Question

What are the names of the endosymbionts found in Tsetse flies and what role do they have in Tsetse fly biology?

Answer 1

Tsetse flies carry 3 maternally-transmitted endosymbionts as well as a salivary gland-associated DNA virus.

• The first of these symbionts is the obligate mutualist Wigglesworthia.

Wigglesworthia provides two well-documented functional benefits to its tsetse host. The first benefit is nutritional, as in the absence of this bacterium, intrauterine larval development is stunted and progeny are aborted. Wigglesworthia's contracted genome encodes an unusually high number of putative vitamin biosynthesis pathways. More than 10% of the retained CDSs are involved in the biosynthesis of cofactors, prosthetic groups and carriers, supporting Wigglesworthia's genetic contributions to de novo metabolism of biotin, thiazole, lipoic acid, FAD (riboflavin, B2), folate, pantothenate, thiamine (B1), pyridoxine (B6), and protoheme. This genotypic feature supports the theory that Wigglesworthia supplements its tsetse host with nutritious metabolites that are naturally present at low titers in vertebrate blood.

Wigglesworthia's second function in tsetse is immunological. When flies undergo intrauterine larval development in the absence of this bacterium they present a severely compromised immune system during adulthood. Under these conditions, Wigglesworthia-free tsetse are unusually susceptible to infection with normally non-pathogenic E. coli K12 and trypanosomes.

• Tsetse's second endosymbiont is the commensal Sodalis, which is a gram-negative organism closely related to free-living microbes within the Enterobacteriacaea.

Sodalis lacks a clearly defined functional role within its tsetse host as several natural tsetse populations lack this bacterium, suggesting that it presents a truly commensal phenotype within its tsetse host. However, Sodalis may play a role in tsetse's ability to vector pathogenic trypanosomes. Sodalis has been reported to increase tsetse's susceptibility to trypanosomes by obstructing the trypanocidal activity of host midgut lectins. Thus, Sodalis appears to favor the establishment of trypanosome infections in tsetse.

• Some tsetse populations also harbor a parasitic bacterium from the genus Wolbachia.

Wolbachia is a wide spread alpha-proteobacteria endosymbiont, infecting approximately 70% insects. It is transmitted transovarially via germ line cells. This bacterium manipulates the reproductive biology of its host through a variety of mechanisms, including cytoplasmic incompatibility (CI), male killing, feminization and parthenogenesis. Expression of CI occurs when a Wolbachia infected male mates with an uninfected female, causing developmental arrest during embryogenesis. In contrast, Wolbachia infected females can mate with uninfected males, or with a male infected with the same Wolbachia strain, and produce viable offspring.