Antibiotic factories on the move: Synthetic bacteria survive drinking water treatment and continuously produce antibiotics.

Synthetic biology enables the creation of high-yield synthetic antibiotic-producing bacteria (HYSAPB) for industrial biomanufacturing. However, HYSAPB may be inadvertently released into the environment. The fate of HYSAPB in natural water and subsequent the whole drinking water supply systems remains unexplored. This study found that a HYSAPB, S. lividans LJ1018, when released into source water, not only survived but retained its engineered advances, including multidrug resistance, enhanced environmental adaptability, and persistent actinomycin D (Act-D) production. Unlike wild-type strains, S. lividans LJ1018 synthesized 12-fold more Act-D in oligotrophic source water, exerting selective pressure that enriched indigenous antibiotic resistance bacteria (ARB). The heightened Act-D production also stimulated indigenous microorganisms to secrete more extracellular polymeric substances (EPS), thereby improving their chlorine resistance. Critically, S. lividans LJ1018 penetrated all barriers of simulated drinking water treatment process, and chlorination failed to abolish its Act-D synthesis capacity. Consequently, S. lividans LJ1018 acted as a mobile antibiotic factory, continuously synthesizing Act-D in treated water, which facilitated the emergence and resuscitation of new ARB in water distribution system. Furthermore, S. lividans LJ1018 attached to pipe surfaces promoted horizontal transfer of antibiotic resistance genes by lysing susceptible bacteria and fostering cell aggregation. These findings revealed that HYSAPB could survive, persistently produce antibiotics, and drive resistance throughout the entire water supply systems from source to tap. This "living antibiotic factory" subverted conventional water safety paradigms, redefining the biosafety risks of synthetic biology microorganisms.