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Physiological and molecular responses of the marine oligotrophic ultramicrobacterium Sphingopyxis Alaskensis rb2256 to visible light and ultraviolet radiation

Ultraviolet radiation reaching the Earth’s surface (UVR, 280-400 nm) may penetrate deep into the clear oligotrophic waters influencing a large part of the euphotic layer. Marine heterotrophic bacteria at the surface of the oceans are especially sensitive to the damaging solar radiation due to their haploid genome with little or no functional redundancy and lack of protective pigmentation. In a context of climate change and ozone depletion, it is clearly important to understand the physiology and underlying molecular UVR responses of abundant marine bacteria species. We chose the marine ultramicrobacterium Sphingopyxis alaskensis as a reference species to study the impact of solar radiation due to its numerical abundance in oligotrophic waters and its photoresistance, previously reported. For this purpose, we focused on the formation of the two major UVB-induced DNA photoproducts (CPDs and 6-4PPs) as well as the differential protein expression under solar radiation. We first demonstrated that the GC content of prokaryotic genome had a major effect on the formation of UVB-induced photoproducts, quantified by HPLC-MS/MS. Due to its high GC content, S. alaskensis presented a favoured formation of highly mutagenic cytosine-containing photoproducts and therefore would be more susceptible to UVinduced mutagenesis. By comparing S. alaskensis to another marine bacterium Photobacterium angustum, we observed for the latter strain a remarkable resistance to high UVB doses associated with a decrease in the rate of formation of CPDs explained by a non-conventional activity of photolyase. We also demonstrated that DNA damage in S. alaskensis was markedly modulated by growth temperature and time spent in stationary phase. In order to assess the effects that environmental UV-R had on regulatory networks and pathways of S. alaskensis, and determine how the cell’s physiology was affected, a quantitative proteomics investigation was performed. Changes in proteome were analyzed, with the recent and powerful mass spectrometry based approach using iTRAQ methodology. Approximately, one third of the proteome of S. alaskensis was identified, with 119 statistically and significantly differentially abundant proteins. Cellular processes, pathways and interaction networks were determined and gave us unique insight into the biology of UV response and adaptation of S. alaskensis.

Identiferoai:union.ndltd.org:ADTP/258596
Date January 2009
CreatorsMatallana Surget, Sabine-Astrid, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW
PublisherAwarded By:University of New South Wales. Biotechnology & Biomolecular Sciences
Source SetsAustraliasian Digital Theses Program
LanguageEnglish
Detected LanguageEnglish
Rightshttp://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright

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