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<p>The mesopelagic zone is an important boundary between the surface and the deep ocean. Heterotrophic bacteria in this region impact the attenuation of organic carbon (C<sub>org</sub>) through its consumption and conversion back to inorganic carbon. While iron (Fe) is known to limit primary production, the impact of Fe on mesopelagic heterotrophic bacteria growth and C<sub>org</sub> degradation is less understood. This study demonstrates serial Fe-limitation and Fe-C<sub>org</sub> colimitation of bacteria growth within mesopelagic waters across an oligotrophic and a productive oceanic region. The addition of Fe increased the total C<sub>org</sub> demand of mesopelagic bacteria. When C<sub>org</sub> was supplied without additional Fe, bacterial growth efficiencies declined and production of Fe-specific chelators (siderophores) increased. Mesopelagic bacteria exhibited cellular Fe quotas substantially higher than those previously reported in surface waters and showed high plasticity in intracellular Fe when C<sub>org</sub> stimulated growth. These findings reveal a dynamic coupling between Fe and C<sub>org</sub> availability that may regulate bacterial metabolism in parts of the mesopelagic, with implications for basin-scale differences in C<sub>org</sub> remineralization and Fe cycling.</p>

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Iron availability modulates bacteria carbon cycling in the mesopelagic

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月18日

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  • Travis Mellett,
  • Patrick Monreal,
  • Korinna Kunde,
  • Lauren E. Manck,
  • Kelsy Cain,
  • François Ribalet,
  • Matthew J. Church,
  • E. Virginia Armbrust,
  • Randelle M. Bundy

摘要

The mesopelagic zone is an important boundary between the surface and the deep ocean. Heterotrophic bacteria in this region impact the attenuation of organic carbon (Corg) through its consumption and conversion back to inorganic carbon. While iron (Fe) is known to limit primary production, the impact of Fe on mesopelagic heterotrophic bacteria growth and Corg degradation is less understood. This study demonstrates serial Fe-limitation and Fe-Corg colimitation of bacteria growth within mesopelagic waters across an oligotrophic and a productive oceanic region. The addition of Fe increased the total Corg demand of mesopelagic bacteria. When Corg was supplied without additional Fe, bacterial growth efficiencies declined and production of Fe-specific chelators (siderophores) increased. Mesopelagic bacteria exhibited cellular Fe quotas substantially higher than those previously reported in surface waters and showed high plasticity in intracellular Fe when Corg stimulated growth. These findings reveal a dynamic coupling between Fe and Corg availability that may regulate bacterial metabolism in parts of the mesopelagic, with implications for basin-scale differences in Corg remineralization and Fe cycling.