Synthetic polymers promote cell aggregation and accelerate cathode-associated layer formation in Kyrpidia spormannii...

Microbial electrosynthesis using Kyrpidia spormannii EA-1 represents a promising approach for sustainable biotechnology, yet the initial biofilm formation on cathode surfaces remains a bottleneck limiting process efficiency. In this study, we investigated the potential of synthetic polymers to accelerate cell aggregation and cathode colonization by this microorganism in bioelectrochemical systems. Polymers were prepared through conjugation, in aqueous conditions, of a poly(hydrazide) (pAcU) with twelve different aldehydes including aromatic, heterocyclic, and aliphatic aldehydes. Crystal violet staining identified four promising polymer-aldehyde conjugates (with 2-naphthaldehyde, 1H-imidazole-4-carbaldehyde, uracil-5-carbaldehyde, and hexanal), one of which significantly increased crystal-violet-retained surface-attached biomass compared to its aldehyde-only control. Growth kinetics revealed that these polymer-aldehyde conjugates initially reduced apparent planktonic growth rates, which may reflect stress responses, reduced viability, or a shift toward an aggregated, surface-associated lifestyle. Live/dead staining demonstrated that cells became entrapped within aggregates, with viability depending on the specific aldehyde used. Transcriptomic analysis revealed upregulation of sporulation genes, toxin-antitoxin systems, and stress response pathways, alongside downregulation of metabolic transporters and carbon metabolism genes, a response compatible with, but not specific to, a biofilm-associated lifestyle. In a bioelectrochemical reactor, addition of the polymer-2-naphthaldehyde conjugate accelerated cathode coverage, with a cathode-associated layer reaching over 1 mm in height within seven days, compared to 0.17 mm in the biotic control and 0.24 mm in an abiotic polymer-only control, indicating a substantial contribution of both cellular aggregation and polymer deposition to layer formation. These findings indicate that synthetic polymer-aldehyde-conjugates represent a promising strategy to accelerate cathode colonization during the start-up phase of microbial electrosynthesis processes with K. spormannii.