Photoelectroheterotrophic production of polyhydroxybutyrate in purple phototrophic bacteria using a microbial electrochemical moving bed reactor.

Due to its metabolic versatility, mixed communities of purple phototrophic bacteria could be exploited for production of added value products using an electrode as electron donor. Indeed, microbial electrosynthesis has already been proved as a suitable strategy for polyhydroxybutyrate production under photoautotrophic conditions. In contrast with classical biofilm-based electromicrobiology studies, fluid-like electrodes can tune planktonic microbial metabolism to enhance biodegradation rates in brewery wastewater. In this work we have explored polyhydroxybutyrate production in a mixed community enriched from brewery wastewater using a photo-microbial electrochemical moving bed reactor (photoME-MBR). The bioelectrochemical reactor was operated under cathodic conditions (-0.8 V vs Ag/AgCl) with acetate as carbon source as a mean to evaluate i) PHB production and ii) bioelectrochemical performance. We observed how a cathodic polarization of the moving electrode played a key role on PHB production stimulating both direct microbial electron uptake from the conductive bed and electrochemically produced hydrogen in the vicinity of the current collector. Overall, the polarized reactor outperformed the non-polarized reactor by four-fold regarding PHB production rate. In addition, microbial communities analysis revealed Rhodopseudomonas sp. and Bradyrhizobium sp. as main genera in combination with other electroactive genera like Geosporobacter sp. This work revealed that cathodic moving beds could present a feasible platform for biorefineries and added value products production.