The Regulation of Secondary Metabolism in Photorhabdus

A general definition of secondary metabolism is that it consists of the metabolic pathways and the products of metabolism that are not absolutely required for the survival of the organism. Using this definition, it is now well established that Photorhabdus elaborate an extensive secondary metabolism during the post-exponential phase of bacterial growth. This secondary metabolism includes, but is not limited to, the production of light, a stilbene antibiotic and an anthraquinone pigment. In this chapter, the role of secondary metabolism during the life cycle of Photorhabdus will be discussed. Recent work has shown that secondary metabolism in Photorhabdus is required for the mutualistic association between the bacteria and its nematode partner, in particular bacterial secondary metabolism is required to support normal nematode growth and development. An isogenic population of Photorhabdus is phenotypically heterogenous and this facilitates functional partitioning within the population. The relationship between secondary metabolism and the various phenotypic and phase variants that exist in populations of Photorhabdus will also be discussed. Finally, this chapter will also describe the various regulatory nodes that have been identified as being part of the complex regulatory network that is used to control the temporal expression of secondary metabolism in Photorhabdus.