Symbiosis, a term used to describe close associations between two (or more) species, can be characterized by the specific nature of the interaction between partners. Commensal symbionts, thought to be intermediary amid obligate mutualists and facultative parasites, offer insight into forces driving the evolutionary transition into mutualism. The symbionts; Sodalis glossinidius of the tsetse fly (Glossina spp; Diptera: Glossinidae), and SOPE (Sitophilus oryzae Primary Endosymbiont) of the rice weevil (Sitophilus oryzae; Coleoptera: Dryophthoridae), are members of a bacterial clade that have recently established symbiotic relations. Their hosts occupy distinct ecological niches and have evolved to survive on restricted diets of blood for tsetse and cereal for the rice weevil. Using macroarrays developed for the free-living close relative, Escherichia coli, a heterologous array hybridization approach was utilized to infer the genomic compositions of Sodalis and SOPE. Statistically significant differences between the two symbionts were found in the proportion of ORFs coding for carbon compound catabolism (P=0.00009), cell structure (P=0.0073), energy metabolism (P=0.0071), fatty acid metabolism (P=0.0253), and transport (P=0.00004). The greatest reductions occurred in carbon catabolism, membrane proteins, and cell structure related genes for Sodalis and in genes involved in cellular processes for SOPE. Modifications in metabolic pathways, in the form of functional losses complimenting particularities in host physiology and ecology, may have occurred upon initial entry from a free-living to symbiotic state. It is possible that these adaptations, streamlining genomes, act to make a free-living state no longer conceivable for the harnessed microbe.
Species 1: Diptera Glossinidae Glossina morsitans (tsetse fly)
Species 2: Coleoptera Curculionidae Sitophilus oryzae (rice weevil)
Keywords: symbiosis, comparative microbial genomics
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