title: [Identification, culture optimization and biotransformation of a stevioside-degrading bacterium].
abstract: OBJECTIVE
  Our study aimed at screening and identifying a specific bacterium capable of degrading stevioside. We also studied the conditions of enzyme production and stevioside conversion.
  
  
  METHODS
  Taxonomic group of the strain was confirmed by physical characterization and phylogenetic analysis by 16S rRNA gene sequence analysis and phylogenetic tree construction of the strain. The optimum conditions of enzyme producing and stevioside degrading were studied by single factor and multi-factor statistical analysis. Degradation product was detected and identified via liquid chromatography-mass spectrometry.
  
  
  RESULTS
  Based on the result of 16S rRNA gene sequence analysis, the strain named J2 shares 100% sequence identity with the sequence of the Bacillus megaterium. The activity of beta-Glucosidase produced by this Bacillus megaterium strain was up to 779.68 U/ml with 4% maize starch, 1% defatted soybean, 0.04% MgSO4 and 0.2% stevioside as culture medium when fermented under the condition of pH 7.0, 37 degrees C, 220 r/min and 10% inoculum for 36 h. The results of conversion showed that 10 mg/ml stevioside can be converted to steviolbioside by 74% after 3 days which has been identified by LC-MS. The ratio of rebaudioside A and stevioside was increased to 0.99 compared to original solution 0.38, which lead to 160.5% increasement of rebaudioside A in the relative amount. Stevioside can be converted completely after 5 days.
  
  
  CONCLUSIONS
  The isolated strain J2 was identified as Bacillus megaterium. It was a novel and safe strain with high, specific conversion stevioside to steviolbioside ability.
authors.affiliation: Jiangsu Engineering and Technology Research Center for Microbiology Resources, College of Life Science, Nanjing Normal University, Nanjing 210046, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Liu
authors.forename: Yuru
authors.initials: Y
authors.lastname: Chen
authors.forename: Zhongyu
authors.initials: Z
authors.lastname: Jiang
mesh_terms: D001410:Bacillus megaterium / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D001711:Biotransformation; D003470:Culture Media / Q000378:metabolism; D045786:Diterpenes, Kaurane / Q000378:metabolism*; D005960:Glucosides / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012988:Soil Microbiology; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D045786:Diterpenes, Kaurane; D005960:Glucosides; C012043:stevioside; D001617:beta-Glucosidase