Zongming Zheng

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.

Effects of biopretreatment on pyrolysis behaviors of corn stalk by methanogen.

The study investigated the effects of methanogen pretreatment on pyrolysis behaviors of corn stalk (CS) by using Py-GC/MS analysis and thermogravimetric analysis. Results indicated that biopretreatment changed considerably the pyrolysis behaviors of CS from four weight loss stages to two weight loss stages. Increasing biopretreatment time from 5 days to 25 days enhanced the kinds and contents of chemicals in volatile products. In pyrolysis products, the contents of sugars, linear ketones and furans decreased from 1.43%, 12.60% and 7.38% to 1.25%, 10.22% and 3.25%, respectively, and the contents of phenols increased from 15.08% to 27.84%. The most content change from 6.83% to 13.63% indicated that methanogen pretreatment improved the pyrolysis selectivity of CS to product the 4-VP, but it was disadvantageous to 5-hydroxymethyl furfural, levoglucose and furfural. The changes of chemical compositions and structure of CS after biopretreatment were the main reason of the differences.

Fast pyrolysis product distribution of biopretreated corn stalk by methanogen.

After pretreated by methanogen for 5, 15 and 25 days, corn stalk (CS) were pyrolyzed at 250, 300, 350, 400, 450 and 500 °C by Py-GC/MS and product distribution in bio-oil was analyzed. Results indicated that methanogen pretreatment changed considerably the product distribution: the contents of sugar and phenols increased; the contents of linear carbonyls and furans decreased; the contents of linear ketones and linear acids changed slightly. Methanogen pretreatment improved significantly the pyrolysis selectivity of CS to phenols especially 4-VP. At 250 °C, the phenols content increased from 42.25% for untreated CS to 79.32% for biopretreated CS for 5 days; the 4-VP content increased from 28.6% to 60.9%. Increasing temperature was contributed to convert more lignin into 4-VP, but decreased its content in bio-oil due to more other chemicals formed. The effects of biopretreatment time on the chemicals contents were insignificant.

Theoretical study on the mechanisms of cellulose dissolution and precipitation in the phosphoric acid–acetone process

Phosphoric acid-acetone fractionation was applied to pretreat lignocellulose for production of cellulosic ethanol. Cellulose solubility properties in H(2)O, H(3)PO(4) and CH(3)COCH(3) were simulated. Atomic geometry and electronic properties were computed using density functional theory with local-density approximation. H(3)PO(4) molecule is adsorbed between two cellulose segments, forming four hydrogen bonds with E(B) of -1.61 eV. Density of state for cellulose in H(3)PO(4)-cellulose system delocalizes without obvious peak. E(gap) of 4.46 eV is much smaller than that in other systems. Molecular dynamics simulation indicates that fragments of double glucose rings separate in the cellulose-H(3)PO(4) interaction system. Icy CH(3)COCH(3) addition leads to re-gathering of separated fragments. Reaction energy of cellulose in three solvents is around 3.5 eV, implying that cellulose is chemically stable. Moreover, theoretical results correspond to the experiments we have performed, showing that cellulose dissolves in H(3)PO(4), flocculates after CH(3)COCH(3) addition, and finally becomes more liable to be hydrolyzed into glucoses.

Lignin Hydrolysis and Phosphorylation Mechanism during Phosphoric Acid–Acetone Pretreatment: A DFT Study

The study focused on the structural sensitivity of lignin during the phosphoric acid–acetone pretreatment process and the resulting hydrolysis and phosphorylation reaction mechanisms using density functional theory calculations. The chemical stabilities of the seven most common linkages (β-O-4, β-β, 4-O-5, β-1, 5-5, α-O-4, and β-5) of lignin in H3PO4, CH3COCH3, and H2O solutions were detected, which shows that α-O-4 linkage and β-O-4 linkage tend to break during the phosphoric acid–acetone pretreatment process. Then α-O-4 phosphorylation and β-O-4 phosphorylation follow a two-step reaction mechanism in the acid treatment step, respectively. However, since phosphorylation of α-O-4 is more energetically accessible than phosphorylation of β-O-4 in phosphoric acid, the phosphorylation of α-O-4 could be controllably realized under certain operational conditions, which could tune the electron and hole transfer on the right side of β-O-4 in the H2PO4− functionalized lignin. The results provide a fundamental understanding for process-controlled modification of lignin and the potential novel applications in lignin-based imprinted polymers, sensors, and molecular devices.

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