Brock Biology of Microorganisms - Chapter 4: Microbial Growth and Its Control

Vocabulary flashcards covering key terms and definitions from Chapter 4 (Microbial Growth and Its Control) of Brock Biology of Microorganisms.

Nutrients

Supply of elements required by cells for growth.

Macronutrients

Nutrients required by microbial cells in large amounts.

Micronutrients

Nutrients required by microbial cells in minute amounts, including trace metals and growth factors.

Heterotroph

An organism that requires organic carbon obtained from the breakdown of organic polymers or uptake of organic monomers.

Autotroph

An organism that synthesizes organic carbon compounds from carbon dioxide ($CO_2$).

Growth Factors

Organic micronutrients, such as vitamins, amino acids, purines, and pyrimidines, that mostly function as coenzymes.

Defined Media

Culture media in which the exact chemical composition is known.

Complex Media

Culture media composed of digests of microbial, animal, or plant products, such as yeast and meat extracts.

Selective Medium

Culture medium containing compounds that selectively inhibit the growth of some microbes but not others.

Differential Medium

Culture medium containing an indicator, such as a dye, that detects specific metabolic reactions during microbial growth.

Colony Morphology

The visible characteristics of isolated microbial colonies on solid media, used to identify microorganisms and assess culture purity.

Aseptic Technique

Manipulations and procedures performed to prevent contamination of cultures and media by airborne or environmental microorganisms.

Microscopic Cell Count

Direct estimation of cell numbers by observing and enumerating cells in dried or liquid samples using microscope slides or counting chambers.

Viable Count

Measurement of the living, reproducing cell population in a sample, determined via plate count methods.

Colony-Forming Unit (CFU)

A unit of measurement representing a single viable cell or group of cells that produces a visible colony on solid medium.

Great Plate Count Anomaly

The phenomenon where direct microscopic cell counts of natural samples reveal far more organisms than those recoverable as colonies on culture plates.

Turbidity

The cloudiness of a cell suspension caused by microbial cells scattering light.

Optical Density (OD)

Unit of light absorbance or scattering in a suspension measured at a specified wavelength using a spectrophotometer (e.g., $OD_{540}$).

Binary Fission

A process of cell division following enlargement of a single cell to twice its original size.

Septum

A partition that forms between dividing cells during cell division and pinches off to form two daughter cells.

Generation Time ($g$)

The time required for microbial cell numbers or a population to double ($g = t/n$).

Batch Culture

A closed-system microbial culture of fixed volume.

Lag Phase

The period between inoculation of a culture and the beginning of exponential growth, needed for enzyme and metabolite synthesis.

Exponential Phase

The period of microbial growth characterized by cell population doubling at regular intervals under balanced growth conditions.

Stationary Phase

The phase in a batch culture where the population growth rate reaches zero due to nutrient depletion or waste product accumulation.

Decline Phase

The phase in a batch culture where total cell numbers decrease over time due to cell death.

Specific Growth Rate ($k$)

The instantaneous rate of population growth during exponential growth ($k = 0.693/g$).

Continuous Culture

An open-system culture method where spent medium and cells are continuously removed while fresh medium is added.

Chemostat

A continuous culture device in which fresh medium is supplied at the same rate spent medium is removed to maintain a constant culture volume and steady state.

Steady State

A condition in continuous culture where cell density and substrate concentration remain constant over time.

Dilution Rate ($D$)

The ratio of flow rate ($F$) of fresh medium addition/removal to total culture volume ($V$), expressed as $D = F/V$.

Planktonic Growth

Growth of microorganisms in liquid suspension as free-floating or free-swimming individual cells.

Sessile Growth

Growth of microorganisms attached to a surface.

Biofilm

An attached community of microbial cells enmeshed within a self-produced extracellular polysaccharide (EPS) matrix.

Microbial Mats

Thick, multilayered microbial sheets containing distinct metabolic communities in each layer.

Budding Cell Division

An alternative cell division process involving unequal cell growth to form a distinct daughter cell.

Hyphae

Long, thin filamentous structures formed by actinomycetes during growth.

Mycelia

Interwoven networks or mats formed by branched hyphae.

Cardinal Temperatures

The minimum, optimum, and maximum temperatures that define the growth parameters of a given microorganism.

Psychrophile

A microorganism with an optimal growth temperature of $< 15\,^\circ\text{C}$, found in permanently cold environments.

Mesophile

A microorganism with a midrange growth temperature optimum, typically around $39\,^\circ\text{C}$ (e.g., $Escherichia\,coli$).

Thermophile

A microorganism with an optimal growth temperature between $45\,^\circ\text{C}$ and $80\,^\circ\text{C}$.

Hyperthermophile

A microorganism with an optimal growth temperature $> 80\,^\circ\text{C}$, inhabiting high-temperature habitats such as hydrothermal vents.

Extremophile

A microorganism adapted to survive and grow under extreme environmental conditions, such as high or low temperatures, pH, or salinity.

Psychrotolerant

A microorganism capable of growing at $0\,^\circ\text{C}$ but possessing a growth optimum between $20\,^\circ\text{C}$ and $40\,^\circ\text{C}$.

Neutrophile

A microorganism that grows optimally at neutral pH ranges between $5.5$ and $7.9$.

Acidophile

A microorganism that grows optimally in acidic conditions at pH $< 5.5$.

Alkaliphile

A microorganism that grows optimally in alkaline conditions at pH $\ge 8$.

Water Activity ($a_w$)

A measure of water availability defined as the ratio of the vapor pressure of air in equilibrium with a substance to the vapor pressure of pure water.

Halophile

A microorganism that requires sodium chloride ($NaCl$) for growth and grows optimally at $a_w = 0.98$.

Halotolerant

A microorganism capable of tolerating elevated solute concentrations but growing best in the absence of added solutes.

Extreme Halophile

A microorganism requiring very high concentrations of salt ($15\text{--}30\%$ $NaCl$) for growth.

Aerobe

A microorganism capable of living and growing in the presence of full atmospheric oxygen ($21\%$ $O_2$) using oxygen for respiration.

Microaerophile

A microorganism that requires oxygen for growth but only at levels lower than atmospheric concentrations (microoxic conditions).

Facultative Anaerobe

A microorganism that can switch between aerobic respiration and anaerobic growth depending on oxygen availability.

Aerotolerant Anaerobe

An anaerobic microorganism that does not use oxygen for respiration but can tolerate and grow in its presence.

Obligate Anaerobe

A microorganism that is inhibited or killed by the presence of oxygen.

Reducing Agent

A chemical compound added to growth media to remove oxygen by reducing it to water (e.g., thioglycolate).

Superoxide Dismutase

An enzyme that catalyzes the conversion of toxic superoxide radicals ($2O_2^-$) into hydrogen peroxide ($H_2O_2$) and oxygen ($O_2$).

Catalase

An enzyme that decomposes toxic hydrogen peroxide ($H_2O_2$) into water ($H_2O$) and oxygen ($O_2$).

Superoxide Reductase

An enzyme found in strict anaerobes that converts superoxide radicals ($O_2^-$) to hydrogen peroxide ($H_2O_2$) without producing oxygen.

Decimal Reduction Time ($D$)

The time required at a given temperature to achieve a $10\text{-fold}$ ($90\%$) reduction in viable microbial numbers.

Thermal Death Time

The time required to kill all microbial cells in a given sample at a specified temperature.

Autoclave

A sealed heating apparatus that uses steam under pressure ($121\,^\circ\text{C}$) to achieve complete sterilization.

Pasteurization

A controlled heat treatment process used to significantly reduce microbial numbers in heat-sensitive liquids without achieving sterilization.

Depth Filter

A filter constructed of fibrous sheets of overlapping paper or glass fibers that traps particles within its structure.

$D_{10}$ Value

The absorbed radiation dose (in grays) required to reduce microbial viability $10\text{-fold}$.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent required to inhibit visible growth of a microorganism.

Zone of Growth Inhibition

A clear region surrounding an antimicrobial disk on agar where microbial growth is prevented.

Sterilant

A chemical agent capable of destroying all forms of microbial life, including bacterial endospores.

Disinfectant

A chemical agent that destroys vegetative pathogens on inanimate objects but does not necessarily eliminate endospores.

Sanitizer

An agent that reduces microbial counts on inanimate objects to levels considered safe by public health standards.

Antiseptic

A non-toxic chemical agent suitable for application to living tissue to kill or inhibit pathogenic microorganisms.