Metabolic Basis for Mutualism between Gut Bacteria and Its Impact on the Drosophila melanogaster Host

Abstract

Interactions between species shape the formation and function of microbial communities. In the gut microbiota of animals, cross-feeding of metabolites between microbes can enhance colonization and influence host physiology. We examined a mutually beneficial interaction between two bacteria isolated from the gut microbiota ofDrosophila, i.e.,Acetobacter fabarumandLactobacillus brevis. After developing anin vitrococulture assay, we utilized a genetic screen to identifyA. fabarumgenes required for enhanced growth withL. brevis. The screen, and subsequent genetic analyses, showed that the gene encoding pyruvate phosphate dikinase (ppdK) is required forA. fabarumto benefit fully from coculture. By testing strains with mutations in a range of metabolic genes, we provide evidence thatA. fabarumcan utilize multiple fermentation products ofL. brevis. Mutualism between the bacteriain vivoaffects gnotobioticDrosophila melanogaster; flies associated withA. fabarumandL. brevisshowed >1,000-fold increases in bacterial cell density and significantly lower triglyceride storage than monocolonized flies. Mutation ofppdKdecreasedA. fabarumdensity in flies cocolonized withL. brevis, consistent with the model in whichAcetobacteremploys gluconeogenesis to assimilateLactobacillusfermentation products as a source of carbonin vivo. We propose that cross-feeding between these groups is a common feature of microbiota inDrosophila.IMPORTANCEThe digestive tracts of animals are home to a community of microorganisms, the gut microbiota, which affects the growth, development, and health of the host. Interactions among microbes in this inner ecosystem can influence which species colonize the gut and can lead to changes in host physiology. We investigated a mutually beneficial interaction between two bacterial species from the gut microbiota of fruit flies. By coculturing the bacteriain vitro, we were able to identify a metabolic gene required for the bacteria to grow better together than they do separately. Our data suggest that one species consumes the waste products of the other, leading to greater productivity of the microbial community and modifying the nutrients available to the host. This study provides a starting point for investigating how these and other bacteria mutually benefit by sharing metabolites and for determining the impact of mutualism on host health.

Metabolic cross-feeding allows a gut microbial community to overcome detrimental diets and alter host behaviour

“…In the tested flies the number of both Ap and Lp cells was consistently higher in the co-culture conditions when compared to the bacterial load in flies inoculated with each of the bacteria alone ( Figure 1B and 1C and Figure S1B and S1C). This is in agreement with other reports showing synergistic effects in bacterial growth of Acetobacter and Lactobacillus species in Drosophila Sommer and Newell, 2019). Interestingly, the increase in bacterial load when the microbes were co-cultured was observed in the complete medium and the media lacking Ile or His ( Figure 1B and 1C and Figure S1B and S1C).…”

“…One such niche is the adult Drosophila gut where Acetobacteracaea and Lactobacilli are often found together (Pais et al, 2018;Ren et al, 2007;Ryu et al, 2008;Wong et al, 2011). The co-occurrence of bacteria from these two genera in the fly has been shown to increase the propagation of both bacteria and to contribute to the impact of the microbiome on physiological traits of the host (Gould et al, 2018;Sommer and Newell, 2019). Although lactate has been proposed to play a role in these interactions (Sommer and Newell, 2019) the mechanisms that promote and sustain bacterial growth in co-cultures and how they modify the host remain largely unexplored.…”

“…The co-occurrence of bacteria from these two genera in the fly has been shown to increase the propagation of both bacteria and to contribute to the impact of the microbiome on physiological traits of the host (Gould et al, 2018;Sommer and Newell, 2019). Although lactate has been proposed to play a role in these interactions (Sommer and Newell, 2019) the mechanisms that promote and sustain bacterial growth in co-cultures and how they modify the host remain largely unexplored. Lactobacilli lack many key genes required for the synthesis of different essential nutrients such as AAs and vitamins Wu et al, 2017).…”

Metabolic cooperation among commensal bacteria supportsDrosophilajuvenile growth under nutritional stress

“…Studies have previously shown that cooperation among the gut microbes can 560 influence other aspects of Drosophila physiology. For example, multiple fermentation products of L. brevis foster the growth of A. fabarum on a fly diet leading to depletion of dietary glucose, consequently triggering reduced TAG levels in the adult host (Newell and Douglas, 2014;Sommer and Newell, 2018). Moreover, multi-microbe interactions among the Acetobacter, Lactobacillus species and yeast were shown to influence additional adult traits such as olfaction and egg laying behavior (Fischer et al, 2017), food choice behavior (Leitão-Gonçalves et al, 2017), lifespan and fecundity (Gould et al, 2018) and immunity (Fast et al, 2020).…”

Drosophila as a model for the gut microbiome

“…Microbiome impacts on the host may result from direct effects of the individual bacterial species or from interactions between them. Interactions between Lactobacillus and Acetobacter species affect fly fat content [33], and genes involved in lactate and acetoin metabolism underlie the bacterial mutualism [34]. The ease of generating gnotobiotic flies and modularity of the fly-microbiome facilitates combinatorial studies to explore the impacts of complexity.…”