Vitamin B ₆ Generated by Obligate Symbionts Is Critical for Maintaining Proline Homeostasis and Fecundity in Tsetse Flies

Abstract

bThe viviparous tsetse fly utilizes proline as a hemolymph-borne energy source. In tsetse, biosynthesis of proline from alanine involves the enzyme alanine-glyoxylate aminotransferase (AGAT), which requires pyridoxal phosphate (vitamin B 6 ) as a cofactor. This vitamin can be synthesized by tsetse's obligate symbiont, Wigglesworthia glossinidia. In this study, we examined the role of Wigglesworthia-produced vitamin B 6 for maintenance of proline homeostasis, specifically during the energetically expensive lactation period of the tsetse's reproductive cycle. We found that expression of agat, as well as genes involved in vitamin B 6 metabolism in both host and symbiont, increases in lactating flies. Removal of symbionts via antibiotic treatment of flies (aposymbiotic) led to hypoprolinemia, reduced levels of vitamin B 6 in lactating females, and decreased fecundity. Proline homeostasis and fecundity recovered partially when aposymbiotic tsetse were fed a diet supplemented with either yeast or Wigglesworthia extracts. RNA interference-mediated knockdown of agat in wild-type flies reduced hemolymph proline levels to that of aposymbiotic females. Aposymbiotic flies treated with agat short interfering RNA (siRNA) remained hypoprolinemic even upon dietary supplementation with microbial extracts or B vitamins. Flies infected with parasitic African trypanosomes display lower hemolymph proline levels, suggesting that the reduced fecundity observed in parasitized flies could result from parasite interference with proline homeostasis. This interference could be manifested by competition between tsetse and trypanosomes for vitamins, proline, or other factors involved in their synthesis. Collectively, these results indicate that the presence of Wigglesworthia in tsetse is critical for the maintenance of proline homeostasis through vitamin B 6 production.

Arsenophonus and Sodalis Symbionts in Louse Flies: an Analogy to the Wigglesworthia and Sodalis System in Tsetse Flies

“…This uncertainty further highlights our limited knowledge on symbiotic systems of blood feeders. Unlike the symbiotic associations in sap-sucking insects (where symbionts provide their hosts with wellknown sets of essential amino acids [59]), it is still quite unclear which B vitamins are provided to blood-sucking hosts and which are needed only for symbionts, with the exception of pyridoxine and thiamine provisioning in the tsetse fly model (11,14,15).…”

“…The two principal symbionts are the obligate mutualist Wigglesworthia glossinidia, housed intracellularly within a bacteriome organ adjacent to the anterior midgut (7), and a facultative symbiont, Sodalis glossinidius, present in almost all tissues (8). Both symbionts are vertically transmitted via milk glands (7,9,10) and are presumed to compensate for the nutritionally unbalanced blood diet (11)(12)(13)(14)(15). This highly specific microbiome of tsetse flies is usually accompanied by reproductive manipulators from the genus Wolbachia (16) and a diversity of other transient bacteria of unknown relationship to the host (17,18).…”

Antimicrobial peptides and cell processes tracking endosymbiont dynamics

“…Particularly frequent in species thriving on nutritionally unbalanced environments, such endosymbioses are believed to impact several aspects of host biology, including physiology, immunity and reproduction [2][3][4][5][6][7][8]. They ensure a nutritional complementation of the host diet by providing vitamins and essential amino acids [3,7,9,10], thus greatly improving host fitness [2,3,7,11,12].…”

A novel intracellular mutualistic bacterium in the invasive antCardiocondyla obscurior

“…Nutrient-providing symbionts are commonly found in hosts with restricted diets, for example, aphids feeding on phloem sap (Baumann, 2005), blood-feeding diptera (Wang et al, 2013) or grain weevils (Heddi et al, 1999). Symbionts can provide essential amino acids, vitamins or help in nitrogen recycling (Nakabachi et al, 2005;Feldhaar et al, 2007;Michalkova et al, 2014;Patino-Navarrete et al, 2014). Such bacteria are commonly harbored in bacteriocytes, specialized host cells that sometimes form special organ-like structures, the bacteriomes (Baumann, 2005) or are confined to the insect gut (Engel and Moran, 2013).…”

“…Such bacteria are commonly harbored in bacteriocytes, specialized host cells that sometimes form special organ-like structures, the bacteriomes (Baumann, 2005) or are confined to the insect gut (Engel and Moran, 2013). Provisioning with nutrients can lead to increased fitness (Michalkova et al, 2014), which may enable invasive species to exploit novel habitats or food sources (Feldhaar, 2011).…”