BIOL 2051 Exam 2: Bacterial Growth, Cell Envelope Architecture, Microbial Physiology, and Control

Comprehensive practice flashcards matching BIOL 2051 Lecture 2 Handout 2, covering bacterial growth phases, cell wall structure, diagnostic staining, motility, transport, sporulation, and physiology.

Lag Phase

A bacterial growth phase where cells adapt to a new environment without dividing, remaining metabolically active while prioritizing cellular repair and adjusting to fresh media.

Autoinducer Concentration in Lag Phase

A low extracellular concentration of signaling molecules due to minimal cell density immediately following inoculation into fresh media.

Cellular Repair in Lag Phase

The metabolic adjustment priority where bacteria recover macromolecular integrity and replenish enzyme reserves from previous starvation or stationary conditions.

Basal Gene Expression in Lag Phase

Baseline transcription that occurs without active group coordination or substantial intercellular signaling network triggering.

Incubation Period

The clinical disease stage corresponding to the bacterial lag phase, during which bacteria adjust to the host and clinical symptoms are usually absent.

Antibiotic Efficacy During Lag Phase

A poor therapeutic window for antibiotic administration because non-dividing bacteria can adapt to the drugs rather than being killed.

Log (Exponential) Phase

The bacterial growth phase characterized by rapid cell division via binary fission, leading to an exponential increase in viable population density.

Binary Fission

The primary asexual reproductive process in bacteria where an individual cell elongates, replicates its chromosome, and divides into two identical daughter cells.

Autoinducer Accumulation in Log Phase

The exponential elevation of quorum sensing signaling molecules in the extracellular environment driven by rapid cell division.

Threshold Concentration Approach

The expanding cultural point during late log growth where autoinducer molecules reach sufficient concentration to initiate signal receptor binding.

Mid-to-Late Log Responsive Genes

Bacterial genes activated toward the end of exponential growth that initiate primary metabolic slowing and early virulence factor production.

Acute Disease Stage

The infection stage corresponding to the log phase where bacterial numbers surge, symptoms appear and peak, and toxins are actively released.

Antibiotic Efficacy During Log Phase

The optimal stage to administer antibiotics because cells are actively synthesizing cell walls and dividing, preventing them from reaching the stationary phase.

Stationary Phase

The growth phase where nutrient depletion and toxic waste accumulation cause growth to plateau, such that the rate of cell division equals the rate of cell death.

Critical Autoinducer Threshold

The peak signaling concentration achieved during the stationary phase that fully triggers the quorum sensing network across a high-density population.

Group Behaviors in Stationary Phase

Coordinated population processes activated via quorum sensing, including biofilm maturation, toxin secretion, sporulation, and stress resistance mechanisms.

Carrying Capacity Adaptation

Metabolic shifts that allow a dense bacterial population to survive severe nutrient depletion and accumulated environmental toxicity.

Chronic Infection / Persister State

The clinical condition correlating with the stationary phase where nutrient scarcity and waste accumulation prompt immune slowing or protective biofilm formation.

Primary Metabolites

Essential biochemical compounds synthesized during rapid exponential growth that are directly required for basic cell division and biomass accumulation.

Secondary Metabolites

Bioactive chemical compounds, including antibiotics, produced primarily during late exponential or stationary phase that aid competition rather than basic growth.

Nutrient Depletion Trigger

The exhaustion of vital culture resources such as carbon, nitrogen, or phosphate that arrests rapid cell division and induces secondary metabolite synthesis.

Metabolic Shift in Stationary Phase

The physiological transition where cells cease manufacturing growth-promoting primary metabolites and begin producing secondary metabolites.

Survival Advantage of Antibiotics

The ecological benefit where secreted antimicrobial metabolites suppress or kill neighboring microbial competitors for remaining food and space.

Penicillin Production Conditions

Secondary metabolite synthesis by Penicillium chrysogenum that occurs predominantly when carbon sources drop and culture growth enters the stationary phase.

Penicillium chrysogenum

The fungal organism utilized to produce penicillin during its stationary phase in response to carbon depletion.

Actinorhodin

A pigmented red antibiotic synthesized by Streptomyces coelicolor specifically during its stationary growth phase.

Streptomyces coelicolor

The actinomycete species responsible for synthesizing the red-colored stationary-phase antibiotic actinorhodin.

Death Phase

The culture growth phase where dying cells outnumber viable cells, leading to an overall logarithmic drop in viable population density.

Endotoxin Release in Death Phase

The clinical complication during infection resolution where dying, lysing Gram-negative bacteria liberate lipid A, temporarily worsening inflammatory pathology.

Long-Term Stationary Phase

The prolonged phase following the death phase where a small subpopulation persists through genetic diversification and nutrient scavenging.

GASP (Growth-Associated Stationary Phase) Cells

Mutant bacterial cells that acquire adaptive genetic changes enabling them to survive severe nutrient limitation and accumulate despite overall population decline.

GASP Genetic Mutations

Heritable alterations that confer elevated fitness and metabolic survival advantages under continuous prolonged nutrient starvation.

Optimal Phase for Antibiotic Production

The late exponential to stationary growth phase when depletion of nutrients triggers the expression of secondary metabolic pathways.

Optimal Phase for Gram Staining

The log (exponential) growth phase, which yields the most consistent, reliable, and interpretable diagnostic staining results.

Peptidoglycan Synthesis in Log Phase

Active cell wall construction that produces uniform, structurally intact peptidoglycan layers capable of consistently retaining crystal violet.

Gram-Variability

Erratic staining outcomes where older Gram-positive cultures incorrectly appear Gram-negative due to cell wall degradation and autolysis.

Autolysis in Stationary Phase

Spontaneous enzymatic self-digestion of the peptidoglycan wall in aging cells that creates structural defects, leading to false Gram-negative results.

Standard Gram Stain Culture Age

An incubation window of $18\text{ to }24\text{ hours}$, corresponding to mid-to-peak log phase, recommended by standard diagnostic microbiology protocols.

Lag Phase Gram Stain Inadequacy

Erratic staining caused by non-uniform cell wall remodeling, cellular repair, and macromolecular adjustment rather than active balanced division.

Endospore Formation Timing

A developmental transition initiated during late log phase and completed in early stationary phase in response to starvation.

Endospore-Forming Genera

Bacterial groups, prominently Bacillus and Clostridium, capable of producing metabolically dormant, environmentally resistant endospores.

Endospore Induction Triggers

Environmental stressors, primarily nutrient starvation (carbon/nitrogen depletion), low moisture, and high cell density signaling.

Asymmetric Division in Sporulation

An unequal cellular division event that splits the vegetative bacterium into a smaller pre-spore and a larger mother cell.

Pre-Spore

The smaller genetic compartment formed during asymmetric septation that develops into the mature, core-containing dormant endospore.

Mother Cell

The larger cellular compartment that surrounds, nourishes, and wraps the developing pre-spore with cortex and proteinaceous coats before lysing.

Endospore Coat Formation

The assembly of durable proteinaceous outer layers and a peptidoglycan-rich cortex around the inner core to confer physical and chemical resistance.

Mother Cell Lysis

The final enzymatic rupture of the vegetative mother cell that releases the fully matured, free endospore into the air or soil.

Optimal Phase for Capsule Formation

The late log (exponential) to early stationary phase when cells have acquired sufficient biomass and fully assemble external protective layers.

Capsular Biosynthesis Nutrient Condition

Growth media containing an excess of specific carbohydrates/carbon sources to fuel extensive exopolysaccharide or polypeptide capsule synthesis.

Klebsiella pneumoniae Capsule Staining Timing

Harvesting during late log to early stationary phase in media supplemented with excess carbohydrates to maximize polysaccharide capsule thickness.

Streptococcus pneumoniae Capsule Timing

Late log phase in carbohydrate-rich growth environments to trigger maximum expression of its protective capsular coat.

Cryptococcus neoformans

A unicellular eukaryotic yeast capable of synthesizing an abundant external protective polysaccharide capsule.

VBNC (Viable But Non-Culturable) State

A dormant survival condition where bacteria maintain intact membrane potential and metabolic activity but fail to form colonies on standard media.

VBNC Environmental Stressors

Harsh environmental pressures including starvation, extreme temperature shifts, altered pH or salinity, oxygen changes, heavy metals, and pasteurization.

Clinical Risk of VBNC Pathogens

The ability of non-culturable pathogens to evade diagnostic detection, survive environmental clearance, and reactivate virulence upon host passage.

Generation Time (Doubling Time)

The precise duration of time required for an entire microbial population to double in cell number via one complete round of binary fission.

Generation Time Measurement Phase

The exponential (log) growth phase, during which population doubling proceeds at a constant and maximal rate.

Vibrio natriegens Growth Speed

A rapid marine bacterium possessing an extremely short doubling time of approximately $10\,\text{min}$, supported by a high surface area-to-volume ratio.

Thiomargarita magnifica Growth Speed

A giant bacterium that exhibits an extremely slow doubling time of approximately two weeks due to a very low surface area-to-volume ratio.

Surface Area-to-Volume Ratio (SA:V)

A geometric ratio that dictates the physical efficiency of nutrient uptake and metabolic waste exchange across the bacterial plasma membrane.

Small Cell SA:V Dynamic

Smaller cell size generates a higher surface area-to-volume ratio, facilitating rapid diffusion-driven nutrient intake and metabolic clearance.

Large Cell SA:V Limitation

As cell dimensions increase, volume expands faster than surface area, lowering SA:V and imposing severe diffusion constraints on metabolic transport.

Transport Bottleneck from Low SA:V

Inadequate membrane exchange capacity relative to cytoplasmic volume, slowing metabolic intake and delaying cell proliferation.

Mycoplasma Generation Time Paradox

Despite being among the smallest self-replicating bacteria, Mycoplasma exhibits slow generation times of several hours due to severe biochemical bottlenecks.

Mycoplasma Reductive Genomic Evolution

Extensive evolutionary genome reduction resulting in truncated metabolic pathways and slow enzymatic turnover that negate SA:V diffusion advantages.

Mycoplasma Cell Wall Absence

The complete lack of a peptidoglycan cell wall, allowing cellular energy conservation and the adoption of flexible, pleomorphic morphologies.

Mycoplasma Host Niche Interaction

The ability of flexible, pleomorphic Mycoplasma cells to adhere tightly and conform directly to host cell plasma membranes.

Mycoplasma Intrinsic Antibiotic Resistance

Complete clinical insensitivity to cell-wall-targeting antimicrobials, including penicillin, due to the total absence of peptidoglycan targets.

Cell Packing

The spatial organization wherein bacteria coordinate rod, sphere, and spiral morphologies to eliminate vacant space and maximize community density.

Surface Sticking

The adhesion of bacteria to solid substrata like interlocking puzzle pieces, forming thick protective microbial biofilms.

Size Matching

The mixture of smaller and larger bacterial cells in a community to plug microscopic voids and maintain continuous structural contact.

Bacterial Growth Shifts

Cellular shape alterations or localized bending during growth that allow bacteria to slide into open spatial niches like falling blocks.

Escherichia coli Morphology and Diffusion

Small rod-shaped architecture measuring a few micrometers that maintains a high SA:V ratio for efficient nutrient uptake and waste expulsion.

Caulobacter crescentus Stalk

A specialized tubular cellular extension developed in nutrient-poor environments to dramatically expand surface area for nutrient absorption.

Caulobacter Stalk Phosphate Scavenging

The physiological role of the stalk in elevating SA:V to capture scarce environmental resources, particularly limiting inorganic phosphate.

Filamentation

A morphological shift where bacteria intentionally elongate into continuous thread-like structures without completing cross-wall septation.

Uropathogenic E. coli (UPEC) Filamentation

An immune evasion mechanism during urinary tract infections where UPEC suppresses division to form filaments too long for phagocytes to engulf.

THP-1 Macrophages

A predatory immune phagocyte model shown to be significantly less effective at engulfing filamentous bacterial forms than short rods.

CrvA Protein

A periplasmic polymer expressed by Vibrio cholerae that localizes along the inner curvature of the cell to drive curved rod (vibrio) morphogenesis.

CrvA Cellular Localization

Assembly in the periplasmic space between the inner and outer membranes along the inner curve of the bacterium.

Asymmetric Cell Wall Assembly by CrvA

Filamentation along the inner concave arc that causes uneven peptidoglycan growth, bending the bacterium into a comma shape.

CrvA Motility Advantage

The hydrodynamic benefit of curved rod architecture that accelerates propulsion through dense, viscous host mucosal hydrogels.

Quorum Sensing Regulation of crvA

Cell-density-dependent transcriptional induction that significantly elevates crvA expression and curvature at high population densities.

CrvA-Mediated Pathogenesis

The promotion of host colonization and diarrheal disease in Vibrio cholerae by facilitating rapid penetration through intestinal mucus.

Spirochetes

A distinct phylum of helical, spiral-shaped bacteria featuring internal periplasmic flagella and corkscrew motility.

Periplasmic Flagella

Internal flagellar filaments sequestered within the periplasm between the cell cylinder and outer sheath that spin to twist the cell body.

Corkscrew Motility

A mechanical drilling locomotion that allows spirochetes to translate rapidly through high-viscosity tissue matrices and mucus barriers.

Leptospirosis

A zoonotic systemic disease caused by pathogenic spirochetes of the genus Leptospira.

Saprophytic Leptospira

Harmless, free-living non-pathogenic species of the genus Leptospira found in aquatic environments.

Lyme Disease Etiology

Tick-borne spirochete infections caused by Borrelia burgdorferi in the United States, and Borrelia afzelii and Borrelia garinii in Europe.

Relapsing Fever Etiology

Recurrent febrile illness caused by Borrelia species, including Borrelia recurrentis and Borrelia hermsii.

Syphilis Etiology

A human sexually transmitted disease caused by infection with the helical spirochete Treponema pallidum.

Oral Treponema Commensals

Non-pathogenic helical species of the genus Treponema that reside as harmless members of the normal human oral microbiota.

Treponema pallidum Tissue Invasiveness

Corkscrew movement and periplasmic propulsion that allow the pathogen to traverse blood vessels, deep tissue stroma, and mucosal barriers.

Helicobacter pylori Morphology

A helical, corkscrew-shaped rod equipped with multiple polar flagella adapted for moving through gastric environments.

Drill-Like Swim Motion

The torque-generating flagellar swimming movement utilized by Helicobacter pylori to burrow through thick stomach mucus.

Helicobacter pylori Urease

An enzyme secreted by H. pylori that hydrolyzes urea into carbon dioxide and ammonia, neutralizing gastric acidity.

Mucin De-Gelling

The liquefaction of the stomach's protective gel-like mucin layer caused by the local pH rise produced by H. pylori urease.

Helicobacter pylori Disease Associations

Chronic bacterial infection that serves as the primary etiologic cause of gastritis, peptic ulcer disease, and gastric adenocarcinoma.

Robin Warren and Barry Marshall

Nobel laureates in Physiology or Medicine (2005) who discovered that stomach inflammation and peptic ulcers are caused by Helicobacter pylori.