Formation of?,?-dodecanedioic acid and?,?-tridecanedioic acid from different substrates by immobilized cells of a mutant ofCandida tropicalis

Improving α, ω-dodecanedioic acid productivity from n-dodecane and hydrolysate of Candida cells by membrane integrated repeated batch fermentation

The aim of the present study is to develop an effective production process for α, ω-dodecanedioic acid (DC₁₂) biosynthesis using n-dodecane and hydrolysate of Candida cells as substrates by membrane integrated repeated batch fermentation. Cells and n-dodecane were simultaneously recycled during the filtration of fermentation broth (FB) with a 150 kDa ceramic membrane under a cross-flow velocity of 4 m/s and a trans-membrane pressure of 0.2 MPa, and it was also revealed that the cells in the broth could alleviate the membrane fouling during the FB filtration. Moreover, the hydrolysate of the collected cells could be successfully used as a nitrogen source to replace 50% yeast extract for decreasing the DC₁₂ production cost. With repeated-batch culture in a membrane bioreactor, the maximal DC₁₂ productivity could be enhanced by 57.8% compared with the batch culture, meanwhile n-dodecane and cells could be recovered and used for the next fermentation cycle.

Role of oxygen supply in α, ω-dodecanedioic acid biosynthesis from n-dodecane by Candida viswanathii ipe-1: Effect of stirring speed and aeration

α, ω-Dodecanedioic acid (DC₁₂) usually serves as a monomer of polyamides or some special nylons. During the biosynthesis, oxygenation cascaded in conversion of hydrophobic n-dodecane to DC₁₂, while the oxidation of n-dodecane took place in the intracellular space. Therefore, it was important to investigate the role of oxygen supply on the cell growth and DC₁₂ biosynthesis. It was found that stirring speed and aeration influenced the dissolved oxygen (DO) concentration which in turn affected cell growth as well as DC₁₂ biosynthesis. However, the effect of culture redox potential (Orp) level on DC₁₂ biosynthesis was more significant than that of DO level. For DC₁₂ biosynthesis, the first step was to form the emulsion droplets through the interaction of n-dodecane and the cell. When the stirring speed was enhanced, slits in the surface layer of the emulsion droplets would be increased. Thus, the substances transportation by water through the slits would be intensified, leading to an enhanced DC₁₂ production. Compared with the batch culture at a lower stirring speed (400 rpm) without culture redox potential (Orp) control, the DC₁₂ concentration was increased by 5 times up to 201.3 g/L with Orp controlled above 0 mV at a higher stirring speed (800 rpm).

α, ω-Dodecanedioic acid production by Candida viswanathii ipe-1 with co-utilization of wheat straw hydrolysates and n-dodecane

Candida viswanathii ipe-1 was used to produce α, ω-dodecanedioic acid (DC₁₂), which showed capability to ferment xylose and glucose simultaneously, while arabinose utilization was less efficient. A low concentration of furfural enhanced cell growth, and the addition of 4.0g/L sodium acetate largely increased DC₁₂ production. It indicated that detoxification of the wheat straw hydrolysates was not necessary for the biosynthesis of DC₁₂. Based on the promising features of our strain, an efficient process was developed to produce DC₁₂ from co-utilization of wheat straw hydrolysates and n-dodecane. Using this process, 129.7g/L DC₁₂ with a corresponding productivity of 1.13g·L^-1·h^-1 could be produced, which was increased by 40.0% compared with a sole carbon of glucose. The improved DC₁₂ yield by the co-utilization of wheat straw hydrolysates and n-dodecane using C. viswanathii ipe-1 demonstrates the great potential of using biomass as a feedstock in the production of DC₁₂.

Whole-cell biocatalysis for selective and productive C-O functional group introduction and modification

During the last decades, biocatalysis became of increasing importance for chemical and pharmaceutical industries. Regarding regio- and stereospecificity, enzymes have shown to be superior compared to traditional chemical synthesis approaches, especially in C-O functional group chemistry. Catalysts established on a process level are diverse and can be classified along a functional continuum starting with single-step biotransformations using isolated enzymes or microbial strains towards fermentative processes with recombinant microorganisms containing artificial synthetic pathways. The complex organization of respective enzymes combined with aspects such as cofactor dependency and low stability in isolated form often favors the use of whole cells over that of isolated enzymes. Based on an inventory of the large spectrum of biocatalytic C-O functional group chemistry, this review focuses on highlighting the potentials, limitations, and solutions offered by the application of self-regenerating microbial cells as biocatalysts. Different cellular functionalities are discussed in the light of their (possible) contribution to catalyst efficiency. The combined achievements in the areas of protein, genetic, metabolic, and reaction engineering enable the development of whole-cell biocatalysts as powerful tools in organic synthesis.

Application of immobilized growing cells

Immobilized living and growing cells are attracting worldwide attention because these biocatalysts have self-proliferating and self-regenerating properties of catalytic systems and are able to catalyze efficiently multifunctional and multistep reactions involving coenzyme regeneration. This article summarizes the application of microbial, plant, and mammalian cells, genetically improved or not, immobilized by different methods to the production of amino acids, organic acids, antibiotics, steroids, medicines, enzymes, bioactive peptides, etc., emphasizing the recent results. Effects of the gel properties on the efficient performance of bioprocesses are also discussed.

Bioconversion of N-Octane to Octanoic Acid by a Recombinant Escherichia Coli Cultured in a Two-Liquid Phase Bioreactor

The alk genes from the catabolic OCT plasmid of Pseudomonas oleovorans, which encode the enzymes involved in the oxidation of n-alkanes to carboxylic acids, were introduced into E. coli W3110. The resulting recombinant converts n-octane in a two-liquid phase medium into the corresponding alkanoate and excretes this compound into the aqueous phase. The rate of octanoic acid production by the recombinant E. coli is equal to or better than the alkane oxidation rate of P. oleovorans, suggesting that two-liquid phase fermentations with E. coli might have future industrial applications.