Bacterial Cell Cycle

Bacterial Cell Cycle

Process by which a bacterial cell grows, replicates its chromosome, and divides into daughter cells.

Growth Phase

Stage of the bacterial cell cycle during which the cell increases in size and synthesizes cellular components.

Chromosome Replication and Partitioning

Stage of the bacterial cell cycle during which DNA is replicated and distributed to future daughter cells.

Cytokinesis

Division of a bacterial cell into two daughter cells.

Binary Fission

Asexual reproductive process in which one bacterial cell divides into two daughter cells.

Replisome

Protein complex responsible for DNA replication.

Septation

Formation of a septum between future daughter cells during cell division.

Z-Ring

Ring of FtsZ proteins that constricts during bacterial cell division.

Divisome

Protein complex responsible for septum formation and peptidoglycan synthesis during cell division.

Budding

Reproductive process in which a daughter cell develops as an outgrowth of the parent cell.

Multiple Fission

Reproductive process in which a cell undergoes multiple rounds of DNA replication before dividing into several offspring.

Spore Formation from Multinucleoid Filaments

Reproductive process in which filamentous cells produce spores that develop into new cells.

Microbial Growth Curve in Batch Culture

Growth pattern of microorganisms in a closed system with a fixed nutrient supply.

Lag Phase

Growth phase during which cells adapt to a new environment with little or no cell division.

Exponential Phase

Growth phase characterized by maximum growth rate and regular population doubling.

Stationary Phase

Growth phase in which cell division and cell death occur at approximately equal rates.

Death Phase

Growth phase in which cell death exceeds cell division, resulting in a decline in viable cells.

Long-Term Stationary Phase

Extended survival phase in which remaining cells persist and continue evolving under nutrient limitation.

Doubling Time

Time required for a microbial population to double in size.

Growth Rate Constant

Number of generations occurring per unit time.

Water Availability

Environmental factor determined by water activity and solute concentration.

Osmophile

Microorganism adapted to environments with very high solute concentrations.

Halophile

Microorganism adapted to environments with high salt concentrations.

Osmotolerant Microbe

Microorganism capable of growing across a wide range of solute concentrations.

Xerotolerant Microbe

Microorganism capable of surviving conditions of extreme water limitation.

Neutrophile

Microorganism that grows best at approximately pH 5.5–8.0.

Acidophile

Microorganism that grows best under acidic conditions.

Alkaliphile

Microorganism that grows best under alkaline conditions.

Ion Exchange

Cytoplasmic pH maintenance mechanism involving exchange of ions across the membrane.

Stress Proteins

Proteins that protect cellular components from damage during environmental stress.

Cation Uptake

Import of positively charged ions to help maintain cellular homeostasis.

Proton Transporters

Membrane proteins that export excess hydrogen ions from the cell.

Membrane Modifications

Structural changes that reduce membrane permeability to protons.

Psychrophile

Microorganism adapted to growth at low temperatures.

Psychrotolerant Microbe

Cold-tolerant microorganism capable of growth at low temperatures but with a higher optimum temperature than psychrophiles.

Mesophile

Microorganism adapted to moderate temperatures.

Thermophile

Microorganism adapted to high temperatures.

Oxygen Toxicity

Cellular damage caused by reactive oxygen species generated during oxygen metabolism.

Reactive Oxygen Species (ROS)

Highly reactive oxygen-containing molecules that can damage DNA, proteins, and membranes.

Superoxide Dismutase (SOD)

Enzyme that converts superoxide radicals into hydrogen peroxide.

Catalase

Enzyme that converts hydrogen peroxide into water and oxygen.

Peroxidase

Enzyme that breaks down hydrogen peroxide.

Obligate Aerobe

Microorganism that requires oxygen for growth.

Microaerophile

Microorganism that requires oxygen at concentrations lower than those found in the atmosphere.

Facultative Anaerobe

Microorganism that can grow with or without oxygen but grows better when oxygen is present.

Aerotolerant Anaerobe

Microorganism that tolerates oxygen but does not use it for metabolism.

Obligate Anaerobe

Microorganism for which oxygen is toxic and prevents growth.

Oligotrophic Environment

Environment containing very low concentrations of nutrients.

Growth Arrest

Physiological state in which cells remain alive but cease cell division.

Starvation Response

Cellular adaptations that promote survival during nutrient limitation.

Resource Conservation

Starvation survival strategy in which ATP is conserved and stored materials are utilized.

Stress Regulation

Cellular control mechanisms that coordinate responses to environmental stress.

RpoS

Alternative sigma factor that regulates stress-response genes in Escherichia coli.

ppGpp

Alarmone that regulates bacterial responses to nutrient starvation.

Virulence

Ability of a microorganism to cause disease.

Viable But Non-Culturable (VBNC) State

Physiological state in which cells remain alive but cannot be cultured using standard laboratory methods.

Persister Cells

Dormant cells that survive antibiotic treatment without possessing resistance genes.

Population Insurance Strategy

Survival strategy in which a subpopulation enters growth arrest even under favorable conditions.

Biofilm

Surface-associated microbial community embedded within an extracellular matrix.

Sessile Microorganisms

Microorganisms attached to a surface rather than freely floating.

Planktonic Microorganisms

Free-floating microorganisms not attached to a surface.

Biofilm Development

Process involving surface attachment, microcolony formation, matrix production, maturation, and cell dispersal.

Physical Protection

Biofilm property that shields microbial cells from environmental stressors.

Increased Stability

Biofilm property characterized by enhanced structural integrity and persistence.

Improved Survival

Biofilm property that increases tolerance to adverse environmental conditions.

Extracellular Polymeric Substances (EPS)

Extracellular matrix that surrounds and supports cells within a biofilm.

Polysaccharides

Carbohydrate polymers that form a major structural component of EPS.

Proteins

Biomolecules within EPS that contribute to biofilm structure and function.

Glycoproteins

Proteins covalently linked to carbohydrate chains that contribute to EPS structure and function.

Glycolipids

Lipids containing carbohydrate groups that are components of EPS.

Extracellular DNA

DNA located outside cells that contributes to biofilm structure and stability.

UV Resistance

Increased tolerance of biofilm-associated microorganisms to ultraviolet radiation.

Antibiotic Tolerance

Reduced susceptibility of microorganisms to antimicrobial agents.

Pathogenesis

Process by which microorganisms cause disease.

Bioluminescence

Production and emission of light by living organisms through biochemical reactions.

Quorum Sensing

Cell-to-cell communication system that coordinates gene expression according to population density.

Pathogenicity

Capacity of a microorganism to produce disease in a host.

Morphological Differentiation

Process in which cells develop distinct structural forms or specialized cell types.

Antibiotic Production

Biosynthesis of antimicrobial compounds by microorganisms.

Conjugation

Horizontal gene transfer process involving direct cell-to-cell DNA transfer.

Autoinducers (AI)

Small signaling molecules used in quorum sensing.

Low Cell Density

Condition in which autoinducer concentration remains below the threshold required for gene activation.

High Cell Density

Condition in which autoinducers accumulate to concentrations sufficient for gene activation.

Defined (Synthetic) Medium

Culture medium with a precisely known chemical composition.

Complex Medium

Culture medium containing ingredients with chemically undefined compositions.

Peptones

Protein hydrolysates used as nutrient sources in complex media.

Yeast Extract

Complex nutrient supplement derived from yeast cells.

Meat Extract

Complex nutrient source prepared from animal tissues.

Agar

Polysaccharide commonly used as a solidifying agent in microbiological media.

General Purpose Medium

Culture medium that supports growth of a wide variety of microorganisms.

Enriched Medium

Culture medium supplemented with additional nutrients to support fastidious organisms.

Blood Agar

Enriched medium containing blood for cultivation of fastidious microorganisms and observation of hemolysis.

Selective Medium

Culture medium that promotes growth of some microorganisms while inhibiting others.

Differential Medium

Culture medium that distinguishes microorganisms based on observable biological characteristics.

Pure (Axenic) Culture

Population of microorganisms derived from a single cell and containing only one species.

Streak Plate

Isolation technique that separates microorganisms across an agar surface to obtain isolated colonies.

Spread Plate

Isolation technique in which a diluted sample is spread across the surface of an agar medium.

Pour Plate

Isolation technique in which microorganisms are mixed with molten agar before solidification.

Enrichment Culture

Cultivation method that favors growth of a desired microorganism from a mixed population.

Continuous Culture System

Cultivation system that maintains microbial growth through continuous nutrient supply and waste removal.