Abstract
Among the different types of UV radiation, UV-B radiation (280-315 nm) has gained much attention mainly due to its increasing incidence on the Earth’s surface leading to imbalances in natural ecosystems. This study deals with the effects of UV-B radiation on the proteome and gene expression in a rice phyllospheric bacterium, Enterobacter cloacae. Of the five bacteria isolated from rice leaves, E. cloacae showed the highest level of resistance to UV-B and total killing occurred after 8 h of continuous exposure to UV-B. Reactive oxygen species were induced by UV-B exposure and increased with increasing duration of exposure. Protein profiling by SDS-PAGE and 2-dimensional gel electrophoresis (2-DE) revealed major changes in the number as well as expression of proteins. Analysis of 2-DE gel spots indicated up/down-regulation of several proteins under the stress of UV-B radiation. Thirteen differentially expressed proteins including two hypothetical proteins were identified by MALDI-TOF MS and assigned to eight functional categories. Both the hypothetical proteins (gi 779821175 and gi 503938301) were over-expressed after UV-B irradiation; gi 503938301 was characterized as a member of FMN reductase superfamily whereas gi 779821175 seems to be a structural protein as it did not show any functional domain. That the expression of certain proteins under UV-B stress is indeed up-regulated was confirmed by qRT-PCR. Transcript analysis of selected gene including genes of hypothetical proteins (cp011650 and cp002886) showed over-expression under UV-B stress as compared to untreated control cultures. Although this study deals with a limited number of proteins, identification of differentially expressed proteins reported herein may prove useful in future studies especially for assessing their significance in the protection mechanism of bacteria against UV-B radiation stress.
Highlights
Sunlight produces a broad spectrum of radiations from which the part reaching the Earth’s surface is composed of visible light, ultraviolet (UV-B and UV-A) and infrared radiation
It was noted that UV-B radiation exposure to five strains of phyllospheric bacteria resulted in the loss of survival and complete killing occurred after prolonged exposure
Our study is the first of its kind and demonstrates changes in the proteome and gene expression of the phyllospheric bacterium E. cloacae isolated from the rice plant
Summary
Sunlight produces a broad spectrum of radiations from which the part reaching the Earth’s surface is composed of visible light, ultraviolet (UV-B and UV-A) and infrared radiation. UV-B radiation is a cytotoxic wavelength range of solar radiation that exerts several structural and physiological effects on living organisms (Bancroft et al, 2007; Singh et al, 2013). Several biological effects of UV-B radiation include alteration in the structure of DNA, proteins, lipids, and other biologically important molecules, enhanced reactive oxygen species (ROS) generation, inhibition of such physiological processes as N2 fixation, photosynthesis and energy production in several organisms (Häder et al, 2007; Santos et al, 2012; Singh et al, 2013; Babele et al, 2015; Chudobova et al, 2015; Kurth et al, 2015). Lesions formed in the DNA result in the blockage of DNA replication and RNA transcription leading to cell death (Santos et al, 2012; Chudobova et al, 2015)
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