Transposon Mutagenisis of Serratia marcescens strain SCBI, a Nematode Symbiont that Enables Insect Killing

Abstract

Entomopathogenic relationships are studied to be used as biological controls, and also more generally to study the evolution of bacteria-host relationships. Since entomopathogenic nematodes are efficient insect larva parasitoids, they could be used to target crop pests. This relationship is very unique with less than 30 known partnerships. So a better understanding of entomopathogenic relationships would greatly benefit the agricultural and biological controls communities.

An Entomopathogenic relationship is a symbiotic relationship between nematodes and bacteria. The ability to swarm has been found to be important to bacteria-nematode relationships. Quorum sensing is the main communication route for bacterial colonies and in the swarming ability of a colony. Quorum sensing has been found to be essential to entomopathogenic relationships.

To better understand the specifics of this relationship, the genetic and physical requirements for an entomopathogenic relationship must be better understood. Serratia marcescens strain South African Caenorhabditis briggsae (SCBI) is a bacterium that is associated with nematodes. Strain SCBI can either form a pathogenic relationship with Caenorhabditis or an entomopathogenic relationship. The goal of this study was to use transposon mutagenesis to create a library of random Strain SCBI mutants to identify bacterial factors critical for the relationship. From these mutants, the swarming ability of the mutants was tested to then infect the nematodes to visualize the effects of the mutations on the relationship. We used a mini-Himar vector to insert a transposon randomly into the Strain SCBI genome, with the long-range goal of collecting 10,000 mutants.