A novel recombinant cyanate hydratase (rTl-Cyn) from the thermophilic fungus Thermomyces lanuginosus for plant growth promotion

Cyanate accumulation poses environmental problems globally due to its frequent use as a potent herbicide, and is also produced as a degradation product of cyanide used in metal industries. Cyanate acts as a potential toxin as it carbamoylates proteins and other molecules thereby changing their structure, charge and function. Cyanase catalyzes the decomposition of cyanate into CO₂ and ammonium, and the cyanate generated ammonium can serve as a source of nitrogen for plant growth. The Cyn gene, which encodes the cyanate hydratase in T. lanuginosus, was cloned into the pET21b vector and the resultant plasmid, pET21b-Cyn was successfully expressed in E. coli BL21 (DE3). Characterization of the enzyme and its applicability on plant growth promotion was also assessed. The purified rTl-Cyn has a molecular mass of ~18 kDa using SDS-PAGE, with Km and V_max (Potassium cyanate), k_cat and k_cat/Km values of 0.33 mM, 3333.33 µmoles mg^-1 min^-1, 2.5 x 10⁴ s^-1 and 7.5x10⁷ M^-1 s^-1, respectively. FTIR analysis revealed the conversion of cyanate into ammonia by rTl-Cyn. KCNO treatment inhibited Vigna radiata germination, and early seedling growth on Murashige and Skoog medium. However, when supplemented with rTl-Cyn growth was achieved. Our findings show that V. radiata can grow on cyanate containing medium, when supplemented with rTl-Cyn utilizing it as a source of energy/nitrogen. Furthermore, this is the first report of any known thermophilic fungal cyanases, which has been expressed, characterized and evaluated.