UV-B Radiation Stress Causes Alterations in Whole Cell Protein Profile and Expression of Certain Genes in the Rice Phyllospheric Bacterium Enterobacter cloacae

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.

Addition of Hydrogen Peroxide to Groundwater with Natural Iron Induces Water Disinfection by Photo‐Fenton at Circumneutral pH and other Photochemical Events

“…UV‐B radiation causes the formation of dimers of cellular DNA. These lesions block DNA replication and RNA transcription, leading to cell death . UV‐A radiation mainly produces single‐ and double‐stranded breaks, alterations in proteins and induced ROS formation .…”

“…These lesions block DNA replication and RNA transcription, leading to cell death . UV‐A radiation mainly produces single‐ and double‐stranded breaks, alterations in proteins and induced ROS formation . Additionally, it has been demonstrated that solar radiation can cause sublethal injuries to E. coli .…”

“…The presence of hydrogen peroxide in the absence of light (GW + H 2 O 2 + Dark) caused the partial decrease in E. coli viability, probably induced by Fenton reactions because, as previously mentioned, the groundwater samples already contained natural dissolved and/or colloidal iron (0.3 mg L −1 ). Ferric complex with humic acids and ferrous ions existing in natural groundwater could induce Fenton reaction which leads to the formation of hydroxyl radicals () that are highly oxidant ( E = 2.8 V vs NHE) and able to attack the external E. coli membrane . Colloidal iron in the presence of H 2 O 2 can also participate in Fenton reactions leading to the production of radicals .…”

Influence of Light on Plant–Phyllosphere Interaction

“…Organisms isolated under UV irradiation at the end of a growing season in Texas, United States, tended to show higher tolerance to UV, and predominant groups in peanut were Bacillus coagulans, Clavibacter michiganensis , and Curtobacterium flaccumfaciens ( Jacobs and Sundin, 2001 ). Large-scale analysis in a UV-B resistant bacteria group isolated from rice, Enterobacter cloacae , revealed broad changes in ROS and in the number and expression of proteins upon exposure to UV-B ( Kumar et al, 2016 ). Future studies in the function of these proteins, together with gene expression profiling, may further elucidate the mechanisms of phyllospheric bacteria resistance and adaptation to UV-B ( Matallana-Surget and Wattiez, 2013 ; Kumar et al, 2016 ).…”

“…Large-scale analysis in a UV-B resistant bacteria group isolated from rice, Enterobacter cloacae , revealed broad changes in ROS and in the number and expression of proteins upon exposure to UV-B ( Kumar et al, 2016 ). Future studies in the function of these proteins, together with gene expression profiling, may further elucidate the mechanisms of phyllospheric bacteria resistance and adaptation to UV-B ( Matallana-Surget and Wattiez, 2013 ; Kumar et al, 2016 ). Effects of UV light on bacterial diversity may as well impact other groups of microorganisms.…”