Yongguang Zhang

The base-free and selective oxidative transformation of 1,3-propanediol into methyl esters by different Au/CeO2 catalysts

Different Au/CeO2 catalysts, prepared by depositing gold on different facets of ceria nanocubes ({100}), nanorods ({110} and {100}) and nanopolyhedra ({111} and {100}), were separately characterized by means of XRD, N2 sorption, TPD and TPR. It was found that certain types of Au/CeO2 could selectively catalyze the oxidative transformation of 1,3-propanediol in methanol to methyl 3-hydroxypropionate, methyl 3-methoxypropionate, methyl acrylate or dimethyl malonate by molecular oxygen in the absence of any base. The selectivities of these Au/CeO2 catalysts depended on the shapes of the supporting CeO2 and the reaction temperature. The Au/CeO2 cube catalyst with less acidic and basic sites exhibited high selectivity towards methyl 3-hydroxypropionate (93.1% at 21.6% conversion). Comparatively, selectivities towards methyl acrylate (41.6% at 92.3% conversion) and methyl 3-methoxypropionate (40.2% at 92% conversion) increased using Au/CeO2 rod and polyhedron catalysts, which contained more acidic and basic sites than the cube catalyst. Moreover, we found the Au/CeO2 cube catalyst could be recycled without losing the gold nanoparticles.

Cloning and transcription analysis of the Candida rugosa propionyl-CoA dehydrogenase gene and its expression in Pichia pastoris

The propionyl‐CoA dehydrogenase (PACD) gene was cloned from Candida rugosa by the cDNA RACE technique. The full cDNA of the PACD gene has a length of 1408 bp, which contains a complete open reading frame (ORF) of 1329 bp, coding for 442 amino acids. The cDNA of PACD was cloned into the expression plasmid pPIC9K and transformed into Pichia pastoris GS115. The recombinant protein was purified by Ni‐NTA affinity chromatography, and its size was observed to be approximately 49 kDa as estimated by SDS‐PAGE. Anti‐His antibodies were used to characterise the recombinant PACD by western‐blot analysis. The recombinant protein retained the activity of catalysing propionyl‐CoA to acryloyl‐CoA. The results of dot‐blotting hybridisation using a PACD cDNA probe indicated that the PACD mRNA level was modified at different stages: mRNA levels were low for the first 36 h, then increased through 48 h and eventually reached a stable level. These results indicate that propionate induction could significantly activate PACD mRNA expression. Information from this study will be helpful in elucidating the metabolic pathway for 3‐hydroxypropionic acid production in C. rugosa. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of ethanol on the growth and propionic acid formation of propionibacterium acidipropionici

This study aimed to assess the effect of ethanol on the growth and propionic acid production of Propionibacterium acidipropionici, and develop a mixed-cultures method to improve propionic acid production. At natural pH, low amount of ethanol (less than 0.5 %, v/v) showed significantly stimulatory effects on the growth and propionic acid production of P. acidipropionici, while not at pH 6.5 controlled. Based on these results, a mixed cultures strategy to improve propionic acid fermentation of P. acidipropionici was developed. The addition of Candida sp. BS-1 (2 %, v/v) to the flasks of P. acidipropionici, the glycerol consumption rates (0.218 g/l/h), and the maximal propionic acid yield (11.3 g/l) were about 24.8 % and 20.9 % higher than those of the single culture fermentation. The results indicated a mixed-culture method would be a potential way to improve propionic acid production.

Extraction of mycelial polysaccharides from submerged-cultured cordyceps militaris (a caterpillar fungus)

Cordyceps militaris, a kind of caterpillar fungus, has therapeutic effects including immunoregulative, anticancer, antibacterial and antifungal effects. Aqueous extraction and alkaline (NaOH) hydrolysis method were comparatively studied in polysaccharides extraction from submerged-cultured C. militaris mycelia. The results indicate that the polysaccharide content and the total extract rate from alkaline extraction method were obviously higher than those from the aqueous extraction method. The extraction process parameters of alkaline extraction were further optimized using response surface methodology (RSM), and a mathematical model was then developed to show the effect of each extraction condition and their interactions on the polysaccharide extraction. The model predicted the optimum alkaline concentration was 1.6 mol/L, extraction temperature 56.7 □, extraction time 1.94, and the extraction rate was 11.57%. Furthermore, verification of the calculated optimum of the model was done with a condition representing this maximum point and obtaining a extraction rate of 11.12 %. The good correlation between predicted and measured values of these experiments justifies the validity of the response model and the existence of an optimum point.

Partial deficiency of G6PDH results in lower osmotolerance to glycerol and glycerol biosynthesis of candida glycerinogenes

Candida glycerinogenes, an osmotolerant yeast, is currently used commercially in China for the production of glycerol. In this study, the osmotolerance of C. glycerinogenes 14-2, a partial glucose 6-phosphate dehydrogenase (G6PDH) deficiency mutant, to high glucose, NaCl or glycerol concentration was tested, and then the fermentation performance of the mutant was investigated. The mutant showed almost the same osmotolerance to glucose and NaCl as the wild type strain, but poor osmotolerance to glycerol. With low glucose (135 g/L), the mutant produced 34.0 g/L glycerol like its parent strain, while 27.7 % less than the control strain with high glucose (252 g/L). Under the both conditions, the specific glucose consumption rate and the specific glycerol formation rate of the mutant were much lower than those of the wild type strain, especially with high glucose. The partial deficiency of G6PDH resulted in declined tolerance to glycerol and poor performance of glycerol fermentation of C. glycerinogenes. The present study indicates that HMP plays important roles in osmoadaptation and glycerol biosynthesis of C. glycerinogenes. The research sheds new light on mechanism of osmoadaptation of yeast.