Raynaud, T. | bioRxiv Science

bioRxiv2021

Community diversity determines the evolution of synthetic bacterial communities under artificial selection

Artificial selection can be conducted at the community level in the laboratory through a differential propagation of the communities according to their level of expression of a targeted function (i.e. community phenotype). Working with communities instead of individuals as selection units brings in additional sources of variation in the considered phenotype that can arise through changes in community structure and influence the outcome of the artificial selection. These sources of variation could even be increased by manipulating species diversity. In this study, we wanted to assess the effect of manipulating initial community richness on artificial selection efficiency, defined as the change in the targeted function over time as compared to a control treatment without artificial selection. We applied artificial selection for a high productivity on synthetic bacterial communities varying for their initial richness level (from one to 16 strains). Our results showed that, overall, the communities that were artificially selected were 16% more productive than the control communities. Community richness positively influenced community productivity and metabolic capacities and was a strong determinant of the dynamics of community evolution. Our results suggested that community richness could influence artificial selection efficiency but a convergence of the community composition might have limited the effect of diversity on artificial selection efficiency. We propose that applying artificial selection on communities varying for their diversity could allow to find communities differing for their level of expression of a function but also for their responsiveness to artificial selection, provided that their initial composition is different enough.

evolutionary biology↗

bioRxiv2021

Changes in wheat rhizosphere microbiota in response to chemical inputs, plant genotype and phenotypic plasticity

Since modern wheat varieties are grown with chemical inputs, we ignore if changes observed in rhizosphere microorganisms between ancient and modern varieties are due to i) breeding-induced changes in plant genotype, ii) modifications of the environment via synthetic chemical inputs, or (iii) phenotypic plasticity, defined as the interaction between the genotype and the environment. In the field, we evaluated the effects of various wheat varieties (modern and ancient) grown with or without chemical inputs (N-fertilizer, fungicide and herbicide together) in a crossed factorial design. We analysed rhizosphere bacteria and fungi by amplicons sequencing and mycorrhizal association by microscopic observations. When considered independently of plant genotype, chemical inputs were responsible for an increase in dominance for bacteria and decrease in evenness for bacteria and fungi. Independently of inputs, modern varieties had richer and more even bacterial communities compared to ancient varieties. Phenotypic plasticity had a significant effect: bacterial and fungal diversity decreased when inputs were applied in ancient varieties but not in modern ones. Mycorrhiza were more abundant in modern than ancient varieties, and less abundant when using chemical inputs. Although neglected, phenotypic plasticity is important to understand the evolution of plant-microbiota associations and a relevant target in breeding programs.

microbiology↗