Quorum sensing and host killing in an insect symbiosis

Sodalis praecaptivus is a recently isolated, novel bacterium that was isolated from a wound on the hand of a 71-year-old human patient. Phylogenetic analysis and comparative genomics revealed that this organism is closely related to members of the Sodalis-allied clade of insect endosymbiotic bacteria. This thesis deals with two investigations of this bacterium. The first is a study providing a physiological and biochemical characterization of this organism. The second is an analysis of the relationship between quorum sensing, virulence modulation against an insect host and a novel self-regulatory population control phenomenon in S. praecaptivus. It is proposed that using a population density signal to modulate virulence and growth could allow this organism to balance the need for host invasion against the need to maintain an asymptomatic infection of high density within an insect vector. This would allow the insect vector to transmit S. praecaptivus between potential plant and animal hosts without significant loss of fitness and might be a crucial step in the conversion of free living antecedent bacteria to mutualistic symbionts.