Adaptability of Klebsiella pneumoniae 2e, a Newly Isolated 1,3-Propanediol-Producing Strain, to Crude Glycerol as Revealed by Genomic Profiling

Abstract

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, <i>Klebsiella pneumoniae</i> 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 <i>K. pneumoniae</i> 2e. The 1,3-PDO yield from crude glycerol by <i>K. pneumoniae</i> 2e reached 0.64 mol 1,3-PDO/mol glycerol, which was higher than that by most reported 1,3-PDO-producing <i>Klebsiella</i> strains. Genomic profiling revealed that <i>K. pneumoniae</i> 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 upregulated during culture in crude glycerol relative to that in pure glycerol. Further comparative genomic analysis revealed a novel glycerol uptake facilitator protein in <i>K. pneumoniae</i> 2e and a higher number of stress response proteins than in other <i>Klebsiella</i> strains. This work confirms the adaptability of a newly isolated 1,3-PDO-producing strain, <i>K. pneumoniae</i> 2e, to crude glycerol and provides insights into the molecular mechanisms involved in its crude glycerol tolerance, which is valuable for industrial 1,3-PDO production from crude glycerol.<b>IMPORTANCE</b> The rapid development of the biodiesel industry has led to tremendous crude glycerol generation. Due to the presence of complex impurities, crude glycerol has low value for industry without costly purification. Obtaining novel microorganisms capable of direct and efficient bioconversion of crude glycerol to value-added products has great economic potential for industrial application. In this work, we characterized a newly isolated strain, <i>Klebsiella pneumoniae</i> 2e, with the capacity to efficiently produce 1,3-propanediol (1,3-PDO) from crude glycerol and demonstrated its adaptation to crude glycerol. Our work provides insights into the molecular mechanisms of <i>K. pneumoniae</i> 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 industrial 1,3-PDO production from crude glycerol.