REVIEW published: 31 May 2021 doi: 10.3389/fcimb.2021.635597 Rekindling of a Masterful Precedent; Bacteriophage: Reappraisal and Future Pursuits Israa M. Abd-Allah 1, Ghadir S. El-Housseiny 1, Ibrahim S. Yahia 2,3, Khaled M. Aboshanab 1* and Nadia A. Hassouna 1 1 Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt, 2 Research Center for Advanced Materials Science (RCAMS), Advanced Functional Materials & Optoelectronic Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, Abha, Saudi Arabia, 3 Nanoscience Laboratory for Environmental and Bio-Medical Applications (NLEBA), Semiconductor Lab., Metallurgical Lab, Physics Department, Faculty of Education, Ain Shams University, Cairo, Egypt Antibiotic resistance is exuberantly becoming a deleterious health problem world-wide. Seeking innovative approaches is necessary in order to circumvent such a hazard. An unconventional fill-in to antibiotics is bacteriophage. Bacteriophages are viruses capable of pervading bacterial cells and disrupting their natural activity, ultimately resulting in their defeat. In this article, we will run-through the historical record of bacteriophage and its Edited by: correlation with bacteria. We will also delineate the potential of bacteriophage as a Ayush Kumar, University of Manitoba, Canada therapeutic antibacterial agent, its supremacy over antibiotics in multiple aspects and Reviewed by: the challenges that could arise on the way to its utilization in reality. Pharmacodynamics, Laura Marise de Freitas, pharmacokinetics and genetic engineering of bacteriophages and its proteins will be University of São Paulo, Brazil fl Miguel Ignacio Uyaguari-Diaz, brie y discussed as well. In addition, we will highlight some of the in-use applications of University of Manitoba, Canada bacteriophages, and set an outlook for their future ones. We will also overview some of the *Correspondence: miscellaneous abilities of these tiny viruses in several fields other than the clinical one. This Khaled M. Aboshanab is an attempt to encourage tackling a long-forgotten hive. Perhaps, one day, the smallest [email protected] of the creatures would be of the greatest help. Specialty section: Keywords: bacteriophage, phage therapy, antibiotic resistance, phage proteins, phage pharmacotherapy This article was submitted to Bacteria and Host, a section of the journal Frontiers in Cellular and INTRODUCTION Infection Microbiology Received: 16 February 2021 With an approximate ubiquity ranging from 1031 to1032 (Carlton, 1999), bacteriophages (phages) Accepted: 13 May 2021 are the least sophisticated yet most numerous biological entities on Earth. They serve as the greatest Published: 31 May 2021 repository for genetic material. This is why they have been pictured as “the dark matter of the Citation: biosphere” (Hatfull, 2015). Technically, bacteriophages are viruses (Gordillo Altamirano and Barr, Abd-Allah IM, El-Housseiny GS, 2019) however, they are distinct from the viral archetype. Named after their inherent vocation, Yahia IS, Aboshanab KM and bacteriophages are obligate parasites that infect bacteria. They are their aboriginal destroyers. The Hassouna NA (2021) Rekindling of a earliest anecdotal news on bacteriophages is traced back to 1896 when the English naturalist, Ernest Masterful Precedent; Bacteriophage: “ Reappraisal and Future Pursuits. Hankin, published an article under the title of The bactericidal action of waters of Jumna and Front. Cell. Infect. Microbiol. 11:635597. Ganges on the Cholera microbe” (Abedon et al., 2011b) in which he described the absurd doi: 10.3389/fcimb.2021.635597 inexplicable observation of Ganges water self-clearing from the bacterium Vibrio cholera Frontiers in Cellular and Infection Microbiology | www.frontiersin.org1 May 2021 | Volume 11 | Article 635597 Abd-Allah et al. Rekindling of a Masterful Precedent; Bacteriophage (Abedon et al., 2011b; Chanishvili, 2012; Nm, 2018). Back then, CHARACTERS, STRUCTURE, this was known as the’’Hankin’s phenomenon’’ (Chanishvili, AND CLASSIFICATION 2012). Twenty years later, the formal chronicle of bacteriophage began. It is believed that phages were identified by Sir Frederick Bacteriophages are viruses that selectively utilize bacterial cells Twort in 1915 and separately two years later by the French- astheirhost.Beingviruses,theyarebasicallymadeupofa Canadian microbiologist Felix d’Hérelle who pursued his nucleic acid genome -either DNA or RNA, single or double discovery by closely investigating the nature of these stranded, encased into a cage of viral capsid proteins (Kasman phenomenal agents (Chanishvili, 2012; Nm, 2018). However, and Porter, 2020). They are mostly assembled as a simple build- obscurity has been always there, tainting the provenance of their up of head and tail. Despite this structure simplicity, discovery (Duckworth, 1976). Anyways, at least their appellation bacteriophages are widely varied in their morphology, size “bacteriophages’’ can be emphatically accredited to d’Herelle and genomic make-up. For example, some have round, cubic (Chanishvili, 2012). Figure 1 shows some of the milestones in or icosahedral heads that are joined to tails, others, though less the history of phages (Gelman et al., 2018). Being natural common, are filamentous. Their sizes range from 30 to 110 nm parasites, they are most likely found wherever their hosts are (Weinbauer and Peduzzi, 1994). Regardless of their appearance, amply present. Locales like sewage, wastewater, hospital bacteriophages are non-motile and are transported only via vicinities, soil, human and animal bodies are always lush Brownian motion (Kasman and Porter, 2020). Due to this high sources. They could be also found in extreme environments diversity, multiple classificationsofphagesareoutthere.For like marine water, ocean depths and the surroundings of low and example, phages are divided according to the genetic material high temperatures (Principi et al., 2019). they harbor into four major categories: single stranded DNA FIGURE 1 | Timeline of the most considerable milestones since phage discovery. Frontiers in Cellular and Infection Microbiology | www.frontiersin.org2 May 2021 | Volume 11 | Article 635597 Abd-Allah et al. Rekindling of a Masterful Precedent; Bacteriophage phages (ssDNA), double stranded DNA phages (dsDNA), Lytic Cycle (Performed by Virulent Phages) single stranded RNA phages (ssRNA), and double stranded RNA phages (dsRNA). Each of these groups is further classified i. Adsorption: After recognition of certain receptors on the into different families based on their morphology and the bacterial cell wall or even other organelles such as sex pili and configuration of their genome; with dsDNA comprising the flagella, phages bind specifically to their hosts mostly using largest number: nine families, followed by ssDNA: two families. specialized attachment structures positioned onto their tails. Relatively, DNA phages are better covered in literature, but ii. Injection: Unlike most of the viruses, no uncoating occurs. limited reports are available on RNA ones. So, in few words, we Bacteriophages manage to insert their nucleic acid relying on are to spot some light on them. RNA phages comprise 2 some enzymes that drill through the bacterial cell wall families. On the dsRNA side: the family of Cystoviridae. Two (Olszak et al., 2017). years ago, a lytic Cystoviridae phage was isolated against For those attached to pili or flagella, the genome Streptococcus salivarius and proved its potential for managing penetrates through these hollow pipes. the infections it causes in the oral cavity (Cystoviridae, 2012; iii. Replication: Once invaded by nucleic acid, the bacterial Beheshti-Maal, 2018). The other family is called Leviviridae macromolecule machinery is commandeered to synthesize which accommodates the ssRNA phages. ssRNA phages are phages’ structural protein components and replicate their probably the simplest of all identified viruses and their genomes nucleic acid. range between 3500 and 4200 nucleotides. They are specificfor iv. Assembly: The resulting phage coat particles assemble Gram negative bacteria with pili. They all code for three around the newly-formed nucleic acid molecules bringing proteins: coat, maturation and replicase. The coat protein about a quiverful of whole bacteriophages. In turn, these lurk builds up so that the capsid is composed of dimers. The inside the cells waiting for release and working for it. maturation protein is the one responsible for the adsorption v. Liberation: Thenceforth, a two-step process led by phage- of the phage particle to the bacterial pili. The replicase protein: encoded enzymes, causes disintegration of the bacterial cell an RNA-dependent RNA polymerase that is used by the wall. Two protein groups are involved: holins and infected cells to synthesize RNA from the RNA template of endolysins. Both together collaborate to form a lytic system the virion. ssRNA phages have been long utilized as study tools that controls the timing of cell burst (Doss et al., 2017). First, in the field of molecular biology because of their structure holins act as a timekeeper; from inside the cell, they punch intelligibility. They were also used to learn about the process of holes in the host’s cell membrane allowing the other protein protein synthesis and its regulation, and to closely examine group to make their way out towards the cell wall each of the RNA replication, viral assembly and protein-RNA peptidoglycan.