ABSTRACTThe tsetse fly is the insect vector for theTrypanosoma bruceiparasite, the causative agent of human African trypanosomiasis. The colonization and spread of the trypanosome correlate positively with the presence of a secondary symbiotic bacterium,Sodalis glossinidius. The metabolic requirements and interactions of the bacterium with its host are poorly understood, and herein we describe a metabolic model ofS. glossinidiusmetabolism. The model enabled the design and experimental verification of a defined medium that supportsS. glossinidiusgrowthex vivo. This has been used subsequently to analyzein vitroaspects ofS. glossinidiusmetabolism, revealing multiple unique adaptations of the symbiont to its environment. Continued dependence on a sugar, and the importance of the chitin monomerN-acetyl-d-glucosamine as a carbon and energy source, suggests adaptation to host-derived molecules. Adaptation to the amino acid-rich blood diet is revealed by a strong dependence onl-glutamate as a source of carbon and nitrogen and by the ability to rescue a predictedl-arginine auxotrophy. Finally, the selective loss of thiamine biosynthesis, a vitamin provided to the host by the primary symbiontWigglesworthia glossinidia, reveals an intersymbiont dependence. The reductive evolution ofS. glossinidiusto exploit environmentally derived metabolites has resulted in multiple weaknesses in the metabolic network. These weaknesses may become targets for reagents that inhibitS. glossinidiusgrowth and aid the reduction of trypanosomal transmission.IMPORTANCEHuman African trypanosomiasis is caused by theTrypanosoma bruceiparasite. The tsetse fly vector is of interest for its potential to prevent disease spread, as it is essential forT. bruceilife cycle progression and transmission. The tsetse’s mutualistic endosymbiontSodalis glossinidiushas a link to trypanosome establishment, providing a disease control target. Here, we describe a new, experimentally verified model ofS. glossinidiusmetabolism. This model has enabled the development of a defined growth medium that was used successfully to test aspects ofS. glossinidiusmetabolism. We presentS. glossinidiusas uniquely adapted to life in the tsetse, through its reliance on the blood diet and host-derived sugars. Additionally,S. glossinidiushas adapted to the tsetse’s obligate symbiontWigglesworthia glossinidiaby scavenging a vitamin it produces for the insect. This work highlights the use of metabolic modeling to design defined growth media for symbiotic bacteria and may provide novel inhibitory targets to block trypanosome transmission.
Enantiospecific antitrypanosomal in vitro activity of eflornithine
