E. coli K-12 strains

Although fructose-6-phosphate aldolase (FSA) does not belong to the DHAP-dependent aldolases group, it deserves to be mentioned in this chapter as it can be considered as an alternative to those enzymes, or at least, an alternative to FBPA. FSA was described for the first time by Schiirmann and Sprenger in E. coli K-12 strain MG1655 [50]. The enzyme is a class I aldolase with a homodecameric... 

Shigella flexneri synthesizes the hydroxamate siderophore aerobactin (and a single outer membrane protein), but certain strains also synthesize enterobactin, a phenolate siderophore, in which case three additional outer membrane proteins are synthesized, similar to those produced by E. coli K.-12 strains.1181... 

Table III. Siderophore Nutrition and Protection of E. coli K-12 Strain RW193 (48)...

The phage lambda (X) ofE. coll is the temperate phage that has been most extensively studied. When any particular strain oiE. coli, say K12, is infected with A, the cells surviving the infection are designated E. coli K 12(A) to indicate that they are carrying the /1-prophage. 

The majority of Fur-regulated gene products are involved in iron uptake. Genes for transport and biosynthesis of enterobactin have been studied in E. coli K-12 (Earhart, 1996). It is assumed that this system is found in nearly every E. coli strain. Also the ferrichrome transport system seems to have a very broad distribution. The ferric citrate transport system (fee), however, is only present in some E. coli strains and may be part of a pathogenicity island. The aerobactin and yersiniabactin biosynthesis and transport systems are not found in all E. coli strains and are integrated into pathogenicity islands (Schubert et al., 1999). The ability to utilize haem seems also to be a specific pathogenicity-related adaptation. Haem transport systems are used in the animal or human host, where transferrin and lactoferrin create an iron-poor environment for bacteria. 

On the other hand, diaryl diselenides, compounds (130-133), had no inhibitory effect on fungal growth. However, the benzisoselenazolones show antibacterial activities against Gram-negative E. coli K-12 Row and Gram-positive S. aureus 209P bacterial strains [240]. 

Figure 7-2. Structure of the cellulose biosynthesis operon bcs in Salmonella typhimurium and Escherichia coli. Arrowheads represent the open reading frames (ORFs). Symbols above the ORFs show overlap of (D) or distance between (A) ORFs in bps. Symbols below the ORFs show insertions (A) or deletions (V), which occur in S. typhimurium LT2 as compared to Escherichia coli K-12. Closed arrow5 just above the ORFs indicate transposon insertions in bcsA and bcsC. The larger arrow indicates the position of the transposon used to study transcriptional regulation of the respective gene. The table summarizes the features of bcs genes using the positioning in the genome of the sequenced LT2 strain. The start codon proposed for bcsC in E. Coli K-12 leads to a shorter ORF (bcsC ).

In general, endogenous metabolism of anaerobic bacteria was found to be more stable, when biocatalysts based on immobilized cells of P. shermanii and E. coli were compared with respect to the reactions shown above (Ikonnikov, 1985). P. shermanii had a higher aspartase activity than P. pentosaceum, P. petersonii and P. technicum (Kalda and Vorobjeva, 1981). After 3 days of incubation with continuous stirring at 37°C and pH 8.5, the extent of substrate conversion (ammonium fumarate) was 95-96% and 75-90% in the case of E. coli K-12 and P. shermanii, respectively. In addition to aspartic acid, the reaction mixtures of the two strains also contained malic acid. Heat treatment of the biomass of P. shermanii (50 C, 1.5 h, pH 5.0) resulted in a complete inactivation of fumarase, while the activity of aspartase was retained (Kalda and Vorobjeva, 1980, 1981). As a result of the elimination of fumarase activity, the yield of L-aspartic acid from ammonium fumarate was increased up to 96-98% the incubation time was also shortened since no substrate was diverted to the side reaction forming malate. 

Mutagenicity tests are also being applied to irradiated foods. For example, Matsuyama et al, examined the mutagenicity of cell sap from irradiated raw or irradiated stored and cooked onions using reverse mutation assays. E. coli strain SD-4 was used either alone or with rat liver fractions for metabolic activation studies. Two strains of E, coli K-12 were used for DNA-repair tests. None of the onion samples (irradiated at 0-300 J/kg) were found to be mutagenic by any of the tests used. 

---