| Description: |
Sodalis glossinidius (strain morsitans) is a maternally transmitted endosymbiont of tsetse flies and resides primarily intra- and extracellularly in the host midgut and can also be found in hemolymph. Its genome consists of a single circular chromosome and three plasmids. It has a coding capacity of only 51% and contains 972 pseudogenes. Several lines of evidence indicate that Sodalis' association with its host is relatively recent: identical 16S rDNA sequences were obtained from Sodalis from different tsetse hosts, Sodalis can be successfully cultivated on insect cells and subsequently in cell-free medium, SodalisA? genome is much larger than genomes of insect obligate symbionts and finally Sodalis contains more than 1800 functional orthologs to E.coli, a feature indicating that it possesses a large functional repertoire. Sodalis glossinidius seems to have retained a large number of the capabilities of free-living bacteria such as functional pathways for glycolysis, gluconeogenesis, the TCA cycle and the pentose phosphate pathway. It encodes only three intact PEP-carbohydrate phosphotransferase systems and lacks glycolytic enzymes such as galactosidase and glucosidase. The pathways for the synthesis of all amino acids except alanine are present. Many of the genes required for amino acid degradation are missing. It has only five sigma factors and eight signal transduction systems. It seems to rely on the direct transport of heme/haemoglobin via a specific ABC transporter. The ferrous iron transporter FeoA is intact but FeoB is degraded and the global regulator Fur is missing. The chromosome encodes three putative Type-III secretion systems that are present in different clusters, the Sodalis symbiosis regions, referred to as SSR-1, SSR-2 and SSR-3. Despite an apparent lack of motility, ninety flagellar-related genes have been identified in two distinct clusters, the second of which contains 15 pseudogenes. |
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