Sodalis glossinidius

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A Microbial Biorealm page on the genus Sodalis glossinidius

Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales; Enterobacteriaceae (1)

Species

Sodalis glossinidius (1)

Description and significance

Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

Symbiotic lifestyle of S. glossinidius (purple) in a haemocyte of the tsetse fly. Image courtesy of Prof. Sue Welburn, University of Edinburgh.

Sodalis glossinidius is a Gram-negative, rod-shaped, filamentous bacteria. It is one of three endosymbionts for the tsetse fly (Glossina spp.), which are all maternally transmitted to progeny.(6,7) It has a mutualistic relationship with the tsetse fly. This secondary endosymbiont resides inter- and intracellularly in the midgut, fat body and haemolymph of the insect. S. glossinidius was the first true insect endosymbiont to be isolated and cultured, achieved in 1999 using a mosquito (Aedes albopictus) feeder cell culture system and a sample from the haemolymph of Glossinia morsitans morsitans.(7) The type strain M1T was isolated.(7) S. glossinidius can grow intracellularly in Aedes albopictus or axenically in semidefined solid medium containing already enzimatically digested proteins as a nitrogen source. This microaerophilic bacterium grows optimally with 5% oxygen and 95% carbon dioxide at 25 °C. Colony morphology is uniform, with defined edges, and off-white.(7)

The tsetse fly is a vector for Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, parasitic protozoa that cause African trypanosomiasis (commonly known as African Sleeping Sickness), an epidemic fatal disease plaguing sub-Saharan Africa.(9) It is important to have the genome of S. glossinidius sequenced because this bacteria is a key player involved in the host-parasite relationship, possibly enabling the creation of tsetse flies that are incapable of transimtting trypanosomes and thus bringing an end to African sleeping sickness (See Ecology for more details).(6) The genome of S. glossinidius also provides an example of an organism that has undergone degenerative adaptations in order to adopt a mutualistic relationship with its host (See Genome structure for more details).(3)

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?

The genome of Sodalis glossinidius is circular and approximately 2 Mb. S. glossinidius has a relatively inactive biochemical profile compared to other organisms in the family Enterobacteriaceae, likely due to its path away from free-existence.(7,3) Genome reduction and function loss undergone by S. glossinidius is less than other intracellular pathogens and obligate symbionts shown by its ability to be cultured in vitro, but its genome size is still smaller than closely related free-living enterics.(2) This suggests that it is in the process of becoming more dependent on the tsetse host cell. S. glossinidius still retained genes dealing with transcription, translation, regulation, and nucleic acid and amino acid biosynthetic pathways.(2) After hybridization to DNA macroarrays of the closely related Escherichia coli, it was found that S. glossinidius has a chitinase gene and pathogenicity island genes, both of which E. coli lacks.(2) In vitro, colonies of G. m. morsitans were thought to have increased trypanosome susceptibility due to Chitinase production of S. glossinidius.(7) TALK ABOUT PATHOGENIC ISLAND GENES FROM "DEGENERATIVE" ARTICLE. PURPOSE TO INVADE INSECT CELLS

The genome of S. glossinidius has an A+T content of only 45%, whereas endosymbiont genomes are typically AT-rich. The A+T content of intracellular pathogen R. prowazekii is 71% and 75% for the mutualist Buchnera. The AT-rich genomes of intracellular pathogens and obligates may be due to the loss of function of DNA repair and recombination functions, suggesting that S. glossinidius has retained these genes.(2)

In addition to b-N-acetylglucosa (7)


Extrachromosomal DNA consists of contained four circular elements. Three are plasmids, pSG1 (82 kb), pSG2 (27 kb), and pSG4 (11 kb), and the fouth is a bacteriophage-like pSG3 (19 kb) element.(4).


We used a novel approach to gain insight into Sodalis genomic contents, i.e., hybridizing its DNA to macroarrays developed for Escherichia coli, a closely related enteric bacterium. In this analysis we detected 1,800 orthologous genes, corresponding to about 85% of the Sodalis genome. The Sodalis genome has apparently retained its genes for DNA replication, transcription, translation, transport, and the biosynthesis of amino acids, nucleic acids, vitamins, and cofactors. However, many genes involved in energy metabolism and carbon compound assimilation are apparently missing, which may indicate an adaptation to the energy sources available in the only nutrient of the tsetse host, blood. We present gene arrays as a rapid tool for comparative genomics in the absence of whole genome sequence to advance our understanding of closely related bacteria.


Though most organisms of the Family Enterobacteriaceae are able to produce catalase, S. glossinidius is not. This is thought to be why this microbe requires a microaerophilic environment. (7)

Strain M1T did produce a-galactosidase and b-N-acetylglucosaminidase. (7)

S. glossinidius has a relatively inactive biochemical profile compared to other organisms in the family Enterobacteriaceae, likely due to its path away from a free-existence. (7,3)



While the P- and Sendosymbionts of tsetse ¯ies are both members of the family Enterobacteriaceae (c subclass of the class Proteobacteria), each endosymbiont forms a distinct lineage within the family Enterobacteriaceae, sharing high 16S rDNA sequence identity with P- and Sendosymbionts found in other insects (Aksoy et al., 1995). Only the P-endosymbionts show concordant evolution with their insect host, having 16S rDNA sequences which mirror the evolution of the Glossina complex (Aksoy et al., 1997). Tsetse S-endosymbionts isolated from different Glossina spp. share almost identical 16S rDNA sequences, suggesting recent acquisition of these organisms and possible horizontal symbiont transfer (Aksoy et al., 1997)

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Female tsetse fly. Image courtesy of United States Department of Agriculture.


When plated in lab, the beginning of the streak where the inoculum was heavy, produced many large colonies that merged. Toward the end of the streak, where innoculum was thinner, colonies were less abundant smaller colonies. (7) Like other microaerophilic bacteria, S. glossinidius has population-dependent growth where growth rate increases with total respiratory capacity. (7)

about if endosymbionts are gone, larvae cant develop

In the tsetse ¯y (Glossina spp.) P- and S-endosymbionts coexist in the gut lumen, with P-endosymbionts occupying specialized mycetocyte cells in the anterior portion of the insect gut and S-endosymbionts occupying midgut epithelial cells (Huebner & Davey, 1974; Pinnock & Hess, 1974). While the role of each micro-organism has not been clearly de®ned, collectively their presence is known to be essential for egg production and larval development in the insect (Nogge, 1981). Elimination of the bacterial endosymbionts with antibiotics, lysozyme and speci®c antibodies leads to reproductive abnormalities and growth retardation in the aposymbiotic host (Hill & Campbell, 1973; Nogge, 1976, 1978; Pinnock & Hess, 1974; Southwood et al., 1975). (7)


Sodalis glossinidius is one of three endosymbionts of the tsetse fly. [3]

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Sodalis glossinidius does not cause any known diseases. bacterial uptake due to protein secretory system [5]

Sodalis glossinidius, a maternally transmitted endosymbiont of tsetse flies, maintains two phylogenetically distinct type-III secretion systems encoded by chromosomal symbiosis regions designated SSR-1 and SSR-2. Although both symbiosis regions are closely related to extant pathogenicity islands with similar gene inventories, SSR-2 has undergone novel degenerative adaptations in the transition to mutualism. Notably, SSR-2 lacks homologs of genes found in SSR-1 (3) ...mutualism so wouldn't be able to survive in another host to infect.

It has been difficult to study the functional role of the obligate endosymbionts in tsetse, as attempts to eliminate them have resulted in retarded growth of the insect and a decrease in egg production, preventing the aposymbiotic host from reproducing (19, 26, 32). The ability to reproduce, however, could be partially restored when the aposymbiotic flies were given a blood meal supplemented with B-complex vitamins (thiamine, pantothenic acid, pyridoxine, folic acid, and biotin), suggesting that the endosymbionts may play a role in metabolism that involves these compounds (25). While the functional significance of Sodalis is unknown, it has been implicated in the susceptibility of tsetse for trypanosome transmission (2)

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

S. glossinidius has lost much of its biochemical profile.(7) Genetic material for compounds and enzymes have drifted into pseudogene status due its specialized environment, the tsetse fly.(3) There are no known biotechnological benefits to society.

Current Research

Enter summaries of the most recent research here--at least three required

Some of the recent research on Sodalis glossinidius:

"The endosymbionts of tsetse flies: manipulating host–parasite interactions" [6]




References

1. "Sodalis glossinidius". NCBI Taxonomy Browser. 26 August 2007. [1]

2. Akman, L., Rio, R., Beard, C., and Aksoy, S. “Genome Size Determination and Coding Capacity of Sodalis glossinidius, an Enteric Symbiont of Tsetse Flies, as Revealed by Hybridization to Escherichia coli Gene Arrays.” Journal of Bacteriology. 2001. Volume 183.15 p. 4517-4525.[2]

3. Dale, C., Jones, T., and Pontes, M. "Degenerative Evolution and Functional Diversification of Type-III Secretion Systems in the Insect Endosymbiont Sodalis glossinidius." Molecular Biology and Evolution. 2005. Volume 22.3 p. 758-766. [3]

4. Darby, A., Lagnel, J., Matthew, C., Bourtzis, K., Maudlin, I., and Welburn, S. "Extrachromosomal DNA of the Symbiont Sodalis glossinidius." Journal of Bacteriology. 2005. Volume 187.14 p. 5003-5007. [4]

5. Collazo, C., and Galán, J. "The invasion-associated type-III protein secretion system in Salmonella – a review." Gene. 1997. Volume 192.1 p. 51-59. [5]

6. Dale, C., and Welburn, S. "The endosymbionts of tsetse flies: manipulating host–parasite interactions." International Journal for Parasitology. 2001. Volume 31.5-6 p. 627-630. [6]

7. Dale, C., and Maudlin, I. "Sodalis gen. nov. and Sodalis glossinidius sp. nov., a microaerophilic secondary endosymbiont of the tsetse fly Glossina morsitans morsitans." International Journal of Systematic Bacteriology. 1999. Volume 49 p. 267–275. [7]

8. Aksoy, S., and Rio, R. "Interactions among multiple genomes: Tsetse, its symbionts and trypanosomes." Insect Biochemistry and Molecular Biology. 2005. Volume 35.7 p. 691-698. [8]

9. Maudlin, I. "African trypanosomiasis." Annals of Tropical Medicine & Parasitology. 2006. Volume 11.8 p. 679–701. [9]

10. Toh, H., Weiss, B., Perkin, S., Yamashita, A., Oshima, K., Hattori, M., and Aksoy, S. "Massive genome erosion and functional adaptations provide insights into the symbiotic lifestyle of 'Sodalis glossinidius in the tsetse host." Genome Research. 2006. Volume 16 p. 149-156. [10]

Edited by Janet Melnyk, student of Rachel Larsen