Molybdenum-dependent nitrogen metabolism drives magnetite formation in magnetotactic bacterium AMB-1.

Magnetotactic bacteria have the ability to biomineralize intracellular magnetite (Fe₃O₄) nanoparticles. Resulting biomagnetite can be efficiently preserved in sedimentary rocks and represents past traces of biological activity that can be searched for paleontological and paleoenvironmental reconstructions. Recent work on trace-element incorporation into magnetite has shown that molybdenum exhibits a strong affinity for biomagnetite, with enrichments up to four orders of magnitude higher than in abiotic magnetite. This enrichment likely reflects molybdenum-dependent metabolic processes, such as nitrate reduction during denitrification, which support cellular energy production and contribute directly to magnetite biomineralization.

            Using a combination of molecular, chemical and magnetic approaches, we show that Mo availability directly stimulates growth and magnetite precipitation in the model microorganism Paramagnetospirillum (formerly Magnetospirillum) magneticum AMB-1 under environmental conditions favoring nitrate reduction. These findings demonstrate a functional link between molybdenum, nitrogen metabolism and biomineralization.

            Altogether, our results clarify the central metabolic role of molybdenum in magnetotactic bacteria and propose a mechanistic framework for interpreting the geochemical signatures of biomagnetite in ancient environments where nitrate-bearing oxidized species were present.