Microbiome interactions shape host fitness

Area of Science:

• Microbiology
• Ecology
• Genetics

Background:

• Gut bacteria influence host fitness traits like development, reproduction, and lifespan.
• The host also shapes its gut microbiome composition.
• The relative importance of individual bacterial species versus their interactions on host fitness remains unclear.

Purpose of the Study:

• To investigate the extent to which bacterial species interactions, rather than individual species, shape host fitness.
• To understand the role of microbial community interactions in mediating life history tradeoffs in *Drosophila melanogaster*.

Main Methods:

• Germ-free *Drosophila melanogaster* were colonized with all possible combinations of five core gut bacterial species.
• Bacterial community abundances and host fitness traits (development, reproduction, lifespan) were measured.
• Mathematical frameworks adapted from genetic epistasis were used to quantify the impact of bacterial interactions on host fitness.

Main Results:

• Bacterial diversity accelerated development, reproduction, and aging, revealing a tradeoff where increased reproduction led to shorter lifespan.
• Host lifespan and microbiome abundances were highly sensitive to interactions between bacterial species.
• Higher-order interactions (3-5 species) were prevalent (13-44%) and affected multiple traits, reflecting life history tradeoffs.

Conclusions:

• Bacterial interactions within the gut microbiome are critical determinants of host fitness, comparable in importance to individual species.
• These interactions are context-dependent and drive life history tradeoffs, influencing multiple host traits simultaneously.
• Understanding microbial community dynamics, particularly inter-species interactions, is essential for comprehending host-microbiome relationships.