(551j) Hydrogel Encapsulation of Probiotic Microbes to Engineer Plant Drought Resistance

In a climate destabilized by increasing warming, the need for plants and food crops which can adapt to extreme conditions is increasing. Drought is an especially pernicious problem for the sustainability of food; over the next decades, some models of grain production forecast a decrease of 15 to 35 percent¹. To feed an expanding world population and conserve the biological resources of the planet, new tools are needed to engineer resilience in crops. The study of probiotic microbes which interact with plants has been ongoing for decades, but the ability to introduce exogenous microbes to a native soil or create lasting changes in the soil microbiome remain elusive². Plant microbiomes and their associated metabolites and enzymes have the ability to affect a large range of plant phenotypes, from activating defense systems, to promoting root growth, but of special interest is their ability to increase resistance to drought.

Delivery of microbes or their associated enzymes and metabolites poses significant challenges to translation beyond the laboratory to the industrial agricultural scale. Introduced microbes are often out-competed or killed by the native rhizosphere, and thus lack the persistence to survive for the life span of the crop. Cell-free formulations suffer especially from this issue, as the lack of a physical scaffold or reinforcement allows for the molecules to wash away and diffuse during watering or rainfall.

Polymer-based hydrogel extended release technologies have shown promise in the past for short-term delivery of soil microbes. By physically encapsulating bacteria in hydrogel capsules, the probiotics are protected from attacks by endogenous microbes and are able to inoculate the soil, colonizing the rhizoplane of plants. In general, release is achieved out to a timepoint of several weeks, but longer-term delivery, especially demonstration of maintained plant phenotypes past that time, has not been demonstrated.

In this talk, I will demonstrate the development of a novel system for the delivery of soil probiotics and cell-free extracts to engineer long-term drought resistance in wheat plants. We optimized the formulations of capsules made from a blend of plant-derived polymers which encapsulate the probiotics and afford the additional benefit of retaining water. These polymer-based capsules are designed to retain bacteria and enzymes but allow for the free exchange of small molecule signaling agents and metabolites. We show that this system has the ability to deliver living cargo as well as encapsulated cell-free extracts which improve the survival and phenotype of drought-stressed wheat plants in longitudinal studies. The cell-free extracts also allow the introduction of multiple synergistic strains of plant microbes without competition, which would reduce efficacy of living cargo. Finally, we demonstrate superior stability of polymer-encapsulated lyophilized cargo, showing promise for agricultural applications.

1) Archibald, B. N.; Zhong, V.; Brophy, J. A. N. Policy Makers, Genetic Engineers, and an Engaged Public Can Work Together to Create Climate-Resilient Plants. PLOS Biology 2023, 21 (7), e3002208. https://doi.org/10.1371/journal.pbio.3002208.

2) Kozaeva, E.; Eida, A. A.; Gunady, E. F.; Dangl, J. L.; Conway, J. M.; Brophy, J. A. Roots of Synthetic Ecology: Microbes That Foster Plant Resilience in the Changing Climate. Current Opinion in Biotechnology 2024, 88, 103172. https://doi.org/10.1016/j.copbio.2024.103172.