The Change Of Bacterial Composition On Aging Flue-cured Tobacco Leaves During Aging And Isolation Of A Microbial Community With The Capacity Of Degrading Pectin

An aging process is typically applied to improve the quality of the flue-cured tobacco. Aging greatly improves the aroma and other qualities desirable in smoking products. Many microorganisms on aging tobacco leaves likely play important roles in the aging process. However, the traditional culture-dependent methods employed in most previous studies might have caused an underestimate of microflora diversity be-cause only a fraction of the bacteria known in natural habitats can be cultivated on laboratory media. In recent years, new culture-independent technologies developed in molecular biology can analyze not only the culturable microorganisms but also the unculturable ones.Three kinds of tobacco leaves growing in Fujian Province, Henan Province and Yunnan Province were sampled during aging in our study, and each kind of tobacco included three grades (C tiao, X21, B22). In total, bacterial composition of36samples of tobacco leaves were analyzed using PCR-DGGE anaysis. The results showed that: there were about ten predominant bacteria on aging flue-cured tobacco leaves from Fujian Province, eleven from Henan Province, and twenty from Yunnan Province. Bacterial composition on three kinds of tobacco leaves was different from each other. There was no one predominant bacterium existing on three all of tobacco leaves. The most extensive presence of bacteria were Bacillus, and uncultured bacterium, which were found on almost all the tobacco leaves. Bacterial community structures on to- bacco leaves from Fujian Province, Henan Province and Yunnan Province were dif-ferent between0and36months aging. The maximum number of bacterial species occurred in12months aging for Fujian samples, while in Henan and Yunnan Wenshan samples, occurred in6months aging. No obvious regular variation pattern of the predominant bacterial composition was observed in the aging process.Excess pectin in tobacco leaves can bring undesirable effects. In order to reduce the ratio of pectin in tobacco leaves and improve tobacco quality, we isolated bacterial community capable of degradating pectin. Liquid fermentation tests of tobacco leaves were conducted using the pectin-degrading bacterial community and a mixed bacterial group including a pectin-degrading bacterial community, a nicotine-degrading bacterial community and a cellulose-degrading bacterial community. The results were as follows:1. The isolated pectin-degrade bacterial community contained four bacteria: Uncultured Enterobactenaceae bacterium, Bacillus methylotrophicus, Burkholderia sp. and Bacillus atrophaeus.2. In the fermentation test using pectin-degrading bacterial community, three days after inoculation, the pectinase activity reached a peak (100U), and then decreased gradually.3.In the fermentation tests using the mixed bacterial group, two days after inoculation, we detected the highest cellulose enzyme activity (180U). The nicotine content was also found to be reduced significantly from0.7g/L to0.3g/L after fermentation, indicating that the mixed bacterial group was able to effectively reduce the content of pectin, cellulose and nicotine in tobacco leaves.