Virulence Regulation in Bacteria

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Questions and Answers

Which of the following is NOT typically an environmental cue that bacteria use to regulate virulence gene expression during infection?

  • Cell density of the bacterial population
  • Temperature change experienced upon host entry
  • Changes in atmospheric pressure (correct)
  • Availability of specific nutrients like iron

What is the primary difference between an operon and a regulon in bacterial gene regulation?

  • Regulons are found in eukaryotes, while operons are exclusive to prokaryotes.
  • Genes in an operon are transcribed from multiple promoters, whereas genes in a regulon are from a single promoter.
  • Genes within an operon are located adjacent to each other and transcribed as a single mRNA, while genes in a regulon are dispersed but controlled by the same regulatory protein. (correct)
  • Operons control catabolic genes, while regulons control anabolic genes.

A bacterial gene is under negative transcriptional control. What would be the effect of a mutation that prevents the repressor protein from binding to the operator?

  • Transcription of the gene will be enhanced by an activator.
  • The gene will no longer be transcribed.
  • The gene will be constitutively transcribed. (correct)
  • The gene will only be transcribed in the presence of an inducer.

Where does a transcriptional activator protein typically bind relative to the promoter of a gene it regulates?

<p>Upstream of the promoter region. (C)</p> Signup and view all the answers

Sigma factors are crucial for bacterial transcription. What is their primary role in gene expression?

<p>To guide RNA polymerase to specific promoters. (C)</p> Signup and view all the answers

Which sigma factor is primarily responsible for transcribing 'housekeeping genes' necessary for general cell growth in E. coli?

<p>σ⁷⁰ (RpoD) (B)</p> Signup and view all the answers

What is the role of sigma factor σ³² (RpoH) in E. coli?

<p>Response to heat shock. (D)</p> Signup and view all the answers

In the context of catabolite repression, why is glucose considered the preferred carbon source for many bacteria?

<p>It is the easiest sugar to digest and catabolize, requiring minimal processing. (B)</p> Signup and view all the answers

How does the presence of glucose affect the levels of cyclic AMP (cAMP) in bacterial cells, and what is the consequence of this change in relation to catabolite repression?

<p>Glucose decreases cAMP levels, reducing the activation of genes for alternative sugar metabolism. (A)</p> Signup and view all the answers

What is the role of the Catabolite Activator Protein (CAP) in catabolite repression?

<p>It activates the expression of genes for alternative sugar metabolism when glucose is scarce and cAMP levels are high. (B)</p> Signup and view all the answers

In the lac operon, under what conditions would you expect to observe the highest level of transcription?

<p>Low glucose, high lactose. (C)</p> Signup and view all the answers

What is the function of the operator site in the lac operon?

<p>It is the binding site for the repressor protein. (C)</p> Signup and view all the answers

CcpE in Staphylococcus aureus regulates virulence factor expression in response to:

<p>Intermediates of the TCA cycle. (A)</p> Signup and view all the answers

According to the information provided, how does CcpE influence the production of staphyloxanthin, a virulence factor in S. aureus?

<p>CcpE activates staphyloxanthin production. (C)</p> Signup and view all the answers

What is the role of DtxR in regulating diphtheria toxin expression in Corynebacterium diphtheriae?

<p>It represses toxin expression in the presence of iron. (B)</p> Signup and view all the answers

Under what environmental condition is diphtheria toxin produced, based on the DtxR regulation mechanism?

<p>Low iron environments. (A)</p> Signup and view all the answers

What would be the consequence of a mutation in DtxR that prevents it from binding iron?

<p>Diphtheria toxin would be constitutively produced, regardless of iron levels. (D)</p> Signup and view all the answers

Which of the following is an example of a regulatory mechanism that allows bacteria to prioritize the use of a readily available carbon source over others?

<p>Catabolite repression. (A)</p> Signup and view all the answers

In the diagram of transcriptional activators and repressors, what is indicated by 'P' and 'O' in the context of the lac operon?

<p>Promoter and operator respectively. (A)</p> Signup and view all the answers

Considering the bacterial response to lysozyme stress via SigV, what is the ultimate outcome of SigV activation?

<p>Activation of genes involved in peptidoglycan modification and lysozyme resistance. (D)</p> Signup and view all the answers

Flashcards

Environmental cues

Environmental cues that bacteria respond to during infection.

Operon

A group of genes transcribed together from a single promoter.

Regulon

Genes at different locations controlled by the same regulatory protein.

Transcriptional Activators

Proteins that bind upstream of target promoters to increase transcription.

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Transcriptional Repressors

Proteins that bind operator sequences to block transcription.

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Catabolite Repression

Regulation where glucose inhibits the expression of other sugar-metabolizing genes.

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Sigma Factors

Proteins that control global gene expression by recognizing specific promoter sequences.

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DtxR

Iron regulation of Diphtheria Toxin.

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Study Notes

Lecture 23: Virulence Regulation

  • Bacteria respond to 8 environmental cues during infection that often differ from their usual environment
  • Key objectives include understanding operons, regulons, transcriptional activators/repressors, sigma factors, and catabolite repression

Importance of Regulation

  • Most genes encode proteins, primarily enzymes with an average gene size of ~1 kb encoding a protein of 333 amino acids
  • E. coli K12 strain has a genome size of 4,639,221 base pairs containing 4,377 genes (4,290 are proteins)
  • Organisms need to respond rapidly to environmental changes to avoid wasting energy and resources
  • Microbial genomes encode more proteins than are present at any given condition

Overview: Gene Regulation

  • Gene regulation guides bacteria in different environments
  • External environment to inside a host
  • One host environment to another
  • One host to another (vector-borne diseases)

Transcriptional Regulation

  • Common environmental factors that drive expression:
  • Temperature
  • pH
  • Iron availability
  • Other divalent cations (Ca++, Mg++, Mn++)
  • Carbon and nitrogen sources (sugars, amino acids)
  • Cell density (quorum sensing)
  • Osmolarity (water availability, salt content)
  • Oxygen & CO2

Types of Transcriptional Regulation

  • Operon - single mRNA transcript for more than one gene initiated from a single promoter
  • Regulon - genes are in different locations but have promoters controlled by the same regulatory protein

Sigma Factors

  • Sigma70 has a consensus sequence of TTGACA (N16-19) TATAAT
  • Sigma54 has a consensus sequence of TTGGCAC N5 TTGCT

SigV Response to Lysozyme Stress

  • Lysozyme triggers a response mediated by SigV
  • Involves a series of steps leading to the expression of target genes

Transcriptional Control

  • Activators generally bind upstream of target promoters
  • Repressors generally bind to operator sequences that overlap promoter sequences or are positioned downstream of the promoter

Catabolite Repression

  • Glucose is the easiest sugar to digest
  • Other sugars are converted to glucose via proteins like β-galactosidase
  • When glucose is present it affects the signal inside the cell resulting in
  • Decreased cAMP
  • Decreased CAP's ability to activate
  • With high glucose there is low cAMP
  • Without glucose being present, CAP is not activated

Sensing of TCA Cycle Intermediates

  • CcpE controls expression of 126 genes, equivalent to ≈4.7% of the S. aureus genome
  • 55 genes are positively regulated while 71 are negatively regulated
  • Impacts Staphyloxanthin, Staphyloferrin, Capsule, Superantigens, and Alpha toxin

Iron Regulation of DT Expression

  • Diphtheria Toxin is produced in low-iron environments.
  • DtxR (Fur-like) represses transcription when iron is present
  • Fe(II)-DtxR binds as a dimer to indirect repeats and prevents RNA polymerase from initiating transcription
  • The apo form of DtxR is unable to bind to the operator in the absence of iron, which allows the tox gene to be transcribed

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