Accumulation of NO₂-cobalamin in nutrient-stressed ammonia-oxidizing archaea and in the oxygen deficient zone of the eastern tropical North Pacific

Cobalamin (vitamin B₁₂) is a precious resource in natural systems that is produced by select prokaryotes and required by a broad range of organisms. In this way, the production of cobalamin reinforces numerous microbial interdependencies. Here we report the accumulation of an unusual form of cobalamin, nitrocobalamin (NO₂-cobalamin), in a marine oxygen deficient zone (ODZ), isolates of ammonia-oxidizing archaea (AOA), and an anaerobic ammonium-oxidizing (anammox) bacteria enriched bioreactor. Low oxygen waters were enriched in NO₂-cobalamin, and AOA isolates experiencing ammonia or copper stress produced more NO₂-cobalamin, though there is wide strain-to-strain and batch-to-batch variability. NO₂-cobalamin has no known biochemical role. We hypothesize that AOA and anammox bacteria are a source of marine NO₂-cobalamin in the environment via a reactive nitrogen intermediate. These findings suggest connections between cobalamin forms and nitrogen transformations, physiological stress and ocean deoxygenation.