Dynamics of Prokaryotic Growth Vocabulary

Vocabulary flashcards covering the key terms, environmental influences, and measurement methods of prokaryotic growth from Nester's Microbiology Chapter 4.

Binary Fission

The process by which a prokaryotic cell increases in size, replicates its DNA, and divides into two equal, identical daughter cells.

Generation Time

The amount of time required for a microbial population to double in number through cell division.

Exponential Growth Formula

Mathematical equation defined as $N_t = N_0 \times 2^n$, where $N_t$ is the cell population at time $t$, $N_0$ is the initial cell population, and $n$ is the number of cell divisions.

Biofilm

A polymer- and polysaccharide-encased community of microorganisms adhered to a surface, such as dental plaque or slime in drains.

Extracellular Polymeric Substances (EPS)

A meshwork of polysaccharides and other polymers secreted by multiplying bacteria in a biofilm that facilitates attachment, cellular communication, and passage of nutrients.

Pure Culture

A population of microbial cells derived from a single original cell, allowing for the study and characterization of a single species.

Aseptic Technique

A set of specific laboratory procedures used to prepare culture media and transfer microorganisms while preventing contamination.

Agar

A complex polysaccharide extracted from seaweed used to solidify culture media; it liquefies above $95^\circ\text{C}$, solidifies below $45^\circ\text{C}$, and cannot be degraded by most microbes.

Streak-Plate Method

The simplest and most commonly used technique for isolating bacteria, involving spreading cells across an agar surface using an inoculating loop to yield individual colonies.

Batch Culture

A closed system culture (such as a tube, flask, or Petri dish) in which nutrients are not renewed and wastes are not removed, resulting in a predictable growth curve.

Continuous Culture

An open system culture where fresh nutrients are continuously supplied and wastes and spent media are removed to maintain constant growth.

Chemostat

A continuous culture device that drips fresh medium into a culture vessel while simultaneously removing an equal volume of spent media and cells to maintain a constant growth rate and cell density.

The Growth Curve

A 5-stage curve characterizing population growth in a batch culture, consisting of the lag phase, exponential (log) phase, stationary phase, death phase, and phase of prolonged decline.

Lag Phase

The initial stage of a growth curve where total cell count does not increase because cells are actively synthesizing enzymes needed for cell division.

Exponential (Log) Phase

The growth stage where cells divide at a constant exponential rate, generation time is measured, and cells are most sensitive to antimicrobial drugs.

Primary Metabolites

Essential compounds synthesized by microorganisms during active cell division in the exponential phase, commonly produced for commercial use.

Secondary Metabolites

Non-essential compounds synthesized by microbes late in the exponential phase and during stationary phase as nutrients deplete and wastes accumulate.

Stationary Phase

The growth curve stage where nutrient levels become too low to sustain exponential multiplication, causing the overall rate of cell division to equal the rate of cell death.

Death Phase

The growth phase where the number of viable cells in a batch culture decreases exponentially at a constant rate.

Phase of Prolonged Decline

The final stage of the growth curve following the death phase, in which a tiny fraction of adapted cells survives by utilizing nutrients released by dying cells.

Extremophiles

Microorganisms (mostly members of Archaea) that inhabit severe environmental conditions, such as hydrothermal vents, polar ice caps, and high-salinity oceans.

Psychrophile

An organism with an optimal growth temperature between $-5^\circ\text{C}$ and $15^\circ\text{C}$, typically found in cold polar regions.

Psychrotroph

An organism with an optimal growth temperature between $20^\circ\text{C}$ and $30^\circ\text{C}$ that can grow at refrigeration temperatures and cause food spoilage.

Mesophile

An organism with an optimal growth temperature between $25^\circ\text{C}$ and $45^\circ\text{C}$, including most human pathogens which prefer $35^\circ\text{C}$ to $40^\circ\text{C}$.

Thermophile

An organism with an optimal growth temperature between $45^\circ\text{C}$ and $70^\circ\text{C}$, commonly found in hot springs.

Hyperthermophile

An organism with an optimal growth temperature of $70^\circ\text{C}$ or greater (up to $110^\circ\text{C}$), usually an Archaeon found in volcanic ocean vents.

Obligate Aerobe

An organism that requires oxygen ($\text{O}_2$) to harvest energy through aerobic respiration and cannot survive without it.

Facultative Anaerobe

An organism that grows best in the presence of oxygen ($\text{O}_2$) using respiration, but can also grow in its absence using fermentation or anaerobic respiration.

Obligate Anaerobe

An organism that cannot grow in the presence of oxygen ($\text{O}_2$) due to the lack of mechanisms to protect against toxic reactive oxygen species.

Microaerophile

An organism that requires small quantities of oxygen ($\text{O}_2$) for aerobic respiration, but is inhibited by higher oxygen concentrations.

Aerotolerant Anaerobe

An obligate fermenter that grows equally well with or without oxygen ($\text{O}_2$) because it does not use oxygen for energy harvesting.

Superoxide Dismutase (SOD)

An enzyme produced by organisms growing in oxygen that inactivates superoxide radicals by converting them into oxygen ($\text{O}_2$) and hydrogen peroxide ($\text{H}_2\text{O}_2$).

Catalase

An enzyme that breaks down damaging hydrogen peroxide ($\text{H}_2\text{O}_2$) into water ($\text{H}_2\text{O}$) and oxygen gas ($\text{O}_2$).

Neutrophile

A microorganism that multiplies within a pH range of 5 to 8 and maintains an optimal internal pH near neutral (pH 7).

Acidophile

A microorganism that grows optimally in acidic environments with a pH below 5.5.

Alkaliphile

A microorganism that grows optimally in alkaline environments with a pH above 8.5.

Plasmolysis

The shrinkage of the cytoplasmic membrane away from the cell wall caused by water diffusing out of the cell via osmosis in a high-solute environment.

Halotolerant

Organisms that can withstand and grow in environments with relatively high salt concentrations up to approximately 10% $\text{NaCl}$.

Halophile

Organisms that require high levels of sodium chloride ($\text{NaCl}$) for growth.

Heterotroph

An organism that uses organic compounds as its primary source of carbon.

Autotroph

An organism that uses inorganic carbon in the form of carbon dioxide ($\text{CO}_2$) via carbon fixation.

Fastidious

Refers to microorganisms with complicated nutritional requirements that require specific growth factors to cultivate in the laboratory.

Photoautotroph

An organism that utilizes sunlight for energy and inorganic carbon dioxide ($\text{CO}_2$) as its carbon source.

Photoheterotroph

An organism that derives energy from sunlight and carbon from organic compounds.

Chemolithoautotroph

An organism that extracts energy from inorganic chemicals (such as $\text{H}_2$, $\text{NH}_3$, $\text{NO}_2^-$, $\text{Fe}^{2+}$, or $\text{H}_2\text{S}$) and uses carbon dioxide ($\text{CO}_2$) for carbon.

Chemoorganoheterotroph

An organism that relies on organic compounds for both its energy source and its carbon source.

Complex Medium

A growth medium containing variable ingredients such as protein digests and meat extracts, where the exact chemical composition is unspecified.

Chemically Defined Medium

A growth medium formulated with exact measured quantities of pure chemical compounds.

Selective Medium

A culture medium containing chemicals that inhibit the growth of specific organisms while permitting the growth of target species.

Differential Medium

A culture medium containing specific indicators that change appearance in a identifiable manner when target microbes carry out particular metabolic reactions.

Capnophile

A microorganism that requires elevated levels of carbon dioxide ($\text{CO}_2$) for optimal growth.

Anaerobic Jar

A sealed container used to cultivate obligate anaerobes by generating an oxygen-free environment through chemical packets and catalysts.

Enrichment Culture

A method using specific culture conditions to selectively encourage the growth of a target species present in small numbers within a mixed sample.

Direct Microscopic Count

A direct cell counting method using a specialized ruled chamber slide under a microscope to enumerate total cells (living and dead), requiring at least $10^7\,\text{cells/ml}$.

Plate Count

A viable cell counting method that measures colony-forming units (CFUs) on agar plates following serial dilution, ideal for sample concentrations of $30$ to $300$ cells per plate.

Membrane Filtration

A viable cell counting procedure used for dilute samples, where a known volume of liquid is filtered through a sterile membrane before placing the filter on agar.

Most Probable Number (MPN)

A statistical estimation method that determines cell density in dilute liquid samples based on gas or acid production across sets of inoculated tubes.

Turbidity

The cloudiness of a liquid culture proportional to cell concentration, measured as optical density using a spectrophotometer.

Durham Tube

An inverted glass vial placed inside liquid broth tubes to catch gas produced by fermenting microorganisms.