Iron reduction and magnetite biomineralization mediated by a deep-sea iron-reducing bacterium Shewanella piezotolerans WP3

摘要

Dissimilatory iron reduction (DIR) plays an important role in element biogeochemical cycling. However, little is known about DIR processes and the mineralization abilities of strains found in deep oceans, where ecology, nutrient availability, and diversity are significantly different. Shewanella piezotolerans WP3 is a psychrotolerant and piezotolerant iron-reducing strain with a complex respiration net which has been recently isolated from West Pacific deep-sea sediments at a water depth of ～1914 m. In this study, we have investigated the biomineralization process of S. piezotolerans WP3 at 0.1 MPa (～1 atmospheric pressure) and 20°C (optimum growth temperature). A series of magnetic measurements in combination with X-ray diffraction, transmission electron microscopy, and chemical methods were applied to characterize the iron reduction process and biominerals. The results demonstrate that S. piezotolerans WP3 can reduce hydrous ferric oxide (HFO) at a much faster rate than that of most other reported strains and produce superparamagnetic magnetite particles with an average grain size of 4-6 nm after 72 h. Time course multiple magnetic parameters can be used to effectively monitor the transformation process from weak antiferromagnetic HFO to strong ferrimagnetic magnetite. Changes in concentration-sensitive and grain size-sensitive magnetic parameters suggest that the biomineralization process is characterized by recurring magnetic mineral formation and particle growth. Owing to its high iron reduction rate, S. piezotolerans WP3 may contribute to iron mineral transformation and element cycling in deep oceans. Our results additionally suggest that the multiple-parameter rock-magnetic method is a fast, sensitive, nondestructive and quantitative approach for monitoring DIR biomineralization processes involving magnetic minerals.