Comparative analysis of microbial succession and biochemical changes in cigar tobacco filler and wrapper leaves...

Bulk fermentation of cigar tobacco leaves couples microbial succession and chemical transformations; however, it remains unclear whether commercially distinct filler and wrapper leaves follow different ecological and biochemical trajectories under identical industrial conditions. Using 16S rRNA and ITS amplicon sequencing, together with conventional chemical indices and volatile profiling, we tracked filler and wrapper leaves (two commercial cultivars, variety 204 and variety 108) through 0, 10, 18, 49, and 89 days of industrial bulk fermentation. The results revealed that reducing sugars declined by 63% in filler leaves (0.57 to 0.21%) and 66% in wrapper leaves (0.59 to 0.20%), whereas alkaloid dynamics differed between materials: filler leaves showed a transient mid-fermentation rise before decline, while wrapper leaves declined from the outset. Bacterial communities shifted from Proteobacteria-dominated early assemblages toward increased Firmicutes during later fermentation, with Acinetobacter, Staphylococcus and Pseudomonas as major genera. Fungal communities were dominated primarily by Ascomycota, with Aspergillus prevalent across fermentation and Papiliotrema becoming more prevalent at later stages. Bray-Curtis based ordination showed structured, directional succession in both bacterial and fungal communities, and fermentation time explained substantially more community variation than material type (bacteria: R² = 0.57 vs. 0.04; fungi: R² = 0.42 vs. 0.08). Correlation, redundancy and network analyses linked both bacterial and fungal community variation to sugars, nitrogenous compounds, alkaloids, and volatile classes, although these associations remain correlative rather than causal. By directly comparing filler and wrapper leaves under identical industrial fermentation environment, this study highlights that commercially distinct cigar materials follow divergent ecological and biochemical trajectories, providing a process-resolved basis for fermentation monitoring and material-specific quality management.