A cooperative cobalamide biosynthesis guild in the endosphere of the edible aquatic plant Wolffia globosa Mankai.

backgroundCobalamin (vitamin B₁₂) is synthesized only by certain bacteria and archaea and is rarely found in plant-derived foods because plants neither synthesize nor require this cofactor. The edible duckweed Wolffia globosa Mankai is unusual in containing bioavailable cobalamin, suggesting a microbial origin. However, how cobalamin biosynthetic capacity is organized within angiosperm-associated microbiomes remains largely unresolved. Here, we investigated bacterial community structure and cobamide biosynthetic potential across the cultivation medium, plant surface, and internal tissues of Mankai to determine how cobalamin production is maintained in this aquatic plant microbiome.

resultsBacterial communities differed significantly among compartments, with the endosphere forming a low-diversity, host-filtered microbiome enriched in specialized taxa. Genome-resolved metagenomics showed that only a minority of endophytic bacteria encoded near-complete cobamide biosynthesis pathways consistent with de novo synthesis. In contrast, many co-occurring taxa lacked multiple biosynthetic steps but were enriched in genes associated with cobamide precursor salvage and remodeling. Network analysis identified putative producer taxa as highly connected hubs linked to salvager populations, consistent with metabolite cross-feeding. Comparative genomic analysis demonstrated reduced cobamide biosynthetic gene complements in endophytic genomes relative to closely related free-living strains, supporting adaptive pathway reduction in the host-associated niche.

conclusionsCobalamin production in the Mankai endosphere appears to arise from a metabolically interdependent bacterial consortium rather than from single autonomous producers. These findings identify cooperative micronutrient biosynthesis as an organizing principle in plant-associated microbiomes and position Mankai as a tractable model for studying cobamide-mediated microbial cooperation in aquatic crops. Understanding these interactions may support microbiome-informed strategies to stabilize micronutrient production and functional resilience in controlled aquatic plant cultivation systems.