Massive genome erosion and functional adaptations provide insights into the symbiotic lifestyle of Sodalis glossinidius in the tsetse host

Abstract

Sodalis glossinidius is a maternally transmitted endosymbiont of tsetse flies (Glossina spp.), an insect of medical and veterinary significance. Analysis of the complete sequence of Sodalis' chromosome (4,171,146 bp, encoding 2,432 protein coding sequences) indicates a reduced coding capacity of 51%. Furthermore, the chromosome contains 972 pseudogenes, an inordinately high number compared with that of other bacterial species. A high proportion of these pseudogenes are homologs of known proteins that function either in defense or in the transport and metabolism of carbohydrates and inorganic ions, suggesting Sodalis' degenerative adaptations to the immunity and restricted nutritional status of the host. Sodalis possesses three chromosomal symbiosis regions (SSR): SSR-1, SSR-2, and SSR-3, with gene inventories similar to the Type-III secretion system (TTSS) ysa from Yersinia enterolitica and SPI-1 and SPI-2 from Salmonella, respectively. While core components of the needle structure have been conserved, some of the effectors and regulators typically associated with these systems in pathogenic microbes are modified or eliminated in Sodalis. Analysis of SSR-specific invA transcript abundance in Sodalis during host development indicates that the individual symbiosis regions may exhibit different temporal expression profiles. In addition, the Sodalis chromosome encodes a complete flagella structure, key components of which are expressed in immature host developmental stages. These features may be important for the transmission and establishment of symbiont infections in the intra-uterine progeny. The data suggest that Sodalis represents an evolutionary intermediate transitioning from a free-living to a mutualistic lifestyle.

Genome streamlining and chemical defense in a coral reef symbiosis

“…Genome reduction appears to be at a much later stage than other low-density genomes, such as the mutualist Sodalis glossinidius, which has a coding density of 51% but a much larger genome than Ca. E. faulkneri (4.2 Mbp vs. 1.48 Mbp) (25). Although S. glossinidius contains many pseudogenes with homology to known proteins (25), Ca.…”

Sexual acquisition of beneficial symbionts in aphids

“…For example, tsetse, the vector of African trypanosome, harbors a symbiont, Sodalis glossinidius, with similarities to the symbionts in this study: it is within the Enterobacteriaceae, possesses type III secretion systems (25), establishes heritable infections after artificial transfer by microinjection (26), and undergoes horizontal transmission among matrilines through an unidentified mechanism (27). Sodalis glossinidia affects vector competency (28), and introduction of trypanosome-incompatible strains has been proposed as a means of reducing vector efficiency.…”

Reductive genome evolution, host–symbiont co-speciation and uterine transmission of endosymbiotic bacteria in bat flies

“…Among them, the endosymbiotic system in tsetse flies, consisting of an obligate endosymbiont W. glossinidia in a midgut-associated bacteriome (Aksoy, 1995) and a facultative endosymbiont Sodalis glossinidius (Dale and Maudlin, 1999), is the best studied, reflecting their medical importance as trypanosome vectors (Aksoy, 2000;Aksoy and Rio, 2005). The complete genome sequences of Wigglesworthia and Sodalis have already been determined (Akman et al, 2002;Toh et al, 2006). By contrast, much less attention has been paid to the endosymbiotic systems of hippoboscids, streblids and nycteribiids (Dale et al, 2006;Trowbridge et al, 2006;Nováková et al, 2009), except for early histological descriptions (Roubaud, 1919;Zacharias, 1928;Aschner, 1931;Buchner, 1965).…”