Characterization and genomic profiling of Klebsiella pneumoniae 2e, a newly isolated 1,3-propanediol-producing strain, revealed its adaptability to crude glycerol

Crude glycerol is largely generated as the main by-product of the biodiesel industry and is unprofitable for industrial application without costly purification. The direct bioconversion of crude glycerol into 1,3-propanediol (1,3-PDO) by microorganisms is a promising alternative for effective and economic utilization. In this study, Klebsiella pneumoniae 2e was newly isolated for the conversion of crude glycerol into 1,3-PDO. Batch fermentation analysis confirmed that crude glycerol and its main impurities had slight impacts on the growth, key enzyme activity and 1,3-PDO production of K. pneumoniae 2e. The 1,3-PDO yield from crude glycerol by K. pneumoniae 2e reached 0.62 mol 1,3-PDO /mol glycerol , which was higher than that of most reported 1,3-PDO-producing Klebsiella strains. Genomic profiling revealed that K. pneumoniae 2e possesses 30 genes involved in glycerol anaerobic metabolism and 1,3-PDO biosynthesis. Quantitative real-time PCR analysis of these genes showed that the majority of the genes encoding the key enzymes for glycerol metabolism and 1,3-PDO biosynthesis were significantly up-regulated during culture in crude glycerol relative to pure glycerol. Further comparative genomic analysis revealed a higher number of stress response proteins and a novel glycerol uptake facilitator protein in K. pneumoniae 2e compared to other Klebsiella strains. This work confirms the adaptability of a newly isolated 1,3-PDO-producing strain, K. pneumoniae 2e, to crude glycerol and provide insights into the molecular mechanisms involved in its crude glycerol tolerance, which is valuable for industrial 1,3-PDO production from crude glycerol. IMPORTANCE The rapid development of biodiesel industry leads to tremendous of crude glycerol generation. Due to the presence of complex impurities, crude glycerol shows low-value for industry without costly purification. Obtaining novel microorganisms capable of direct and efficient bioconversion of crude glycerol to value-added products shows great economic potential for industrial application. In this work, we characterized a newly isolated strain, K. pneumoniae 2e, with capacity to efficiently produce 1,3-PDO from crude glycerol, and demonstrated its adaptation to crude glycerol. Our work provided insights into the molecular mechanisms of K. pneumoniae 2e adaptation to crude glycerol and the expression patterns of its genes involved in 1,3-PDO biosynthesis, which will contribute to the development of the industrial 1,3-PDO production from crude glycerol.