Toward development of soil-derived Bacillus isolates as lung cancer cytotoxic agents

The wide-ranging impact of the human microbiome on health and disease has sparked growing interest in employing bacteria as live therapeutics. Natural properties of bacteria have been enhanced using synthetic biology to treat diverse diseases, from infections to inflammation and cancer. However, a major obstacle in this area is identifying specific bacterial hosts and molecular payloads that are both safe and effective for specific diseases or cancers. In this study, we explored environmental microbial diversity as a promising source of new therapeutic agents that could be engineered for bacterial drug delivery systems. We collected and characterized soil bacteria from 25 urban public parks, then evaluated their secreted metabolites for anti-cancer activity using both monolayer and three-dimensional spheroid models of lung cancer. Metagenomic analysis, toxicity profiling, and co-culture assays revealed that several Bacillus species isolated from Manhattan park soils produced compounds with strong, dose-dependent cytotoxic effects on lung cancer cells. Furthermore, we demonstrated that Bacillus subtilis-a well-characterized, gram-positive model organism-was capable of colonizing lung tumor spheroids, suggesting its potential as a safe and effective chassis for bacterial cancer therapy. Complementing these experiments, we developed a mechanistic ordinary differential equation (ODE) model of the bacteria-spheroid co-culture that is consistent with our bacterial and spheroid growth data. Overall, our findings highlight a discovery platform for the screening of environmental microbes as chassis or payload sources for microbial cancer therapies.