Project description:Sodalis praecaptivus is a close relative and putative environmental progenitor of the widely distributed, insect-associated, Sodalis-allied symbionts. Mutant strains of S. praecaptivus, lacking critical components of a quorum sensing (QS) apparatus acquire a rapid and potent killing phenotype following microinjection into an insect host. Transcriptomic and genetic analyses indicate that insect killing occurs as a consequence of virulence factors, including insecticidal toxins and enzymes that degrade the insect integument that are normally repressed by QS at high infection densities. This unorthodox method of regulation ensures that virulence factors are only utilized to initiate the insect-bacterial association. Once bacteria reach a sufficient infection density in host tissues, the QS circuit represses the expression of these harmful genes, facilitating a long-lasting and benign association. We discuss the implications of the functionality of this QS system in the context of the establishment and evolution of mutualistic relationships involving these bacteria.
Project description:The majority of bacterial genomes have high coding efficiencies, but there are an few genomes of the intracellular bacteria that have low gene density. The genome of the endosymbiont Sodalis glossinidius contains almost 50% pseudogenes containing mutations that putatively silence them at the genomic level. We have applied multiple omic strategies: combining single molecule DNA-sequencing and annotation; stranded RNA-sequencing and proteome analysis to better understand the transcriptional and translational landscape of Sodalis pseudogenes, and potential mechanisms for their control. Between 53% and 74% of the Sodalis transcriptome remains active in cell-free culture. Mean sense transcription from Coding Domain Sequences (CDS) is four-times greater than that from pseudogenes. Core-genome analysis of six Illumina sequenced Sodalis isolates from different host Glossina species shows pseudogenes make up ~40% of the 2,729 genes in the core genome, suggesting are stable and/or Sodalis is a recent introduction across the Glossina genus as a facultative symbiont. These data further shed light on the importance of transcriptional and translational control in deciphering host-microbe interactions, and demonstrate that pseudogenes are more complex than a simple degrading DNA sequence. For this reason, we show that combining genomics, transcriptomics and proteomics represents an important resource for studying prokaryotic genomes with a view to elucidating evolutionary adaptation to novel environmental niches.
