Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.     

Phosphorylation of elF-4E and initiation of protein synthesis in P19 embryonal carcinoma cells

Mitogenic stimulation of protein synthesis is accompanied by an increase in elF-4E phosphorylation. The effect on protein synthesis by induction of differentiation is less well known. We treated P19 embryonal carcinoma cells with the differentiating agent retinoic acid and found that protein synthesis increased during the first hour of addition. However, the phosphorylation state, as well as the turnover of phosphate on elF-4E, remained unchanged. Apparently, the change in protein synthesis after RA addition is regulated by another mechanism than elF-4E phosphorylation. By using P19 cells overexpressing the EGF receptor, we show that the signal transduction pathway that leads to phosphorylation of elF-4E is present in P19 cells; the EGF-induced change in phosphorylation of elF-4E in these cells is likely to be regulated by a change in elF-4E phosphatase activity. These results suggest that the onset of retinoic acid-induced differentiation is triggered by a signal transduction pathway which involves changes in protein synthesis, but not elF-4E phosphorylation. © 1995 Wiley-Liss, Inc.     

Discovery of new low-molecular-weight p53–Mdmx disruptors and their anti-cancer activities

Although several p53–Mdm2-binding disruptors have been identified to date, few studies have been published on p53–Mdmx-interaction inhibitors. In the present study, we demonstrated that o-aminothiophenol derivatives with molecular weights of 200–300 selectively inhibited the p53–Mdmx interaction. S-2-Isobutyramidophenyl 2-methylpropanethioate (K-178) (1c) activated p53, up-regulated the expression of its downstream genes such as p21 and Mdm2, and preferentially inhibited the growth of cancer cells with wild-type p53 over those with mutant p53. Furthermore, we found that the S-isobutyryl-deprotected forms 1b and 3b of 1c and S-2-benzamidophenyl 2-methylpropanethioate (K-181) (3c) preferentially inhibited the p53–Mdmx interaction over the p53–Mdm2 interaction, respectively, by using a Flag-p53 and glutathione S-transferase (GST)-fused protein complex (Mdm2, Mdmx, DAPK1, or PPID). In addition, the interaction of p53 with Mdmx was lost by replacing a sulfur atom with an oxygen atom in 1b and 1c. These results suggest that sulfides such as 1b, 3b, 4b, and 5b interfere with the binding of p53–Mdmx, resulting in the dissociation of the two proteins. Furthermore, the results of oral administration experiments using xenografts in nude mice indicated that 1c reduced the volume of tumor masses to 49.0% and 36.6% that of the control at 100 mg/kg and 150 mg/kg, respectively, in 40 days.     

Immunofluorescent analysis of meiotic recombination in the domestic cat

The paper presents the analysis of the frequency, density, and distribution of recombination sites in the male meiosis of the domestic cat (Felis silvestris catus). The study was carried out using immunofluorescent staining of synaptonemal complex (SC) proteins, centromeric proteins and mismatch repair protein MLH1, a reliable marker of crossingover sites. We mapped 2633 sites of crossing over in 1098 individual autosomes. Based on these data, we estimated the total length of the genetic map of the domestic cat to be 2176 centimorgans. Positive correlation between the length of SC and the number of recombination sites common for mammalians was also found in the domestic cat. It was shown that this species was characterized by the highest density of recombination and the lowest interference in mammals.     

Calcium-dependent binding of EDTA-extractable proteins to calf lens fiber membrane structures

Calf lens fiber membranes and fractions enriched in junction-like structures have been isolated in the absence and presence of EDTA. Their biochemical features have been studied. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting experiments have provided evidence that a distinct group of EDTA-extractable proteins, being one of the main protein components of calf lens fiber membranes and very likely also of junction-like structures, is bound to these membranes via calcium ions. In addition to these proteins, four polypeptides with apparent molecular weights between 14 000 and 17 000 are characteristic for detergent-insoluble lens fiber structures prepared in calcium-rich medium. The absence of EDTA-extractable proteins in the urea-soluble calcium-containing fraction implies that they are not components of the cytoskeleton and that the calcium-dependent binding of these proteins to the membrane is urea-resistant. The use of EDTA throughout the whole membrane isolation procedure results in their complete removal from the membranes which already starts during buffer washing. This indicates that EDTA-extractable proteins exclusively consist of extrinsic membrane proteins which probably are not involved in cytoskeleton binding.     

Macromolecular synthesis in organ cultures of neonatal rat lung

Organ cultures of newborn rat lungs synthesize and accumulate DNA, RNA, collagen and noncollagenous proteins almost at a linear rate for at least 5 days. During this period the synthesis of collagen consistently exceeds the synthesis of noncollagenous proteins in a pattern similar to neonatal lung growth in vivo. Although some morphological characteristics of lung architecture are distorted after culture, fundamental structural similarities to lungs growing in intact animals are retained. When these cultures are maintained in atmospheres rich in oxygen, increased collagen synthesis is observed, a response similar to that of lungs in intact animals exposed to high oxygen concentrations in vivo. Our studies suggest that lung organ cultures may be a suitable system for investigating the biochemical aspects of lung tissue-environmental interaction. These studies were supported in parts by NIH Grant HL-19668, a contract (68-03-2005) from the U.S. Environmental Protection Agency, and grants from the California Lung Association.     

Resistance of Anhydrobiotic Aphelenchus avenae to Methyl Bromide Fumigation

The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes.     

The stable evolutionary fixation of a bifunctional tyrosine-pathway protein in enteric bacteria

Abstract The bifunctional T-protein (chorismate mutase-T: cyclohexadienyl dehydrogenase) of l -tyrosine biosynthesis was found to be present in all genera making up the enteric bacteria. The dehydrogenase component of the T-protein was active with both prephenate and l -arogenate, showing it to be a cyclohexadienyl dehydrogenase. The dehydrogenase component, but not the mutase component, of the T-protein was feedback-inhibited by l -tyrosine. Unlike some other bifunctional proteins, the T-protein has evolved recently and is not ubiquitous. However, once the biochemical specialization of bifunctionality becomes established, the results indicate that such character states are strongly conserved through evolutionary time. Thus, bifunctional proteins can provide particularly reliable markers for small (recent origin), intermediate, and large (ancient origin) phylogenetic clusters.