The possible two operons cadCA and cadB/DX are induced in cadmium resistance Mechanism by Frankia alni ACN14a
Rehan, Medhat | Alhusays, Ahmed | Serag, Ahmed M. | Boubakri, Hasna | Pujic, Petar | Normand, Philippe
Cadmium (Cd²⁺) is one of the highly toxic heavy metals and is considered as a carcinogenic agent. Our aim was to confirm Frankia alni ACN14a ability to resist Cd²⁺ and determine the genes involved in the resistance. Up to 10 and 22 times in Cd²⁺ accumulation were detected in F. alni ACN14a and Frankia casuarinae CcI3 hyphae when exposure to 1 mM, respectively. Scanning Electron Microscopy (SEM) exhibited a stable Cd²⁺ precipitate to the cell surface and increase in Cd²⁺ weight level reached attached 16.45 % when evaluated with SEM-EDAX analysis. Potential two Cd²⁺ operons were identified: 1- cadCA operon encoding a copper-transporting P-type ATPase A (cadA, FRAAL0989), ArsR family regulator (cadC, FRAAL0988) with 37- and 70-fold increases in their expression by qRT-PCR, respectively; 2- cadB/DX which encodes a putative cobalt-zinc-cadmium resistance protein (cadD, FRAAL3628) and heavy metal-associated domain protein (cadX, FRAAL3626) with 22- and 16-fold up-regulation when exposure to Cd²⁺-stress. Cd²⁺ tolerance by F. alni ACN14a involved effluxing Cd²⁺ outside the cells and binding it to the membrane surface. Our results indicate the existence of two cadmium-resistance mechanisms in Frankia strains which support the idea of using them as bioremediation agent.
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