Documents in support of
statements made in the PhD thesis "Evolutionary divergence of the insect
disease-encoding Serratia plasmid
pADAP" by Thomas Lesley SitterAbstract for the thesisThe larvae of the New Zealand grass-grub (Costelytra givenii), cause significant
damage to New Zealand’s pastures. Two diseases of grass-grub larvae, instigated
by strains of Serratia entomophila and S. proteamaculans, have
been identified and are being used as commercial biocontrol agents. The main virulence determinants of these Serratia strains, an
Anti-feeding-prophage and an ABC-toxin-complex, are encoded on a 153-kb
conjugative plasmid pADAP.
Recently 75 Serratia strains with atypical disease phenology were sequenced
with the goal of defining evolutionary points of divergent between plasmid
variants and define potential co-evolution between plasmid and host.
Phylogenetic analysis of the conserved
plasmid “backbone”, residing between a conserved integrase (Int2) and the end
of a conjugative pili cluster (PilL), revealed clustering of all the S. entomophila plasmids. Within the
predicted backbone region, several intergenic replication and conjugation regions
contained DNA inserts, one of which, positioned between TraG and TraC,
demarcates chronic disease related plasmids from the non-chronic plasmids.
These inserted regions were used as a marker to track the evolutionary
divergence between the plasmids variants.
A key finding was that all
ABC-toxin-complex variants are co-located with a fimbria cluster, eluding to a
role of fimbriae for the proper functionality of the ABC-toxin-complex.
Keywords: Insecticidal
activity, plasmids, evolutionary divergence, horizontal gene transfer,
pan-genome, genome wide association study, grass grub, pADAP, Sep, Afp.
