Abstract The fatty acid α-ketol 13-hydroxy-12-oxo-9( Z)-octadecenoic acid (methyl ester) was incubated with a bacterial culture isolated from soil. The bacteria (tentatively identified as Ralstoniasp.) exhibited strong monooxygenase activity growing on 2-tridecanone as sole source of carbon. They catalyzed a Baeyer–Villiger type of oxidation and converted the α-ketol to 3( Z)-dodecendioic acid. 3( Z)-Dodecendioic acid was isolated from the incubation mixture and identified by comparison with an authentic reference compound. These findings offer both a physiological role for α-ketol fatty acids in plant lipid hydroperoxide metabolism and new insights into an alternative biosynthetic pathway leading to traumatic acid (2( E)-dodecendioic acid).