Comparative Genomics of Insect-Symbiotic Bacteria: Influence of Host Environment on Microbial Genome Composition

Abstract

Commensal symbionts, thought to be intermediary amid obligate mutualists and facultative parasites, offer insight into forces driving the evolutionary transition into mutualism. Using macroarrays developed for a close relative, Escherichia coli, we utilized a heterologous array hybridization approach to infer the genomic compositions of a clade of bacteria that have recently established symbiotic associations: Sodalis glossinidius with the tsetse fly (Diptera, Glossina spp.) and Sitophilus oryzae primary endosymbiont (SOPE) with the rice weevil (Coleoptera, Sitophilus oryzae). Functional biologies within their hosts currently reflect different forms of symbiotic associations. Their hosts, members of distant insect taxa, occupy distinct ecological niches and have evolved to survive on restricted diets of blood for tsetse and cereal for the rice weevil. Comparison of genome contents between the two microbes indicates statistically significant differences in the retention of genes involved in carbon compound catabolism, energy metabolism, fatty acid metabolism, and transport. The greatest reductions have occurred in carbon catabolism, membrane proteins, and cell structure-related genes for Sodalis and in genes involved in cellular processes (i.e., adaptations towards cellular conditions) for SOPE. Modifications in metabolic pathways, in the form of functional losses complementing particularities in host physiology and ecology, may have occurred upon initial entry from a free-living to a symbiotic state. It is possible that these adaptations, streamlining genomes, act to make a free-living state no longer feasible for the harnessed microbe.

Two Tsetse Fly Species, Glossina palpalis gambiensis and Glossina morsitans morsitans , Carry Genetically Distinct Populations of the Secondary Symbiont Sodalis glossinidius

“…‫,ء‬ primer labeled for detection. related microorganisms, in agreement with hypotheses on the origin and evolution of S. glossinidius (24).…”

“Wigglesworthia morsitans” Folate (Vitamin B 9 ) Biosynthesis Contributes to Tsetse Host Fitness

“…Research on ancient obligate host associations (i.e., in which bacteria display an extensive concordant evolution with their host) has demonstrated that microbial symbiont genome evolution can be influenced by microbial community dynamics (1)(2)(3)(4)(5)(6), in addition to host physiology and ecology (7)(8)(9). One extreme case has been described within the mealybug, where dual symbiont species and the host have retained complementary loci that, only when integrated as a symbiotic system (i.e., a holobiont) and not as individual species, are capable of producing specific requisite nutrients (3,9).…”

Interspecific Transfer of Bacterial Endosymbionts between Tsetse Fly Species: Infection Establishment and Effect on Host Fitness

“…However, the large number of pseudogenes (972) present on the Sodalis chromosome, in conjunction with an unusually low protein coding density (49.2%), may represent early genome erosion events during the course of symbiosis as the organism adapted to its host's physiological environment (1,35). Using Escherichia coli macroarrays, Rio et al (30) utilized a heterologous array hybridization approach to determine that significant differences exist between the genomes of Sodalis and another, closely related symbiotic bacterium (Sitophilus oryzae primary endosymbiont [SOPE]) from the rice weevil (18). These differences may account for the fact that each organism has adapted to the unique nutritional requirements of its host.…”