Domain Bacteria: Diversity, Structure, and Physiology

Comprehensive practice flashcards covering the taxonomy, cellular structure, physiology, ecological roles, and medical importance of Domain Bacteria based on lecture notes.

On what biochemical and structural criteria is Domain Bacteria differentiated from Domain Archaea?

Domain Bacteria is differentiated from Archaea based on ribosome form and structure ($16\text{S rRNA}$), lipid type and linkage, cell membrane structure, and type of RNA polymerase.

What are the major structural differences in the cell wall between Gram-positive and Gram-negative bacteria shown in the diagram?

Gram-positive bacteria possess a thick peptidoglycan layer situated above a single plasma membrane, whereas Gram-negative bacteria have an outer membrane containing lipopolysaccharide, a thin peptidoglycan layer, and an inner plasma membrane.

What is the proper sequence of reagents and steps used in the Gram staining procedure depicted in the diagram?

The correct sequence is: Fixation, crystal violet application, iodine treatment, decolorization, and counter staining with safranin.

Phylogenetically, how do Gram-positive bacteria differ from Gram-negative bacteria regarding clade structure?

Gram-positive bacteria comprise a monophyletic clade, while the remaining Gram-negative bacteria represent a paraphyletic group.

What are the updated Phylum names for Proteobacteria, Firmicutes, and Cyanobacteria established under the ICN 2021?

Under ICN 2021, Proteobacteria is Phylum Pseudomonadota, Firmicutes is Phylum Bacilliota, and Cyanobacteria is Phylum Cyanobacteriota.

What is the etymological origin and meaning of the phylum name Pseudomonadota?

The name is derived from Greek words meaning "changeable and little sticks."

According to the endosymbiotic theory, which bacterial group gave rise to the ancestral mitochondrion?

The ancestral mitochondrion arose from a microbial endosymbiont (the protomitochondrion line) within Phylum Pseudomonadota.

Which five distinct classes within Proteobacteria were defined by Stackebrandt et al. (1988) using $16\text{S rRNA}$ sequences?

Alphaproteobacteria ($\alpha$), Betaproteobacteria ($\beta$), Gammaproteobacteria ($\gamma$), Deltaproteobacteria ($\delta$), and Epsilonproteobacteria ($\epsilon$).

According to the modern taxonomic shift shown in the table, what are the modern phylum classifications for Epsilonproteobacteria and Deltaproteobacteria?

Epsilonproteobacteria was elevated to the Phylum Campylobacterota, and Deltaproteobacteria was split into three phyla: Desulfobacterota, Myxococcota, and Bdellovibrionota.

What common synonyms or functional groups are included under Class Alphaproteobacteria?

$\alpha$-proteobacteria, rickettsias, purple nonsulfur bacteria, nitrogen-fixing bacteria, and nodule-forming bacteria.

What are the cell forms and flagellar arrangements found in Class Alphaproteobacteria?

Cells are unicellular rods, cocci, spirals, or filaments; they are non-motile or motile via polar or peritrichous flagella.

How do chemolithotrophic and chemoorganotrophic Alphaproteobacteria differ in substrate utilization?

Chemolithotrophs use inorganic sources for energy and reducing power to fix carbon dioxide into food, whereas chemoorganotrophs utilize organic sources for energy and food production.

What metabolic products are released by purple nonsulfur bacteria and symbiotic rhizobia in Class Alphaproteobacteria?

Purple nonsulfur bacteria produce reduced organic compounds, while symbiotic rhizobia reduce ammonium compounds and release glutamine and other N-rich compounds to their host plant.

What disease is caused by Rickettsia japonica, and how does this organism generate ATP?

Rickettsia japonica is the causative agent of oriental spotted fever; it has limited metabolic ability and relies entirely on the host cell for ATP synthesis.

Which tick species shown in the image serves as a vector for oriental spotted fever / spotted fever group rickettsiae?

Amblyomma maculatum.

What type of symbiotic association is formed by Rhizobium sp. and which plant hosts are involved?

Rhizobium sp. forms an endosymbiotic nitrogen-fixing association with the roots of legumes, such as clover, alfalfa, and beans.

What plant disease is depicted in the photograph, and which bacterium causes it using a Ti plasmid?

Crown galls (plant tumors), caused by Agrobacterium tumefaciens injecting DNA from its Ti plasmid into the host plant.

Why is Agrobacterium tumefaciens utilized as an important tool in plant biotechnology?

It possesses a natural ability to transfer DNA (from its Ti plasmid) into the genomes of host plants.

What are the structural and physiological characteristics of Class Betaproteobacteria?

They are Gram-negative, variable in shape (rods, cocci, spirals, filaments), motile, non-motile, or mobile (moving without flagella on a substrate), and are aerobes or facultative anaerobes producing oxidized carbon, nitrogen, and sulfur compounds.

What specific human diseases are caused by Neisseria gonorrhoeae and Neisseria meningitidis?

Neisseria gonorrhoeae causes gonorrhea, and Neisseria meningitidis causes meningitis.

On what specific culture medium are pathogenic Neisseria species typically grown in the laboratory?

Chocolate agar (partially hemolyzed red blood cells).

What is the metabolic function of Nitrosomonas europaea, and in which ecological applications is it useful?

It is a chemoautotroph that oxidizes ammonia into nitrite; it is useful in treating industrial and sewage waste and in bioremediation.

What are the general synonyms and group types encompassed within Class Gammaproteobacteria?

$\gamma$-proteobacteria, purple sulfur bacteria, enterobacteria, pseudomonads, vibrios, and bioluminescent bacteria.

How do purple sulfur bacteria in Class Gammaproteobacteria carry out photosynthesis?

They are obligate anaerobes that capture light using bacteriochlorophylls $a$ and $b$, reducing carbon dioxide with electrons from hydrogen sulfide, yielding elemental sulfur and sulfate.

Why does the opportunistic human pathogen Pseudomonas aeruginosa exhibit low antibiotic susceptibility?

It possesses antibiotic resistance genes and exhibits low permeability of its bacterial cell wall.

What is the pathogenic mechanism and disease associated with Vibrio cholerae?

It causes cholera by producing a toxin that induces hypersecretion of water and electrolytes in the gastrointestinal tract.

What are the salient morphological and physiological features of the family Enterobacteriaceae?

They are Gram-negative rods, facultative anaerobes, lactic acid fermenters, non-spore formers, possessing peritrichous fimbriae for host adherence, and most are flagellated members of normal gut flora.

What distinct clinical infections are caused by Escherichia coli and Proteus vulgaris?

Escherichia coli causes urinary tract infections (UTI) and traveler's diarrhea; Proteus vulgaris causes UTIs and wound infections.

What infections are caused by Shigella dysenteriae and Salmonella typhi?

Shigella dysenteriae causes shigellosis; Salmonella typhi causes enteric fever (typhoid fever) and acute gastroenteritis.

What morphological feature of Klebsiella pneumoniae protects it from the host immune system?

A prominent capsule that provides resistance against host phagocytosis.

What is the Latin origin and meaning of the former phylum name Firmicutes (now Bacilliota)?

It comes from the Latin root firmus, meaning "durable."

What major physiological subgroups are included in Phylum Bacilliota?

Endospore-forming bacteria, lactic acid bacteria, aerobic and anaerobic cocci, coryneform bacteria, and mycoplasmas.

What are the oxygen tolerance and fermentation end products of Class Clostridia?

They are obligate anaerobes whose fermentation products include small organic acids, ethanol, $\text{CO}_2$, $\text{NH}_3$, and sometimes $\text{H}_2$.

How potent is the botulism toxin produced by Clostridium botulinum in terms of minimum lethal dose compared to potassium cyanide?

The minimum lethal dose for botulism toxin is $0.00003\,\mu\text{g/kg}$, whereas potassium cyanide has a lethal dose of $100\text{--}200\,\text{mg/kg}$.

What are documented therapeutic and clinical applications of botulinum toxin (Botox)?

Inducing muscle relaxation to treat facial lines and creases, and treating chronic conditions such as migraine headaches and spasms.

What disease does Clostridium perfringens cause, and what are its characteristic clinical symptoms?

It causes gas gangrene (clostridial myonecrosis); symptoms include severe tissue destruction, gas production in muscle/tissue, and a foul-smelling wound discharge.

How does Class Bacilli differ from Class Clostridia regarding oxygen tolerance and metabolism?

Class Bacilli consists of obligate or facultative aerobes with oxidative or fermentative metabolism, whereas Class Clostridia consists of obligate anaerobes.

What are the probiotic and commercial benefits of Lacticaseibacillus casei?

It is a probiotic found in the normal flora of the human mouth and intestine that improves digestion, reduces lactose intolerance, and is used commercially in dairy products.

What primary illness and severe downstream complications are caused by Streptococcus pyogenes?

It causes pharyngitis (or scarlet fever); if left untreated, it can lead to Rheumatic Fever, which affects the joints and heart.

What is the 30-day fatality rate of MRSA (methicillin-resistant Staphylococcus aureus) cited by Blot et al. (2002)?

MRSA has a reported fatality rate of $58\%$ over a 30-day period.

What are the structural features and natural habitats of Bacillus subtilis?

It is a Gram-positive, rod-shaped bacterium with peritrichous flagella that forms dormant endospores, abundant in topsoil, decomposing matter, water, and animal guts.

What distinctive cellular arrangement and mode of pathogenic action characterize the bacterium shown in the micrograph?

Corynebacterium diphtheriae exhibits a "Chinese letter" or cuneiform arrangement of club-shaped bacilli and produces diphtheria toxin, which enters the host cytoplasm to inhibit protein synthesis.

In the absence of flagella, how do certain cyanobacteria achieve movement and buoyancy regulation?

They achieve irregular gliding movement via the streaming of secreted sheath mucilage against a substrate, and some regulate buoyancy using gas vesicles.

What primary photosynthetic and accessory pigments are present in cyanobacteria?

Chlorophyll $a$ (green), phycobilin pigments in phycobilisomes (phycocyanin - blue, phycoerythrin - red), and xanthophylls and carotene (yellow and orange).

In what specific forms do cyanobacteria store their reserved carbohydrates and amino acids?

Carbohydrates are stored as cyanophyte starch (related to glycogen), and amino acid reserves are stored as cyanophycin granules (polymers of arginine and aspartic acid).

What broad range of temperature extremes can cyanobacterial species tolerate in natural environments?

They tolerate hot springs at temperatures up to $85^\circ\text{C}$, as well as freezing rocks in symbiosis with fungi at temperatures from $-60^\circ\text{C}$ to $-15^\circ\text{C}$.

How is the internal protoplast of a cyanobacterial cell differentiated?

It is differentiated into an outer colored portion termed the chromoplasm and an inner colorless portion termed the central body, which contains the genetic material.

What distinct functions do heterocysts and akinetes perform in filamentous cyanobacteria?

Heterocysts are enlarged, thick-walled cells specialized for nitrogen fixation; akinetes are thick-walled, dormant resting cysts containing food reserves resistant to desiccation and temperature extremes.

What morphological characteristics define the cyanobacterial genus Gloeocapsa shown in the image?

Gloeocapsa sp. forms unicellular colonies of 2 to several physiologically independent cells enclosed within concentric, stratified gelatinous sheaths, reproducing exclusively by binary fission.

What cellular morphology and reproductive mechanism are characteristic of Oscillatoria sp. shown in the micrograph?

Oscillatoria sp. forms unbranched filaments resembling stacks of coins without heterocysts or akinetes, reproducing by fragmentation into hormogonia, and thrives in anaerobic, sulfide-rich environments.