Screening and identification of 2,3-butanediol-producing strains by xylose fermentation and optimization of fermentation conditions

In this study, using xylose as the only carbon source, the 2,3-butanediol-producing strains were screened from snail samples through enrichment culture, primary screening and re-screening, purification, and the strains were identified by morphological observation and molecular biology techniques. The composition of xylose fermentation products of screened strains were analyzed by gas chromatography (GC) and gas chromatography- mass spectrometry (GC-MS). The strains with high yield of 2,3-butanediol were screened by xylose, glucose and xylose mixed sugar fermentation, and the fermentation conditions were optimized. The results showed that five strains (numbered as SN1-SN5) were selected to produce 2,3-butanediol from xylose, and all of them were identified as Klebsiella variicola. The results of GC and GC-MS analysis showed that 2,3-butanediol was the main product of xylose fermentation of the screened strains, and SN5 had the strongest fermentation ability to produce 2,3-butanediol, and the yield of 2,3-butanediol was (14.26±0.18) g/L under aerobic conditions. 2,3-butanediol (21.83±0.66) g/L was produced in the fermentation condition of mixed sugar of glucose and xylose 2∶1 for 48 h. The optimal fermentation conditions of strain SN5 were peptone addition 5 g/L, fermentation temperature 37 ℃, time 48 h, initial pH 6.0 and initial xylose contents 80 g/L. Under the optimized conditions, the 2,3-butanediol yield was (26.58±0.26) g/L, which was 89% higher than that before optimization, and the conversion rate reached (0.53±0.01) g/g.