Microbial cell systems

Although individual microbial cell systems usually grow under only a narrow range of physical conditions, there are many cell types which are adapted to extreme but specific environmental conditions. Cells have a series of cardinal conditions, i.e. a maximum, a minimum and an optimum with respect to physical conditions. Environmental conditions such as temperature, pressure, pH and ion concentration can all affect the growth of cells. For the more detailed explanation of the physical conditions of growth the reader is referred to specific texts on the subject"3 U). 

Radman, R. Saez, T. Bucke, C. Keshavarz, T. Elicitation of plants and microbial cell systems. Biotechnol. Appl. Biochem. 2003, 37 (Pt 1), 91-102. 

Three immobilized enzyme or microbial cell systems currently used industrially in synthesis of chiral amino acids plus one presently under development are described. L-amino acids are produced by enzymatic hydrolysis of DL-acylamino acid with aminoacylase immobilized by ionic binding to DEAE-Sephadex. Escherichia coli cells immobilized by K-carrageenan crosslinked with glutaraldehyde and hexamethylenediamine are used to convert fumaric acid and cimmonia to L-aspartic acid and Brevibacterium flavum cells similarly immobilized are used to hydrate fumaric acid to L-malic acid. The decarboxylation of L-aspcirtic acid by immobilized Pseudomonas dacunhae to L-alanine is currently under investigation. 

As described above, the polyacrylamide gel method is advantageous for Immobilization of microbial cells and for industrial application. However, there are some limitations in this method. That is, some enzymes are inactivated during Immobilization procedure by the action of acrylamide monomer, 8-dimethylamino-propionitril, potassium persulfate or heat of the polymerization reaction. Therefore, this method has limitation in application for immobilization of enzymes and microbial cells. Thus, to find out more general Immobilization technique and to Improve the productivities of Immobilized microbial cell systems we studied new immobilization techniques. As the results, we have found out K-carrageenan is very useful for Immobilization of cells [8]. <-Carrageenan, which is composed of unit structure of B-D-galactose... 

This volume contains most of the papers presented at the symposium. In addition, several chapters written by leading experts in the field have also been included. Several important aspects of immobilized microbial cell technology are discussed here carriers for immobilization, methods of cell attachment, biophysical and biochemical properties, reactor design, and process engineering of bound cell systems. A number of applications in the food, pharmaceutical, and medical areas— including those commercialized already— have been described. In essence, this is a comprehensive single volume state-of-the-art presentation of immobilized microbial cell systems. 

Recovery. The principal purpose of recovery is to remove nonproteinaceous material from the enzyme preparation. Enzyme yields vary, sometimes exceeding 75%. Most industrial enzymes are secreted by a microorganism, and the first recovery step is often the removal of whole cells and other particulate matter (19) by centrifugation (20) or filtration (21). In the case of ceU-bound enzymes, the harvested cells can be used as is or dismpted by physical (eg, bead mills, high pressure homogenizer) and/or chemical (eg, solvent, detergent, lysozyme [9001 -63-2] or other lytic enzyme) techniques (22). Enzymes can be extracted from dismpted microbial cells, and ground animal (trypsin) or plant (papain) material by dilute salt solutions or aqueous two-phase systems (23). 

The bioreactor is the heart of any biochemical process in which enzymes, microbial, mammalian or plant cell systems are used for manufacture of a wide range of useful biological products. The performance of any bioreactor depends on many functions, such as those listed below ... 

Wang et al.2 and Najafpour et al.3A worked with immobilised microbial cells of Nitrobacer agilis, Saccharomyces cerevisiae and Pseudomonas aeruginosa in gel beads, respectively. They found separately that the cells retained more than 90% of their activity after immobilisation by using specific oxygen uptake rate (SOUR) [mg 02g 1 (dry biomass) h 11 as the biomass activity indicator. Such differences in immobilised biomass and activity between free and immobilised biomass activities depend strongly on the particular characteristics of the microbial systems and their interaction with the support matrix. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

In the biocatalytic system, a second organic phase consisting of bis(2-ethyUiexyl)phthalate and containing the substrate is added at a phase ratio of 1 1. This procedure enables in situ product extraction and protects the microbial cells from toxic effects of the substrate and... 

In the past, copper was believed to be toxic to most microbiological species. Although this may be true in a test tube under laboratory conditions, it is not generally true in the real world. In this real world, microbial communities excrete slime layers which tend to sequester the copper ions and prevent their contact with the actual microbial cells, Aus preventing the copper from killing the microbes. Many cases of MIC in copper and copper alloys have been documented, especially of heat-exchange tubes, potable water, and fire protection system piping. 

Steinborn, G., Boer, E., Scholz, A. et al. (2006) Application of a wide-range yeast vector (CoMed) system to recombinant protein production in dimorphic Arxula adeninivorans, methylotrophic Hansenula polymorpha and other yeasts. Microbial Cell Factories, 5, 33. 

The separation method targets recovery of the aqueous phase from oil/water mixtures of microbial reactions by filtration through a ceramic filter module [154], The invention particularly referred to a two-phase system resulting from a process used for production of 2,6-naphthalenedicarboxylic acid using S. paucimobilis AK2M16 (PERM P-13996). The aqueous phase is said to be recovered free of microbial cells and oil. Although, it is mentioned that the reaction product can be recovered readily in high yield, the need for an additional unit operation looks obvious. 

Disruption of microbial cells is rendered difficult due to the presence of the microbial cell wall. Despite this, a number of very efficient systems exist that are capable of disrupting large quantities of microbial biomass (Table 6.1). Disruption techniques, such as sonication or treatment with the enzyme lysozyme, are usually confined to laboratory-scale operations, due either to equipment limitations or on economic grounds. 

Genotoxic Effects. No studies were located regarding the genotoxic effects of hexachloroethane in humans after inhalation, oral, or dermal exposure. In vitro studies of hexachloroethane using microbial, fungal, and rodent cell assays are summarized in Table 2-4. Tests of prokaryotic cell systems failed to detect gene mutation (Haworth et al. 1983 Roldan-Arjona et al. 1991 Simmon and Kauhanen 1978 ... 

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