Osmium-grafted magnetic nanobeads improve microbial current generation via culture-free and quick enrichment of electrogenic bacteria

Abstract

The conventional methods of enriching electrogenic bacteria from the natural microbial inoculum rely on time-consuming pre-incubation, substantially limiting the applicability of microbial electrochemical technologies. Therefore, developing a rapid and feasible approach to enrich electrogenic bacteria is beneficial for implementing microbial electrochemical technologies. Here, labeling electrogenic bacteria from a microbiota was successfully achieved by polymerizing the osmiophilic 3,3′-diaminobenzidine (DAB) monomers to form the DAB polymer and then depositing these on the cell surface, which was catalytically triggered by electron transfer enzymes such as outer-membrane cytochromes (OMCs) on the surface of electrogenic bacteria. These osmiophilic DAB-labeled electrogenic bacteria were rapidly enriched through specific conjugation with magnetic nanoparticle surfaces where folic acid and osmium tetroxide (OsO4) were sequentially grafted to form osmium-DAB conjugation. Higher enrichment of OMC-rich Shewanella oneidensis MR-1 than OMC-deficient Escherichia coli K12 under DAB-labeled magnetic separation was confirmed by imaging, protein, and electrochemical analyses. Upon treating environmental microbiota by the DAB-labeled magnetic separation process, 16S rRNA gene analysis showed that the relative abundance of potential electrogenic bacteria increased, resulting in a 16-fold higher current production than the original sample. Furthermore, the enriched electrogenic bacteria showed higher performance for sustainable bioelectricity production than the initial microbiota during a week and more of electrochemical incubation. Our novel enrichment strategy reveals the massive potential in improving the efficiency of microbial electrochemical technologies and facilitating the identification of electrogenic bacteria from unexplored microbial resources.