Alkaline autofermentation of Nostoc muscorum enhances organic acid production and antimicrobial activity against Salmonella enterica and Campylobacter jejuni

Foodborne pathogens such as Salmonella enterica and Campylobacter jejuni remain leading causes of bacterial gastroenteritis and are frequently associated with poultry production systems. Increasing restrictions on antibiotic use in animal agriculture have intensified the need for sustainable antimicrobial alternatives. Cyanobacteria represent a promising resource for producing antimicrobial metabolites; however, their antimicrobial potential has primarily been explored using solvent extracts derived from fresh biomass. While alkaline autofermentation and organic acid production in cyanobacteria have been previously reported, including in our earlier work, the antimicrobial potential of autofermentation-derived aqueous extracts, which are primarily composed of organic acids, remains largely unexplored. This study establishes, for the first time, a dual-product autofermentation framework in Nostoc muscorum that enhances antimicrobial activity through the generation of organic acid–rich extracts and metabolite-enriched residual biomass. Autofermentation was conducted at pH 8.4 and 10.3, and organic acid production and antimicrobial activity against S. enterica and C. jejuni were evaluated using minimum inhibitory concentration assays. Alkaline autofermentation significantly enhanced metabolite production, yielding 12.31 g L −1 total organic acids after 24 h at pH 10.3, a 1.6-fold increase compared with pH 8.4. Butyric acid was the dominant fermentation product, reaching 9.11 g L −1 under alkaline conditions (pH 10.3), and contributed substantially to antimicrobial activity. Organic acid–rich extracts inhibited both pathogens, while methanolic extracts from autofermented biomass exhibited greater potency than fresh biomass extracts. These findings demonstrate that alkaline autofermentation enhances the antimicrobial potential of cyanobacterial biomass and highlight N. muscorum as a promising platform for developing antibiotic-free pathogen control strategies in poultry production systems.