Identifying Anti-host Effectors in Photorhabdus

The death of the insect host is an essential part of the life cycle of Photorhabdus, and as a result, this bacterium comes equipped with a dazzlingly large array of toxins and virulence factors that ensure rapid insect death. Elucidation of the key players in insect infection and mortality has therefore proved difficult using traditional microbiological techniques such as individual gene knockouts due to the high level of functional redundancy displayed by Photorhabdus virulence factors. Thus, knockout of any individual toxin gene may serve to delay time to death but not to render the bacteria avirulent due to the continued presence of an array of other toxins and virulence factors in the single-gene mutant. This functional redundancy had led to the necessary development of an array of techniques and new model systems for identifying and dissecting apart the action of anti-insect effectors produced by Photorhabdus. These have been pivotal in both the identification of new toxins and virulence factors and in ascribing functions to them. These techniques have gone on to prove valuable in pathogenic bacteria other than Photorhabdus and are likely to be useful in many others.