The role of Bacterial-Fungal interactions in cigar tobacco fermentation: insights from community dynamics and physicochemical correlations.

During the fermentation of cigar tobacco leaves, cross-kingdom interactions between fungal and bacterial communities collectively regulate the formation of flavor compounds and reduce the content of irritating compounds. However, the interaction mechanisms among key microbial taxa and their regulatory effects on flavor metabolism remain poorly understood. There is an urgent need to elucidate the synergistic patterns of core microorganisms during this fermentation process, so as to provide a theoretical basis for the targeted improvement of tobacco leaf quality. This study utilized the cigar tobacco variety QX103 to systematically determine the conventional chemical components throughout its fermentation stages, analyze the microbial community structure on the leaf surface via high-throughput sequencing, and investigate microbial interactions using multi-omics approaches. This study identified Aspergillus (fungi) and Pseudomonas (bacteria) as the key microbial taxa critical for enhancing the fermentation quality of the wrapper tobacco QX103. Community diversity analysis revealed that the α-diversity of these two microbial groups increased during the initial fermentation stage but decreased after the mid-phase. Meanwhile, shifts in β-diversity indicated that bacterial community restructuring occurred earlier than fungal succession. Based on time-series analysis of Bray-Curtis dissimilarity, the fermentation process was clearly delineated into three dynamic phases: a rapid change phase (T1-T3), a slow change phase (T3-T5), and a stable phase (T5-T7). Network analysis further revealed a strong positive correlation between Proteobacteria and Ascomycota, wherein Pseudomonas and Aspergillus, as functional hubs, collaboratively maintained the stability of the fermentation ecosystem. Their synergistic metabolism may potentially contribute to nicotine degradation and the formation of volatile compounds, which are known to influence sensory attributes in fermented tobacco. This study reveals the pivotal role of the cross-kingdom microbial interaction network during cigar tobacco leaf fermentation. It elucidates the microbial regulatory principles governing the fermentation quality of QX103, thereby providing a novel strategy for constructing functional microbial consortia to achieve targeted regulation of cigar flavor.