Previous research identified several microorganisms and pathways capable of degrading the mycotoxin fumonisin B₁ (FB₁). Degradation of FB₁ by microorganisms seems to comprise two essential steps: hydrolysis to hydrolyzed fumonisin B₁ (HFB₁) and deamination of the hydrolysis product. One of the previously studied microorganisms was the Gram negative bacterium ATCC 55552. The gene corresponding to the first step of FB₁ degradation in this bacterium was identified, but the genetic basis for deamination of the hydrolyzed intermediate remained unexplained (Duvick et al. 2000, PCT patent application WO200004158). Here we report the sequence and HFB₁-deaminating activity of a novel aminotransferase encoded by the bacterium ATCC 55552. The corresponding gene was identified, sequenced, and over-expressed in Escherichia coli. Cell lysates of the recombinant E. coli strain showed distinct HFB₁-deaminating activity in the presence of pyridoxal phosphate and pyruvate, as was demonstrated by liquid chromatography-mass spectrometry. Thus, we suggest the novel enzyme to be part of the fumonisin catabolic pathway of the bacterium ATCC 55552.