The present invention concerns a new method combining evolution and rational design for the preparation of a strain of micro-organism for the production of 1,2-propanediol from a carbon source.The said method comprises: growing an initial strain under selection pressure in an appropriate growth medium, said initial bacterial strain comprising an attenuation of the expression of the tpiA gene and an attenuation the expression of at least one gene involved in the conversion of methylglyoxal to lactate, in order to promote evolution in said initial strain, then selecting and isolating the evolved strain having an increased 1,2 propanediol production rate, then reconstructing a functional tpiA gene in the evolved strain; The present invention also concerns the evolved strain such as obtained, that may be furthermore genetically modified in order to optimize the conversion of a carbon source into 1,2-propanediol without by-products and with the best possible yield.