Bottom-up design of native bacterial consortia improves Chlorella sorokiniana growth performance and vitamin B12 content from laboratory to pilot scale

Abstract Interactions between microalgae and associated bacteria can enhance growth performance and biomass quality, yet their evaluation beyond laboratory scale remains limited. Here, 124 bacterial strains were isolated from industrial autotrophic Chlorella sorokiniana cultures and rationally assembled into a three-member consortium (MC-3) comprising Comamonas koreensis , Pseudomonas fluorescens , and Stenotrophomonas rhizophila through structured pairwise and multi-strain screening. At laboratory scale, MC-3 doubled the specific growth rate and enriched methylcobalamin (MeCbl) content by up to 19-fold relative to axenic controls. Validation in 100-L flat-panel photobioreactors (FP-PBR) and 2.5 m³ tubular photobioreactors (T-PBR) confirmed that MC-3 increased final cell concentration, by 30% in the FP-PBRs and 62% in the T-PBRs, and enriched MeCbl by 56% and 59%, respectively, while maintaining overall biochemical stability. Phytohormone profiling in the T-PBRs revealed lower 1-aminocyclopropane-1-carboxylic acid levels and higher gibberellin and auxin concentrations in MC-3 cultures, indicating a system-level correlation between consortium inoculation and growth-promoting hormonal shifts. Finally, consortium persistence across production systems was confirmed by 16S rRNA amplicon sequencing. These results demonstrate that ecologically compatible bacterial consortia can be rationally designed from industrial microbiomes and deployed as scalable tools to improve both productivity and nutritional value of C. sorokiniana under real production conditions.