The Microbial Cell

Microbiology can be defined as the study of organisms that are too small to be clearly visible to the naked eye. This will include all organisms with a diameter of less than approximately 1 mm. 

Micro-organisms are widely distributed between different taxonomic groups and include bacteria, protozoa, fungi, and algae. Viruses, although frequently considered in microbiology text books, are not cells. 

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Enzymatic Process. Chemically synthesized substrates can be converted to the corresponding amino acids by the catalytic action of an enzyme or the microbial cells as an enzyme source, t - Alanine production from L-aspartic acid, L-aspartic acid production from fumaric acid, L-cysteine production from DL-2-aminothiazoline-4-catboxyhc acid, D-phenylglycine (and D-/> -hydtoxyphenylglycine) production from DL-phenyUiydantoin (and DL-/)-hydroxyphenylhydantoin), and L-tryptophan production from indole and DL-serine have been in operation as commercial processes. Some of the other processes shown in Table 10 are at a technical level high enough to be useful for commercial production (24). Representative chemical reactions used ia the enzymatic process are shown ia Figure 6. 

Considerable work has been done to try to explain why quats are antimicrobial. The following sequence of steps is beheved to occur in the attack by the quat on the microbial cell (/) adsorption of the compound on the bacterial cell surface (2) diffusion through the cell wall (J) binding to the cytoplasmic membrane (4) dismption of the cytoplasmic membrane (5) release of cations and other cytoplasmic cell constituents (6) precipitation of cell contents and death of the cell. 

The resultant fermentation broth was centrifuged to harvest the microbial cells, and they were washed with water and centrifuged a second time, whereupon a living cell paste was obtained. (There was obtained an amount of cells equivalent to 54 parts on a dry basis, which contained 920 /Jg of ubiquinone-10 per gram of dry cells.)... 

Study the unlabelled block diagram, and then replace the question marks with the words and phrases to give a generalised scheme of an industrial fermentation. Assume in this example that the product is excreted from the microbial cells. 

Although exopolysaccharides do not normally have a structural role, they do form structures that can be detected by either light or electron microscopy. Exopolysaccharides may form part of a capsule closely attached to the microbial cell surface, or appear as loose slime secreted by the cell but not directly attached to it mucoid Exopolysaccharide producing cells usually form mucoid colonies on solid media and colonies liquid cultures of these cells may become very viscous. However, growth conditions can... 

Since amino adds are used as essential components of the microbial cells and their biosynthesis is regulated to maintain an optimal level, they are normally synthesised in feedback limited amounts and are subjed to negative feedback control. The main problem using control strains is, therefore, the production of minor amounts of amino adds at an early... 

Sometimes poor centrifugation behaviour of cells can be improved by adding flocculation agents. These agents neutralise the anionic charges (carboxyl and phosphate groups) on the surface of the microbial cells. Examples of flocculation agents are alum, caldum and ferric salts, tannic add etc. 

A strain of Azotobacter vinelandii was cultured in a 15 m3 stirred fermenter for the production of alginate. Under current conditions the mass transfer coefficient, kLa, is 0.18 s. Oxygen solubility in the fermentation broth is approximately 8 X 10 3 kgm-3.9 The specific oxygen uptake rate is 12.5 mmol g 1 h. What is the maximum cell density in the broth If copper sulphate is accidentally added to the fermentation broth, which may reduce the oxygen uptake rate to 3 mmol g 1 h 1 and inhibit the microbial cell growth, what would be the maximum cell density in this condition ... 

Figure 3.11 illustrates the mass transfer coefficient for batch-grown R. rubrum and was computed with various acetate concentrations at 200 rpm agitation speed, 500 lux light intensity, and 30 °C. As the experiment progressed, there was an increase in the rate of carbon monoxide uptake in the gas phase and a gradual decrease in die partial pressure of carbon monoxide. Also, a decrease in the partial pressure of carbon monoxide was affected by acetate concentration in the culture media. The value of the slope of the straight line increased with the decrease in acetate concentrations, i.e. 2.5 to 1 g-l. The maximum mass transfer coefficient was obtained for 1 g-l 1 acetate concentration (KLa = 4.3-h 1). The decrease in mass transfer coefficient was observed with the increase in acetate concentration. This was due to acetate inhibition on the microbial cell population as acetate concentration increased in the culture media. The minimum KLa was 1.2h 1 at 3g l 1 acetate concentration. 

As shown in Figure 8.1a, the carrier binding method is based on binding microbial cells directly to water-insoluble carriers. The binding is due to ionic forces between the microbial cells and the water-insoluble carriers. This technique has rarely been used, however, because of lyses dming the enzyme reactions. Microbial cells may leak from the earner, thereby disrupting the immobilisation. Therefore, this method has not been applied successfully.6... 

Hugo W.B. (ed.) (1971) The Inhibition and Destruction of the Microbial Cell. London Academic Press. 

The microbial cell surface constitutes a multiplicity of different antigens. These antigens may be common to different species or types of microorganisms or may be highly specific for that one type only. 

This is important not only in field investigations. Even in laboratory experiments on the metabolism of xenobiotics, problems of association between the substrate and the microbial cells may occur. If this were not quantitatively evaluated or eliminated, the results and interpretation of such experiments would be seriously compromised. 

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... 

The primary metabolism of an organic compound uses a substrate as a source of carbon and energy. For the microorganism, this substrate serves as an electron donor, which results in the growth of the microbial cell. The application of co-metabolism for bioremediation of a xenobiotic is necessary because the compound cannot serve as a source of carbon and energy due to the nature of the molecular structure, which does not induce the required catabolic enzymes. Co-metabolism has been defined as the metabolism of a compound that does not serve as a source of carbon and energy or as an essential nutrient, and can be achieved only in the presence of a primary (enzyme-inducing) substrate. 

Farkade VD, Harrison STL, Pandit AB (2005) Heat induced translocation of proteins and enzymes within the cells an effective way to optimize the microbial cell disruption process. Biochem Eng J 23 247-257... 

Unimmobilized Corynebacterium propinquum (CGMCC No. 0886) cells containing a cobalt-dependent NHase were employed in either batch or continuous reactions for the production of nicotinamide from 3-cyanopyridine [24]. In the continuous process, membrane filtration separated precipitated product (>5 wt%) and the microbial cell catalyst from the reaction mixture, where the catalyst was then recovered and returned to the reactor using a continuous addition of aqueous 3-cyanpyridine to maintain substrate concentration at <20% (w/v), a final conversion of >99% was obtained. 

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. 

N. Ishii, M. Robert, Y. Nakayama, A. Kanai, and M. Tomita, Toward large scale modeling of the microbial cell for computer simulation. J. Biotechnol. 113, 281 294 (2004). 

Only 1.2% of the carbon of 2,4-D added to stream water was converted to organic particulate matter, the solids fraction in water containing the microbial cells. This lack of significant carbon assimilation may be a result of the inability of the microorganisms to obtain carbon and energy for biosynthetic purposes at these low concentrations, the immediate use of the carbon for respiration in order for the cells to maintain their viability (i. e., for maintenance energy), or the rapid decomposition and mineralization of the cells and their constituents. 

Should the enzymes catalyzing the initial degradation be intracellular, the molecule to be degraded must penetrate the microbial cell wall to the internal sites where the enzyme acts. Alternatively, the products of an extracellular reaction must penetrate the cell wall for the transformation to proceed further. 

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