"Two-in-one" magneto-optical bacteria have been produced using the probiotic Lactobacillus fermentum for the first time. We took advantage of two features of bacteria to synthesize this novel and bifunctional nanostructure: their metal-reducing properties, to produce gold nanopartides, and their capacity to incorporate iron oxide nanoparticles at their external surface. The magneto-optical bacteria survive the process and behave as a magnet at room temperature.