Investigation into the Response of Listeria
monocytogenes to 470 nm Blue Light
A. L. Dorey1, K. NicAogáin1, B. O’Donoghue1, C. Bennett2, A. Conneely2,
C. P. O’Byrne1
1Bacterial
Stress Response Group, NUI Galway; 2National Centre for Laser Applications, NUI Galway
1. Introduction
Blue light is known to have an inhibitory effect on L. monocytogenes and resistance to blue light is mediated by the alternative sigma factor σB via the general stress response (O’Donoghue et
al., 2016; Ondrusch and Kreft, 2011). The activation of σB has been shown to be maximal at stationary phase (Utratna et al., 2011), and L. monocytogenes has been shown to have an increased
resistance to acid stress in stationary phase compared to exponential phase (Davis et al., 1999). Furthermore, growth temperature has been documented to affect the susceptibility of L.
monocytogenes to acid stress (Ivy et al., 2012).
The aims of this study were to determine the effects of growth phase and growth temperature on the susceptibility of L. monocytogenes to blue light, investigate the existence of a protective
adaptive response, and the potential role σB may play in resistance to blue light.
5. Limited evidence that exposure to a sub-lethal dose of blue light
leads to an adaptive response
2. Materials and Methods
L. monocytogenes EGDe wild-type and EGDe ΔsigB mutant strains were used. All cells
were grown in BHI broth and resuspended in PBS for exposure to blue light (470 nm)
using the light apparatus.
***
****
****
1000
S u r v iv a l ( % )
****
*
10000
100
*
10
1
0 .1
0 .0 1
0 .0 0 1
P re -E x p o s u re
L ig h t
+
-
-
+
-
-
+
+
-
+
+
-
 s ig B
W ild - T y p e
• Cells were either pre-exposed to 2 mW/cm-2 blue light or darkness for 30 min then
exposed to 35 mW/cm-2 blue light for 6 h
• Wild-type cells pre-exposed to a sub-lethal dose of visible light were more resistant to a
lethal dose than wild-type cells that had not been pre-exposed
• The ΔsigB mutant cells did not show an adaptive response after pre-exposure
3. L. monocytogenes cells in stationary phase are more resistant to
blue light than those exponential phase
****
1000
*
Light
-
+
-
Growth
Phase
S
E
E
-C
+C
-
+
-
S
E
E
S u r v iv a l ( % )
100
10
• Anti-eGFP Western blot showing σB activation via an eGFP reporter under the control
of the lmo2230 promoter
• Wild-type cells exposed to 2 mW/cm-2 blue light visible light for 30 min show a greater
level of σB activation compared to wild-type cells kept in darkness
1
0 .1
0 .0 1
0 .0 0 1
L ig h t
-
+
+
-
 s ig B
WT
-
+
-
 s ig B
WT
S ta tio n a ry
+
E x p o n e n tia l
6. Conclusions
• Cells were exposed to 25 mW/cm-2 blue light for 15 h
• Wild-type cells at stationary phase were significantly more resistant to visible light than
wild-type cells at exponential phase
• The ΔsigB mutant cells were significantly more susceptible to visible light than the
wild-type cells at stationary phase, but not at exponential phase
4. L. monocytogenes cells grown at 30°C are more resistant to blue
light than those grown at 37°C
• L. monocytogenes cells in the stationary phase of growth are more resistant to
inhibition by visible light than those in the exponential phase
• L. monocytogenes cells grown at 30°C are more resistant to killing by visible light than
those grown at 37°C
• Resistance to blue light is more dependent upon σB at stationary than exponential phase
• Sigma B plays a greater role in resistance to blue light at 30°C than at 37°C
• Pre-exposure to a sub-lethal dose of visible light may lead to a protective adaptive
response
• Sigma B is activated within 30 min of exposure to visible light
*
1000
**
S u r v iv a l ( % )
100
7. Acknowledgements
10
1
0 .1
0 .0 1
0 .0 0 1
L ig h t
-
+
WT
+
-
 s ig B
3 0C
-
+
WT
+
-
 s ig B
3 7C
8. References
• Cells were exposed to 35 mW/cm-2 blue light for 8 h
• Wild-type cells grown at 30°C were significantly more resistant to visible light
compared to wild-type cells grown at 37°C
• The ΔsigB mutant was significantly more susceptible to visible light than the wild-type
at 30°C, but not at 37°C
Amber L. Dorey
Bacterial Stress Response Group
NUI Galway
University Road
Galway
Ireland
[email protected]
Davis, M.J., Coote, P.J. & O’Byrne, C.P., 1996. Acid tolerance in Listeria monocytogenes: the adaptive acid tolerance response (ATR) and growth-phase-dependent acid resistance. Microbiology
(Reading, England), 142 ( Pt 1(10), pp.2975–82.
Ivy, R.A., Wiedmann, M. & Boor, K.J., 2012. Listeria monocytogenes grown at 7° C shows reduced acid survival and an altered transcriptional response to acid shock compared to L. monocytogenes
grown at 37° C. Applied and environmental microbiology, 78(11), pp.3824–36.
O’Donoghue, B. et al., Inhibition of Listeria monocytogenes growth by blue light is mediated by reactive oxygen species: a role for sigma B and the blue light sensor, Lmo0799. Available at:
http://aem.asm.org/content/early/2016/04/25/AEM.00685-16.full.pdf
Ondrusch, N. & Kreft, J., 2011. Blue and Red Light Modulates SigB-Dependent Gene Transcription, Swimming Motility and Invasiveness in Listeria monocytogenes. PLoS ONE, 6(1), pp.1–16.
Utratna, M. et al., 2011. Rapid, transient, and proportional activation of σ B in response to osmotic stress in Listeria monocytogenes. Applied and Environmental Microbiology, 77(21), pp.7841–7845.