Understanding of the extreme microorganisms that possess extracellular electron transfer (EET) capabilities is pivotal to advance electromicrobiology discipline and to develop niche-specific microbial electrochemistry-driven biotechnologies. Here, we report on the microbial electroactive biofilms (EABs) possessing the outward EET capabilities from a haloalkaline environment of the Lonar lake. We used the electrochemical cultivation approach to enrich haloalkaliphilic EABs under 9.5 pH and 20 g/L salinity conditions. The electrodes controlled at 0.2 V vs. Ag/AgCl yielded the best-performing biofilms in terms of maximum bioelectrocatalytic current densities of 548 ± 23 and 437 ± 17 µA/cm² with acetate and lactate substrates, respectively. Electrochemical characterization of biofilms revealed the presence of two putative redox-active moieties with the mean formal potentials of 0.183 and 0.333 V vs. Ag/AgCl, which represent the highest values reported to date for the EABs. 16S-rRNA amplicon sequencing of EABs revealed the dominance of unknown Geoalkalibacter sp. at ~80% abundance. Further investigations on the haloalkaliphilic EABs possessing EET components with high formal potentials might offer interesting research prospects in electromicrobiology.

对具有细胞外电子转移（EET）功能的极端微生物的理解，对于推进电微生物学学科和发展特定于生态位的微生物电化学驱动的生物技术至关重要。在这里，我们报告了微生物电活性生物膜（EABs）从Lonar湖的盐碱性环境中具有向外的EET能力。我们使用电化学培养方法在9.5 pH和20 g / L盐度条件下富集了卤代碱EAB。与Ag / AgCl相比，将电极控制在0.2 V电压下，就最大生物电催化电流密度为548±23和437±17 µA / cm ²而言，电极表现出最佳的生物膜。分别具有乙酸盐和乳酸盐底物。生物膜的电化学表征显示存在两个假定的氧化还原活性部分，相对于Ag / AgCl的平均形式电位分别为0.183和0.333 V，这是迄今为止报道的EAB的最高值。EAB的16S-rRNA扩增子测序揭示了未知的Geoalkalibacter sp。的优势。约80％的丰度。具有高形式势的EET成分的卤代碱EAB的进一步研究可能会为电微生物学提供有趣的研究前景。