The role of heterotrophic bacteria in iron-limited ocean ecosystems

Abstract

IRON availability limits phytoplankton growth in large areas of the world's oceans1–3 and may influence the strength of the biological carbon pump4,5. Very little is known of the iron requirements of oceanic heterotrophic bacteria, which constitute up to 50% of the total particulate organic carbon in open ocean waters6,7 and are important in carbon cycling as remineralizers of dissolved organic matter and hence producers of CO2 (ref. 8). Here we report that oceanic bacteria contain more iron per biomass than phytoplankton. In the subarctic Pacific, they constitute a large fraction of biogenic iron and account for 20–45% of biological iron uptake. Bacterial iron quotas in the field are similar to those of iron-deficient laboratory cultures, which exhibit reduced elec-tron transport, slow growth, and low carbon growth efficiency. Heterotrophic bacteria therefore play a major role in the biogeo-chemical cycling of iron. In situ iron limitation of heterotrophic metabolism may have profound effects on carbon flux in the ocean.