Modulation of lambda plasmid and phage DNA replication by Escherichia coli SeqA protein

Antibacterial potential and mechanism of action of dithiocyano-methane as a bactericidal agent for farm disinfection

AIMS

This study aimed to investigate the antibacterial ability and action mechanism of dithiocyano-methane against Aeromonas hydrophila, so as to provide a reference for its application in farm disinfection.

METHODS AND RESULTS

After exposing the bacteria to dithiocyano-methane, the minimum inhibitory concentration (MIC), minimum bactericide concentration (MBC), activities of alkaline phosphatase, aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase and electric conductivity in bacterial suspensions were determined, transmission electron microscope images on cellular structure and SDS-PAGE profile of bacterial proteins were analysed and the expression of genes related to the above experimental observations was confirmed by real-time quantitative PCR. The MIC and MBC of dithiocyano-methane against three tested strains was 1·46 and 2·93 mg l^-1 respectively. The results showed that dithiocyano-methane significantly damaged bacterial cell structure, inhibited the biosynthesis of bacterial proteins and changed the integrity and permeability of bacterial cell wall and cell membrane.

CONCLUSIONS

Dithiocyano-methane showed remarkable antibacterial ability against three tested strains, indicating it is a potential effective bactericidal agent for preventing animal diseases resulted from Aer. hydrophila.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our best knowledge, this is the first report to examine the antibacterial ability and action mechanism of dithiocyano-methane against bacteria. The results demonstrate the great potential of dithiocyano-methane as a disinfectant against Aer. hydrophila in settings such as aquaculture ponds and livestock farms.

Sak and Sak4 recombinases are required for bacteriophage replication in Staphylococcus aureus

DNA-single strand annealing proteins (SSAPs) are recombinases frequently encoded in the genome of many bacteriophages. As SSAPs can promote homologous recombination among DNA substrates with an important degree of divergence, these enzymes are involved both in DNA repair and in the generation of phage mosaicisms. Here, analysing Sak and Sak4 as representatives of two different families of SSAPs present in phages infecting the clinically relevant bacterium Staphylococcus aureus, we demonstrate for the first time that these enzymes are absolutely required for phage reproduction. Deletion of the genes encoding these enzymes significantly reduced phage replication and the generation of infectious particles. Complementation studies revealed that these enzymes are required both in the donor (after prophage induction) and in the recipient strain (for infection). Moreover, our results indicated that to perform their function SSAPs require the activity of their cognate single strand binding (Ssb) proteins. Mutational studies demonstrated that the Ssb proteins are also required for phage replication, both in the donor and recipient strain. In summary, our results expand the functions attributed to the Sak and Sak4 proteins, and demonstrate that both SSAPs and Ssb proteins are essential for the life cycle of temperate staphylococcal phages.

A dual promoter system regulating λ DNA replication initiation

Transcription and DNA replication are tightly regulated to ensure coordination of gene expression with growth conditions and faithful transmission of genetic material to progeny. A large body of evidence has accumulated, indicating that encounters between protein machineries carrying out DNA and RNA synthesis occur in vivo and may have important regulatory consequences. This feature may be exacerbated in the case of compact genomes, like the one of bacteriophage λ, used in our study. Transcription that starts at the rightward pR promoter and proceeds through the λ origin of replication and downstream of it was proven to stimulate the initiation of λ DNA replication. Here, we demonstrate that the activity of a convergently oriented pO promoter decreases the efficiency of transcription starting from pR. Our results show, however, that a lack of the functional pO promoter negatively influences λ phage and λ-derived plasmid replication. We present data, suggesting that this effect is evoked by the enhanced level of the pR-driven transcription, occurring in the presence of the defective pO, which may result in the impeded formation of the replication initiation complex. Our data suggest that the cross talk between the two promoters regulates λ DNA replication and coordinates transcription and replication processes.

Different effects of ppGpp on Escherichia coli DNA replication in vivo and in vitro

Inhibition of Escherichia coli DNA replication by guanosine tetraphosphate (ppGpp) is demonstrated in vitro. This finding is compatible with impairment of the DnaG primase activity by this nucleotide. However, in agreement to previous reports, we were not able to detect a rapid inhibition of DNA synthesis in E. coli cells under the stringent control conditions, when intracellular ppGpp levels increase dramatically. We suggest that the process of ppGpp-mediated inhibition of DnaG activity may be masked in E. coli cells, which could provide a rationale for explanation of differences between ppGpp effects on DNA replication in E. coli and Bacillus subtilis.

Phage λ--new insights into regulatory circuits

Bacteriophage λ, rediscovered in the early 1950s, has served as a model in molecular biology studies for decades. Although currently more complex organisms and more complicated biological systems can be studied, this phage is still an excellent model to investigate principles of biological processes occurring at the molecular level. In fact, very few other biological models provide possibilities to examine regulations of biological mechanisms as detailed as performed with λ. In this chapter, recent advances in our understanding of mechanisms of bacteriophage λ development are summarized and discussed. Particularly, studies on (i) phage DNA injection, (ii) molecular bases of the lysis-versus-lysogenization decision and the lysogenization process itself, (iii) prophage maintenance and induction, (iv), λ DNA replication, (v) phage-encoded recombination systems, (vi) transcription antitermination, (vii) formation of the virion structure, and (viii) lysis of the host cell, as published during several past years, will be presented.

Coupling of transcription and replication machineries in λ DNA replication initiation: evidence for direct interaction of Escherichia coli RNA polymerase and the λO protein

Transcription proceeding downstream of the λ phage replication origin was previously shown to support initial steps of the λ primosome assembly in vitro and to regulate frequency and directionality of λ DNA replication in vivo. In this report, the data are presented indicating that the RNA polymerase β subunit makes a direct contact with the λO protein, a replication initiator of λ phage. These results suggest that the role of RNA polymerase during the initiation of λ phage DNA replication may be more complex than solely influencing DNA topology. Results demonstrated in this study also show that gyrase supercoiling activity stimulates the formation of a complex between λO and RNA polymerase, suggesting that the introduction of negative supercoils by DNA gyrase, besides lowering the energy required for DNA strand separation, may play an additional role in modeling protein–protein interactions at early steps of DNA replication initiation.

Mechanisms of physiological regulation of RNA synthesis in bacteria: new discoveries breaking old schemes

Although in bacterial cells all genes are transcribed by RNA polymerase, there are 2 additional enzymes capable of catalyzing RNA synthesis: poly(A) polymerase I, which adds poly(A) residues to transcripts, and primase, which produces primers for DNA replication. Mechanisms of actions of these 3 RNA-synthesizing enzymes were investigated for many years, and schemes of their regulations have been proposed and generally accepted. Nevertheless, recent discoveries indicated that apart from well-understood mechanisms, there are additional regulatory processes, beyond the established schemes, which allow bacterial cells to respond to changing environmental and physiological conditions. These newly discovered mechanisms, which are discussed in this review, include: (i) specific regulation of gene expression by RNA polyadenylation, (ii) control of DNA replication by interactions of the starvation alarmones, guanosine pentaphosphate and guanosine tetraphosphate, (p)ppGpp, with DnaG primase, (iii) a role for the DksA protein in ppGpp-mediated regulation of transcription, (iv) allosteric modulation of the RNA polymerase catalytic reaction by specific inhibitors of transcription, rifamycins, (v) stimulation of transcription initiation by proteins binding downstream of the promoter sequences, and (vi) promoter-dependent control of transcription antitermination efficiency.