Membranes fabricated from bacteria-produced cellulose have many practical and technological advantages over other means of cellulose fiber production, however, their functionality for targeted applications is limited and requires complex, multi-stage processing, while the mechanisms underpinned the optimum improvements remain largely unknown. Focusing on one of the highest-demand applications in wastewater treatment, here we resolve the three persistent issues in bacterial cellulose membranes (BCMs), namely poor fibrillar network quality, insufficient functionality and unsatisfactory performance, and discover the counterintuitive, yet most effective mechanism of imparting the multifunctional properties. First, innovative application of the Hestrin-Shramm medium instead of the CM0986 medium stimulated Taonella mepensis to produce BCMs with higher yields, more uniform fibrils and developed fibrillar networks, higher crystallinity indexes, better mechanical and thermal properties. Second, a novel but facile electroadsorption method was developed to enhance BCM functionality via bonding a natural bactericidal peptide-Nisin to the deliberately activated terminals on the BCM surface, achieving great antibacterial activity, good durability, well-preserved nanoporous network, outstanding water retention and low toxicity. Third, due to the synergetic effects of surface adsorption, ionic bonding, physical retention and active microbial killing, the Nisin-decorated BCMs enabled outstanding organic dye removal and excellent disinfection performance, among the best in the available reports. Collectively, this study demonstrates that electroadsorption is a promising and potentially generic strategy to fabricate Nisin-decorated and functionalized BCMs for next-generation membrane filters toward water purification.