{"id":197,"date":"2018-08-21T08:26:27","date_gmt":"2018-08-21T08:26:27","guid":{"rendered":"https:\/\/coliphages.ixole.es\/?page_id=197"},"modified":"2024-07-01T11:42:27","modified_gmt":"2024-07-01T11:42:27","slug":"reproduction","status":"publish","type":"page","link":"https:\/\/coliphages.ixole.es\/index.php\/reproduction\/","title":{"rendered":"Reproduction"},"content":{"rendered":"

[et_pb_section fb_built=\u00bb1″ _builder_version=\u00bb4.16″ global_colors_info=\u00bb{}\u00bb][et_pb_row module_class=\u00bb et_pb_row_fullwidth\u00bb _builder_version=\u00bb4.16″ width=\u00bb89%\u00bb width_tablet=\u00bb80%\u00bb width_last_edited=\u00bbon|desktop\u00bb max_width=\u00bb89%\u00bb max_width_tablet=\u00bb80%\u00bb max_width_last_edited=\u00bbon|desktop\u00bb custom_padding=\u00bb2px|0px|25.85px|0px|false|false\u00bb make_fullwidth=\u00bbon\u00bb locked=\u00bboff\u00bb global_colors_info=\u00bb{}\u00bb column_structure=\u00bb2_3,1_3″ width_phone=\u00bb80%\u00bb max_width_phone=\u00bb80%\u00bb][et_pb_column type=\u00bb2_3″ _builder_version=\u00bb4.16″ custom_padding=\u00bb|||\u00bb global_colors_info=\u00bb{}\u00bb custom_padding__hover=\u00bb|||\u00bb][et_pb_text _builder_version=\u00bb4.16″ text_font=\u00bb|700|||||||\u00bb text_text_color=\u00bb#256168″ text_font_size=\u00bb44px\u00bb text_line_height=\u00bb1.1em\u00bb header_font=\u00bb||||||||\u00bb header_line_height=\u00bb1.7em\u00bb text_font_size_tablet=\u00bb\u00bb text_font_size_phone=\u00bb33px\u00bb text_font_size_last_edited=\u00bbon|phone\u00bb global_colors_info=\u00bb{}\u00bb]How do bacteriophages reproduce?
\n[\/et_pb_text][et_pb_text _builder_version=\u00bb4.16″ text_font=\u00bb||||||||\u00bb text_text_color=\u00bb#256168″ text_font_size=\u00bb25px\u00bb text_line_height=\u00bb1.1em\u00bb background_color=\u00bb#eaeddb\u00bb custom_margin=\u00bb|||\u00bb custom_padding=\u00bb60px||60px|95px|true\u00bb custom_padding_tablet=\u00bb\u00bb custom_padding_phone=\u00bb40px|20px|40px|30px|true\u00bb custom_padding_last_edited=\u00bbon|phone\u00bb text_font_size_tablet=\u00bb\u00bb text_font_size_phone=\u00bb20px\u00bb text_font_size_last_edited=\u00bbon|phone\u00bb locked=\u00bboff\u00bb global_colors_info=\u00bb{}\u00bb]2.1<\/strong> Lytic cycle<\/a>
\n2.2<\/strong> Lysogenic cycle<\/a>
\n[\/et_pb_text][et_pb_text _builder_version=\u00bb4.16″ text_font=\u00bb||||||||\u00bb text_line_height=\u00bb1.3em\u00bb header_font=\u00bb||||||||\u00bb header_2_font=\u00bb|700|||||||\u00bb header_2_text_color=\u00bb#0a2d31″ header_2_font_size=\u00bb33px\u00bb text_font_size_tablet=\u00bb\u00bb text_font_size_phone=\u00bb18px\u00bb text_font_size_last_edited=\u00bbon|phone\u00bb global_colors_info=\u00bb{}\u00bb]<\/p>\n

Bacteriophages<\/strong> are non-cellular<\/strong> and non-metabolic<\/strong> living organisms. This means that they are forced parasites<\/strong> and thus they can only replicate inside a bacterial cell<\/strong>, usually called a host cell (host bacteria).<\/p>\n

Bacterial cell-supporting phage replication needs<\/strong> to meet two fundamental requirements: it has to be a living cell<\/strong>, and it has to be metabolically active<\/strong>.<\/p>\n

Bacteriophages follow two strategies for reproducing: the lytic cycle<\/strong> and the lysogenic cycle. The one that matters for the purpose of using phages as indicators<\/strong> is the lytic one, as no free virions are produced in the lysogenic cycle. (Adams, 1959, Bott, 2014)<\/p>\n

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2.1 Lytic cycle<\/h2>\n

The process of the lytic cycle<\/strong> is divided into five steps.<\/p>\n

First of all, the virus has to find and attach<\/strong> to the surface of the target bacteria. This attachment<\/strong> depends on the presence of specific receptors on the cell surface<\/strong> and determines the specificity and host range<\/strong> of a given bacteriophage. Different bacteriophages have different strategies or target molecules.<\/p>\n

Most bacteriophages use cell wall molecules as receptors<\/strong>. These are known as somatic bacteriophages<\/strong>. Myoviridae<\/em>, Siphoviridae<\/em>, Podoviridae<\/em> and Microviridae<\/em> belong to this group. Another strategy is to use cell appendixes like F pili or flagella. These are called F-specific bacteriophages<\/strong>, which use the F or sexual pili as receptors and as a channel for \u201cinjecting\u201d their nucleic acid<\/strong>. The Inoviridae<\/em> and Leviviridae<\/em> belong to this group.<\/p>\n

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There is no active positive attraction (positive taxis) between phages and host bacteria and consequently meeting of bacteria and phages depends on random encounters<\/strong>. Whether these encounters occur or not depends<\/strong> to a great extent on the concentrations of bacteria and bacteriophages<\/strong>. Some studies performed with somatic coliphages indicate that the sum of log10<\/sub><\/strong> concentrations of phages and host bacteria per ml that guarantee replication is around 6.5<\/strong> (Jofre, 2009).<\/p>\n

The second step is penetration<\/strong>, which consists of the injection of the viral genome and seldom molecules<\/strong> contained inside the capsid into the bacterial cytoplasm. This can happen through the cell wall (somatic bacteriophages) or through an appendage (flagella and the sexual pili).<\/p>\n

Then the viral genome, using the metabolic tools of the host cell<\/strong>, starts replicating<\/strong> and the production of viral proteins takes place. This step requires the host to be metabolically active<\/p>\n

When feces exit the gut, the change of environment causes a stress<\/strong> on the great majority of fecal bacteria, including coliform bacteria, that leads<\/strong> first to metabolic inactivity and<\/strong> then to death<\/strong>. This, together with the difficulties for viruses to come across a cell in a liquid matrix with a relatively poor concentration of phages and bacteria, makes viral reproduction outside the gut barely possible<\/strong> (Jofre, 2009).<\/p>\n

The fourth step is the assembly of<\/strong> the different proteins and the genome, forming the capsomers<\/strong> that bind<\/strong> with each other<\/strong> and with the genetic material<\/strong> to build the capsid<\/strong>, and hence producing newborn virions<\/strong> which become visible (by electron microscopy) inside the bacterial cytoplasm.<\/p>\n

Finally, the bacterial cell breaks<\/strong>, in a process known as lysis<\/strong>, due to enzymatic action of some proteins coded in the viral genome, and new bacteriophages<\/strong> are released<\/strong> to the media. Some bacteriophages, such as for example M13, do not lyse the cell, but this seems to be exceptional.<\/p>\n

All this process can happen in less than 30 minutes, and at the end between 100<\/strong> and 200<\/strong> (depending on the bacteriophage) new infectious phage particles are released<\/strong>.<\/p>\n

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The amount of phages formed inside a host<\/strong> bacterium and released by cell lysis is known as the burst size<\/strong>.<\/p>\n

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During steps 2 and 3 the infectious and visible virions disappear.<\/p>\n

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2.2 Lysogenic cycle<\/h2>\n

This cycle follows the same start as<\/strong> the lytic<\/strong> one, but once the viral genome<\/strong> penetrates, it integrates within<\/strong> the bacterial DNA<\/strong> or in some cases remains as a plasmic. When integrated, it replicates at the same time as the bacterial one. It can replicate at its own rate if it forms a plasmid, but no virions are produced unless it passes to a lytic cycle due to lysogenic induction<\/strong>, usually as a consequence of a stress situation<\/strong>. This cycle is important for bacterial genetic variability<\/strong> but not for detecting fecal contamination, as we cannot quantify the virus that are in a lysogenic cycle.<\/p>\n

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References<\/p>\n

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Adams, M.H. (1959).<\/em> Bacteriophages<\/strong>. Interscience Publishers. Inc. New York.<\/p>\n

Bott, R. (2014).<\/em> Brock Biology of Microorganisms<\/strong>, 14th Edition, Madigan, M.T. Igarss 2014.<\/p>\n

Jofre, J. (2009).<\/em> Is the replication of somatic coliphages in water environments significant?<\/strong> J. Appl. Microbiol 106 : 1059-1069.<\/p>\n

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How do bacteriophages reproduce? 2.1 Lytic cycle 2.2 Lysogenic cycle Bacteriophages are non-cellular and non-metabolic living organisms. This means that they are forced parasites and thus they can only replicate inside a bacterial cell, usually called a host cell (host bacteria). Bacterial cell-supporting phage replication needs to meet two fundamental requirements: it has to be […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-197","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/pages\/197","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/comments?post=197"}],"version-history":[{"count":35,"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/pages\/197\/revisions"}],"predecessor-version":[{"id":966,"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/pages\/197\/revisions\/966"}],"wp:attachment":[{"href":"https:\/\/coliphages.ixole.es\/index.php\/wp-json\/wp\/v2\/media?parent=197"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}