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Vitamin B6 generated by obligate symbionts is critical for maintaining proline homeostasis and fecundity in tsetse flies.

ABSTRACT: The 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 B6) 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 B6 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 B6 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 B6 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 B6 production.

SUBMITTER: Michalkova V

PROVIDER: S-EPMC4178588 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Vitamin B6 generated by obligate symbionts is critical for maintaining proline homeostasis and fecundity in tsetse flies.

Michalkova Veronika V Benoit Joshua B JB Weiss Brian L BL Attardo Geoffrey M GM Aksoy Serap S

Applied and environmental microbiology 20140718 18

The 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 B6) 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 B6 for maintenance of proline homeostasis, specifically during the energetically exp ...[more]

PMID: 25038091

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Project description:Beneficial microbial symbionts serve important functions within their hosts, including dietary supplementation and maintenance of immune system homeostasis. Little is known about the mechanisms that enable these bacteria to induce specific host phenotypes during development and into adulthood. Here we used the tsetse fly, Glossina morsitans, and its obligate mutualist, Wigglesworthia glossinidia, to investigate the co-evolutionary adaptations that influence the development of host physiological processes. Wigglesworthia is maternally transmitted to tsetse's intrauterine larvae through milk gland secretions. We can produce flies that lack Wigglesworthia (Gmm(Wgm-) yet retain their other symbiotic microbes. Such offspring give rise to adults that exhibit a largely normal phenotype, with the exception being that they are reproductively sterile. Our results indicate that when reared under normal environmental conditions Gmm(Wgm-) adults are also immuno-compromised and highly susceptible to hemocoelic E. coli infections while age-matched wild-type individuals are refractory. Adults that lack Wigglesworthia during larval development exhibit exceptionally compromised cellular and humoral immune responses following microbial challenge, including reduced expression of genes that encode antimicrobial peptides (cecropin and attacin), hemocyte-mediated processes (thioester-containing proteins 2 and 4 and prophenoloxidase), and signal-mediating molecules (inducible nitric oxide synthase). Furthermore, Gmm(Wgm-) adults harbor a reduced population of sessile and circulating hemocytes, a phenomenon that likely results from a significant decrease in larval expression of serpent and lozenge, both of which are associated with the process of early hemocyte differentiation. Our results demonstrate that Wigglesworthia must be present during the development of immature progeny in order for the immune system to function properly in adult tsetse. This phenomenon provides evidence of yet another important physiological adaptation that further anchors the obligate symbiosis between tsetse and Wigglesworthia.

Project description:Symbiosis between insects and bacteria result in a variety of arrangements, genomic modifications, and metabolic interconnections. Here, we present genomic, phylogenetic, and morphological characteristics of a symbiotic system associated with Melophagus ovinus, a member of the blood-feeding family Hippoboscidae. The system comprises four unrelated bacteria representing different stages in symbiosis evolution, from typical obligate mutualists inhabiting bacteriomes to freely associated commensals and parasites. Interestingly, the whole system provides a remarkable analogy to the association between Glossina and its symbiotic bacteria. In both, the symbiotic systems are composed of an obligate symbiont and two facultative intracellular associates, Sodalis and Wolbachia. In addition, extracellular Bartonella resides in the gut of Melophagus. However, the phylogenetic origins of the two obligate mutualist symbionts differ. In Glossina, the mutualistic Wigglesworthia appears to be a relatively isolated symbiotic lineage, whereas in Melophagus, the obligate symbiont originated within the widely distributed Arsenophonus cluster. Although phylogenetically distant, the two obligate symbionts display several remarkably similar traits (e.g., transmission via the host's "milk glands" or similar pattern of genome reduction). To obtain better insight into the biology and possible role of the M. ovinus obligate symbiont, "Candidatus Arsenophonus melophagi," we performed several comparisons of its gene content based on assignments of the Cluster of Orthologous Genes (COG). Using this criterion, we show that within a set of 44 primary and secondary symbionts, "Ca. Arsenophonus melophagi" is most similar to Wigglesworthia. On the other hand, these two bacteria also display interesting differences, such as absence of flagellar genes in Arsenophonus and their presence in Wigglesworthia. This finding implies that a flagellum is not essential for bacterial transmission via milk glands.

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Project description:Purpose: The aim was, in the frame of an anti-vector strategy, to use such genes to control Human and/or animal trypanosomiasis. The present objective was to verify whether field tsetse fly gene expression was modified in response to natural infection with trypanosomes as it was when insectary-raised flies were experimentally infected. Method: mRNA from 10 samples of Glossina palpalis (5 non-infected and 5 infected by Trypanosoma congolense s.l.) were sequenced on a high-output flow cell (400M clusters) using the NextSeq® 500/550 High Output v2 150 cycles kit (Illumina), in paired-end 75/75nt mode. The sequenced reads that passed quality filter were mapped onto the genome with the local alignment algorithm subread-align (Liao et al., 2013). Differential analysis was done with the SARTools R package (Varet et al., 2016), which runs separately DESeq2 (Love et al., 2014) and egdeR (Robinson et al., 2010). We identified orthologs between Glossina and Drosophila based on the identification of bidirectional best hits (BBH) using blastp (Altschul et al., 1997), and then made functional enrichment and pathway mapping of these DEGs. Results: Using the RNA-seq approach, differentially expressed genes (DEGs) have been identified in infected versus non-infected tsetse flies, including down-regulated genes and up-regulated genes. Some of the genes, whether down- or up-regulated, were very highly differentially expressed. Down-regulated genes were mainly involved in transcription/translation processes, while up-regulated encoded genes governing amino acid and nucleotide biosynthesis pathways. The data on the molecular cross-talk between the host and the parasite (and the fly microbiome that is always present) recorded when using an experimental biological model have its counterpart in field flies which in turn validates the use of experimental host/parasite couples. Conclusion: This study is the first evaluation of transcriptomic mechanisms related to infection in field tsetse flies. This opens up prospects for vector-based control strategies, and more precisely the blocking of transmission.

Dataset Information

Vitamin B6 generated by obligate symbionts is critical for maintaining proline homeostasis and fecundity in tsetse flies.

Publications

Vitamin B6 generated by obligate symbionts is critical for maintaining proline homeostasis and fecundity in tsetse flies.

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