Promiscuous nitrilase from Bacillus subtilis for herbicide degradation and plant growth promotion

The growing use of nitrile-containing herbicides in agriculture has raised concerns about the environment and human health. In this research, the ability of the bacterial isolate to produce a thermostable enzyme that can degrade nitrile-containing compounds was analysed. The promiscuous nature of the nitrile-degrading enzyme was analysed based on substrate specificity. The enzyme exhibited a notable degradation profile on the nitrile-containing dichlobenil (526.3 µmol/min.mL) and the highest activity towards the native substrate acrylonitrile (555.5 µmol/min.mL). Additionally, divalent metal ions, including Ca²⁺, Mg²⁺, and Fe²⁺, increased the activity of the enzyme but Cu²⁺, Co²⁺, Mn²⁺, Zn²⁺, and K⁺ decreased it. The enzymatic breakdown of dichlobenil into its corresponding carboxylic acids was determined by FTIR and GC-MS/MS. The 16 S rRNA gene was used to characterise the bacterial isolate, and sequence similarities verified that it was Bacillus subtilis. Subsequently, the sequence was deposited in GenBank with the accession number PX891009. B. subtilis possesses plant growth-promoting traits such as indoleacetic acid and gibberellic acid, ammonia production, phosphate solubilization, and produces hydrolytic enzymes that stimulate defence mechanisms. These results suggest that B. subtilis has the potential to degrade nitrile-containing herbicides to improve soil fertility. This work also contributes to the Sustainable Development Goals (SDGs), especially SDGs 2, 3, 6, 12, and 15, by supporting the biological degradation of herbicides to enhance soil quality.