SUMMARYResearch backgroundThis study provides insight into the use of a designed microbial community to produce biohydrogen in simple, single-chamber microbial electrolysis cells (MECs). The ability of MECs to stably produce biohydrogen relies heavily on the setup and microorganisms working inside the system. Despite having the most straightforward configuration and effectively avoiding costly membranes, single-chamber MECs are prone to competing metabolic pathways. We present in this study one possible way of avoiding this problem using characteristically defined, designed microbial consortium. Here, we compare the performance of MECs inoculated with a designed consortium to MECs operating with a naturally occurring soil consortium.Experimental approachWe adapted a cost-effective and simple single-chamber MEC design. The MEC was gastight, 100 mL in volume, and equipped with continuous monitoring for electrical output using a digital multimeter. Microorganisms were sourced from Indonesian environmental samples, either as denitrifying bacterial isolates grouped as a designed consortium or natural soil microbiome used in its entirety. The designed consortium consisted of five species from thePseudomonasandAcinetobactergenera. The headspace gas profile was monitored periodically with a gas chromatograph. At the end of the culture, the composition of the natural soil consortium was characterized by next generation sequencing and the growth of the bacteria on the surface of the anodes by field emission scanning electron microscopy.Results and conclusionsWe found that MEC using a designed consortium presented a better H2production profile, with the ability of the system to maintain headspace H2concentration relatively stable for a long time after reaching stationary growth period. In contrast, MECs inoculated with soil microbiome exhibited a strong decline in headspace H2profile within the same time frame.Novelty and scientific contributionThis work utilizes a designed, denitrifying bacterial consortium isolated from Indonesian environmental samples that can survive in a nitrate-rich environment. Here we propose using a designed consortium as a biological approach to avoid methanogenesis in MECs, as a simple and environmentally friendly alternative to current chemical/physical methods. Our findings offer an alternative solution to avoid the problem of H2loss in single-chamber MECs along with optimizing biohydrogen production through bioelectrochemical routes.