Electroactive haloalkaliphiles exhibit exceptional tolerance to free ammonia

Abstract

Electrochemical activity in bacteria has been observed in numerous environments and conditions. However, enrichments in circumneutral freshwater media where acetate is the main electron donor seem to invariably lead to the dominance of Geobacter spp. Here we report on an electroactive bacterial consortium which was enriched on acetate as electron donor, but in a medium which reproduces hydrolysed urine (high pH, high salinity and high free ammonia). The consortium was found to be free of Geobacter species, whereas a previously undescribed community dominated by species closely related to Pseudomonas and Desulfuromonas was established. The salient features of this community were: (i) high electroactivity, with anodic current densities up to 47.4 ± 2.0 A m^-2; (ii) haloalkaliphilicity, with top performance at a medium pH of 10 and 19.5 ± 0.5 mS cm⁻¹; and (iii) a remarkably high tolerance to free ammonia toxicity at over 2,200 mgNH₃-N L⁻¹. This community is likely to find applications in microbial electrochemical technology for nutrient recovery from source-separated urine.