Recombinants Pseudomonas putida BO14 and Escherichia coli QEFCA8 capable of ferulic acid biotransformation to vanillin mere constructed using homologous recombination and a PCR based cloning strategy, respectively. In the liquid culture of P. putida BO14, 26.81+/-2.30 mu g vanillin ml(-1) of culture filtrate was detected. In the case of recombinant E. coli QEFCA8, 19.37+/-1.95 mu g vanillin ml(-1) of culture filtrate was detected. Results indicate that the strains could be useful for the biotechnological production of vanillin, a very important flavoring substance.