Geobacter sulfurreducens' unique metabolism results in cells with a high iron and lipid content

Abstract

Geobacter sulfurreducens is a ubiquitous iron reducing bacterium in soils, and in engineered systems it can respire an electrode to produce measurable electric current. Its unique metabolism, heavily dependent on an extensive network of cytochromes, requires a unique cell composition. In this work we used metallomics, cell fraction and elemental analyses, and transcriptomics to study and analyze the cell composition of G. sulfurreducens. Elemental composition studies (C,H,O,N, ash content) showed a high C:O and H:O ratios of approximately 1.7:1 and 0.25:1, indicative of more reduced cell composition that is consistent with a high lipid content. Our study shows that G. sulfurreducens cells have a large amount of iron (2 {+/-} 0.2 g/gdw) and lipids (32 {+/-} 0.5% dw/dw) and that this composition does not change whether the cells are grown with a soluble or an insoluble electron acceptor. The high iron concentration, higher than similar microorganisms, is attributed to the production of cytochromes that are abundant in transcriptomic analyses in both solid and soluble electron acceptor growth. The unique cell composition of G. sulfurreducens must be considered when growing this microorganism for lab studies and commercial applications. ImportanceGeobacter sulfurreducens is an electroactive microorganism. In nature, it grows on metallic minerals by transferring electrons to them, effectively breathing metals. In a manmade system, it respires an electrode to produce an electric current. It has become a model organism for the study of electroactive organisms. There are potential biotechnological applications of an organism that can bridge the gap between biology and electrical signal, and as a ubiquitous iron reducer in soils around the world, G. sulfurreducens and its relatives impact the global iron cycle. We measured the concentrations of metals, macromolecules, and basic elements in G. sulfurreducens to define this organisms composition. We also used gene expression data to discuss which proteins those metals could be associated with. We found that G. sulfurreducens has a large amount of lipid and iron compared to other bacteria -- these observations are important for future microbiologists and biotechnologists working with the organism.