Screening and evaluation of bacteria for multi-target macromolecular substance degradation in aged tobacco strips

To effectively degrade macromolecular substances in tobacco strips and improve their quality, bacteria that could simultaneously degrade a variety of macromolecular substances in aged tobacco strips from different producing areas were isolated and screened. In addition, morphological and molecular biological identification and optimization of fermentation conditions were conducted, and the degradation effects of bacteria on macromolecular substances in aged tobacco strips were investigated. The results showed that 286 bacterial strains were isolated from the surface of aged tobacco strips and 7 strains of degrading bacteria capable of simultaneously degrading 2 or more macromolecular substances in tobacco were obtained through primary and secondary screening. Among them, JLZY-5 strain had the best degrading effect on cellulose, pectin, starch and protein. Based on morphological observation and 16S rDNA gene sequencing results, it was concluded that JLZY-5 was a methylotrophic Bacillus methylotrophicus. The results from the optimized fermentation conditions showed that the optimal fermentation culture conditions for JLZY-5 strain were 30 ℃, pH 7.0, 10% liquid loading, 3% inoculum size, 200 r/min rotation speed, and 40 h fermentation time. Under these conditions, the enzyme activities of cellulose, starch, protein and pectinase in the fermented liquor were 21.7, 27.65, 0.733 and 2.05 U/mL, respectively, and the degradation rates of cellulose, starch, protein and pectin in aged tobacco strips were 28.73%, 21.24%, 16.15% and 4.56%, respectively.