Molecular analysis of antioxidant genes in the extremohalophile marine bacterium Exiguobacterium sp. CNU020

Exiguobacterium sp. CNU020, an alkaliphile and extremohalophile bacterium, is resistant to 20 mM H(2)O(2), a concentration that is lethal to most bacteria. Representative antioxidant genes of catalase and superoxide dismutase (SOD), obtained by PCR amplification of the genomic DNA, were characterized: the 252-bp catalase gene shared 77% similarity in the deduced amino acid sequence to that of E. oxidotolerans T-2-2(T). The 420-bp SOD gene had the closest similarity (94.3%) to the manganese-SOD of E. sibiricum 255-15. Through activity-staining analysis, stain CNU020 had at least four catalase isoforms: C1, C2, C3 and C4. Expression of each catalase isoform was dependent on the growth phase and oxidants but two catalases (C3 and C4) were always induced and expressed at a similar rate, indicating that they were constitutively expressed. RT-PCR-based expression analysis at the transcriptional level suggested that the catalase gene is strongly expressed in response to 2 mM H(2)O(2), 0.2 mM Paraquat and 0.2 mM menadione. However, the SOD gene exhibited no observable expression pattern with 2 mM H(2)O(2) despite its strong expression when exposed to Paraquat and menadione.