and Health | 10.4 | 2012
doi: 10.2166/wh.2012.072
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