Application of a molecular biology concept for the detection
of DNA damage and repair during UV disinfection
Jacqueline Su
¨
ß
a,b
, Sabrina Volz
a
, Ursula Obst
a
, Thomas Schwartz
a,
*
a
Forschungszentrum Karlsruhe, Institute of Functional Interfaces, Microbiology of Natural and Technical Interfaces Department,
Hermann-von Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
b
University of Karlsruhe, Competence Center for Material Moisture, Adenauerring 20b, 76131 Karlsruhe, Germany
article info
Article history:
Received 19 December 2008
Received in revised form
15 May 2009
Accepted 26 May 2009
Published online 16 June 2009
Keywords:
UV disinfection
DNA damage
Regeneration
Wastewater
PCR
abstract
As nucleic acids are major targets in bacteria during standardised UV disinfection (254 nm),
inactivation rates also depend on bacterial DNA repair. Due to UV-related DNA modifica-
tions, PCR-based approaches allow for a direct detection of DNA damage and repair during
UV disinfection. By applying different primer sets, the correlation between amplicon length
and PCR amplification became obvious. The longer the targeted DNA fragment was, the
more UV-induced DNA lesions inhibited the PCR. Regeneration of Pseudomonas aeruginosa,
Enterococcus faecium, and complex wastewater communities was recorded over a time
period of 66 h. While phases of intensive repair and proliferation were found for P. aeru-
ginosa, no DNA repair was detected by qPCR in E. faecium. Cultivation experiments verified
these results. Despite high UV mediated inactivation rates original wastewater bacteria
seem to express an enhanced robustness against irradiation. Regeneration of dominant
and proliferation of low-abundant, probably UV-resistant species contributed to a strong
post-irradiation recovery accompanied by a selection for b-Proteobacteria.
ª 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Wastewater disinfection has gained importance due to the
emergence of waterborne pathogens that are resistant to
conventional wastewater treatment technologies (Crockett,
2007; Hijnen et al., 2006). Their deposition and distribution in
the environment can substantially reduce the quality of
receiving waters and represent a considerable risk for human
health, if they reach water suppliers via hydrological
connections (Crockett, 2007).
In recent years, UV light was increasingly used as a disin-
fectant, as it effectively inactivates bacteria without the
formation of toxic by-products (Hijnen et al., 2006). The inac-
tivating effects of UV rays are due to DNA alterations (e.g.,
strand breaks, formation of thymine dimers) that result in an
inhibition of replication and, in case of lethal doses, in a loss of
reproducibility. However, microbes possess several mecha-
nisms to enable cell survival following UV exposure. To
a certain extent, DNA damage can be tolerated by the cell until
repair occurs (Friedberg, 2005). The mechanism by which
microbes recover replication activity through a direct rever-
sion of thymine dimers is called photoreactivation (Oguma
et al., 2001). This process is catalysed by the DNA repair
enzyme photolyase and requires visible light. Apart from
photoreactivation, numerous light-independent repair
mechanisms exist that are regulated by the expression of the
single-strand DNA binding protein RecA (Sinha and Ha
¨
der,
2002). Regardless of which process enables survival of bacteria
* Corresponding author. Tel.: þ49 72 4782 6802; fax: þ49 72 4782 6858.
E-mail address: thomas.schwartz@ifg.fzk.de (T. Schwartz).
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2009.05.048
water research 43 (2009) 3705–3716