Characterization of a thermotolerant strain inhibiting tobacco-specific nitrosamines in cigar fermentation.

Tobacco-specific nitrosamines (TSNAs), potent carcinogens formed during tobacco fermentation, accumulate more readily at high temperatures, particularly during cigar production. This study isolated thermotolerant bacterial strains able to degrade nitrite (as major TSNAs precursor) and suppress TSNAs formation at elevated temperatures. A novel strain, Mixta calida LYS12 belonging to the Erwiniaceae family, isolated from cigar tobacco leaves, exhibited > 95% nitrite degradation efficiency at 44 °C and tolerated nitrite concentrations up to 2.0 g/L. In tobacco fermentation experiments, this thermotolerant strain lowered nitrite content by 33.58% and total TSNAs levels by 19.97%. Significant reductions occurred in individual TSNAs: N-nitrosophenethyl nicotine decreased by 17.13%, 4-(nitrosomethylamino)-1-(3-pyridyl)-1-butanone by 14.64%, and N-nitrosoanabasine by 22.72%. Whole-genome sequencing identified 28 nitrogen metabolism–associated genes involved in dissimilatory and assimilatory nitrate reduction. Among these genes, nirBD and nasB encode pathways converting nitrite to ammonia. These findings highlight the studied strain’s potential as a biological control agent for enhancing cigar safety and quality through targeted reduction of harmful compounds.