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      The Effect of Created Local Hyperosmotic Microenvironment in Microcapsule for the Growth and Metabolism of Osmotolerant Yeast Candida krusei

      research-article
      Author(s): 1 , * , 2
      Publication date (Electronic):
      Journal: BioMed Research International
      Publisher: Hindawi Publishing Corporation

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          Abstract

          Candida krusei is osmotolerant yeast used for the production of glycerol. Addition of osmolyte such as NaCl into culture medium can increase the production of glycerol from glucose, but osmolytes may burden the glycerol separation. A coencapsulation method was suggested to create local extracellular hyperosmotic stress for glycerol accumulation. Firstly, the influence of osmotic stress induced by the addition of PEG4000 on growth and metabolism of free cell was studied in detail. Glycerol accumulation could be improved by employing PEG4000 as osmoregulator. Secondly, cells and PEG4000 were coentrapped in NaCS/PDMDAAC capsules to create local hyperosmotic stress. The effects of local hyperosmotic microenvironment on the cell growth and metabolism were studied. The coentrapment method increased the glycerol concentration by 25%, and the glycerol concentration attained 50 gL −1 with productivity of 18.8 gL −1Day −1 in shake flask. More importantly, the glycerol could be directly separated from the encapsulated cells. The entrapped cells containing PEG4000 were also cultivated for 15 days in an airlift reactor. The yield and productivity were ca. 35% and 21 gL −1Day −1, respectively.

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          Microencapsulation of microbial cells.

          J.K. Park, H.N. Chang (2000)
          The high level of biocatalysts such as microbial cells and enzymes plays an important role in increasing the productivity of a bioreactor. The beads entrapped with microbial cells are not strong enough for long-term use. The small void space of polymer matrix and the leakage of cells limit a final cell loading in the beads. The recent success of encapsulating microbial cells makes it possible to prepare dense biocatalyst composed of recombinant microbial cells. In addition to encapsulating microbial cells, immobilization of animal and plant cells in capsules is also briefly described.
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            Glycerol production by microbial fermentation: a review.

            J Zhuge, R Prior, X. Wang … (2001)
            Microbial production of glycerol has been known for 150 years, and glycerol was produced commercially during World War I. Glycerol production by microbial synthesis subsequently declined since it was unable to compete with chemical synthesis from petrochemical feedstocks due to the low glycerol yields and the difficulty with extraction and purification of glycerol from broth. As the cost of propylene has increased and its availability has decreased especially in developing countries and as glycerol has become an attractive feedstock for production of various chemicals, glycerol production by fermentation has become more attractive as an alternative route. Substantial overproduction of glycerol by yeast from monosaccharides can be obtained by: (1) forming a complex between acetaldehyde and bisulfite ions thereby retarding ethanol production and restoring the redox balance through glycerol synthesis; (2) growing yeast cultures at pH values near 7 or above; or (3) using osmotolerant yeasts. In recent years, significant improvements have been made in the glycerol production using osmotolerant yeasts on a commercial scale in China. The most outstanding achievements include: (1) isolation of novel osmotolerant yeast strains producing up to 130 g/L glycerol with yields up to 63% and the productivities up to 32 g/(L day); (2) glycerol yields, productivities and concentrations in broth up to 58%, 30 g/(L day) and 110-120 g/L, respectively, in an optimized aerobic fermentation process have been attained on a commercial scale; and (3) a carrier distillation technique with a glycerol distillation efficiency greater than 90% has been developed. As glycerol metabolism has become better understood in yeasts, opportunities will arise to construct novel glycerol overproducing microorganisms by metabolic engineering.
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              Glycerol export and glycerol-3-phosphate dehydrogenase, but not glycerol phosphatase, are rate limiting for glycerol production in Saccharomyces cerevisiae.

              F Remize, S Dequin, L Barnavon (2001)
              Glycerol, one of the most important by-products of alcoholic fermentation, has positive effects on the sensory properties of fermented beverages. It was recently shown that the most direct approach for increasing glycerol formation is to overexpress GPD1, which encodes the glycerol-3-phosphate dehydrogenase (GPDH) isoform Gpd1p. We aimed to identify other steps in glycerol synthesis or transport that limit glycerol flux during glucose fermentation. We showed that the overexpression of GPD2, encoding the other isoform of glycerol-3-phosphate dehydrogenase (Gpd2p), is equally as effective as the overexpression of GPD1 in increasing glycerol production (3.3-fold increase compared to the wild-type strain) and has similar effects on yeast metabolism. In contrast, overexpression of GPP1, encoding glycerol 3-phosphatase (Gpp1p), did not enhance glycerol production. Strains that simultaneously overexpress GPD1 and GPP1 did not produce higher amounts of glycerol than a GPD1-overexpressing strain. These results demonstrate that GPDH, but not the glycerol 3-phosphatase, is rate-limiting for glycerol production. The channel protein Fps1p mediates glycerol export. It has recently been shown that mutants lacking a region in the N-terminal domain of Fps1p constitutively release glycerol. We showed that cells producing truncated Fps1p constructs during glucose fermentation compensate for glycerol loss by increasing glycerol production. Interestingly, the strain with a deregulated Fps1 glycerol channel had a different phenotype to the strain overexpressing GPD genes and showed poor growth during fermentation. Overexpression of GPD1 in this strain increased the amount of glycerol produced but led to a pronounced growth defect. Copyright 2001 Academic Press.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Biomed Res Int
                Journal ID (iso-abbrev): Biomed Res Int
                Journal ID (publisher-id): BMRI
                Title: BioMed Research International
                Publisher: Hindawi Publishing Corporation
                ISSN (Print): 2314-6133
                ISSN (Electronic): 2314-6141
                Publication date (Print): 2013
                Publication date (Electronic): 5 November 2013
                Volume: 2013
                Electronic Location Identifier: 467263
                Affiliations
                1Department of Biotechnology and Bioengineering, Huaqiao University, Xiamen 361021, China
                2Department of Chemical and Biochemical Engineering, Zhejiang University, Hangzhou 310027, China
                Author notes

                Academic Editor: Hongjuan Liu

                Article
                DOI: 10.1155/2013/467263
                PMC ID: 3835448
                SO-VID: ceec8c16-24ec-43ab-a82a-a33378ce94b2
                Copyright © Copyright © 2013 G. Chen and S. Yao.
                License:

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 2 April 2013
                Date revision received : 15 September 2013
                Date accepted : 16 September 2013
                Funding
                Funded by: http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China
                Award ID: 20906035
                Categories
                Subject: Research Article

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