Overexpression of Cyanase in Chlamydomonas reinhardtii: a Promising Approach for Biodegradation of Cyanate in Aquatic Systems

Cyanate and its derivatives are considered as highly dangerous materials that threaten human health and environment. Cyanate arises from both natural resources and anthropogenic activities including various chemical industries, herbicide production, and mining wastewater. Despite its toxicity, cyanate is considered as an important nitrogen (N) source in marine ecosystems. Cyanase (CYN) catalyzes the decomposition of cyanate into CO2 and NH3 in a bicarbonate-dependent reaction. In marine cyanobacteria, endogenous cyanases participate in detoxification of low concentrations of cyanate. However, this cyanate biodegradation system is seemingly inconvenient especially at contaminated sites due to high cyanate concentrations. In the current study, we have transferred the activity of the cyanobacterial enzyme cyanase into the micro-alga, Chlamydomonas reinhardtii, via Agrobacterium tumefaciens-mediated transformation method. The recombinant cyanase enzyme was shown to be active in transgenic C. reinhardtii lines. When variable concentrations of cyanate (up to 30mM) is applied to growth medium, transgenic lines showed higher rate of NH3 release, reduced loss of pigmentation symptoms, decreased levels of induced antioxidant enzymes, and low percentage of growth retardation compared to wild-type controls. Results of this study provide an effective eco-friendly phytoremediation system for cyanate detoxification using micro-algae compared to previously reported plant systems.