Exploring the Potential of Microalgae Cocultivation on Bacterial Community Dynamics in a Nile Tilapia and Garlic Aquaponic System

The cocultivation of microalgae in aquaponic systems can improve nutrient removal and enhance water quality. Moreover, it can promote the biological and physicochemical balance in aquaponic ecosystems. However, the bacterial communities in aquaponic systems have not yet been comprehensively characterized and the effects of microalgae cocultivation remain unclear. Using 16S rRNA gene sequencing, we sought to elucidate the effects of a cocultivation of Chlorella vulgaris, Scenedesmus species, and Spirulina platensis cocultivation on the bacterial communities in the rearing tanks and the biofilter of a garlic (Allium sativum L.) and Nile tilapia (Oreochromis niloticus L.) aquaponic system during a 56-days experiment. Feed intake, weight gain, and survival rates of Nile tilapia significantly improved in experimental groups cocultivated with microalgae compared to the control group, while garlic plant biomass, leaf number, and shoot length were not significantly different from the control. Alpha-diversity analysis revealed significantly higher richness and evenness in the bacterial communities from the biofilter and rearing tanks of the cocultivated systems when compared with the control system. The cocultivation also had a statistically significant effect on the bacterial composition: nonmetric multidimensional scaling analysis of a Bray–Curtis dissimilarity matrix demonstrated unique clustering patterns, indicating distinct bacterial communities in the biofilter and rearing tank water cocultivated with microalgal strains. We found significantly decreased abundances of the potentially pathogenic bacterial genera Janthinobacterium, Aeromonas, Pseudomonas, and Flavobacterium in aquaponic systems cocultivated with microalgae when compared to the control. Furthermore, the beneficial bacterial genera Fusibacter, Geothrix, Thiobaca, and Treponema were significantly enriched in the microalgae cocultivated systems. The results clearly demonstrate that integrating microalgae into an aquaponic recirculating aquaculture system (RAS), not only improves weight gain and survival rates of Nile tilapia, but also enriches beneficial bacterial genera and reduces potentially pathogenic microorganisms, offering a promising strategy to reduce antibiotic use and enhance water quality in aquaponics, without growth impairments of cocultivated plants.