Cobamide-based interactions between soil bacteria can be predicted based on monoculture growth.

Cobamide concentration predicts which soil Caulobacter isolate predominates in co-culture, revealing niche differentiation despite genomic redundancy.

• Why it matters: Understanding microbial interactions is crucial for deciphering community structure and function, but the complexity of co-occurring interactions makes mechanistic insights difficult to obtain.
• What they did: The study measured cobamide-dependent growth of two Caulobacter isolates in monoculture and co-culture, and analyzed cobamide sharing by soil bacteria, using genome-based metabolic predictions across four isolates.
• The result: Cobamide levels determine isolate dominance and support coexistence in tri-cultures, suggesting cobamides as key shared nutrients that enable prediction of bacterial interactions in complex communities.