Isolation and characterization of microalgal growth-enhancing bacteria from a wastewater treatment facility

Microalgae-bacteria interactions represent a promising approach for improving microalgal growth and biomass productivity, with potential applications in biofuel production, wastewater remediation, and the synthesis of value-added bioproducts. In this study, enriched microalgae consortia from the Tallahassee Wastewater Treatment Facility were first characterized using shotgun metagenomic sequencing to assess their taxonomic composition and functional potential. The consortia were dominated by Chlorella species and associated with diverse bacterial communities. Subsequently, bacterial strains were isolated and characterized to evaluate their potential as natural growth enhancers for microalgae. Eight bacterial isolates, Mesorhizobium sp., Enterococcus avium, Stenotrophomonas sp., Agrobacterium tumefaciens, Citrobacter freundii, Cellulosimicrobium sp., Stenotrophomonas pavanii, and Mycobacterium sp. SMC-4 were identified through 16 S rRNA sequencing and phylogenetic analysis. The influence of these isolates on microalgae was assessed using a membrane-separated coculture system that enabled metabolite exchange without direct cell-to-cell contact. Microalgal growth, monitored through optical density (OD) at 680 nm over 18 days, showed significant enhancement across all bacterial treatments compared to the reference (microalgae without bacteria). The most pronounced effects were observed with Mesorhizobium sp., Enterococcus avium, Stenotrophomonas sp., and Agrobacterium tumefaciens, which exhibited the highest growth responses. These findings suggest that wastewater-derived bacteria can substantially enhance microalgal growth performance, likely through metabolite-mediated interactions. This study expands the repository of algal-supportive bacterial taxa and highlights the potential of targeted microalgae-bacteria consortia for scalable and sustainable bioprocessing.