Abstract
Shewanella oneidensis MR-1 is an electroactive bacterium, capable of reducing extracellular insoluble electron acceptors, making it important for both nutrient cycling in nature and microbial electrochemical technologies, such as microbial fuel cells and microbial electrosynthesis. When allowed to anaerobically colonize an Ag/AgCl solid interface, S. oneidensis has precipitated silver nanoparticles (AgNp), thus providing the means for a surface enhanced confocal Raman microscopy (SECRaM) investigation of its biofilm. The result is the in-situ chemical mapping of the biofilm as it developed over time, where the distribution of cytochromes, reduced and oxidized flavins, polysaccharides and phosphate in the undisturbed biofilm is monitored. Utilizing AgNp bio-produced by the bacteria colonizing the Ag/AgCl interface, we could perform SECRaM while avoiding the use of a patterned or roughened support or the introduction of noble metal salts and reducing agents. This new method will allow a spatially and temporally resolved chemical investigation not only of Shewanella biofilms at an insoluble electron acceptor, but also of other noble metal nanoparticle-precipitating bacteria in laboratory cultures or in complex microbial communities in their natural habitats.
Highlights
Shewanella species are gram-negative facultative anaerobes, members of the class of electroactive bacteria, known as exoelectrogens [1]
The development of S. oneidensis MR-1 biofilms at a Ag/AgCl solid interface has been monitored in time by digital photography, light microscopy, scanning electron-microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDX) and surface enhanced confocal Raman microscopy (SECRaM)
We have shown that the development and chemical composition of a S. oneidensis MR-1 biofilm formed at a Ag/AgCl solid interface can be followed in situ using surface enhanced confocal Raman microscopy, without the need to open the system and add soluble Ag(I) salts and/or abrasive reduction agents, as had been done before to investigate bacteria using SERS
Summary
Shewanella species are gram-negative facultative anaerobes, members of the class of electroactive bacteria, known as exoelectrogens [1]. Electroactive bacteria can reduce extracellular insoluble electron acceptors (IEA), such as insoluble metal oxides and positively poised electrodes, as part of their respiratory chain [1,2,3,4,5,6,7]. They are very important for metal cycling in nature, as they transform insoluble minerals, such as Fe2O3, into bioavailable ones, such as Fe(II) [4,5,7,8,9,10,11,12]. In primary METs an PLOS ONE | DOI:10.1371/journal.pone.0145871 December 28, 2015
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