Non-target effects of a harmful algal bloom biocontrol technology (DinoSHIELD) in an in-situ mesocosm experiment

Harmful algal blooms (HABs) of toxic dinoflagellates, including Karenia brevis, pose significant threats to marine organisms and human health worldwide. Previous research identified a naturally occurring algicidal bacterium, Shewanella sp. IRI-160, which secretes algicidal compounds that limit the growth of dinoflagellates. More recent research focused on the development of a HAB bio-control technology, now called DinoSHIELD, using alginate hydrogel to immobilize Shewanella sp. IRI-160. DinoSHIELD continuously releases bacteria-derived algicides that target dinoflagellate growth while limiting bacterial dispersion. In this study, an in-situ mesocosm experiment using natural microbial communities was conducted to assess the environmental impacts of DinoSHIELD. This study aimed to evaluate the effects of DinoSHIELD on water quality and on non-target microbial communities under non-HAB conditions. At an application rate effective at controlling the growth of K. brevis in laboratory cultures, DinoSHIELD had minimal effects on water quality within the mesocosms. There was no significant effect on overall photosynthetic biomass or the abundance of non-target microbial organisms during the 6-day mesocosm experiment. Although there was no significant change in microbial eukaryotic community structure, 18S rRNA gene sequencing analysis showed that DinoSHIELD significantly increased species richness in the treatment compared to controls. Importantly, analysis of total bacterial and Shewanella sp. IRI-160-specific cell densities showed limited release of bacteria from DinoSHIELD and no change in total bacterial densities. Overall, these results support the eventual use of DinoSHIELD as a biocontrol strategy for managing dinoflagellate HABs without negatively affecting natural microbial communities or the surrounding environment.