| The style characteristics of cigar leaves are affected by microorganisms,metabolites and functional enzymes.It is of great theoretical and practical significance to clarify the microbial community structure and metabolic characteristics of cigar leaves,and reveal their relationship with sensory quality of cigar leaves.Hainan is one of the most promising producing areas in China,whose geographical and climatic conditions are closest to Cuba,the world’s high-quality cigar raw material producing area.Its cigar leaf quality,production technology and production facilities are currently at the leading level in China.In this paper,three cigar varieties(Haiyan 101,Haiyan109,Haiyan 201)in Guangcun and Wuzhishan of Hainan province were selected as the research objects.High-throughput sequencing technology was used to analyze the bacterial and fungal community structure on the leaf surface,analyze the response of cigar tobacco leaf microbial community to the genetic background and ecological environment of cigar tobacco and its impact on the sensory quality of tobacco leaves.Through the construction of molecular ecological network,the coexistence mode and network topological properties of tobacco leaf microorganisms were studied.The functional modules related to the sensory quality of tobacco leaves in the molecular ecological network were analyzed and the key species in the molecular ecological networkweredetermined.Based on the zero model analysis,the ecological process of tobacco leaf microbial community assembly was studied to reveal the correlation mechanism between tobacco leaf microbial assembly mechanism and sensory quality.Metabonomics technology was used to analyze the components of metabolites in cigar leaves,clarified the different distribution of metabolites in different genetic background and ecological environment,and the key metabolites affecting the sensory quality of cigar leaves and their relationship with leaf microorganisms was determined.The main results are as follows:(1)The sensory quality of cigar leaves is various with different ecological areas.Among them,HY201 had the largest difference in sensory quality between the two ecological regions,followed by HY109 and HY101.The bacterial community on cigar leaves was dominated by the phylum Proteobacteria and Cyanobacteria,and their relative abundances were more than 95%,while the fungal communities were dominated by the phylum of Ascomycota and Basidiomycota,and their relative abundances were more than 94%.The bacterial and fungal communities were significantly affected by ecological environment,but less affected by genetic background.The diversity of bacterial and fungal communities has significant positive correlations with the sensory indexes of aftertaste,the mellow sense of smoke,and the mellow sense of aroma,while had significant negative correlation with the green miscellaneous gas.(2)The molecular ecological networks of bacteria and fungi on cigar tobacco leaves were non-random and have modular structures.Their network characteristics are significantly related to the sensory qualities of cigar leaves.The network modules of bacteria community were more than fungi,but the network density of the former is lower than that of the latter.In the bacterial ecological network,Proteobacteria and actinobacteria had the largest number of connections.Meanwhile,there were three modules related to fat and powder aroma,one module related to resin aroma and one module related to leather aroma.In fungal ecological network,Ascomycota and Basidiomycota had the largest number of connections,but there was no network module significantly related to sensory qualities.(3)The assembly processes of microbial community on cigar leaf have significant impacts on some sensory qualities indicators,and the contribution of bacteria was greater than that of fungi.In the process of local community assembly,the bacterial community and fungal community were dominated by environmental selection,and there was a phenomenon of phylogenetic over-aggregation,which was more intense in fungal than bacterial community.In the process of regional diffusion,the bacterial and fungal communities were mainly controlled by drift,limited dispersion and homogeneous dispersion.There were significant negative correlations between the mean phylogenetic distance(MPD)of bacteria community and the sense of mellowness,mellowness and purity,and significant positive correlations between the mean nearest taxon distance(MDTD)and the aroma,aroma and woodiness.For fungal community,there was a significant negative correlation between the MPD and liquidambar,and significant negative correlations between MNTD and lignum.(4)The metabolism of cigar leaves was significantly affected by genetic background and ecological environment.Among them,34 metabolites could significantly affect sensory quality,including L-serine、L(+)-Arginineand so on.KEGG enrichment analysis showed that the metabolites were mainly related to the pathway of secondary metabolisms and amino acid metabolisms.The metabolites related to metabolism pathway of global and overview maps were significantly positively correlated with aroma and mellow sensation,the metabolites related to membrane transport pathway were significantly negatively correlated with protein breath and scorch gas,and the metabolites related to unknown pathway were significantly negatively correlated with combustion characteristics.In conclusion,the dominant bacteria on the cigar leaf were Proteobacteria and cyanobacteria,and the dominant fungi were Ascomycota and Basidiomycota.The microbial community structure and sensory quality were affected by the ecological environment and genetic background,and the ecological environment had a greater impact.There were network modules in the molecular ecological network of cigar leaf bacteria that significantly related to the aroma of fat powder,resin and leather,but no one in fungi.Both ecological environment and genetic background had significant effects on the metabolic characteristics of cigar leaves.It was found that 34 metabolites such as L-serine and L-arginine were significantly correlated with sensory quality.The above research results lay a theoretical foundation for improving the quality of domestic cigar raw materials. |
