Synthetic community derived from grafted watermelon rhizosphere provides protection for ungrafted watermelon against Fusarium oxysporum via microbial synergistic effects.

BACKGROUND: Plant microbiota contributes to plant growth and health, including enhancing plant resistance to various diseases. Despite remarkable progress in understanding diseases resistance in plants, the precise role of rhizosphere microbiota in enhancing watermelon resistance against soil-borne diseases remains unclear. Here, we constructed a synthetic community (SynCom) of 16 core bacterial strains obtained from the rhizosphere of grafted watermelon plants. We further simplified SynCom and investigated the role of bacteria with synergistic interactions in promoting plant growth through a simple synthetic community. RESULTS: Our results demonstrated that the SynCom significantly enhanced the growth and disease resistance of ungrafted watermelon grown in non-sterile soil. Furthermore, analysis of the amplicon and metagenome data revealed the pivotal role of Pseudomonas in enhancing plant health, as evidenced by a significant increase in the relative abundance and biofilm-forming pathways of Pseudomonas post-SynCom inoculation. Based on in vitro co-culture experiments and bacterial metabolomic analysis, we selected Pseudomonas along with seven other members of the SynCom that exhibited synergistic effects with Pseudomonas. It enabled us to further refine the initially constructed SynCom into a simplified SynCom comprising the eight selected bacterial species. Notably, the plant-promoting effects of simplified SynCom were similar to those of the initial SynCom. Furthermore, the simplified SynCom protected plants through synergistic effects of bacteria. CONCLUSIONS: Our findings suggest that the SynCom proliferate in the rhizosphere and mitigate soil-borne diseases through microbial synergistic interactions, highlighting the potential of synergistic effects between microorganisms in enhancing plant health. This study provides a novel insight into using the functional SynCom as a promising solution for sustainable agriculture. Video Abstract.

Active microbial population dynamics and life strategies drive the enhanced carbon use efficiency in high-organic matter soils.

Microbial carbon use efficiency (CUE) is a critical parameter that controls carbon storage in soil, but many uncertainties remain concerning adaptations of microbial communities to long-term fertilization that impact CUE. Based on H218O quantitative stable isotope probing coupled with metagenomic sequencing, we disentangled the roles of active microbial population dynamics and life strategies for CUE in soils after a long-term (35 years) mineral or organic fertilization. We found that the soils rich in organic matter supported high microbial CUE, indicating a more efficient microbial biomass formation and a greater carbon sequestration potential. Organic fertilizers supported active microbial communities characterized by high diversity and a relative increase in net growth rate, as well as an anabolic-biased carbon cycling, which likely explains the observed enhanced CUE. Overall, these results highlight the role of population dynamics and life strategies in understanding and predicting microbial CUE and sequestration in soil.IMPORTANCEMicrobial CUE is a major determinant of global soil organic carbon storage. Understanding the microbial processes underlying CUE can help to maintain soil sustainable productivity and mitigate climate change. Our findings indicated that active microbial communities, adapted to long-term organic fertilization, exhibited a relative increase in net growth rate and a preference for anabolic carbon cycling when compared to those subjected to chemical fertilization. These shifts in population dynamics and life strategies led the active microbes to allocate more carbon to biomass production rather than cellular respiration. Consequently, the more fertile soils may harbor a greater microbially mediated carbon sequestration potential. This finding is of great importance for manipulating microorganisms to increase soil C sequestration.

Nutrient status changes bacterial interactions in a synthetic community.

Microbial interactions affect community stability and niche spaces in all ecosystems. However, it is not clear what factors influence these interactions, leading to changes in species fitness and ecological niches. Here, we utilized 16 monocultures and their corresponding pairwise co-cultures to measure niche changes among 16 cultivable bacterial species in a wide range of carbon sources, and we used resource availability as a parameter to alter the interactions of the synthetic bacterial community. Our results suggest that metabolic similarity drives niche deformation between bacterial species. We further found that resource limitation resulted in increased microbial inhibition and more negative interactions. At high resource availability, bacteria exhibited little inhibitory potential and stronger facilitation (in 71% of cases), promoting niche expansion. Overall, our results show that metabolic similarity induces different degrees of resource competition, altering pairwise interactions within the synthetic community and potentially modulating bacterial niches. This framework may lay the basis for understanding complex niche deformation and microbial interactions as modulated by metabolic similarity and resource availability.IMPORTANCEUnderstanding the intricate dynamics of microbial interactions is crucial for unraveling the stability and ecological roles of diverse ecosystems. However, the factors driving these interactions, leading to shifts in species fitness and ecological niches, remain inadequately explored. We demonstrate that metabolic similarity serves as a key driver of niche deformation between bacterial species. Resource availability emerges as a pivotal parameter, affecting interactions within the community. Our findings reveal heightened microbial inhibition and more negative interactions under resource-limited conditions. The prevalent facilitation is observed under conditions of high resource availability, underscoring the potential for niche expansion in such contexts. These findings emphasize that metabolic similarity induces varying degrees of resource competition, thereby altering pairwise interactions within the synthetic community and potentially modulating bacterial niches. Our workflow has broad implications for understanding the roles of metabolic similarity and resource availability in microbial interactions and for designing synthetic microbial communities.