Name: prophage integration in bacteria
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 43 s
Channel: JoVE

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from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Lysogenic Cycle of Bacteriophages

כאשר מספר רב של בקטריופאג'ים נוכחים, הם יכולים להיכנס למצב שכפול חלופי, המסלול הליזוגני, שבו פאג'ים יכולים להתרבות בלי להרוג את המארח שלהם. מסלול זה מתחיל בדומה למסלול הליטי. הפאג'מתחבר תחילה לתא המארח ומזריק את הדנ"א שלו.עם זאת, לאחר החדירה, דנ"א הפאג'מתחבר מחדש ומשתלב עם הגנום החיידקי, ויוצר פרופאג'הפרופאג'עצמו אינו פעיל, ואינו מניע ייצור פאג'ים חדשים. במקום זאת, כאשר התא המארח מתחלק, הוא משוכפל יחד עם דנ"א המארח.

קסטרו, ויניסיוס סילבה, ריקרדו ססאר טבארס קרבאליו, קרלוס אדם קונטה ג'וניור ואדוארדו אוסטקיו סוזה פיגירדו. "Shiga-toxin לייצר Escherichia coli: פתוגניות, supersheding, שיטות אבחון, התרחשות, התפרצויות מזון." סקירות מקיפות במדעי המזון ובטיחות מזון 16, מס '6 (2017): 1269–80. [<a href="https://doi.org/10.1111/1541-4337.12302" target="__blank">מקור</a>]

מלטון-סלסה, אנג'לה ר. "Shiga Toxin (Stx) סיווג, מבנה ותפקוד." מיקרוביולוגיה ספקטרום 2, מס '2 (2014). [<a href="https://doi.org/10.1128/microbiolspec.EHEC-0024-2013" target="__blank">מקור</a>]

מחזור ליזוגני של בקטריופגים

<div style="direction:rtl">בניגוד למחזור הליטי, פאגים המדביקים חיידקים דרך המחזור הליזוגני אינם הורגים מיד את התא המארח שלהם. במקום זאת, הם משלבים את הגנום שלהם עם הגנום המארח, ומאפשרים לחיידקים לשכפל את ה-DNA הפאג יחד עם הגנום החיידקי. העותק המשולב של גנום הפאג' נקרא הפרופאג. חלק מהפרופגים יכולים להפעיל מחדש ולהיכנס למחזור הליטי. זה קורה לעתים קרובות בתגובה להפרעה, כגון נזק ל-DNA, אך יכול להתרחש גם בהיעדר רמזים חיצוניים. <h4>המרה ליזוגנית</h4> במקרים מסוימים, הגנים המקודדים על ידי פרופאגים יכולים לשנות את הפנוטיפ של החיידק הנגוע, תהליך המכונה המרה ליזוגנית. חלק מהפאגים מקודדים לחלבונים או רעלים הנקראים גורמי ארס שיכולים להקל על זיהומים חיידקיים. באמצעות המרה ליזוגנית, בדרך כלל חיידקים לא פתוגניים יכולים להפוך לארסניים מאוד באמצעות זיהום על ידי פאג הנושא גורמי ארסיות. לדוגמה, פאגים כאלה אחראים במידה רבה לפתוגניות של מיני החיידקים הגורמים לבוטוליזם (Clostridium botulinum), דיפתריה (Corynebacterium diphtheriae) וכולרה (Vibrio cholerae). ללא המרה ליזוגנית, חיידקים אלו אינם גורמים בדרך כלל למחלה. דוגמה שנחקרה במיוחד להמרה ליזוגנית היא זו של זן Escherichia coli O157:H7. מספר ריקולי מזון מסיביים נבעו מזיהום על ידי E. coli O157:H7. זן זה של E. coli נגוע בפאג' המקודד רעלן דמוי שיגלה (Stx), שעלול לגרום לדימום מעיים ואי ספיקת כליות. במחזור הליזוגני, Stx אינו מיוצר, והחיידקים אינם גורמים למחלות. הפאג' חייב להיכנס מחדש למחזור הליטי כדי ש-Stx יופק. לרוע המזל, אנטיביוטיקה מסויימת יכולה לעורר את השראת הנבואה ולייצור Stx כתוצאה מכך, מה שמקשה על הטיפול בזיהומים אלה. המחקר הנוכחי חוקר טיפולים חדשים המונעים את התחלת הנבואה.</div>

בניגוד למחזור הליטי, פאגים שמדביקים חיידקים דרך המחזור הליזוגני אינם הורגים מיד את התא המארח שלהם. במקום זאת, הם משלבים את ...

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prophage integration in bacteria

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates.

Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again.

Prophages can also change the traits of the bacteria they infect. This effect is called lysogenic conversion. In this process, phage genes can give bacteria virulence factors, such as toxins or proteins that help infection. As a result, bacteria that were usually harmless can become much more harmful after phage infection.

This kind of conversion helps explain the disease-causing power of Clostridium botulinum, Corynebacterium diphtheriae, and Vibrio cholerae. It also plays a major role in Escherichia coli O157:H7, a strain linked to food recalls. In this strain, the phage carries the gene for Shiga-like toxin, or Stx, which can cause intestinal bleeding and kidney failure. Stx is not produced during lysogeny, and the bacteria do not cause disease until the phage enters the lytic cycle.

Treatment can be complicated because some antibiotics may trigger prophage induction and lead to Stx production. That is why current research is looking for new therapies that stop prophages from starting the lytic cycle.

Prophage Integration in Bacteria

what are viruses?

How Viruses Infect Cells and Multiply

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses. After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it.

viral structure

How Virus Shapes Help Infection

Viruses have specific structures that help them infect host cells and trigger immune responses. Each virus has a core that contains either a DNA-based or RNA-based genome. That core is surrounded by a protective protein coat called the capsid. The capsid is made of smaller subunits called capsomeres. The capsid and the genome-containing core together are called the nucleocapsid. Viruses are often grouped by capsid design. Most viruses have either icosahedral or helical capsids, but some have...

lytic cycle of bacteriophages

How Phages Infect and Burst Bacteria

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface. After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of...

lysogenic cycle of bacteriophages

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates. Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again. Prophages can...

retrovirus life cycles

How Retroviruses Replicate in Host Cells

Retroviruses replicate by copying their RNA genome into DNA inside a host cell. After entry, the viral enzyme reverse transcriptase makes a double-stranded DNA copy from the single-stranded RNA genome. The viral DNA is then carried into the nucleus and inserted into the host genome by integrase. Once integrated, the retroviral DNA is transcribed whenever the host genome is transcribed. This produces new viral RNA that can be copied and used again. The new RNA moves into the cytoplasm, where it...

viral recombination

How Viruses Swap Genes and Spread

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment. These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the...

viral mutations

How Virus Mutations Drive Outbreaks

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA. RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material...

key terms and concepts

Learn how bacteriophages integrate into bacterial DNA, form prophages, and can change bacterial traits through lysogenic conversion and toxin genes.

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HS-LS1-4

Prophage Integration in Bacteria

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