Effect of anodic potential and feeding strategies on intracellular polymer storage in electro-active microbial biofilms

Polyhydroxyalkanoates (PHAs) are a family of polyesters stored by microorganisms and completely biodegradable. PHA production is typically accomplished through fermentative metabolism under aerobic conditions. At commercial scale, this process incurs significant operational costs, primarily due to the continuous oxygen supply required to maintain microbial activity. Bioelectrochemical systems (BES) are devices that use electro-active microorganisms to catalyse electrochemical reactions. In a nutshell, in BES microbes couple their metabolism with electron transfer to and from the electrodes, enabling various applications including energy recovery from waste, or production of chemicals through electro-fermentation and electrosynthesis. Implementing PHA production in BES can potentially reduce oxygen supply needs, as electro-active organisms would utilize the anode as electron sink under anaerobic conditions. Despite the potential benefits for biopolymer production, current literature provides limited evidence on PHA accumulation by these organisms. In this work, we tested the ability of electro-active microorganisms to produce PHA from a model organic substrate under various anode potentials (0.0 V, +0.2 V, +0.4 V vs. SHE) and feeding strategies. Results showed significant conversion of organic carbon to intracellular polymers across all conditions. The 0.0 V potential with coupled feeding achieved higher PHA conversion (15 % vs 9 % with uncoupled feeding), suggesting that limiting electron flux to the anode favours storage compound formation. The presence of PHA was confirmed using staining techniques, while 16S rRNA sequencing revealed Geobacter dominance in the microbial community, suggesting PHA storage may be common among electro-active microorganisms. These findings demonstrate BES viability for sustainable PHA production from waste-derived organic acids.