The toxin complex (tc) genes of Photorhabdus encode insecticidal, high molecular 
weight Tc toxins. These toxins have been suggested as useful alternatives to 
those derived from Bacillus thuringiensis for expression in insect-resistant 
transgenic plants. Although Photorhabdus luminescens is symbiotic with nematodes 
that kill insects, tc genes have recently been described from other 
insect-associated bacteria such as Serratia entomophila, an insect pathogen, and 
Yersinia pestis, the causative agent of bubonic plague, which has a flea vector. 
Here, recent advances in our understanding of the tc gene family are reviewed in 
view of their potential development as insect-control agents.