Screening of natural phenazine producers for electroactivity in bioelectrochemical systems

Abstract

Mediated extracellular electron transfer (EET) might be a great vehicle to connect microbial bioprocesses with electrochemical control in stirred-tank bioreactors. However, mediated electron transfer to date is not only much less efficient but also much less studied than microbial direct electron transfer to an anode. For example, despite the widespread capacity of pseudomonads to produce phenazine natural products, only Pseudomonas aeruginosa has been studied for its use of phenazines in bioelectrochemical applications. To provide a deeper understanding of the ecological potential for the bioelectrochemical exploitation of phenazines, we here investigated the potential electroactivity of over 100 putative diverse native phenazine producers and the performance within bioelectrochemical systems. Five species from the genera Pseudomonas, Streptomyces, Nocardiopsis, Brevibacterium and Burkholderia were identified as new electroactive bacteria. Electron discharge to the anode and electric current production correlated with the phenazine synthesis of Pseudomonas chlororaphis subsp. aurantiaca. Phenazine-1carboxylic acid was the dominant molecule with a concentration of 86.1 μg/ml mediating an anodic current of 15.1 μA/cm 2 . On the other hand, Nocardiopsis chromatogenes used a wider range of phenazines at low concentrations and likely yet-unknown redox compounds to mediate EET, achieving an anodic current of 9.5 μA/cm 2 . Elucidating the energetic and metabolic usage of phenazines in these and other species might contribute to improving electron discharge and respiration. In the long run, this may enhance oxygenlimited bioproduction of value-added compounds based on mediated EET mechanisms.F I G U R E 1 (A) Three-electrode BES configuration for the exploration of potential EAB through self-produced phenazines as electron shuttles to mediate electron transfer. Green cells, limited to growing on the anode perform direct electron transfer (green arrow). Planktonic cells (all other colours to show diversity), occupying the whole reactor volume, perform mediated electron transfer to the (distant) anode through successive reduction and oxidation cycles (red and blue arrows) of phenazines. Working, reference and counter electrode (WE, RE and CE respectively). I, V, represent the potentiostat connections. (B) Key steps of the phenazine biosynthesis pathway.

The Microbial Communities of Anaerobic Respiration and Fermentation Degrading Chitin Exist in the Anaerobic Sludge of Microbial Fuel Cell Anodes

“…Nitrosomonas were the nitrogen transformation functional bacteria in the microbial fuel cell system [36]. Thiomona, Burkholderia, and Geobacter were EAB [37][38][39]. These findings indicated that bacteria associated with electrogenesis were the domain genera in MFCs.…”

Exploiting synergies between microbial electrochemical technologies and synthetic biology

“…The molecular mechanism of this phenazine‐based EET and its efficiency remain to be further clarified and improved, which, however, could likely be strain and environmental conditions‐specific. In this special issue, (Franco et al, 2022 ) screened over 100 seemly phenazine producers based on their genomes. A strong mismatch between the genome capability and the active phenotype was found, and only five species were finally demonstrated on the physiological level with reasonable EET activities.…”

Electricity generation and real oily wastewater treatment by Pseudomonas citronellolis 620C in a microbial fuel cell: pyocyanin production as electron shuttle

“…It was reported that phenazine-based metabolites such as pyocyanin and phenazine-1-carboxamide produced by some Pseudomonas spp., in most cases in a synergetic effect with biosurfactants. These molecules function as electron shuttles, enabling the bacterium to achieve its EET [ 36 – 39 ].…”