Stable culture

After metabolically stable cultures have been obtained, pure cultures of the relevant organisms may then be obtained by any of three basic procedures ... 

The Middle Eastern traditions stem from the ancient civilizations of the area known as the Fertile Crescent. This area stretches from the eastern Mediterranean coast that is now part of Syria, Lebanon, and Israel, to the fertile lands that exist between the Tigris and Euphrates Rivers as they flow to the Persian Gulf. To the ancient Greeks this eastern end was known as Mesopotamia and it is now part of Syria, Turkey, Iran, and Iraq. Unlike Egypt, with its insular and stable culture, the Fertile Crescent was inhabited by several cultures, which migrated, conquered, and merged over the centuries. 

Because apparent metabolic yields can be determined without knowledge of n, Y values can be monitored to detect changes in metabohc patterns of cells in immobilized-cell bioreactors. For example, yj[ac,gic is easy to obtain and provides a good measure of the fate of the primary nutrient glucose. Relatively constant values for F[ac,gic NH3,gic Oz.gic other )delds provide a good indication of a stable culture environment. Under these conditions. Equation 4.2.44 may be used with confidence to estimate changes in the viable cell density. 

Variants that formed stable cultures could be obtained by growth limitation with both benzoate and 2,5-dichlorobenzoate. 

Figure 5 Effects of light attenuation conditions on culture stability and biomass productivity. For low residence time, low biomass concentration results in light transmission and high rate of photon absorption (ie, high light received per cell) inducing possible culture drift. For high residence time, the dark volume then generated can have a negative effect on biomass productivity due to the promotion of respiration activity, but also results in more stable culture because of a lower rates of photon absorption (ie, lower light received per cell).

Concerning this aspect of cell selection differing results have been obtained so far for the production of benzylisoquinolines. The formation of berberine by cell cultures of Coptis japonica for example, produces a very stable culture which even increased its productivity during 3 years of continuous subcultivation and reached a maximal content of 1.67 g I l medium in one culture period (Fukui et al. 1982). However, Sato and Yamada (1984) could not stabilize the berberine production in their cell lines of Coptis japonica. A further example of instability of a culture is that... 

Continuous culture A method of eultivation in whieh nutrients are supplied and produets are removed eontinuously at volumetrieally equal rates maintaining the eells in a eondition of stable multiplieation and growth. 

The multi-stream multi-stage system is a valuable means for obtaining steady-state growth when, in a simple chemostat, the steady-state is unstable eg when the growth-limiting substrate is also a growth inhibitor. This system can also be used to achieve stable conditions with maximum growth rate, an achievement that is impossible in a simple chemostat (substrate-limited continuous culture). 

In a gas and liquid system, when gas is introduced into a culture medium, bubbles are formed. The bubbles rise rapidly through the medium and dispersion of the bubbles occurs at surface, forming froth. The froth collapses by coalescence, but in most cases the fermentation broth is viscous so this coalescence may be reduced to form stable froth. Any compounds in the broth, such as proteins, that reduce the surface tension may influence foam formation. The stability of preventing bubbles coalescing depends on the film elasticity, which is increased by the presence of peptides, proteins and soaps. On the other hand, the presence of alcohols and fatty acids will make the foam unstable. 

Escherichia coli Adenine and adenosine are inhibitory74 and the synthesis of thiamine can be derepressed by culture in their presence.13,75 adth- Mutants are known.76 [l4C]Formate incorporates at C-2 of pyramine without dilution of molar activity. Glycine labeled with stable isotopes was fed to E. coli and the pyramine was analyzed by mass spectrometry. The two carbon atoms of glycine separated during the biosynthesis. The carboxyl was found12 at C-4, and the C-N fragment was the precursor of C-6-N-1. In conclusion, it is beyond doubt that pyramine synthesis follows the AIR pathway in E. coli. 

Figure 3. Growth phases of short-term cultures. Upon initiation of short-term cultures, growth rapidly increases (Phase 1). A stable growth rate is maintained for a defined number of passages (Phase 2). Finally, most cells undergo a crisis of senescence and ultimately die (Phase 3). In some cases immortal cell lines are established.

An Overview of Causes for Stable Isotopic Variations in Past European Human Populations Environmental, Ecophysiological, and Cultural Effects... 

Van Klinken, G. J., Richards, M.P. and Hedges, R.E.M. this volume Stable isotopic variations in past European human populations environmental, ecophysiological and cultural effects. In Ambrose, S. and Katzenberg, M.A., eds.. Close to the Bone. Biogeochemical Approaches to... 

Macko, S.A., Estep, M.L.F., Hare, PE. and Hoering, T.C. 1983 Stable nitrogen and carbon isotopic composition of individual amino acids isolated from cultured microorganisms. Carnegie Institute of Washington Yearbook 82 404-410. 

Bressan, R.A., Singh, N.K., Handa, A.K., Kononowicz, A. Hasegawa, P.M. (1985). Stable and unstable tolerance to NaCl in cultured tobacco cells. In Plant Genetics, ed. M. Freeling, pp. 755-69. New York Alan R. Liss. 

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