Enrichment media

An important advance on these studies was the possibility of isolating AORs from Fe enriched media with obvious interest for an iron-sulfur center site labeling, with enhanced sensitivity of the Mossbauer studies. The work developed with bacterial systems is advantageous as compared with mammalian systems for isotopic labeling and opens the possibility of a direct measurement of substrate binding. Spectra of the enzyme in oxidized, partially reduced, benzaldehyde-reacted, and fully reduced states were recorded at different temperatures and with variable externally applied magnetic fields (222). In the oxidized enzyme, the clusters are diamag-... 

Geng, T., Hahm, B. K., and Bhunia, A. K. (2006a). Selective enrichment media affect the antibody-based detection of stress-exposed Listeria monocytogenes due to differential expression of antibody-reactive antigens identified by protein sequencing. /. Food Prot. 69,1879-1886. 

Kachkova, E., Kuchta, T., Kay, H., and Gray, D. (2001). Separation of Listeria from cheese and enrichment media using antibody-coated microbeads and centrifugation. /. Microbiol. Methods 46, 63-67. 

In addition, nucleic acid-based assays are limited in that they can only indicate the genetic potential of a microorganism to produce toxin or to express virulence and do not give any information on toxins in foods or environmental samples. Use of selective enrichment media overcomes the difficulties that may arise in direct PCR by increasing the amount of target DNA and decreasing the amount of inhibitors of PCR that may be present in samples. 

Grow cells on enriched media containing the mutagen A-methyl-N, -nitro-Ar-nitrosoguanidine (MNNG) at 0.5/ig/ml or ethyl methane sulphonate (EMS) at 200/tg/ml for 16 h. 

One of the most economic sources of organic forms of Se is yeast grown in Se-enriched media [83]. The popularity of selenized yeast-based food supplements... 

Figure 1. EPR spectra of the molybdenum-iron protein of Azotobacter vine-landii, enriched as indicated by isolation of the protein from bacteria grown on isotopically enriched media.

The introduction and implementation of heteronuclear-based multidimensional techniques have revolutionized the protein NMR field. Large proteins (> 100 residues) are now amenable to detailed NMR studies and structure determination. These techniques, however, necessarily require a scheme by which and isotopes can be incorporated into the protein to yield a uniformly labeled sample. Additional complications, such as extensive covalent post-translational modifications, can seriously limit the ability to efficiently and cost effectively express a protein in isotope enriched media - the c-type cytochromes are an example of such a limitation. In the absence of an effective labeling protocol, one must therefore rely on more traditional proton homonuclear NMR methods. These include two-dimensional (1) and, more recently, three-dimensional H experiments (2,3). Cytochrome c has become a paradigm for protein folding and electron transfer studies because of its stability, solubility and ease of preparation. As a result, several high-resolution X-ray crystal structure models for c-type cytochromes, in both redox states, have emerged. Although only subtle structural differences between redox states have been observed in these... 

It became evident that not all strains of Streptomyces griaeus were capable of producing streptomycin and that streptomycin-producing strains formed active and inactive variants. On the basis that those strains which can actively produce streptomycin would be more resistant to the antibiotic, it was proposed to utilize streptomycin-enriched media for the purification of active cultures of Streptomyces griseus from inactive variants. 

Initial results with ICAT labelling were shown for different protein expression in the yeast S. cerevisiae grown on either ethanol or galactose as carbon source [13]. The potential of MudPIT (Ch. 18.3.2) for the quantitative proteomics was evaluated by means of mixing soluble portions of the S. cerevisiae proteome grown on either natural or N-enriched media in various ratios (1 1 to 10 1) [82]. Reproducibility in quantitative peptide analysis by means of metabolic labelling of S. cerevisiae was evaluated by Washburn et al. [83]. 

The idea that in vivo bacfer may serve as an electron store has been investigated by Fe Mossbauer spectroscopy. Cells of P. aeruginosa grown to the stationary phase on Fe-enriched media were shown to contain bacfer in which at least 90% of the iron was oxidized (72). Therefore, bacfer is unlikely to act simply as an electron store. 

Enrichment cultures are intended to increase the dominance of a numerically minor component of a mixed culture such that it can be readily detected on an agar plate. Enrichment media are always liquid and are intended to provide conditions that are favourable for the growth of the desired organism and unfavourable for the growth of other likely isolates. This can be achieved either through manipulation of the pH and tonicity of the medium or by the inclusion of chemicals that inhibit the growth of unwanted species. Thus, MacConkey broth con-... 

Table 1 Enrichment media used for STEC detection...

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