Physiology and Growth
Paul Pumpens in Single-Stranded RNA Phages, 2020
Direct arguments for the lysogeny in the case of the phage f2 were published by Vera Zgaga (1977). The reaction of Charles Weissmann (1978) followed immediately and clarified the situation. It was noted thatthe state in which bacterial cultures produce phage without lysing and are resistant to superinfection has been called “carrier state” or “viral persistence” without implying any mechanism… The term “lysogeny” implies that the viral genome is present in the host in a noninfectious form, in particular that it is integrated into the host genome; until evidence for such criteria is adduced in the case of RNA phages it would be preferable to retain the original designation of “carrier state” (Weissmann 1978).
Composition and Diversity of Human Oral Microbiome
Chaminda Jayampath Seneviratne in Microbial Biofilms, 2017
As mentioned earlier, the viral population of the oral microbiome is made up predominantly of bacteriophages of the oral bacteria. In general, bacteriophages may have a lytic or a lysogenic life cycle [91]. In the lytic phage, the bacteriophase replicates and lyse the bacterial cell while in the lysogenic phage, the viral genome integrates with bacterial DNA. As many of the oral bacteriophages have been identified to have lysogenic lifestyles, they have the capability to alter the oral bacteriome substantially. In addition, oral viruses tend to live in a dynamic equilibrium with the bacterial host because the virions of lysogenic viruses are stable components of the oral ecosystem [92,93]. Thus, bacteriophage may have roles both as ‘commensals’ [94] and as ‘pathogens’ [95]. Although the gut bacteriome is considered to be more populous than the mouth, the oral microbiome has a higher degree of mobile genetic elements (including viruses, plasmids and transposons) as compared to that of stool [96]. Healthy humans harbour a persistent community of double-stranded DNA viruses in their saliva, with the exclusive identification of bacteriophage as the most abundant virus types [74]. Studies based on epifluorescence microscopy have visualised VLPs to an approximate concentration of 108 VLPs/mL of fluid from oropharyngeal swabs [81], 108 VLPs/mL of saliva [74] and 107 VLPs/mg of dental plaque [97].
Introduction to virus structure, classification, replication, and hosts
Avindra Nath, Joseph R. Berger in Clinical Neurovirology, 2020
Some viruses will bypass the replicative cycle and instead will make use of an alternative pathway termed the lysogenic cycle. Among the herpesviruses, this is generally known as latency, but lysogeny refers to the general phenomenon, originally described for some bacterial viruses. In the lysogenic cycle, the viral DNA will undergo some alteration that results in the viral replicative cycle being arrested. In some cases (e.g., the bacterial virus lambda), the viral DNA integrates into the host cell chromosome. This effectively puts the viral replicative cycle “on hold,” because no progeny virions will be produced. Once integrated, the viral DNA can persist there indefinitely; each daughter cell will contain one or more copies of the viral DNA, because the incorporated DNA is replicated along with the cell’s DNA. As part of the host DNA, the viral DNA can remain silent, can serve to express a low copy number of genes, or can be induced to complete the replicative cycle. Exactly how induction is carried out in the host remains poorly understood, but stress, sunlight, other infections, and certain chemicals can function as inducers. The herpesviruses arrest their replicative cycles and enter latency by a different mechanism. In this case, the viral DNA circularizes and persists in the host cell’s nucleus, being passed to daughter cells, and may eventually be induced.
Bacteriophages for ESKAPE: role in pathogenicity and measures of control
Published in Expert Review of Anti-infective Therapy, 2021
Amrita Patil, Rajashri Banerji, Poonam Kanojiya, Santosh Koratkar, Sunil Saroj
Bacteriophages are viruses, which specifically infect bacterial cells and are one of the most abundant organisms in the environment (total population of ~1030–1032). Bacteriophage possesses tremendous diversity in morphology and genomic content enclosed in its capsid. The basal plate of the bacteriophage consists of tail fibers required for the initial attachment to the host cells. The bacteriophage genetic material is introduced to the host cell via the sheath region, often surrounded by sheath proteins [13]. Inside the host bacterial cell, bacteriophage undergoes either lytic (virulent) or lysogenic (non-virulent) life cycle. The bacteriophage is dependent on the host machinery for the synthesis of bacteriophage particles, assisted by early proteins synthesized during the lytic cycle. The genetic material is then packaged into the capsid constructing a new daughter bacteriophage that eventually bursts into the surrounding after lysis of the host bacterial cell. However, during the lysogenic cycle, rather than undergoing lysis, bacteriophage persists in the host in a dormant state. Bacteriophages and hosts in the lysogenic cycle are known as prophage and lysogen, respectively [14]. Based on the environmental cues, such as changes in pH, nutrients, temperature, and exposure to foreign DNA, hydrogen peroxide, antibiotics, or other agents causing DNA damage prophage enter into a lytic cycle and lead to lysis of the host cell [15] (Figure 1).
The prevalence and impact of lysogeny among oral isolates of Enterococcus faecalis
Published in Journal of Oral Microbiology, 2019
Roy H. Stevens, Hongming Zhang, Christine Sedgley, Adam Bergman, Anil Reddy Manda
In a previous communication we reported our generation and isolation of a cured E. faecalis strain [16]. Briefly, allelic exchange mutagenesis was employed to delete a module of six lysogeny-related genes and insert a selectable antibiotic resistance gene (erythromycin) into the ɸEf11 prophage of lysogenic E. faecalis TUSoD11. PCR screening of the recombinant transformant clones selected on erythromycin plates confirmed the absence of the targeted prophage genes in the cells of the recovered colonies. Surprisingly, in addition to the deletion of the six genes of the targeted lysogeny gene module, the cells of a few of the recovered colonies also lacked any other of the ɸEf11 prophage genes, for which they were screened, as well. Because the phage ɸEf11 genome is circularly permuted, deletion of the entire prophage from the TUSoD11 chromosome could have occurred through homologous recombination between the gene exchange vector that was used and homologous regions that could be positioned at either end of the ɸEf11 prophage. PCR screening was conducted using ɸEf11 prophage-specific primers and template DNA from presumptive recombinant clones selected on the antibiotic (erythromycin) plates. Those clones, no longer possessing any detectable ɸEf11 prophage genes, were considered cured of the prophage, and designated E. faecalis TUSoD11(ΔɸEf11). By this process we have obtained the isogenic pair of lysogenic and non-lysogenic E. faecalis strains [TUSoD11 and TUSoD11(ΔɸEf11)], differing only in the presence or absence of the ɸEf11 prophage.
Merits of the ‘good’ viruses: the potential of virus-based therapeutics
Published in Expert Opinion on Biological Therapy, 2021
Qianyu Zhang, Wen Wu, Jinqiang Zhang, Xuefeng Xia
Phages play important roles in bacterial pathogenicity and evolution [10]. They can be categorized into obligate lytic (virulent) phages and lysogenic (temperate) phages. As for the anti-bacterial applications, lytic phages are more suitable than lysogenic phages as they are more similar to antibiotic drugs which induce rapid bacterial death [11]. Besides, the lysogenic conversion induced by lysogenic phages might lead to harmful consequences such as endowing bacteria with pathogenic traits or even antibiotic resistance [11]. In early years phages were investigated to manage conditions like typhoid fever, colitis, peritonitis, skin infections, surgical infections, septicemia, urinary tract infections, and otolaryngology infections [12]. However, data collected from early clinical studies lacked standardization such as blinding and the inclusion of appropriate control groups. The interest in phage therapy against bacterial infection was rekindled after Smith & Huggins devised pioneering studies against antibiotic-resistant bacterial strains in human and multiple animal models of septicemia and meningitis in the 1980s. There have been case reports on the antibacterial therapy using bacteriophages in recent years, and clinical trials have been carried out as well [13].