The NMR structure of the Orf63 lytic developmental protein from lambda bacteriophage

The orf63 gene resides in a region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed during infection. In lambda phage and Shiga toxin (Stx) producing phages found in enterohemorrhagic Escherichia coli (EHEC) associated with food poisoning, Orf63 expression reduces the host survival and hastens the period between infection and lysis thereby giving it pro-lytic qualities. The NMR structure of dimeric Orf63 reveals a fold consisting of two helices and one strand that all make extensive intermolecular contacts. Structure-based data mining failed to identify any Orf63 homolog beyond the family of temperate bacteriophages. A machine learning approach was used to design an amphipathic helical ligand that bound a hydrophobic cleft on Orf63 with micromolar affinity. This approach may open a new path towards designing therapeutics that antagonize the contributions of Stx phages in EHEC outbreaks.

Complex effects of the exo-xis region of the Shiga toxin-converting bacteriophage Φ24B genome on the phage development and the Escherichia coli host physiology

Lambdoid bacteriophages are excellent models in studies on molecular aspects of virus-host interactions. However, some of them carry genes encoding toxins which are responsible for virulence of pathogenic strains of bacteria. Shiga toxin-converting bacteriophages (Stx phages) encode Shiga toxins that cause virulence of enterohemorrhagic Escherichia coli (EHEC), and their effective production depends on Stx prophage induction. The exo-xis region of the lambdoid phage genome consists of genes which are dispensable for the phage multiplication under laboratory conditions; however, they might modulate the virus development. Nevertheless, their exact effects on the phage and host physiology remained unclear. Here, we present results of complex studies on the role of the exo-xis region of bacteriophage Φ24B, one of Stx2b phages. Transcriptomic analyses, together with proteomic and metabolomic studies, provided the basis for understanding the functions of the exo-xis region. Genes from this region promoted lytic development of the phage over lysogenization. Moreover, expression of the host genes coding for DnaK, DnaJ, GrpE, and GroELS chaperones was impaired in the cells infected with the Δexo-xis phage mutant, relative to the wild-type virus, corroborating the conclusion about lytic development promotion by the exo-xis region. Proteomic and metabolomic analyses indicated also modulation of gad and nrf operons, and levels of amino acids and acylcarnitines, respectively. In conclusion, the exo-xis region controls phage propagation and host metabolism by influencing expression of different phage and bacterial genes, directing the virus to the lytic rather than lysogenic developmental mode.

The NMR structure of the Ea22 lysogenic developmental protein from lambda bacteriophage

The ea22 gene resides in a relatively uncharacterized region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed upon infection. In lambda and Shiga toxin-producing phages found in enterohemorrhagic E. coli (EHEC) associated with food poisoning, Ea22 favors a lysogenic over lytic developmental state. The Ea22 protein may be considered in terms of three domains: a short amino-terminal domain, a coiled-coiled domain, and a carboxy-terminal domain (CTD). While the full-length protein is tetrameric, the CTD is dimeric when expressed individually. Here, we report the NMR solution structure of the Ea22 CTD that is described by a mixed alpha-beta fold with a dimer interface reinforced by salt bridges. A conserved mobile loop may serve as a ligand for an unknown host protein that works with Ea22 to promote bacterial survival and the formation of new lysogens. From sequence and structural comparisons, the CTD distinguishes lambda Ea22 from homologs encoded by Shiga toxin-producing bacteriophages.

Analysis of Phage Regulatory RNAs: Sequencing Library Construction from the Fraction of Small Prokaryotic RNAs Less Than 50 Nucleotides in Length

So far, bacterial regulatory sRNAs of length less than 50 nucleotides have been poorly understood, and a low number of such molecules has been identified. The first microRNA-size functional ribonucleic acid occurring in a bacterial cell has been described only recently, and it was found to be encoded by a bacteriophage. One of the reasons for such a scarcity in this field is the lack of procedures intended for the isolation and selection of molecules of this size from bacterial cells. To meet these difficulties, we describe here the few-step procedure of isolation, purification, selection, and sequencing library preparation that is dedicated to the fraction of very small, bacterial RNA molecules.

Bacteriophage-encoded 24B_1 molecule resembles herpesviral microRNAs and plays a crucial role in the development of both the virus and its host

The 24B_1 small non-coding RNA molecule has been identified in Escherichia coli after induction of Shiga toxin-converting bacteriophage Φ24B. In this work, we focused on its direct role during phage and bacterial host development. We observed that in many aspects, this phage sRNA resembles herpesviral microRNAs. Similar to microRNAs, the mature 24B_1 is a short molecule, consisting of just 20 nucleotides. It is generated by cleaving the 80-nt long precursor transcript, and likely it undergoes a multi-step maturation process in which the Hfq protein plays an important role, as confirmed by demonstration of its binding to the 24B_1 precursor, but not to the 24B_1 mature form. Moreover, 24B_1 plays a significant role in maintaining the prophage state and reprogramming the host's energy metabolism. We proved that overproduction of this molecule causes the opposite physiological effects to the mutant devoid of the 24B_1 gene, and thus, favors the lysogenic pathway. Furthermore, the 24B_1 overrepresentation significantly increases the efficiency of expression of phage genes coding for proteins CI, CII, and CIII which are engaged in the maintenance of the prophage. It seems that through binding to mRNA of the sdhB gene, coding for the succinate dehydrogenase subunit, the 24B_1 alters the central carbon metabolism and causes a drop in the ATP intracellular level. Interestingly, a similar effect, called the Warburg switch, is caused by herpesviral microRNAs and it is observed in cancer cells. The advantage of the Warburg effect is still unclear, however, it was proposed that the metabolism of cancer cells, and all rapidly dividing cells, is adopted to convert nutrients such as glucose and glutamine faster and more efficiently into biomass. The availability of essential building blocks, such as nucleotides, amino acids, and lipids, is crucial for effective cell proliferation which in turn is essential for the prophage and its host to stay in the lysogenic state.

Discriminating macromolecular interactions based on an impedimetric fingerprint supported by multivariate data analysis for rapid and label-free Escherichia coli recognition in human urine

This manuscript presents a novel approach to address the challenges of electrode fouling and highly complex electrode nanoarchitecture, which are primary concerns for biosensors operating in real environments. The proposed approach utilizes multiparametric impedance discriminant analysis (MIDA) to obtain a fingerprint of the macromolecular interactions on flat glassy carbon surfaces, achieved through self-organized, drop-cast, receptor-functionalized Au nanocube (AuNC) patterns. Real-time monitoring is combined with singular value decomposition and partial least squares discriminant analysis, which enables selective identification of the analyte from raw impedance data, without the use of electric equivalent circuits. As a proof-of-concept, the authors demonstrate the ability to detect Escherichia coli in real human urine using an aptamer-based biosensor that targets RNA polymerase. This is significant, as uropathogenic E. coli is a difficult-to-treat pathogen that is responsible for the majority of hospital-acquired urinary tract infection cases. The proposed approach offers a limit of detection of 11.3 CFU/mL for the uropathogenic E. coli strain No. 57, an analytical range in all studied concentrations (up to 105 CFU/mL), without the use of antifouling strategies, yet not being specific vs other E.coli strain studied (BL21(DE3)). The MIDA approach allowed to identify negative overpotentials (-0.35 to -0.10 V vs Ag/AgCl) as most suitable for the analysis, offering over 80% sensitivity and accuracy, and the measurement was carried out in just 2 min. Moreover, this approach is scalable and can be applied to other biosensor platforms.

Extraordinary Multi-Organismal Interactions Involving Bacteriophages, Bacteria, Fungi, and Rotifers: Quadruple Microbial Trophic Network in Water Droplets

Our observations of predatory fungi trapping rotifers in activated sludge and laboratory culture allowed us to discover a complicated trophic network that includes predatory fungi armed with bacteria and bacteriophages and the rotifers they prey on. Such a network seems to be common in various habitats, although it remains mostly unknown due to its microscopic size. In this study, we isolated and identified fungi and bacteria from activated sludge. We also noticed abundant, virus-like particles in the environment. The fungus developed absorptive hyphae within the prey. The bacteria showed the ability to enter and exit from the hyphae (e.g., from the traps into the caught prey). Our observations indicate that the bacteria and the fungus share nutrients obtained from the rotifer. To narrow the range of bacterial strains isolated from the mycelium, the effects of bacteria supernatants and lysed bacteria were studied. Bacteria isolated from the fungus were capable of immobilizing the rotifer. The strongest negative effect on rotifer mobility was shown by a mixture of Bacillus sp. and Stenotrophomonas maltophilia. The involvement of bacteriophages in rotifer hunting was demonstrated based on molecular analyses and was discussed. The described case seems to be an extraordinary quadruple microbiological puzzle that has not been described and is still far from being understood.

Bacteriophage-Derived Depolymerases against Bacterial Biofilm

In addition to specific antibiotic resistance, the formation of bacterial biofilm causes another level of complications in attempts to eradicate pathogenic or harmful bacteria, including difficult penetration of drugs through biofilm structures to bacterial cells, impairment of immunological response of the host, and accumulation of various bioactive compounds (enzymes and others) affecting host physiology and changing local pH values, which further influence various biological functions. In this review article, we provide an overview on the formation of bacterial biofilm and its properties, and then we focus on the possible use of phage-derived depolymerases to combat bacterial cells included in this complex structure. On the basis of the literature review, we conclude that, although these bacteriophage-encoded enzymes may be effective in destroying specific compounds involved in the formation of biofilm, they are rarely sufficient to eradicate all bacterial cells. Nevertheless, a combined therapy, employing depolymerases together with antibiotics and/or other antibacterial agents or factors, may provide an effective approach to treat infections caused by bacteria able to form biofilms.

Characterization of the Bacteriophage vB_EfaS-271 Infecting Enterococcus faecalis

A newly isolated bacteriophage infecting Enterococcus faecalis strains has been characterized, including determination of its molecular features. This phage, named vB_EfaS-271, has been classified as a Siphoviridae member, according to electron microscopy characterization of the virions, composed of a 50 nm-diameter head and a long, flexible, noncontractable tail (219 × 12.5 nm). Analysis of the whole dsDNA genome of this phage showed that it consists of 40,197 bp and functional modules containing genes coding for proteins that are involved in DNA replication (including DNA polymerase/primase), morphogenesis, packaging and cell lysis. Mass spectrometry analysis allowed us to identify several phage-encoded proteins. vB_EfaS-271 reveals a relatively narrow host range, as it is able to infect only a few E. faecalis strains. On the other hand, it is a virulent phage (unable to lysogenize host cells), effectively and quickly destroying cultures of sensitive host bacteria, with a latent period as short as 8 min and burst size of approximately 70 phages per cell at 37 °C. This phage was also able to destroy biofilms formed by E. faecalis. These results contribute to our understanding of the biodiversity of bacteriophages, confirming the high variability among these viruses and indicating specific genetic and functional features of vB_EfaS-271.

Bacteriophages as sources of small non-coding RNA molecules

Bacteriophages play an essential role in the transferring of genes that contribute to the bacterial virulence and whose products are dangerous to human health. Interestingly, phages carrying virulence genes are mostly temperate and in contrast to lytic phages undergo both lysogenic and lytic cycles. Importantly, expression of the majority of phage genes and subsequent production of phage encoded proteins is suppressed during lysogeny. The expression of the majority of phage genes is tightly linked to lytic development. Among others, small non-coding RNAs (sRNAs) of phage origin are involved in the regulation of phage gene expression and thus play an important role in both phage and host development. In the case of bacteria, sRNAs affect processes such as virulence, colonization ability, motility and cell growth or death. In turn, in the case of phages, they play essential roles during the early stage of infection, maintaining the state of lysogeny and silencing the expression of late structural genes, thereby regulating the transition between phage life cycles. Interestingly, sRNAs have been identified in both lytic and temperate phages and they have been discussed in this work according to this classification. Particular attention was paid to viral sRNAs resembling eukaryotic microRNAs.

Ea22 Proteins from Lambda and Shiga Toxin-Producing Bacteriophages Balance Structural Diversity with Functional Similarity

Enterohemorrhagic Escherichia coli (EHEC) outbreaks are commonly associated with contaminated food sources. Unlike normal intestinal bacteria, EHEC are lysogens of lambdoid bacteriophages that also carry a gene for Shiga toxin. Oxidative attack by the immune system or other stressors on the bacterial host can activate the lytic pathway of the latent phage genome to produce phage progeny and the release of Shiga toxin into the surrounding tissues. Within the genomes of bacteriophage λ and Shiga toxin-expressing (Stx⁺) phages such as φ24_B and φP27, there is a conserved set of open reading frames that is located between the exo and xis genes that influences the lysogenic-lytic decision. In this report, we have focused on the largest exo-xis region open reading frame termed ea22 that has been shown previously to have prolysogenic properties. Using a variety of biophysical and bioinformatic methods, we demonstrate that λ and φP27 Ea22 proteins are tetrameric in solution and can be considered in terms of an amino-terminal region, a central coiled-coil region, and a carboxy-terminal region. The carboxy-terminal regions of λ and φ24_B Ea22, expressed on their own, form dimers with exceptional thermostability. Limited proteolysis of φP27 Ea22 also identified a C-terminal region along the predicted boundaries. While the three Ea22 proteins all appear to have the hallmarks of a domain in their respective C-terminal regions, each sequence is remarkably dissimilar. To reconcile this difference among Ea22 proteins from λ and Stx⁺ phages alike, we speculate that each Ea22 may achieve the same function by targeting different components of the same regulatory process in the host.

Characterization of a bacteriophage, vB_Eco4M-7, that effectively infects many Escherichia coli O157 strains

The characterization of a recently isolated bacteriophage, vB_Eco4M-7, which effectively infects many, though not all, Escherichia coli O157 strains, is presented. The genome of this phage comprises double-stranded DNA, 68,084 bp in length, with a GC content of 46.2%. It contains 96 putative open reading frames (ORFs). Among them, the putative functions of only 35 ORFs were predicted (36.5%), whereas 61 ORFs (63.5%) were classified as hypothetical proteins. The genome of phage vB_Eco4M-7 does not contain genes coding for integrase, recombinase, repressors or excisionase, which are the main markers of temperate viruses. Therefore, we conclude that phage vB_Eco4M-7 should be considered a lytic virus. This was confirmed by monitoring phage lytic development by a one-step growth experiment. Moreover, the phage forms relatively small uniform plaques (1 mm diameter) with no properties of lysogenization. Electron microscopic analyses indicated that vB_Eco4M-7 belongs to the Myoviridae family. Based on mass spectrometric analyses, including the fragmentation pattern of unique peptides, 33 phage vB_Eco4M-7 proteins were assigned to annotated open reading frames. Importantly, genome analysis suggested that this E. coli phage is free of toxins and other virulence factors. In addition, a similar, previously reported but uncharacterized bacteriophage, ECML-117, was also investigated, and this phage exhibited properties similar to vB_Eco4M-7. Our results indicate that both studied phages are potential candidates for phage therapy and/or food protection against Shiga toxin-producing E. coli, as the majority of these strains belong to the O157 serotype.

The ea22 gene of lambdoid phages: preserved prolysogenic function despite of high sequence diversity

The exo-xis region of lambdoid phages contains open reading frames and genes that appear to be evolutionarily important. However, this region has received little attention up to now. In this study, we provided evidence that ea22, the largest gene of this region, favors the lysogenic pathway over the lytic pathway in contrast to other characterized exo-xis region genes including ea8.5, orf61, orf60a, and orf63. Our assays also suggest some functional analogies between Ea22 and the phage integrase protein (Int). While it is unsurprising that Ea22 operates similarly in both λ and Stx phages, we have observed some distinctions that may arise from considerable sequence dissimilarity at the carboxy termini of each protein.

Role of orf73 in the development of lambdoid bacteriophages during infection of the Escherichia coli host

Shiga toxin-producing Escherichia coli (STEC) is a group of pathogenic strains responsible for human infections that result in bloody diarrhea and hemorrhagic colitis, often with severe complications. The main virulence factors of STEC are Shiga toxins encoded by stx genes located in genomes of Shiga toxin-converting bacteriophages (Stx phages). These bacterial viruses are clustered in the lambdoid bacteriophages family represented by phage λ. Here, we report that expression of orf73 from the exo-xis region of the phage genome promotes the lysogenic pathway of development of λ and Φ24B phages. We demonstrated that the mutant phages with deletions of orf73 revealed higher burst size during the lytic cycle. Moreover, survival rates of E. coli infected with mutant bacteriophages were lower relative to wild-type viruses. Additionally, orf73 deletion negatively influenced the lysogenization process of E. coli host cells. We conclude that orf73 plays an important biological role in the development of lambdoid viruses, and probably it is involved in the network of molecular mechanism of the lysis-vs.-lysogenization decision.

Characterization of Bacteriophage vB-EcoS-95, Isolated From Urban Sewage and Revealing Extremely Rapid Lytic Development

Morphological, biological, and genetic characteristics of a virulent Siphoviridae phage, named vB-EcoS-95, is reported. This phage was isolated from urban sewage. It was found to infect some Escherichia coli strains giving clear plaques. The genome of this phage is composed of 50,910 bp and contains 89 ORFs. Importantly, none of the predicted ORFs shows any similarity with known pathogenic factors that would prevent its use in medicine. Genome sequence analysis of vB-EcoS-95 revealed 74% similarity to genomic sequence of Shigella phage pSf-1. Compared to pSf-1, phage vb-EcoS-95 does not infect Shigella strains and has an efficient bacteriolytic activity against some E. coli strains. One-step growth analysis revealed that this phage has a very short latent period (4 min), and average burst size of 115 plaque forming units per cell, which points to its high infectivity of host cells and strong lytic activity. The bacteriolytic effect of vB-EcoS-95 was tested also on biofilm-producing strains. These results indicate that vB-EcoS-95 is a newly discovered E. coli phage that may be potentially used to control the formation of biofilms.

Inhibition of Shiga toxin-converting bacteriophage development by novel antioxidant compounds

Oxidative stress may be the major cause of induction of Shiga toxin-converting (Stx) prophages from chromosomes of Shiga toxin-producing Escherichia coli (STEC) in human intestine. Thus, we aimed to test a series of novel antioxidant compounds for their activities against prophage induction, thus, preventing pathogenicity of STEC. Forty-six compounds (derivatives of carbazole, indazole, triazole, quinolone, ninhydrine, and indenoindole) were tested. Fifteen of them gave promising results and were further characterized. Eleven compounds had acceptable profiles in cytotoxicity tests with human HEK-293 and HDFa cell lines. Three of them (selected for molecular studies) prevent the prophage induction at the level of expression of specific phage genes. In bacterial cells treated with hydrogen peroxide, expression of genes involved in the oxidative stress response was significantly less efficient in the presence of the tested compounds. Therefore, they apparently reduce the oxidative stress, which prevents induction of Stx prophage in E. coli.

Biodiversity of bacteriophages: morphological and biological properties of a large group of phages isolated from urban sewage

A large scale analysis presented in this article focuses on biological and physiological variety of bacteriophages. A collection of 83 bacteriophages, isolated from urban sewage and able to propagate in cells of different bacterial hosts, has been obtained (60 infecting Escherichia coli, 10 infecting Pseudomonas aeruginosa, 4 infecting Salmonella enterica, 3 infecting Staphylococcus sciuri, and 6 infecting Enterococcus faecalis). High biological diversity of the collection is indicated by its characteristics, both morphological (electron microscopic analyses) and biological (host range, plaque size and morphology, growth at various temperatures, thermal inactivation, sensitivity to low and high pH, sensitivity to osmotic stress, survivability upon treatment with organic solvents and detergents), and further supported by hierarchical cluster analysis. By the end of the research no larger collection of phages from a single environmental source investigated by these means had been found. The finding was confirmed by whole genome analysis of 7 selected bacteriophages. Moreover, particular bacteriophages revealed unusual biological features, like the ability to form plaques at low temperature (4 °C), resist high temperature (62 °C or 95 °C) or survive in the presence of an organic solvents (ethanol, acetone, DMSO, chloroform) or detergent (SDS, CTAB, sarkosyl) making them potentially interesting in the context of biotechnological applications.

A simple and rapid procedure for the detection of genes encoding Shiga toxins and other specific DNA sequences

A novel procedure for the detection of specific DNA sequences has been developed. This procedure is based on the already known method employing PCR with appropriate primers and a sequence-specific DNA probe labeled with the fluorescent agent 6-carboxylfluorescein (FAM) at the 5′ end and the fluorescence quencher BHQ-1 (black hole quencher) at the 3′ end. However, instead of the detection of the fluorescence signal with the use of real-time PCR cyclers, fluorescence/luminescence spectrometers or fluorescence polarization readers, as in all previously-reported procedures, we propose visual observation of the fluorescence under UV light directly in the reaction tube. An example for the specific detection of the Shiga toxin-producing Escherichia coli (STEC) strains, by detecting Shiga toxin genes, is demonstrated. This method appears to be specific, simple, rapid and cost effective. It may be suitable for use in research laboratories, as well as in diagnostic units of medical institutions, even those equipped only with a thermocycler and a UV transilluminator, particularly if rapid identification of a pathogen is required.

UV-Sensitivity of Shiga Toxin-Converting Bacteriophage Virions Φ24B, 933W, P22, P27 and P32

Shiga toxin-converting bacteriophages (Stx phages) are present as prophages in Shiga toxin-producing Escherichia coli (STEC) strains. Theses phages can be transmitted to previously non-pathogenic E. coli cells making them potential producers of Shiga toxins, as they bear genes for these toxins in their genomes. Therefore, sensitivity of Stx phage virions to various conditions is important in both natural processes of spreading of these viruses and potential prophylactic control of appearance of novel pathogenic E. coli strains. In this report we provide evidence that virions of Stx phages are significantly more sensitive to UV irradiation than bacteriophage λ. Following UV irradiation of Stx virions at the dose of 50 J/m², their infectivity dropped by 1–3 log₁₀, depending on the kind of phage. Under these conditions, a considerable release of phage DNA from virions was observed, and electron microscopy analyses indicated a large proportion of partially damaged virions. Infection of E. coli cells with UV-irradiated Stx phages resulted in significantly decreased levels of expression of N and cro genes, crucial for lytic development. We conclude that inactivation of Stx virions caused by relatively low dose of UV light is due to damage of capsids that prevents effective infection of the host cells.

Defects in RNA polyadenylation impair both lysogenization by and lytic development of Shiga toxin-converting bacteriophages

In Escherichia coli, the major poly(A) polymerase (PAP I) is encoded by the pcnB gene. In this report, a significant impairment of lysogenization by Shiga toxin-converting (Stx) bacteriophages (Φ24B, 933W, P22, P27 and P32) is demonstrated in host cells with a mutant pcnB gene. Moreover, lytic development of these phages after both infection and prophage induction was significantly less efficient in the pcnB mutant than in the WT host. The increase in DNA accumulation of the Stx phages was lower under conditions of defective RNA polyadenylation. Although shortly after prophage induction, the levels of mRNAs of most phage-borne early genes were higher in the pcnB mutant, at subsequent phases of the lytic development, a drastically decreased abundance of certain mRNAs, including those derived from the N, O and Q genes, was observed in PAP I-deficient cells. All of these effects observed in the pcnB cells were significantly more strongly pronounced in the Stx phages than in bacteriophage λ. Abundance of mRNA derived from the pcnB gene was drastically increased shortly (20 min) after prophage induction by mitomycin C and decreased after the next 20 min, while no such changes were observed in non-lysogenic cells treated with this antibiotic. This prophage induction-dependent transient increase in pcnB transcript may explain the polyadenylation-driven regulation of phage gene expression.

The most widespread problems in the function-based microbial metagenomics

Metagenomics is a powerful tool to better understand the microbial niches, especially these from extreme habitats like oceans and seas, hot springs or deserts. However, one who is going to face the metagenomic studies should realize the challenges which might occur in the course of experiments. This manuscript indicates common problems in function-driven metagenomics, especially factors that influence gene expression are taken into account. Codon usage bias, internal cell accumulation, correct protein folding or presence of proper initiation factors are discussed and possible ways to overcome these problems are proposed. Finally, the annotation process is described, including possible limitations that one should take under consideration. What is more, the most popular databases for metagenomic data are mentioned and discussed.

Different expression patterns of genes from the exo-xis region of bacteriophage λ and Shiga toxin-converting bacteriophage Ф24B following infection or prophage induction in Escherichia coli

Lambdoid bacteriophages serve as useful models in microbiological and molecular studies on basic biological process. Moreover, this family of viruses plays an important role in pathogenesis of enterohemorrhagic Escherichia coli (EHEC) strains, as they are carriers of genes coding for Shiga toxins. Efficient expression of these genes requires lambdoid prophage induction and multiplication of the phage genome. Therefore, understanding the mechanisms regulating these processes appears essential for both basic knowledge and potential anti-EHEC applications. The exo-xis region, present in genomes of lambdoid bacteriophages, contains highly conserved genes of largely unknown functions. Recent report indicated that the Ea8.5 protein, encoded in this region, contains a newly discovered fused homeodomain/zinc-finger fold, suggesting its plausible regulatory role. Moreover, subsequent studies demonstrated that overexpression of the exo-xis region from a multicopy plasmid resulted in impaired lysogenization of E. coli and more effective induction of λ and Ф24_B prophages. In this report, we demonstrate that after prophage induction, the increase in phage DNA content in the host cells is more efficient in E. coli bearing additional copies of the exo-xis region, while survival rate of such bacteria is lower, which corroborated previous observations. Importantly, by using quantitative real-time reverse transcription PCR, we have determined patterns of expressions of particular genes from this region. Unexpectedly, in both phages λ and Ф24_B, these patterns were significantly different not only between conditions of the host cells infection by bacteriophages and prophage induction, but also between induction of prophages with various agents (mitomycin C and hydrogen peroxide). This may shed a new light on our understanding of regulation of lambdoid phage development, depending on the mode of lytic cycle initiation.

The use of fosmid metagenomic libraries in preliminary screening for various biological activities

BACKGROUND

It is generally believed that there are many natural sources of as yet unknown bioactive compounds with a high biotechnological potential. However, the common method based on the use of cell extracts in the preliminary screening for particular molecules or activities is problematic as amounts of obtained compounds may be low, and such experiments are hardly reproducible. Therefore, the aim of this work was to test whether a novel strategy to search for previously unknown biological activities can be efficient. This strategy is based on construction of metagenomic libraries and employment of Escherichia coli strains as cell factories producing compounds of properties potentially useful in biotechnology.

RESULTS

Three cyanobacterial metagenomic libraries were constructed in the fosmid system. The libraries were screened for various biological activities. Extracts from selected E. coli clones bearing constructs with fragments of cyanobacterial genomes revealed antimicrobial or anticancer activities. Interestingly, stimulation of growth of host bacteria bearing particular plasmids with certain cyanobacterial genes was detected, suggesting a potential possibility for improvement of E. coli cultivation during biotechnological production. The most interesting plasmids were sequenced, and putative mechanisms of biological effects caused by cyanobacterial gene products are discussed.

CONCLUSIONS

The strategy of exploring cyanobacteria as sources of bioactive compounds, based on E. coli cell factories producing compounds due to expression of genes from metagenomic libraries, appears to be effective.

Metagenomic approach in the investigation of new bioactive compounds in the marine environment

The marine environment is estimated to be one of the most significant sources of biological activity in the world. In the last few decades an increase in the research intensity conducted on marine microorganisms has been observed, which confirms the great potential of these organisms in the field of bioactive compounds' production. In order to efficiently use the natural resources of the marine environment, metagenomics can be applied. This powerful technique allows for efficient screening of microbial biodiversity for bioactive compounds. The primary aim of this review is to present some aspects of the construction of metagenomic libraries, and strategies of screening for novel bioactives in the marine surrounding. This paper also illustrates several examples of the application of metagenomic methods in the discovery of novel enzymes and drugs in various marine environments.

Metagenomic approach in the investigation of new bioactive compounds in the marine environment

The marine environment is estimated to be one of the most significant sources of biological activity in the world. In the last few decades an increase in the research intensity conducted on marine microorganisms has been observed, which confirms the great potential of these organisms in the field of bioactive compounds' production. In order to efficiently use the natural resources of the marine environment, metagenomics can be applied. This powerful technique allows for efficient screening of microbial biodiversity for bioactive compounds. The primary aim of this review is to present some aspects of the construction of metagenomic libraries, and strategies of screening for novel bioactives in the marine surrounding. This paper also illustrates several examples of the application of metagenomic methods in the discovery of novel enzymes and drugs in various marine environments.

Escherichia coli O104:H4 outbreak--have we learnt a lesson from it?

Shiga toxin-producing Escherichia coli (STEC) strains belong to the group of pathogens that cause bloody diarrhea and hemorrhagic colitis with often severe complications. The main problem with human pathogenic E. coli strains, including STEC, is a wide spectrum of phenotypes and clinical manifestations. It is related to a variety of exchangeable genetic elements, like plasmids, bacteriophages, transposons and pathogenicity islands, that take part in horizontal gene transfer which influences creation of new dangerous bacterial strains. A good example of this phenomenon is a novel Shiga toxin-producing E. coli O104:H4 serotype that was associated with a widespread and severe foodborne disease outbreak in Germany in 2011. The O104:H4 strain was created by a number of horizontal gene transfer events between two distinct pathogens, resulting in the emergence of the new, atypical strain. That outbreak proved that also rare and unusual serotypes of STEC may be a significant risk factor and that the procedures recommended for STEC detection were not suitable to deal with this kind of pathogens. With respect to new combinations of chromosomal and extrachromosomal elements in susceptible bacterial hosts, epidemics and frequent human infections caused by STEC strains, we suggest that more attention should be paid to the development and improvement of diagnostic methods. It is difficult to determine STEC bacteria by general microbiological, biochemical and immunological assays, because strains can vary dramatically in their phenotypic and serotypic properties. It is postulated that standardized genetic tests, based on detection of features most frequently presented by STEC, particularly those located on easily exchangeable elements (such as Shiga toxin-encoding phages), can be more adequate for STEC detection.

Escherichia coli O104:H4 outbreak--have we learnt a lesson from it?

Shiga toxin-producing Escherichia coli (STEC) strains belong to the group of pathogens that cause bloody diarrhea and hemorrhagic colitis with often severe complications. The main problem with human pathogenic E. coli strains, including STEC, is a wide spectrum of phenotypes and clinical manifestations. It is related to a variety of exchangeable genetic elements, like plasmids, bacteriophages, transposons and pathogenicity islands, that take part in horizontal gene transfer which influences creation of new dangerous bacterial strains. A good example of this phenomenon is a novel Shiga toxin-producing E. coli O104:H4 serotype that was associated with a widespread and severe foodborne disease outbreak in Germany in 2011. The O104:H4 strain was created by a number of horizontal gene transfer events between two distinct pathogens, resulting in the emergence of the new, atypical strain. That outbreak proved that also rare and unusual serotypes of STEC may be a significant risk factor and that the procedures recommended for STEC detection were not suitable to deal with this kind of pathogens. With respect to new combinations of chromosomal and extrachromosomal elements in susceptible bacterial hosts, epidemics and frequent human infections caused by STEC strains, we suggest that more attention should be paid to the development and improvement of diagnostic methods. It is difficult to determine STEC bacteria by general microbiological, biochemical and immunological assays, because strains can vary dramatically in their phenotypic and serotypic properties. It is postulated that standardized genetic tests, based on detection of features most frequently presented by STEC, particularly those located on easily exchangeable elements (such as Shiga toxin-encoding phages), can be more adequate for STEC detection.

Inhibition of development of Shiga toxin-converting bacteriophages by either treatment with citrate or amino acid starvation

OBJECTIVES

Shiga toxin-producing Escherichia coli (STEC) are pathogenic strains, whose virulence depends on induction of Shiga toxin-converting prophages and their subsequent lytic development. We explored which factors or conditions could inhibit development of these phages, potentially decreasing virulence of STEC.

MATERIALS AND METHODS

Lytic development of Shiga toxin-converting bacteriophages was monitored after mitomycin C-provoked prophage induction under various conditions. Phage DNA replication efficiency was assessed by measurement of DNA amount in cells using quantitative polymerase chain reaction.

RESULTS

We demonstrated that the use of citrate delayed Shiga toxin-converting phage development after prophage induction. This effect was independent on efficiency of prophage induction and phage DNA replication. However, an excess of glucose reversed the effect of citrate. Amino acid starvation prevented the phage development in bacteria both able and unable to induce the stringent response.

CONCLUSIONS

Lytic development of Shiga toxin-converting bacteriophages can be inhibited by either the presence of citrate or amino acid starvation. We suggest that the inhibition caused by the latter condition may be due to a block in prophage induction or phage DNA replication or both.

APPLICATIONS

Our findings may facilitate development of procedures for treatment of STEC-infected patients.