The constitutively expression system for P. putida nitrilase was firstly constructed to improve the nicotinic acid production and reduce the production costs. High density culture strategy was employed to enhance the biomass and nitrilase production of recombinant strain. The total nitrilase activity reached up to 654 U . mL(-1) without the induction. 541 g . L-1 nicotinic acid was accumulated via fed batch mode of substrate feeding through 290 min of conversion.