Towards Underwater Probiotic Delivery for Corals

The accelerating global decline of coral reefs highlights the urgent need for innovative conservation technologies that can operate at molecular and microscale levels. Nanobiotechnology and materials science offer powerful approaches for developing targeted interventions, including delivery systems for beneficial microorganisms for corals (BMCs). A major barrier to advancing microbial therapies for corals is the lack of targeted and stable delivery systems for administering probiotics to corals. In this study, we introduce natural, biodegradable alginate-based delivery systems engineered as beads, hydrogels, and macrofibers as a method for targeted probiotic release. Using Pseudoalteromonas peptidolytica as a model probiotic, we achieved encapsulation efficiencies of 7.33 × 10⁴ ± 2.5 × 10³ CFU/g of polymer, with materials exhibiting robust mechanical stability upon immersion in seawater. In vitro probiotic diffusion assays demonstrated that the encapsulated probiotic remained viable and proliferative, and migrated beyond its delivery vehicles. After an initial lag phase, the release of probiotics increased markedly, reaching a maximum at 24 hours. This enabled a targeted release during the breakdown of the alginate matrix, as confirmed by scanning electron microscopy analysis of the delivery material. During in vivo coral experiments, we compared the three alginate delivery systems and microbiome sequencing verified a partial uptake and suggested a possible temporal persistence of the introduced strain after deployment of the alginate materials, demonstrating their specificity and functional delivery capacity. Microbiome analysis and energy-dispersive X-ray spectroscopy (EDX) indicated that degradation of all three delivery systems was driven by a combination of biological and chemical mechanisms. As first underwater delivery systems engineered for coral probiotics, these alginate-based materials demonstrate how bioengineered micro- and nanoscale systems can enhance precision interventions in coral restoration. This work highlights the potential of material science to bridge the gap between laboratory development and field application, advancing therapeutic and restoration strategies for reef conservation.