Bacterial Cell Biology, Division, Differentiation, and Culturing

Comprehensive vocabulary flashcards covering bacterial cell envelopes, motility mechanisms, internal inclusions, genetic replication, cell division complexes, differentiation states, and lab culturing principles.

Periplasm

The region found only in gram-negative bacteria between the plasma membrane and outer membrane that contains the cell wall, hydrolytic enzymes, transport proteins, and synthesizing proteins for peptidoglycan and outer membrane assembly.

Pseudoperiplasm

A cellular space found in archaea that is functionally and structurally analogous to the bacterial periplasm.

Gram Stain

A differential staining procedure developed by Christian Gram that distinguishes bacteria based on cell wall thickness and the presence of an outer membrane using crystal violet, iodine, alcohol, and safranin.

S Layer

A paracrystalline monolayer of identical proteins anchored to the core cell envelope in bacteria and archaea that provides structural support, serves as a selective barrier, shields against host immune responses, and assists surface adhesion.

Capsule

A well-organized, firmly attached polysaccharide outer layer with defined boundaries that excludes India ink particles and protects pathogenic bacteria by masking surface features from host immune cells.

Slime Layer

A diffuse, disorganized, and loosely attached polysaccharide coating that does not exclude India ink particles; it forms the primary matrix in biofilms and aids bacterial gliding motility.

Fimbriae

Short, thin filamentous protein appendages produced by bacteria that primarily facilitate attachment to surfaces and host tissues, contributing directly to virulence.

Type IV Pili

Specialized surface protein filaments that adhere to host tissues, mediate natural genetic transformation, and generate twitching motility through cycles of extension and retraction.

Conjugative Pili (Sex Pili)

Filamentous protein projections present exclusively in gram-negative bacteria that physically bridge donor and recipient cells to facilitate direct horizontal gene transfer.

Flagella

Long, thin helical appendages composed of a hollow flagellin filament, a connecting hook, and a basal body motor embedded in the cell envelope, driven by proton motive force to rotate like propellers.

Archaella

Motility structures found in archaea that are simpler and thinner than bacterial flagella, assembled from the base using non-hollow archaellin subunits, and powered by ATP hydrolysis via a motor-associated ATPase.

Peritrichous Flagellar Arrangement

A structural pattern where multiple flagella are distributed across the entire cell surface; counter-clockwise (CCW) rotation bundles them for straight swimming, while clockwise (CW) rotation disperses the bundle, causing the cell to tumble.

Twitching Motility

A form of surface movement powered by ATP hydrolysis, where Type IV pili extend outward, attach to a substrate, and rapidly retract to pull the cell forward.

Gliding Motility

A flagella- and pili-independent bacterial surface movement where proton motive force drives an internal looped helical protein track, rotating gliding motors that transmit force to surface adhesion proteins.

Taxis

The directed movement of a microorganism toward an attractant or away from a repellent stimulus, mediated through swimming, twitching, or gliding.

Poly-$\beta$-hydroxyalkanoate

A water-repelling carbon- and energy-storage inclusion surrounded by a protein or lipid shell, synthesized intracellularly when carbon is in excess.

Phosphate Granules

Naked cytoplasmic inclusions formed by the accumulation of inorganic phosphate during nutrient surplus, reserved for the synthesis of nucleic acids and phospholipids.

Magnetosomes

Intracellular biomineralized inclusions of magnetic iron oxide enclosed within invaginated plasma membrane vesicles, allowing aquatic sediment bacteria to align with Earth's magnetic field to locate optimal oxygen concentrations.

Electron Cryotomography (Cryo-ET)

A specialized transmission electron microscopy (TEM) method utilizing rapid freezing and vitrification without chemical fixatives or heavy metal stains, taking tilted images from multiple angles to reconstruct 3D models of hydrated cellular structures.

Nucleoid

An irregularly-shaped, non-membrane-bound cytoplasmic region in prokaryotes that contains double-stranded chromosomal DNA compacted by supercoiling, condensins, and nucleoid-associated proteins or histones.

Plasmids

Small, circular, autonomously replicating extrachromosomal DNA molecules that carry accessory genes conferring selective advantages such as antibiotic resistance, distinct metabolic abilities, or toxin synthesis.

Binary Fission

The standard mode of prokaryotic cell division wherein cell elongation, DNA replication, macromolecular expansion, and new cell wall synthesis culminate in the symmetrical production of two daughter cells over one doubling time.

B Period

The initial stage of the bacterial cell cycle extending from the moment of cell birth until the initiation of chromosome replication.

C Period

The bacterial cell cycle phase that spans from the initiation of DNA replication at $oriC$ through its complete duplication.

D Period

The terminal bacterial cell cycle phase beginning at the completion of chromosome replication and concluding with final cell division.

DnaA

The bacterial replication initiator protein that recognizes and binds to the AT-rich sequence at $oriC$, unwinding the DNA helix and recruiting the replisome machinery.

SeqA

A regulatory protein that binds the $oriC$ region immediately following replication initiation to prevent premature re-initiation of chromosome copying.

ParABS System

A chromosome partitioning complex in Caulobacter vibrioides consisting of the DNA-binding site parS, the adapter protein parB, and an ATP-dependent parA gradient that pulls the newly replicated chromosome toward the opposite cell pole.

Polysome Exclusion Model

A chromosome segregation mechanism described in E. coli where high concentrations of mid-cell mRNA-ribosome translation complexes (polysomes) accumulate and exert physical pressure to separate chromosomes toward opposite poles.

FtsZ

A conserved tubulin-like bacterial protein that polymerizes into short filaments beneath the plasma membrane, forming the contractile Z-ring that dictates the division plane and recruits cell wall synthesizing enzymes.

Min System

A site-selection protein system (MinC, MinD, MinE) that oscillates from pole to pole, actively preventing FtsZ polymerization at cell ends to restrict Z-ring assembly exclusively to the mid-cell.

Lipid II

The core peptidoglycan building block composed of alternating NAG and NAM disaccharides and a pentapeptide stem attached to a membrane-anchored lipid carrier.

Flippase

A dedicated transmembrane transport protein that translocates Lipid II across the bacterial inner plasma membrane into the periplasmic space for cell wall assembly.

Autolysins

Bacterial enzymes that selectively hydrolyze glycosidic bonds within pre-existing peptidoglycan, opening controlled gaps for insertion of newly synthesized cell wall subunits.

Transpeptidases

Bacterial enzymes that catalyze covalent peptide cross-links between tetrapeptide chains of adjacent peptidoglycan strands to rigidify the cell wall.

MreB

An actin-like cytoskeletal protein that forms helical bands beneath the inner membrane of rod-shaped bacteria, guiding the elongasome complex to deposit new peptidoglycan along the lateral cell wall.

Myxospores

Specialized resting spores formed when individual rod-shaped bacteria aggregate into macroscopic fruiting bodies in response to starvation.

Arthrospores

Dispersal spores formed when filamentous bacterial hyphae, such as those in Streptomyces, undergo septation at their tips to divide interconnected filaments into discrete cells.

Endospores

Dormant, highly resistant survival structures formed internally by certain gram-positive Firmicutes (such as Bacillus anthracis and Clostridium botulinum) during severe nutrient depletion or stress.

Small Acid-Soluble Spore Proteins (SASPs)

Specialized proteins that bind to and saturate endospore DNA to protect it from ultraviolet (UV) radiation and heat, later serving as an immediate carbon and energy reserve during germination.

Dipicolinic Acid

A compound unique to the endospore core that forms a complex with calcium ($Ca^{2+}$), dehydrating the cytoplasm and stabilizing cellular enzymes in an inactive, heat-resistant state.

Exosporium

A lipid- and protein-rich hydrophobic outer layer surrounding the protein coat of certain bacterial endospores that primarily functions in surface adhesion.

Defined Media

A microbial growth medium in which every chemical component is pure, known, and provided at an exact, reproducible concentration.

Complex Media

A nutrient-rich microbial culture medium composed of crude biological digests (such as yeast extract, peptone, or beef extract) containing at least one ingredient of unknown chemical composition and concentration.

Fastidious Bacteria

Microorganisms with elaborate nutritional requirements that cannot synthesize essential organic molecules on their own and require enriched media supplemented with specific growth factors.

MacConkey Agar

A selective and differential culture medium containing bile salts and crystal violet that inhibits gram-positive bacteria while differentiating lactose fermenters (red/pink colonies) from non-fermenters (pale/colorless colonies).

Alpha Hemolysis

The partial or incomplete lysis of red blood cells on blood agar, producing a characteristic greenish halo around bacterial colonies (e.g., oral Streptococcus pneumoniae).

Beta Hemolysis

The complete destruction and clear zone of lysis of red blood cells surrounding bacterial colonies on blood agar (e.g., Staphylococcus aureus).

Gamma Hemolysis

The absence of red blood cell lysis on blood agar, resulting in no color or transparency change in the media around bacterial colonies (e.g., Staphylococcus epidermidis).