Continuous-culture selection

Sghir A, Chow JM, Mackie RI. Continuous culture selection of bifidobacteria and lactobacilli from human faecal samples using fructooligosaccharide as selective substrate. / Appl Microbiol. 1998 85 769-777. 

Carbon limiting is also used to encourage enzyme induction, place the population under selective pressure for degradation of recalcitrant substrates, and favor the simultaneous rather than sequential metabolism of a mixed carbon source.33 Carbon-limiting conditions can be achieved either through continuous culture (chemostat) or through a fed batch reaction. 

Two days after transfection, add hygromycin to a final concentration at 200 pg/mL to obtain stable transformants. When the cells grow nearly confluent, dilute the culture 3-5x by adding RPM II640/10% FCS/200 pg/mL hygromycin. Continue culture under the selection with 200 pg/mL hygromycin at least for a week and until total cell number becomes over 2 x 107. 

B lymphocytes will be eliminated during continuous culture because these cells have a short life span in culture. Commercially available myeloma cells for hybridoma production have mutations in one of the enzymes of the salvage pathway of purine nucleotide biosynthesis. Hybridoma cells are cultured in medium that forces the cells to utilize the salvage pathway for nucleotide synthesis. The mutated myeloma cells or hybridization products of two myeloma cells will die in this selection medium since they are incapable of nucleotide synthesis under these propagation conditions. However, myeloma cells that have fused to the B lymphocytes derived from the spleen of the immunized animal will have an intact salvage pathway and will survive in the selection medium. Thus, only the B lymphocytes-myeloma hybridomas will survive prolonged culture in the selection medium. 

Harrison, P. J., Turpin, D. H., Bienfang, P. K., and Davis, C. O. (1986). Sinking as a factor affecting phytoplankton species succession The use of selective loss semi-continuous cultures. J. Exp. Mar. Biol. Ecol. 99, 19-30. 

Gottschall J. C. and Kuenen J. G. (1980) Selective enrichment of facultatively chemoUthotrophic thiobacilli and related organisms in continuous culture. FEMS Microbiol. Lett. 7, 241-247. 

This improvement in cellulase production averaged a doubling every 2 years between 1972 and 1984 and resulted from a combination of mutation/selection of strains and the optimization of fed-batch and continuous culture. 

Therefore, continuous culture offers the opportunity to control the rate of cell growth. From Fig. 4, this allows one to select the for high enzyme production. 

Illanes A, Altamirano C, AUlapan A et al. (1998) Packed-bed reactor performance with immobilized lactase under thermal inactivation. Enzyme Microb Technol 23 3-9 Impoolsup A, Caunt P, Greenfield PE (1989) Effect of growth rate on stability of a recombinant plasmid during continuous culture of Saccharomyces cerevisiae in non-selective medium. J Biotechnol 10(2) 171-180... 

Villano and co-workers [36] presented the production and recovery of PHA using mixed microbial cnltnres (MMC). The process was carried out sequentially from lab-scale batch reactor, for culture selection, and then PHA accumulation reactor and extraction reactor. It is a continuous process and is at a high process rate for at least 4 months. In this study, IM NaOH and NaClO with 5% active liquid chlorine were investigated. It was found that digestion with... 

Mutation may be induced using chemical or physical mutagenic agents or spontaneously occurring mutants selected from a population. Selection of spontaneous mutants has the advantage that undesired mutations which may result from the use of mutagens, are not present. Continuous culture... 

---