The insecticidal toxin complexes (Tcs) are produced by several Enterobacteriaceae associated with insects, such as Photorhabdus luminescens, Serratia entomophila and Xenorhabdus nematophilus. Genome sequences revealed tc-like genes in Yersinia spp., but insecticidal activity of this genus associated with the toxins has not been described. Through the search for genes upregulated at low growth temperatures in Yersinia enterocolitica strain W22703, a genomic island of 19 kb termed tc-PAI(Ye) with homologues of the toxin genes tcaA, tcaB, tcaC and tccC was identified. Southern blot and polymerase chain reaction (PCR) analysis of 34 strains demonstrated that the tc-PAI(Ye) is present in biovars 2, 3 and 4, but neither in biovars 1A and 1B, nor in five Yersinia species apathogenic in humans. Using the luxCDABE operon as reporter, the expression of the toxin genes was shown to be completely repressed in cells cultured at 37 degrees C, and to increase by 4.6 orders of magnitude when the growth temperature was decreased gradually to 10 degrees C. These data provide the first indication that temperature is a critical parameter for induction or repression of tc gene transcription. Whole-cell extracts of Y. enterocolitica strain W22703 cultivated at 10 degrees C, but not at 30 degrees C, led to insect mortality when fed to Manduca sexta larvae, in contrast to an insertional tcaA mutant. Overall the results suggest that the tc-PAI(Ye) could play an important role in the transmission and survival of pathogenic Y. enterocolitica strains outside mammalian hosts.