Strain selection

Although winemakers often have strain preferences for particular applications, the issue continues to be one of debate. A generalized list of desirable traits of wine yeasts can be found in Table 8.2. Each strain possesses different characteristics including varying fermentation rate and production of H2S (Ough and Groat, 1978 Jiranek et al., 1995c). 

White wines are generally fermented at lower temperatures (10°G/50°F to 18 G/65 F) for better aroma retention, whereas red wines are fermented at higher temperatures (18 G/65 F to 29 G/85 F) for increased color and tannin extraction (Ough and Amerine, 1966). Peynaud (1984) recommended slightly different fermentation temperatures, 18°G/65°F to 20 G/68 F for making white and rose wines and 26 G/79 F to 30°G/86°F for red wines. Margalit (2004) suggested that white as well as rose and blush wines be fermented at even cooler temperatures, 8 G/46 F to 14°G/57°F, whereas red fermentation should be conducted at 22 G/72 F to 30°G/86°F. 

As expected, fermentation rates by Saccharomyces 3xy viiih temperature. Ough (1964) reported that fermentations are relatively slow at 10 G/50 F compared with those conducted at 15°G/60°F or 27°G/80 F. Temperature also affects the population balance between Saccharomyces and non-Saccharomyces yeasts. In red wine fermentations (20°G/68°F to 30°G/86 F), Saccharomyces cerevisiae represents the dominant species (Sharf and Margalith, 1983), partially due to the warmer temperature of fermentation. At lower fermentation temperatures such as those used in white wine production, non-Saccharomyces yeasts can proliferate to yield much higher populations (Section 6.2.2). 

Refs Abou-Chaar 1961 Adams 1964 Amici 1966 1967 1969 Arcamone 1961 Berman 1954 Brady 1960 Cherewick 1956 Hareven 1970 Kelleher 1969 1971 Memtle 1969 1976 Michener 1950 Mizrahi 1968 Ogunlana 1969 Pacifici 1962 1963 Paul 1954 Ramstad 1955 Societa Farmaceutici Italia 1961 Taber 1966 lyier 1954) After several strains have been obtained, they are then cultivated industrially in large fermenters, which are just large pressure cookers. Large equipment is impractical for most individuals. Canning jars or pressure cookers can be successfully used. Industrial Fermentation Equipment (Cleverdon 1955) (Dworschack 1954) (Fuld 1957). 

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Species such as carp, salmon, trout, channel catfish, and tilapia have been bred for many generations in captivity though they usually differ httle in appearance or genetically from their wild counterparts. A few exceptions exist, such as the leather carp, a common carp strain selectively bred to produce only one row of scales, and the Donaldson trout, a strain of rainbow trout developed over numerous generations to grow more rapidly to larger size and... 

To obtain reproducible antibiotic production by fermentation, it is necessary to obtain a pure culture of the producing organism. Pure cultures are isolated from mixed soil sample populations by various streaking and isolation techniques on nutrient media. Once a pure culture has been found that produces a new antibiotic typically on a mg/L scale, improvement in antibiotic yield is accompHshed by modification of the fermentation medium or strain selection and mutation of the producing organism. Production of g/L quantities may take years to accomplish. 

Purification. Enzyme purity, expressed in terms of the percent active enzyme protein of total protein, is primarily achieved by the strain selection and fermentation method. In some cases, however, removal of nonactive protein by purification is necessary. The key purification method is selective precipitation of the product or impurities by addition of salt, eg, sodium sulfate, or solvent, eg, ethanol or acetone by heat denaturation or by isoelectric precipitation, ie, pH adjustments. Methods have been introduced to produce crystalline enzyme preparations (24). 

From this one ancestral fungus each penicillin manufacturer has evolved a particular production strain by a series of mutagenic treatments, each followed by the selection of improved variants. These selected variants have proved capable of producing amounts of penicillin far greater than those produced by the wild strain, especially when fermented on media under particular control conditions developed in parallel with the strains. These strain selection procedures have become a fundamental feature of industrial biotechnology. 

Balzarini J, Karlsson A, Vandamme A-M, Perez-Perez M-J, Zhang H, Vrang L, Oberg B, Backbro K, Unge T, San-Felix A, Velazquez S, Camarasa M-J, De Clercq E. Human immunodeficiency virus type 1 (HIV-1) strains selected for resistance against the HIV-l-specific [2, 5 -bis-0-(rert-butyldi-methylsilyl)-3 -spiro-5"-(4"-amino-1", 2"-oxathiole-2", 2"-dioxide)]-fi-D-pen-tofuranosyl (TSAO) nucleoside analogues retain sensitivity to HIV-l-specific nonnucleoside inhibitors. Proc Natl Acad Sci USA 1993 90 6952-6956. 

This work lead by Kilbane was carried out in collaboration with Petrobras and gave rise to three patents [371,375,376], which protected not only P. ayucida IGTN9m (ATCC N° PTA-806, but also the thermophilic culture Aneurinibacillus sp. IGTN4T (ATCC N° PTA-4581), and strains, P. stutzeri, Yokenella sp., and P. nitroreducen. The P. stutzeri strain was selectively enriched using carbazole as the sole nitrogen source. The experimental results also indicated that the considered strain selectively cleaved the C—N bonds in carbazole. The same behavior was also observed for Yokenella sp. when cultured according to the principles described before. The specific metabolites produced by the conversion of carbazole have not yet been determined. 

Abbad-Andaloussi, S. Lagnel, C. Warzywoda, M., and Monot, F., Multi-Criteria Comparison of Resting Cell Activities of Bacterial Strains Selected for Biodesulfurization of Petroleum Compounds. Enzyme, and Microbial Technology, 2003. 32(3-4) pp. 446 154. 

Fig. 4. Pleiotropism of Phycomyces strains selected as phototropic defective mutants. Mutants madA and madB are defective in all photoresponses, mutants madD, E, F, G only in tropic and growth responses...

The specific volumetric rate of hydrogen photoproduction depends on the rate of hydrogen production by one unit of biomass and on the concentration of the biomass in a photobioreactor. The improvement of a biomass activity is the basic problem for strain selection or construction. The specific volumetric rate might be increased technologically by increase of biomass concentration. 

Reversion Tests Background. There are several excellent references describing the background and use of bacteria for reversion tests (Brusick, 1987 Gatehouse et al., 1990). Three different protocols have been widely used plate incorporation assays, treat and plate tests, and fluctuation tests. These methods are described in detail in the following sections. Fundamental to the operation of these tests is the genetic compositions of the tester strains selected for use. 

The availability of an adequate historical data base is often cited as an important criterion for species/strain selection. Historical control data can sometimes be useful... 

Most of the enzymes in commerce today were derived from natural isolates by the classical approaches of screening, strain selection/mutagenesis for overproduction and fermentation development While these techniques have certainly proven useful in the past to identify and develop enzymes, there are limits to the effectiveness of this type of approach. There are two major difficulties facing the industrial microbiologist in developing future products. 

There is a continuing debate as to whether inbred or outbred strains of rodents should be used. In theory, inbred strains are preferable because a more accurate knowledge of back-grormd tumour incidence is available. It may be, however, that a particular inbred strain may metabolise the test material in a certain way or have a genetic resistance to the development of a specific tumour type. Usually outbred strains of rat or hamster are used, but occasionally inbred mice strains are included. An FI hybrid mouse strain is frequently employed. In some circumstances outbred Syrian hamsters may be the species of choice. The most important factor is to have a sound knowledge of the background incidence of tumours in the species or strain selected. This information complements the concurrent control data and provides information on the susceptibility of the strain to rare tumour t)rpes. Modif)dng factors, such as diet, cage density, etc., must be kept as constant as possible to enable correct interpretation of the results. ... 

The bacterial and mammalian cell assays for gene mutation were developed to measure statistically significant increases in the numbers of mutant colonies derived from rare events many millions of exposed cells must be plated out to allow the assessment of mutation frequency. The Salmonella typhimurium reverse mutation assay ( Ames test) is carried out in a variety of different mutant strains selected to identify the various classes of mutation. The test generates many hundreds of Petri dishes for counting and is not practical for profiling. 

Berrettini WH, Harris N, Ferraro TN, Vogel WH (1994) Maudsley reactive and non-reactive rats differ in exploratory behavior but not learning. Psychiatr Genet 4 91-94 Bizard DA, Altman HJ, Freedman LS (1982) The peripheral sympathetic nervous system in rat strains selectively bred for differences in response to stress. Behav Neural Biol 34 319-325... 

Strains selected for differences in learning performance Roman high avoidance (RHA) versus Roman low avoidance (RLA). In addition to the different performances displayed on the acquisition of an active avoidance task (RHA > RLA rats) these two strains have been described to differ in emotionality/level of anxiety (RHA < RLA) (e.g. Gentsch et t//., 1988). 

Ataev, C.L. and Coustau, C. (1999) Cellular response to Echinostoma caproni infection in Biomphalaria glabrata strains selected for susceptibility/resistance. Developmental and Comparative Immunology 23, 187-1 98. 

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