Yun-Zhen Xu

Metabolism in 1,3-propanediol fed-batch fermentation by a D-lactate deficient mutant of Klebsiella pneumoniae.

Klebsiella pneumoniae HR526, a new isolated 1,3‐propanediol (1,3‐PD) producer, exhibited great productivity. However, the accumulation of lactate in the late‐exponential phase remained an obstacle of 1,3‐PD industrial scale production. Hereby, mutants lacking D‐lactate pathway were constructed by knocking out the ldhA gene encoding fermentative D‐lactate dehydrogenase (LDH) of HR526. The mutant K. pneumoniae LDH526 with the lowest LDH activity was studied in aerobic fed‐batch fermentation. In experiments using pure glycerol as feedstock, the 1,3‐PD concentrations, conversion, and productivity increased from 95.39 g L−1, 0.48 and 1.98 g L−1 h−1 to 102. 06 g L−1, 0.52 mol mol−1 and 2.13 g L−1 h−1, respectively. The diol (1,3‐PD and 2,3‐butanediol) conversion increased from 0.55 mol mol−1 to a maximum of 0.65 mol mol−1. Lactate would not accumulate until 1,3‐PD exceeded 84 g L−1, and the final lactate concentration decreased dramatically from more than 40 g L−1 to <3 g L−1. Enzymic measurements showed LDH activity decreased by 89–98% during fed‐batch fermentation, and other related enzyme activities were not affected. NADH/NAD+ enhanced more than 50% in the late‐exponential phase as the D‐lactate pathway was cut off, which might be the main reason for the change of final metabolites concentrations. The ability to utilize crude glycerol from biodiesel process and great genetic stability demonstrated that K. pnemoniae LDH526 was valuable for 1,3‐PD industrial production. Biotechnol. Bioeng. 2009; 104: 965–972.

1,3-Propanediol and its copolymers: Research, development and industrialization

1,3‐Propanediol (PDO), is now taking the transition from a traditional “specialty chemical” to a “commodity chemical”. The market for PDO is growing rapidly as the technology develops. With the advancing PDO production technology, polytrimethylene terephthalate (PTT) as a new type of polyester has been applied in carpet and textile fibers, monofilaments, films, and nonwoven fabrics, and in the engineering thermoplastics area, because PTT has unique properties compared to other polymers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Responding to the environmental and sustainability factors, one‐ or two‐step fermentation technology for PDO production has attracted peoples attention. A novel flexible process for PDO production by using aerobic fermentation from glycerol or glucose has been developed and demonstrated with a facility capacity of 4000 t/year in a pilot plant. By using engineered Escherichia coli, 135 g/L PDO was obtained with glucose as feedstock. Since the bio‐process of PDO production consumes 40% less energy and reduces greenhouse gas emissions by 20% versus petroleum‐based propanediol, the bio‐based PTT is more environmentally friendly and sustainable compared with the fossil fuel‐based polymers, which made PTT more attractive with good prospects for the future.

Physiologic mechanisms of sequential products synthesis in 1,3-propanediol fed-batch fermentation by Klebsiella pneumoniae

The glycerol fed‐batch fermentation by Klebsiella pneumoniae CGMCC 1.6366 exhibited the sequential synthesis of products, including acetate, 1,3‐propanediol (1,3‐PD), 2,3‐butanediol, ethanol, succinate, and lactate. The dominant flux distribution was shifted from acetate formation to 1,3‐PD formation in early‐ exponential growth phase and then to lactate synthesis in late‐exponential growth phase. The underlying physiological mechanism of the above observations has been investigated via the related enzymes, nucleotide, and intermediary metabolites analysis. The carbon flow shift is dictated by the intrinsic physiological state and enzymatic activity regulation. Especially, the internal redox state could serve as a rate‐controlling factor for 1,3‐PD production. The q1,3‐PD formation was the combined outcomes of regulations of glycerol dehydratase activity and internal redox balancing. The qethanol/qacetate ratios demonstrated the flexible adaptation mechanism of K. pneumoniae preferring ATP generation in early‐exponential growth phase. A low PEP to pyruvate ratio corresponded LDH activity increase, leading to lactate accumulation in stationary phase. Biotechnol. Bioeng. 2008;100: 923–932.

Integrated production for biodiesel and 1,3-propanediol with lipase-catalyzed transesterification and fermentation

Biodiesel, a renewable alternative to fossil energy, has shown great prospects for global proliferation in the past decade. Lipase catalyzed transesterification for biodiesel production, as a biological process with many advantages has drawn increasing attention. As a by-product, glycerol accounts for about 10% w/w of biodiesel during the process of biodiesel production. As a result, the conversion of glycerol has become a common problem which has to be resolved if considering large amount of biodiesel production. Glycerol can be fermented into 1,3-propanediol, a high value added chemical with a promising future in the polymers, for example, polytrimethylene terephthalate, and also fermentation approaches for 1,3-propanediol production which have drawn more and more attention due to advantages such as relatively low investment, mild reaction conditions and using renewable sources as the starting materials. Based on the latest technology advancements in lipase-mediated transformation for biodiesel production, the aerobic fermentation technology and genetic engineering for 1,3-propanediol production, and the integrated production of 1,3-propanediol from crude glycerol could be a promising way to improve the profit of the whole process during biodiesel production.

Erratum to: Ammonium and phosphate limitation in 1,3-propanediol production by Klebsiella pneumoniae

Following publication of the above article (DOI: 10.1007/s10529-009-0150-y) in the October 2009 issue of Biotechnol Lett (32:289–294), it was found that the author affiliation name had been published incorrectly as: National Engineering Laboratory for Power Generation Equipment, School of Renewable Energy, North China Electric University, Beijing 102206, China The correct author affiliation name is listed below: National Engineering Laboratory for Biomass Power Generation Equipment, School of Renewable Energy, North China Electric Power University, Beijing 102206, China