Electricity-generating bacteria in the seafloor: optical characterization of extracellular polymeric sheaths

Very recently, long filamentous bacteria have been discovered in marine sediments that are able to generate electrical currents and mediate the transport of electrons across centimeter-scale distances. These electrogenic bacteria let the ocean floor operate like a natural battery, and have an enormous potential for various bio-electric applications. These bacteria belong to the family Desulfobulbaceae and have been identified in sulphide-rich and fauna-poor environments. At NIOZ we have a specific culture facility dedicated to these bacteria. However, because they are only recently discovered, they remain enigmatic in many aspects. One particular feature is that these long filamentous bacteria are surrounded by a polymer sheath. Little is known about this sheath and its composition (proteins or rather polysaccharides?). In this project, we will study these sheaths using a novel technique – digital holographic microscopy (DHM), which is a new type of microscopy that allows the quantification of optical density information of particles and substances. We recently acquired the newest generation of such a microscope (D³HM instrument), which opens an exciting new way of studying cell morphology. The goal of this project is to use the optical density information to observe the polymer sheaths surrounding the filaments and combine this with classical staining methods, to gain a better understanding of its composition and role in these bacteria. The research activities will consist of field sampling (Dutch delta area), the cultivation of marine organisms (filamentous bacteria), sample preparation, microscopic imaging, and the processing and analysis of images.