Screening and Effect Evaluation of Starch Degrading Bacteria in Tobacco Leaf

In order to effectively degrade tobacco leaf starch and improve the quality and safety of tobacco, one strain of starch degrading bacteria named as Bacillus subtilis YA14, was fermentation-optimized and then sprayed onto tobacco leaves 48 h before curing. The changes of starch and protein content, related enzyme activities, conventional chemical composition, appearance quality and sensory quality of tobacco leaves were analyzed during the curing process of YA14 sprayed and controlled tobacco leaves. Amplicon sequencing technology was used to analyze the changes of microbial communities in tobacco leaves after YA14 treatment. The results showed that the amylase activity of YA14 strain under optimized fermentation conditions reached 146.38 mg/(mg∙min), and YA14 bacterial solution sprayed before curing significantly reduced the starch content of tobacco leaf with the degradation rate of 37.17%, while had no obvious degradation effect on the protein content of tobacco leaf. The activities of peroxidase (POD), superoxide dismutase (SOD) and amylase were increased by spraying YA14 and the activities of polyphenol oxidase (PPO), starch branching enzyme (SBE) and nitrate reductase (NR) were decreased. In addition, YA14 treatment could improve the richness and species diversity of tobacco microbial communities, especially improve the abundance of dominant microbes Bacillus and Aspergillus. It also reduce the relative abundance of Stenotrophomonas, Gibberella and other microbes. After application of YA14, the chemical composition of cured tobacco leaves was harmonized, and the appearance and sensory quality were better than the control, which indicated that the application of starch degrading strain YA14 had great significance for improving the quality of cured tobacco leaves.