Bacteria – Structure, Physiology & Importance

Vocabulary flashcards covering bacterial structure, physiology, reproduction, ecology, and applied importance based on the lecture notes.

Bacteria

Oldest, smallest, most abundant unicellular prokaryotic organisms on Earth.

Prokaryotic

Cell type lacking a true nucleus and membrane-bound organelles.

Ubiquitous

Present everywhere; describes bacteria’s ability to inhabit diverse environments.

Deinococcus radiodurans

Radiation-resistant bacterium surviving up to 3 million rads.

Picrophilus oshimae

Extremely acid-tolerant archaeon that grows at pH 0.03.

Cell wall

Rigid bacterial layer made primarily of peptidoglycan that provides shape and prevents osmotic lysis.

Peptidoglycan

Polymer of NAG-NAM sugars cross-linked by short peptides in bacterial cell walls.

Gram-positive bacteria

Bacteria with thick peptidoglycan layer, teichoic acids, and no outer membrane.

Gram-negative bacteria

Bacteria with thin peptidoglycan, periplasm, and outer membrane containing lipopolysaccharide.

N-acetylglucosamine (NAG)

One of the two alternating sugars forming peptidoglycan chains.

N-acetylmuramic acid (NAM)

Peptidoglycan sugar that carries peptide side chains for cross-linking.

Teichoic acid (TA)

Polymer embedded in gram-positive walls; stabilizes and anchors the peptidoglycan.

Lipoteichoic acid (LTA)

Teichoic acid variant anchored in the plasma membrane of gram-positive cells.

Lipopolysaccharide (LPS)

Endotoxin molecule of gram-negative outer membrane composed of lipid A, core, O-polysaccharide.

Brown’s lipoprotein (BLP)

Protein that links gram-negative peptidoglycan to the outer membrane.

Periplasm

Space between inner membrane and outer membrane in gram-negative bacteria.

Plasma (cytoplasmic) membrane

Phospholipid bilayer where bacterial metabolic processes occur in absence of mitochondria.

Cytoplasm

Gel-like interior of bacterial cell containing DNA, ribosomes, and enzymes.

Chromosome (nucleoid)

Single circular double-stranded DNA molecule housing essential bacterial genes.

Plasmid

Small circular extra-chromosomal DNA carrying non-essential but advantageous genes.

Ribosome 70S

Prokaryotic protein-synthesizing complex composed of 50S and 30S subunits.

50S subunit

Large ribosomal subunit containing 23S & 5S rRNA plus ~34 proteins.

30S subunit

Small ribosomal subunit containing 16S rRNA and ~21 proteins.

Capsule

Gelatinous polysaccharide layer outside cell wall that aids adhesion and evades host defenses.

Slime layer (mucous layer)

Loosely attached polysaccharide coating easily removed from cell surface.

Sheath

Structured, often multilayered external covering encrusted with metal oxides.

Attachment heel

Amorphous polar material used for surface contact by some bacteria.

Flagellum

Long whip-like appendage enabling bacterial motility through rotation.

Pilus (plural pili)

Short protein appendage used for attachment or DNA transfer (conjugation).

Fimbriae

Numerous hairlike pili specialized for adhesion to surfaces.

Taxis

Directed movement toward or away from a stimulus.

Chemotaxis

Bacterial movement in response to chemical gradients.

Bacillus (bacilli)

Rod-shaped bacterial morphology.

Coccus (cocci)

Spherical bacterial morphology.

Spirillum / Spirilla

Rigid spiral-shaped bacteria.

Diplococcus

Pair of cocci resulting from division in one plane.

Streptococcus

Chain of cocci produced by successive divisions.

Staphylococcus

Grape-like cluster of cocci divisions in multiple planes.

Lag phase

Initial growth phase with metabolic activity but no increase in cell number.

Log (exponential) phase

Period of rapid, exponential bacterial cell division.

Stationary phase

Growth phase where cell division equals cell death due to nutrient depletion.

Decline (death) phase

Stage where viable cell numbers decrease logarithmically.

Endospore

Dormant, highly resistant bacterial structure formed under harsh conditions.

Binary fission

Asexual bacterial reproduction by splitting into two equal daughter cells.

Generation time

Time required for a bacterial population to double.

Transformation

Uptake of free DNA from the environment by a bacterium.

Conjugation

Direct DNA transfer between bacteria via pilus-mediated cell contact.

Transduction

DNA transfer between bacteria mediated by bacteriophages.

Saprophyte

Heterotrophic bacterium feeding on dead or decaying matter.

Parasite

Organism that obtains nutrients from a living host, potentially causing harm.

Symbiont

Bacterium living in mutualistic association with another organism.

Photosynthetic bacteria

Autotrophs that capture sunlight to produce energy (e.g., cyanobacteria).

Chemosynthetic bacteria

Autotrophs obtaining energy by oxidizing inorganic compounds.

Rhizobium

Nitrogen-fixing bacteria that form root nodules on legumes.

Nitrogen fixation

Conversion of atmospheric N₂ into ammonia or related compounds usable by plants.

Obligate anaerobe

Bacterium that cannot survive in the presence of oxygen.

Obligate aerobe

Bacterium that requires oxygen for growth.

Facultative anaerobe

Bacterium capable of growing with or without oxygen.

Microaerophile

Bacterium that grows best in low oxygen concentrations.

Psychrophile

Cold-loving bacterium with optimum growth at 15–20 °C.

Mesophile

Bacterium with optimum growth at 25–40 °C; includes most pathogens.

Thermophile

Heat-loving bacterium growing best at 50–60 °C.

Acidophile

Bacterium thriving at pH 0.1–5.4.

Neutrophile

Bacterium preferring pH 5.4–8.0.

Alkaliphile

Bacterium growing best at pH 7.0–11.5.

Endotoxin

Lipopolysaccharide toxin released from gram-negative outer membrane (e.g., E. coli).

Exotoxin

Protein toxin secreted mainly by gram-positive bacteria (e.g., tetanus toxin).

Antibiotic

Drug that inhibits bacterial growth or kills bacteria by targeting vital processes.

Penicillin

β-lactam antibiotic that blocks bacterial cell wall synthesis.

Tetracycline

Broad-spectrum antibiotic that inhibits protein synthesis by binding 30S ribosomal subunit.

Sulfa drugs

Synthetic antimicrobials that inhibit folic acid synthesis in bacteria.

Cephalosporin

β-lactam antibiotic group similar to penicillin with broader spectrum.

Botulism

Fatal illness caused by Clostridium botulinum toxin in improperly sterilized foods.

Bacteriophage

Virus that infects and replicates within bacteria, used in transduction.

Autoclave

Device that sterilizes materials under high pressure and temperature to kill endospores.

Saprophytic decomposition

Process by which bacteria break down dead organic matter, recycling nutrients.

Bioremediation

Use of bacteria to clean up environmental pollutants such as oil spills.

Lactic acid bacteria

Group used to ferment foods like yogurt and cheese producing lactic acid.

Peritrichous flagellation

Flagella distributed over the entire bacterial cell surface.