Immobilized cell reactors

Najafpour, G.D., Younesi, H. and Ku Ismail, K.S., Ethanol Fermentation in Immobilized Cell Reactor (ICR) Using Saccharomyces cerevisiae , Bioresource Technology, vol. 92/3, 2004, pp. 251-260. 

Tan et al. [29] demonstrated the use of a plug flow reactor of immobilized Lactobacillus kefiri cells for the synthesis of the intermediate (5I )-hydroxyhexane-2-one. This immobilized-cell reactor operated at a maximum conversion yield of 100% and a selectivity of 95%. The production of (5/ )-hydroxyhexane-2-one was extended to an operation time of 6 days. During this time (91 residence times), a space-time yield of 87gL xday 1 and a productivity of 07 8 gwet cell weight 1 were obtained. 

The use of immobilized cell reactors have shown improved biocatalyst stability, however, the specific rates of desulfurization have been much lower than for suspended cell (stirred) reactors. Mass transfer limitations have been significant resulting in lower rates. Thus, the activity is sacrificed to achieve stability. Further work in this area and improved immobilization matrices can help improve the activity along with the stability. 

An immobilized cell reactor is classified as a continuous biological system that may follow either plug flow theory or fluidized-bed theory depending on the mode of operation. 

Immobilized Cell Reactors An immobilization technique consists of attaching the cells to a gel matrix. A high cell concentration can be obtained. Agitation, cell separation and recycling are not needed. Immobilized cells can be used in fixed-bed and fluidized-bed reactors. The substrate solution flows continuously through the reactor, while the immobilized cells convert the sugar to ethanol. A maximum ethanol productivity of 53.8g/l was achieved at a dilution rate of 4.6 h 1 and an initial glucose concentration of 127 g/1. 

Webb, C., Biomass Holdup in Immobilized Cell Reactors, Chap. 8 in Process Engineering Aspects of Immobilized Cell Systems, pp. 117-133. Instn. Chem. Engrs. (London), 1986. Weber, G., New Lift Technique, Oil Gas J., IS (1952). 

Secondary metabolite production has been increased by applying immobilization procedures alone (9 19). Development of immobilized cell reactors, where cells remain viable and fully active biosynthetically after permeabilization treatment, would allow the continuous production of valuable secondary metabolites from a combined immobilization/permeabilization system as previously attempted by us (K), 18, Beaumont, M.D. and Knorr, D., Univ. of Delaware, unpublished data). This would also give higher product yields as compared to utilizing freely-suspended non-permeabilized cells. 

Typical commercial cell culture systems include batch or fed-batch suspension reactors and perfused immobilized-cell reactors. However, the transient nature of batch culture causes difficulties in studying the effects of external stimuli on growth, metabolism and product formation. Due to metabolite concentration gradients, and the difficulty of obtaining representative cell samples, immobilized-cell reactors are also poorly suited for the analysis of cell growth and metabolism. As a result it is desirable to use well-defined model systems. Continuous-flow suspension reactors allow metabolic parameters to be measured at steady state, after cells have adapted to new (and possibly inhibitory) conditions. Perfusion reactors (with cells immobilized on suspended or stationary supports) extend these benefits to anchorage-dependent cells, and provide model systems for cell responses in vivo. However, while it is instructive to study the behaviour of cells under well-defined conditions, the results obtained must be verified in the culture system selected for commercial production. 

Cell density is rarely measured directly in immobilized-cell reactors because it is not possible to obtain a single-cell suspension suitable for counting without disturbing the reactor. Specialized techniques are available for indirect non-invasive determination of cell density, but most researchers estimate cell density via nutrient consumption rates. Methods for estimation of cell density from nutrient consumption rates and an analysis of the reliability of such estimates are discussed below. 

The equations in this section are applicable to any system in which the viable cell density can be determined. This includes all of the systems described above except for immobilized cell reactors. 

It is also relevant to consider the product yield on substrate in immobilized-cell reactors. The apparent yield of product from substrate, Fpg, can be monitored over time to detect changes in the yield. If other yields are relatively constant, then changes in Fps may indicate changes in the specific production rate (gp). However, if some or all of the other calculated metabolic yields change, then it would be very difficult to attribute changes in production rate directly to changes in 9p. Inhibition of substrate consumption or growth by waste products may contribute to a decrease in product yield. 

While the Immediate benefit from such an understanding would be an extended production phase In batch fermentations, this knowledge should also be central In designing alternative whole-cell processes (e.g.. Immobilized cell reactors). In which keeping the enzymes "alive" In their native Intracellular micro-environment could be the optimal approach In the operational transition from a batch to a continuous process. 

Bacillus agaradhaerens P-Cyclodextrin Integrated immobilized cell-reactor adsorption system [12]... 

Martins RE, Plieva EM, Santos A, Hatti-Kaul R (2005) Integrated immobilized cell reactor-adsorptimi system for p-cyclodextrin production A model study using PVA-ciyogel entrapped Raci//t/s agaradharens. Biotechnol Lett 25 1537-1543... 

Gordito MP, Kotsis DH, Minteer SD, Spence DM (2003) Flow-based amperometric detection of dopamine in an immobilized cell reactor. J Neurosci Methods 124 129-134... 

Several bioreactor designs are used to produce bioproducts, and include, but are not limited to batch reactors, fed-batch reactors, continuous cultivation reactors, plug flow reactors, recycle bioreactor systems, immobilized cell reactors, biofilm reactors, packed bed reactors, fluidized-bed reactors, and dialysis cultivation reactors (Williams 2002). These reactor types can contain either mixed or pure cultures, and can stimulate heterotrophic and/or phototrophic cellular functions depending on the specific reactor design. Additionally, these reactor schemes can be used to produce products directly, or to harvest biomass or other products for downstream processes. Due to the complex nature of bioreactors, particularly anaerobic digesters, the use of metagenomics is helpful to understand the physiology of such systems. 

Lactic acid production in immobilized cell reactors... 

Pflugmacher U, Gottschalk G (1994) Development of an immobilized cell reactor for the production of 1,3-propanediol by Citrobacter freundii. Appl Microbiol Biotechnol 41 313-316... 

Amin, G.A., Al-Talhi, A., 2007. Production of L-glutamic acid by immobilized cell reactor of the bacterium Corynebac-terium glutamicum entrapped into carrageenan gel beads. World Applied Sciences Journal 2 (1), 61-(>7. 

Yan, S., Wang, P., Zhai, Z., Yao, J., 2011a. Fuel ethanol production from concentrated food waste hydrolysates in immobilized cell reactors by Saccharomyces cerevisiae H058. Journal of Chemical Technology and Biotechnology 86 (5), 731—738. 

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