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Escherichia coli (E. coli) is a gram-negative, facultative anaerobic bacterium, typically inhabiting the lower intestine of warm-blooded organisms.
Answer: True
Explanation: This statement accurately describes the fundamental characteristics and common habitat of *Escherichia coli*.
*E. coli*'s cell wall structure, characterized by a thin peptidoglycan layer and an outer membrane, contributes to its Gram-negative staining and resistance to certain antibiotics, such as penicillin.
Answer: True
Explanation: The Gram-negative cell wall composition of *E. coli*, featuring a thin peptidoglycan layer and an outer membrane, is indeed responsible for its staining properties and provides a degree of antibiotic resistance.
Under anaerobic conditions, *E. coli* primarily utilizes mixed acid fermentation, producing byproducts such as lactate and carbon dioxide.
Answer: True
Explanation: Mixed acid fermentation is a key metabolic pathway for *E. coli* when oxygen is absent, yielding various acidic byproducts.
*E. coli* primarily relies on the Entner-Doudoroff (EDP) pathway for glucose metabolism, although the EMPP pathway is thermodynamically more favorable.
Answer: False
Explanation: *E. coli* predominantly utilizes the Embden-Meyerhof-Parnas (EMPP) and Pentose Phosphate Pathways (OPPP) for glucose metabolism, with the EDP pathway being more active during growth on gluconate.
Catabolite repression in *E. coli* causes the bacterium to repress genes for less preferred sugars when preferred sugars are available.
Answer: True
Explanation: Catabolite repression ensures that *E. coli* prioritizes the metabolism of more energetically favorable sugars, repressing the genes for less preferred ones when they are present.
*E. coli* optimally grows at temperatures around 10°C (50°F).
Answer: False
Explanation: The optimal growth temperature for *E. coli* in laboratory settings is approximately 37°C (99°F).
The doubling rate of *E. coli* is influenced by nutrient availability and can be as fast as every 20 minutes under favorable conditions.
Answer: True
Explanation: Under optimal nutrient conditions, *E. coli*'s rapid cell cycle allows for a doubling time as short as 20 minutes.
Synchronous replication in *E. coli* involves the simultaneous initiation of replication from all origins, leading to a 2n pattern of replication forks.
Answer: True
Explanation: Synchronous replication in *E. coli* is characterized by the coordinated initiation of DNA replication from multiple origins, resulting in a 2n (or higher) number of replication forks.
Cellular aging in *E. coli* is characterized by the accumulation of damage in the "old pole" cell, which can lead to division arrest under stress.
Answer: True
Explanation: The "old pole" of an *E. coli* cell can accumulate damage over successive divisions, potentially leading to division arrest and demonstrating a form of cellular aging.
Histidine phosphorylation is a rare post-translational modification in *E. coli* proteins compared to serine phosphorylation.
Answer: False
Explanation: Histidine phosphorylation is a notable post-translational modification observed in *E. coli* proteins, alongside serine, threonine, and tyrosine phosphorylation.
*E. coli* usually colonizes a newborn's gastrointestinal tract within 40 hours of birth, functioning as a benign commensal.
Answer: True
Explanation: Early colonization of the infant gut by *E. coli* is typical, and most strains function as commensals, contributing to the normal microbiota.
What is the primary role of most *E. coli* strains in the human gut?
Answer: Producing vitamin K2 and preventing colonization by harmful bacteria.
Explanation: Most *E. coli* strains are commensal and contribute to host health by synthesizing vitamin K2 and inhibiting the growth of pathogenic bacteria.
Which of the following is a key characteristic of *E. coli*'s cell wall that contributes to its Gram-negative staining?
Answer: A thin peptidoglycan layer and the presence of an outer membrane.
Explanation: The Gram-negative staining of *E. coli* is a direct result of its cell wall structure, which includes a thin peptidoglycan layer and an outer membrane.
Under anaerobic conditions, *E. coli* primarily utilizes which metabolic process?
Answer: Mixed acid fermentation
Explanation: In the absence of oxygen, *E. coli* relies on mixed acid fermentation to generate energy.
What is catabolite repression in *E. coli*?
Answer: A process where *E. coli* represses genes for less preferred sugars when preferred sugars are available.
Explanation: Catabolite repression is a regulatory mechanism that prioritizes the metabolism of preferred carbon sources, suppressing the expression of genes for less preferred ones.
What is the optimal growth temperature for *E. coli* in a laboratory setting?
Answer: 37°C (99°F)
Explanation: The optimal temperature for the growth of *E. coli* in laboratory conditions is 37°C.
What was the initial name given to *E. coli* by its discoverer, Theodor Escherich?
Answer: Bacterium coli commune
Explanation: Theodor Escherich initially named the bacterium *Bacterium coli commune* upon its discovery in 1885.
What type of organism is *E. coli* classified as?
Answer: A bacterium
Explanation: *Escherichia coli* is classified as a bacterium.
*E. coli* is a crucial model organism in biotechnology and microbiology due to its ease of cultivation and well-characterized genetic structure, not its complexity or difficulty in cultivation.
Answer: True
Explanation: The statement is corrected to reflect that *E. coli*'s utility as a model organism stems from its simplicity and ease of laboratory manipulation, not complexity or difficulty.
*E. coli*'s metabolism can be engineered to function as an autotroph by introducing carbon fixation genes and utilizing formate.
Answer: True
Explanation: Through genetic engineering and laboratory evolution, *E. coli* can be adapted to fix carbon dioxide, thereby exhibiting autotrophic capabilities.
Studies investigating the *E. coli* interactome have shown limited overlap between different research studies, despite identifying thousands of interactions.
Answer: True
Explanation: Research into the *E. coli* protein-protein interaction network (interactome) has revealed numerous interactions, but data consistency across studies remains a challenge, leading to limited overlap.
E. coli is favored for producing recombinant proteins because it naturally exports many proteins into the periplasm, simplifying recovery.
Answer: False
Explanation: While *E. coli* can be engineered for protein export, it does not naturally export a large quantity of proteins into the periplasm. The simplification of protein recovery and reduction of cross-contamination are achieved through other means, such as cell lysis, rather than extensive natural periplasmic export. Its popularity stems more from low cost, rapid growth, and ease of genetic modification.
Why is *E. coli* considered an important model organism in scientific research?
Answer: It has been intensively investigated and is easily grown and cultured.
Explanation: *E. coli*'s extensive study history, coupled with its ease of cultivation and genetic manipulation, makes it a cornerstone model organism in microbiology and biotechnology.
Which of the following is a key advantage of using *E. coli* for producing recombinant proteins?
Answer: It has a low cost, rapid growth, and ease of genetic modification.
Explanation: *E. coli*'s cost-effectiveness, rapid proliferation, and amenability to genetic manipulation make it highly advantageous for recombinant protein production.
*E. coli*'s role in creating recombinant DNA, pioneered by Cohen and Boyer, was foundational for producing which of the following?
Answer: Human insulin
Explanation: The groundbreaking work using *E. coli* for recombinant DNA technology paved the way for the production of therapeutic proteins, notably human insulin.
Which of the following is a practical use of *E. coli* mentioned in the source?
Answer: Generating synthetic propane
Explanation: *E. coli* has been engineered for various biotechnological applications, including the synthesis of compounds like synthetic propane.
What is the significance of *E. coli*'s genetic tractability in biotechnology?
Answer: It allows for easy genetic modification, enabling applications like vaccine development.
Explanation: The genetic tractability of *E. coli* is fundamental to its widespread use in biotechnology, facilitating applications such as the development of vaccines and the production of therapeutic proteins.
The majority of *E. coli* strains are non-pathogenic; pathogenic strains cause disease primarily through fecal-oral transmission.
Answer: True
Explanation: While many *E. coli* strains are commensal, pathogenic strains exist and are transmitted via the fecal-oral route, causing various illnesses.
*E. coli* serves as an indicator organism because its presence in environmental samples can signify fecal contamination, as it survives outside the host for a limited period.
Answer: True
Explanation: *E. coli*'s ability to survive in the environment for a time makes it a reliable indicator of fecal contamination in water and food sources.
Strain-specific characteristics of *E. coli* are not useful for identifying the source of fecal contamination in environmental samples.
Answer: False
Explanation: The unique characteristics of different *E. coli* strains, such as host specificity, are indeed valuable for tracing the origin of fecal contamination in environmental contexts.
What types of diseases can virulent *E. coli* strains cause?
Answer: Gastroenteritis, UTIs, neonatal meningitis, and sepsis.
Explanation: Virulent strains of *E. coli* are associated with a spectrum of diseases, including gastroenteritis, urinary tract infections, neonatal meningitis, and sepsis.
How does Shiga toxin produced by *E. coli* O157:H7 lead to severe illness?
Answer: It causes inflammation and destroys red blood cells, potentially leading to kidney damage.
Explanation: Shiga toxin from *E. coli* O157:H7 induces inflammation and hemolysis, which can obstruct kidney filtration and result in hemolytic-uremic syndrome (HUS).
What is the primary mode of transmission for Enterotoxigenic *E. coli* (ETEC)?
Answer: Contaminated food or drinking water
Explanation: Enterotoxigenic *E. coli* (ETEC) is typically transmitted through the ingestion of contaminated food or water.
Why is Carbapenem-resistant *E. coli* (CREC) a significant concern in healthcare?
Answer: It produces an enzyme that inactivates carbapenem antibiotics, drugs of last resort.
Explanation: Carbapenem-resistant *E. coli* (CREC) poses a major threat due to its resistance to carbapenems, critical last-resort antibiotics, conferred by carbapenemase enzymes.
What is the typical incubation period for Shiga toxin-producing *E. coli* (STEC) infections?
Answer: 3-4 days (ranging from 1 to 10 days)
Explanation: The incubation period for STEC infections typically ranges from 1 to 10 days, with an average of 3 to 4 days.
Which diagnostic method is described as faster and offering higher sensitivity and specificity for *E. coli* infections compared to traditional stool cultures?
Answer: Point-of-care molecular diagnostic tests
Explanation: Point-of-care molecular diagnostic tests offer a more rapid and sensitive approach for identifying *E. coli* infections and associated resistance markers compared to conventional methods.
What is the primary treatment focus for most *E. coli* infections?
Answer: Assessing and replacing lost fluids and electrolytes.
Explanation: Management of *E. coli* infections primarily involves supportive care, focusing on rehydration and electrolyte balance, as antibiotic use is often reserved or guided by resistance patterns.
What is the current status of vaccine development for ETEC?
Answer: Several candidates are in various stages of clinical testing, but no licensed vaccines exist.
Explanation: While vaccine candidates for enterotoxigenic *E. coli* (ETEC) are undergoing clinical trials, no licensed vaccines are currently available.
Which of the following is an example of an intestinal anti-inflammatory agent, excluding corticosteroids?
Answer: Sulfasalazine
Explanation: Sulfasalazine is an aminosalicylate used as an intestinal anti-inflammatory agent, distinct from corticosteroid treatments.
*E. coli* adapts genetically primarily through vertical gene transfer and mutation.
Answer: False
Explanation: *E. coli* undergoes significant genetic adaptation through horizontal gene transfer (HGT) mechanisms, in addition to mutation and vertical gene transfer.
Only about 20% of genes in a typical *E. coli* genome are shared among all strains, indicating significant genetic diversity.
Answer: True
Explanation: The core genome shared by all *E. coli* strains is small, with approximately 80% of the genome exhibiting variation, highlighting substantial genetic diversity.
The concept of "taxa in disguise" suggests that *Shigella* species are genetically very different from *E. coli*.
Answer: False
Explanation: The concept of "taxa in disguise" indicates that *Shigella* species are phylogenetically nested within *E. coli*, suggesting they are genetically very similar, not different.
*E. coli* strains are commonly subdivided by their metabolic pathways, such as fermentation types.
Answer: False
Explanation: *E. coli* strains are primarily subdivided based on serotype, determined by surface antigens (O, H, and K antigens), rather than metabolic pathways.
The Red Queen hypothesis describes how *E. coli* evolves to maintain its fitness in response to its predators' adaptations.
Answer: True
Explanation: The Red Queen hypothesis applies to *E. coli*'s co-evolutionary arms race with its predators, where continuous adaptation is necessary for survival.
Phylogenetic classification of *E. coli* shows a strong link between phylogenetic distance and pathology, meaning closely related strains are always equally pathogenic.
Answer: False
Explanation: While phylogeny can indicate relationships, the link between phylogenetic distance and pathogenicity in *E. coli* is not always direct or uniform; closely related strains can exhibit varying levels of pathogenicity.
The first complete genome sequence of *E. coli*, published in 1997, revealed a genome of approximately 4.6 million base pairs.
Answer: True
Explanation: The initial sequencing of the *E. coli* K-12 genome in 1997 established its size at approximately 4.6 million base pairs.
The *E. coli* pangenome, representing all genes found across sequenced strains, is estimated to be around 5,000 genes.
Answer: False
Explanation: The *E. coli* pangenome is considerably larger than 5,000 genes, estimated to contain over 16,000 genes in total, with a significant portion acquired through horizontal gene transfer.
Genes in *E. coli* are typically named using three-letter acronyms, which are italicized, and the corresponding proteins are named with uppercase acronyms.
Answer: True
Explanation: The standard nomenclature for *E. coli* genes involves italicized three-letter acronyms for genes and uppercase acronyms for their corresponding proteins.
By 2006, about 38% of the predicted proteins from the *E. coli* genome sequence had been experimentally identified.
Answer: True
Explanation: Early proteomic studies confirmed a significant portion of the predicted proteins from the *E. coli* genome sequence, with around 38% identified by 2006.
How does *E. coli* facilitate genetic adaptation and the spread of traits like toxin production?
Answer: Through horizontal gene transfer mechanisms like conjugation and transduction.
Explanation: Horizontal gene transfer, including conjugation and transduction, plays a critical role in the genetic adaptation and acquisition of new traits, such as virulence factors, by *E. coli*.
What is the approximate percentage of genes in a typical *E. coli* genome that are shared among all strains?
Answer: 20%
Explanation: Only about 20% of the genes in a typical *E. coli* genome are conserved across all strains, indicating substantial genetic diversity.
The concept of "taxa in disguise" in relation to *E. coli* and *Shigella* refers to:
Answer: Shigella species being genetically similar to E. coli strains.
Explanation: The "taxa in disguise" concept highlights the close phylogenetic relationship between *Shigella* and *E. coli*, suggesting *Shigella* should be classified within *E. coli*.
How are *E. coli* strains commonly subdivided?
Answer: By serotype, based on major surface antigens.
Explanation: *E. coli* strains are primarily classified and subdivided based on their serotypes, which are determined by variations in their surface antigens (O, H, and K).
Which of the following is a key characteristic of the Red Queen hypothesis as applied to *E. coli*?
Answer: E. coli's adaptations are countered by predator evolution, creating an ongoing arms race.
Explanation: The Red Queen hypothesis describes a scenario where *E. coli* must continuously adapt to counter the evolving adaptations of its predators, leading to a perpetual evolutionary struggle.
What was revealed by the first complete genome sequence of *E. coli* in 1997?
Answer: A genome of 4.6 million base pairs containing 4,288 protein-coding genes.
Explanation: The first complete genome sequence of *E. coli* (strain K-12) in 1997 revealed a genome of approximately 4.6 million base pairs encoding 4,288 protein-coding genes.
What is the *E. coli* pangenome?
Answer: The total number of different genes found across all sequenced *E. coli* strains.
Explanation: The *E. coli* pangenome encompasses the complete set of genes present in all known strains of the species.
What is the standard system for naming genes in *E. coli*?
Answer: Three-letter acronyms, italicized for genes and uppercase for proteins.
Explanation: The established nomenclature for *E. coli* genes uses italicized three-letter acronyms for genes and uppercase acronyms for the corresponding proteins.
What is the relationship between *E. coli* and *Shigella* from a phylogenetic perspective?
Answer: Shigella species are nested within E. coli strains.
Explanation: Phylogenetic analyses indicate that *Shigella* species are closely related to and nested within *E. coli* strains.
What is the *E. coli* pangenome estimated to contain, and what is the origin of a significant portion of it?
Answer: Over 16,000 genes, with two-thirds originating from horizontal gene transfer.
Explanation: The *E. coli* pangenome is vast, estimated at over 16,000 genes, with a substantial fraction acquired through horizontal gene transfer from other species.
The neotype strain for *E. coli* is U5/41^T, but common laboratory strains like K-12 MG1655 are not used in studies.
Answer: False
Explanation: While U5/41^T is the neotype strain, common laboratory strains such as K-12 MG1655 are extensively used in research studies.
Most commonly used research strains of *E. coli*, such as Clifton's K-12 strain, belong to Phylogenetic Group A.
Answer: True
Explanation: Research strains derived from K-12 and other common laboratory strains are typically classified under Phylogenetic Group A.
Which *E. coli* strain is specifically mentioned as being used for maintaining cultures of the nematode *Caenorhabditis elegans*?
Answer: E. coli OP50
Explanation: *E. coli* strain OP50 is commonly used as a food source for maintaining cultures of the nematode *Caenorhabditis elegans*.
What is Uropathogenic *E. coli* (UPEC)?
Answer: A major cause of urinary tract infections (UTIs).
Explanation: Uropathogenic *E. coli* (UPEC) is a significant etiological agent responsible for the majority of urinary tract infections.