Visible laser and UV-A radiation impact on a PNP degrading Moraxella strain and its rpoS mutant.
The role of stationary phase sigma factor gene (rpoS) in the stress response of Moraxella strain when exposed to radiation was determined by comparing the stress responses of the wild-type (WT) and its rpoS knockout (KO) mutant. The rpoS was turned on by starving the WT cultures for 24 h in minimal salt medium. Under non-starved condition, both WT and KO planktonic Moraxella cells showed an increase in mortality with the increase in duration of irradiation. In the planktonic non-starved Moraxella, for the power intensity tested, UV radiation caused a substantially higher mortality rate than did by the visible laser light (the mortality rate observed for 15-min laser radiation was 53.4 +/- 10.5 and 48.7 +/- 8.9 for WT and KO, respectively, and 97.6 +/- 0 and 98.5 +/- 0 for 25 s of UV irradiation in WT and KO, respectively). However, the mortality rate decreased significantly in the starved WT when exposed to these two radiations. In comparison, rpoS protected the WT against the visible laser light more effectively than it did for the UV radiation. The WT and KO strains of Moraxella formed distinctly different types of biofilms on stainless steel coupons. The KO strain formed a denser biofilm than did the WT. Visible laser light removed biofilms from the surfaces more effectively than did the UV. This was true when comparing the mortality of bacteria in the biofilms as well. The inability of UV radiation to penetrate biofilms due to greater rates of surface absorption is considered to be the major reason for the weaker removal of biofilms in comparison to that of the visible laser light. This result suggests that high power visible laser light might be an effective tool for the removal of biofilms.
Department of Biology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada.
Kanavillil
K
Nandakumar
Werden
W
Keeler
Heidi
H
Schraft
Kam T
KT
Leung
D000818:Animals; D018441:Biofilms / Q000528:radiation effects*; D002244:Carbon / Q000378:metabolism; D007834:Lasers; D018613:Microscopy, Confocal; D009016:Moraxella / Q000166:cytology / Q000235:genetics* / Q000254:growth & development / Q000528:radiation effects*; D010933:Plankton / Q000166:cytology / Q000254:growth & development / Q000528:radiation effects; D012808:Sigma Factor / Q000172:deficiency / Q000235:genetics*; D014466:Ultraviolet Rays
D012808:Sigma Factor; D002244:Carbon