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.     

Human milk lactoferrin binds two DNA molecules with different affinities.

Evidence is presented that lactoferrin (LF), an Fe3+-binding glycoprotein, possesses two DNA-binding sites with different affinities for specific oligonucleotides (ODNs) (Kdl = 8 nM; Kd2 approximately 0.1 mM). The high affinity site became labeled after incubation with affinity probes for DNA-binding sites; like the antibacterial and polyanion-binding sites, this site was shown to be located in the N-terminal domain of LF. Interaction of heparin with the polyanion-binding site inhibits the binding of ODNs to both sites. These data suggest that the DNA-binding sites of LF coincide or overlap with the known polyanion and antimicrobial domains of the protein.     

Structural organization of kinetoplast DNA and its compactization in a model system in vitro

Studies on compactization and decompactization of the genome are of great importance for elucidation of structural mechanisms taking part in the regulation of gene activity. Kinetoplast DNA (kpDNA) is a convenient model for studies of compactization processes. KpDNA represents unique structure ("network"), consisting of catenated circular molecules of two types: minicircles (900 b.p.) and maxicircles (40 000 b.p.). The compactization process of kpDNA in vitro caused by interaction with synthetic peptide-dansylhydraside trivaline was studied. It was shown that at the initial stages the hairpins are observed on minicircles as if triple rings are being organized. The formation of hairpin is probably favoured by the presence in the minicircles of bent DNA, a specific nucleotide sequence causing rigid bending of the DNA helix. The hairpin does not make contact with the neighbouring DNA segment to form a triple ring, because the sizes of minicircles are too small. The minicircles compactization is finished with a complete collapse of the minicircles with the formation of rod-like structures. The catenation causes branching of rod-like structures. As a result of their intermolecular interaction, the branched rod-like structures become thicker. The process is completed with formation of the compact network, its diameter being 3-6 times smaller compared to the initial one.     

DNA complexes with synthetic oligopeptides: a model for studying the regularity of DNA compactization in vivo

The electron microscopic data on compactization of DNA at interaction with the synthetic oligopeptides having the trend of beta-structures formation in solutions are summarized. The new types of intramolecular and intermolecular compact structures are described in brief. Sequence of compactization process steps is discussed, the models of DNA packaging in the structures are presented. On the basis of the data presented the general principles of arrangement of the described compact structures are formulated, the mechanisms are proposed for formation of different types of compact particles on the final stage of the process of DNA condensation. Some processes of the genetic material compactization in vivo are discussed in which the proposed mechanisms for compact structures formation may have realization.     

Interaction of trivaline with single-stranded polyribonucleotides]

Binding of tripeptide H-Val3-(NH)2-Dns (TVP) to polyribonucleotides was studied by fluorescence methods, circular and flow linear dichroism, equilibrium dialysis and electron microscopy. It was found that TVP binds to poly(U) in monomer, dimer and tetramer forms with binding constants of about 10(3), 40, 18.10(4) M, respectively. The cooperativity parameter for peptide dimer binding is 2000. The peptide forms tetramer complexes with poly(A), poly(C), poly(G) also. The formation of a complex between the peptide tetramer and nucleic acid is accompanied by a significant increase in the fluorescence intensity. The cooperative binding of TVP dimers to poly(U), poly(A), poly(C) is accompanied by a dramatic decrease in the flexibility of polynucleotide chains. However, it has a small effect (if any) on the flexibility of the poly(G) chain. The observed similarity of thermodynamic, optical and hydrodynamic++ properties of TVP complexes with single-stranded and double-stranded nucleic acids may reflect a similarity in the geometries of peptide complexes with nucleic acids. Electron microscopy studies show that peptide binding to poly(U) and dsDNA leads to compactization of the nucleic acids caused by interaction between the peptide tetramers bound to a nucleic acid. At the first stage of the compactization process the well-organized rod-like particles are formed, each consisting of one or more single-stranded polynucleotide fibers. Increasing the peptide concentration stimulates a side-by-side association and folding of the rods with the formation of macromolecular "leech-like" structures with the thickness of 20-50 nm.