Adaptive Laboratory Evolution of Cupriavidus necator to Improve Energy Demand in Bioelectrochemical Cultivations

This study investigates adaptive laboratory evolution (ALE) to improve the tolerance of Cupriavidus necator H16 ΔPHB to high electrolyte concentrations, enabling more energy-efficient electroautotrophic cultivation. Over 3 months, strains were gradually adapted to up to 400 mM Na2SO4. Compared to the wild type, adapted strains exhibited higher growth under elevated salt conditions, maintaining viability at concentrations up to 300 mM. In bioelectrochemical systems, the addition of Na2SO4 significantly increased medium conductivity, reducing the cell voltage required under galvanostatic conditions. As a result, energy demand for cultivation decreased. Experiments demonstrated that the adapted strain grew comparably to the wild type under standard conditions but performed markedly better under high-salt conditions, shortening lag phases and reaching higher optical densities. Calculations revealed an energy saving of approximately 11% during 204 hr of cultivation when using the adapted variant in electrolyte-supplemented media. This work highlights the potential of combining biological robustness with optimized electrochemical conditions to reduce energy input in microbial electrosynthesis. Unlike purely technical optimizations, ALE provides a straightforward, natural, and transferable strategy to adapt production hosts to electrochemical process conditions. The findings demonstrate a practical route toward more sustainable bioelectrochemical processes by lowering energy consumption without compromising microbial performance.