Neutralization of radical toxicity by temperature-dependent modulation of extracellular SOD activity in coral bleaching pathogen Vibrio shiloi and its role as a virulence factor.
Vibrio shiloi is the first and well-documented bacterium which causes coral bleaching, particularly, during summer, when seawater temperature is between 26 and 31 degrees C. Coral bleaching is the disruption of the symbiotic association between coral hosts and their photosynthetic microalgae zooxanthellae. This is either due to lowered resistance in corals to infection or increased virulence of the bacterium at the higher sea surface temperature. The concentration of the oxygen and resulting oxygen radicals produced by the zooxanthellae during photosynthesis are highly toxic to bacteria, which also assist corals in resisting the infection. Hence, in this study we examined the effect of different temperatures on the activity of a novel extracellular SOD in V. shiloi. We also partially characterized the SOD and clearly confirmed that the extracellular SOD produced by V. shiloi is Mn-SOD type, as it was not inhibited by H2O2 or KCN. Performing chemical susceptibility killing assay, we confirmed that extracellular SOD may act as first line of defense for the bacteria against the reactive oxygen species. Since, increased activity of novel Mn-SOD at higher temperature, leads to the neutralization of radical toxicity and facilitates the survival of V. shiloi. Hence, the extracellular Mn-SOD may be considered as a virulence factor.
Department of Biochemistry, University of Madras, Guindy Campus, Chennai, 600025 Tamilnadu, India.
Malliga Raman
MR
Murali
Subramaniya Bharathi
SB
Raja
Sivasitambaram Niranjali
SN
Devaraj
D000818:Animals; D037421:Anthozoa / Q000382:microbiology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D011190:Potassium Cyanide / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000378:metabolism*; D014733:Vibrio / Q000201:enzymology* / Q000254:growth & development / Q000472:pathogenicity; D037521:Virulence Factors / Q000378:metabolism*
D037521:Virulence Factors; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D011190:Potassium Cyanide