Microbial Growth

Vocabulary practice flashcards covering physical and chemical growth requirements, oxygen tolerances, culture media types, biofilms, and measurement techniques from Chapter 6: Microbial Growth.

Microbial Growth

An increase in the total number of cells in a microbial population or colony, rather than an increase in individual cell size.

Psychrophiles

Cold-loving microorganisms capable of growing at low temperatures, with an optimum growth temperature typically around 10^\bottom\text{--}15^\circ\text{C}.

Psychrotrophs

Microorganisms that grow between $0^\circ\text{C}$ and $20\text{--}30^\circ\text{C}$, which are known for causing low-temperature food spoilage in refrigerators.

Mesophiles

Moderate-temperature-loving microorganisms with an optimum growth temperature between $25^\circ\text{C}$ and $40^\circ\text{C}$.

Thermophiles

Heat-loving microorganisms with an optimum growth temperature between $50^\circ\text{C}$ and $60^\circ\text{C}$.

Hyperthermophiles

Extreme heat-loving microorganisms that have an optimum growth temperature of $80^\circ\text{C}$ or higher, frequently isolated from deep-sea hydrothermal vents at temperatures exceeding $100^\circ\text{C}$.

Acidophiles

Organisms that tolerate or thrive in highly acidic growth environments, typically below a $pH$ of $5.5$.

Plasmolysis

The shrinkage or contraction of the bacterial cytoplasm away from the cell wall caused by the osmotic loss of water in a hypertonic environment.

Obligate Halophiles

Organisms that strictly require high osmotic pressure and high salt concentrations to grow, also known as extreme halophiles.

Facultative Halophiles

Microorganisms that do not require high salt concentrations for survival, but are able to tolerate and grow in elevated osmotic pressures up to about $2\%$ salt.

Nitrogen Fixation

The metabolic process by which certain bacteria assimilate gaseous atmospheric nitrogen ($N_2$) directly into usable nitrogenous compounds.

Trace Elements

Inorganic elements (such as iron, copper, molybdenum, and zinc) required by microorganisms in minute quantities, typically serving as enzyme cofactors.

Obligate Aerobes

Organisms that strictly require molecular oxygen ($O_2$) for cellular respiration and growth, possessing superoxide dismutase (SOD) and catalase to neutralize toxic oxygen species.

Facultative Anaerobes

Microorganisms capable of both aerobic and anaerobic growth that grow more efficiently and abundantly in the presence of oxygen.

Obligate Anaerobes

Microorganisms that grow only in the complete absence of oxygen and cease growth or die when exposed to oxygen because they lack enzymes to neutralize toxic forms of oxygen.

Aerotolerant Anaerobes

Microbes that carry out only anaerobic metabolism and cannot use oxygen, but tolerate its presence because they possess the enzyme superoxide dismutase (SOD).

Microaerophiles

Organisms that require oxygen for aerobic growth, but only at low concentrations that have diffused below standard atmospheric levels.

Superoxide Dismutase (SOD)

An enzyme that protects aerobic cells by converting toxic superoxide free radicals ($O_2^{\bullet-}$) into molecular oxygen ($O_2$) and hydrogen peroxide ($H_2O_2$).

Catalase

An enzyme that breaks down toxic hydrogen peroxide ($H_2O_2$) into water ($H_2O$) and molecular oxygen ($O_2$), visible as bubbling.

Peroxidase

An enzyme that neutralizes hydrogen peroxide ($H_2O_2$) by reducing it to water ($H_2O$) without releasing oxygen gas.

Biofilm

A structured microbial community that adheres to a surface, embedded in an extracellular slime or hydrogel matrix that shares nutrients and shelters cells from harmful environmental factors.

Quorum Sensing

A mechanism of cell-to-cell chemical communication that allows bacteria in a biofilm to coordinate activities and attract other bacterial cells.

Culture Medium

A nutrient material prepared in the laboratory to support the growth and multiplication of microorganisms.

Sterile

The condition of being completely free of all living microorganisms, including viable vegetative cells and spores.

Inoculum

The specific microorganisms that are introduced into a sterile culture medium to initiate growth.

Culture

Microorganisms that grow and multiply in or on a culture medium.

Agar

A complex polysaccharide derived from marine algae used as a solidifying agent in culture media; it liquefies at $100^\circ\text{C}$ and solidifies at approximately $40^\circ\text{C}$.

Chemically Defined Media

Culture media whose exact chemical composition and specific quantity of every ingredient are precisely known.

Complex Media

Culture media composed of nutrient-rich extracts and digests of yeasts, meat, or plants whose precise chemical composition varies from batch to batch.

Reducing Media

Growth media containing chemical agents (such as sodium thioglycolate or oxyrase) that react with and deplete dissolved oxygen, used for cultivating obligate anaerobes.

Capnophiles

Microorganisms that grow best under conditions of elevated carbon dioxide ($CO_2$) concentration.

Biosafety Level 4 (BSL-4)

The highest laboratory containment level for dangerous and exotic pathogens, utilizing sealed negative-pressure suites and double-filtered exhaust air.

Differential Media

Culture media formulated to make it easy to distinguish colonies of different microbes growing on the same plate based on distinct visual characteristics.

Selective Media

Culture media designed to suppress the growth of unwanted microorganisms while encouraging the growth of desired microbes.

Enrichment Culture

A culture medium and incubation method designed to favor the growth of very small numbers of a specific desired organism from a mixed community to detectable numbers.

Colony

A visible mass of microbial cells arising from a single cell, spore, or group of attached cells on a solid medium, often designated as a colony-forming unit (CFU).

Streak Plate Method

A microbiological isolation technique in which an inoculum is spread sequentially across the surface of an agar plate using an inoculating loop to obtain isolated colonies.

Deep-Freezing

A long-term preservation technique in which a pure bacterial culture is frozen in a protective liquid medium at temperatures ranging from $-50^\circ\text{C}$ to $-95^\circ\text{C}$.

Lyophilization (Freeze-Drying)

A bacterial preservation method wherein cells are quickly frozen at $-54^\circ\text{C}$ to $-72^\circ\text{C}$ and dehydrated by removing water under high vacuum.

Binary Fission

The primary method of prokaryotic cell division, where a single cell elongates, replicates its nucleoid DNA, synthesizes a cross-wall, and splits into two identical daughter cells.

Generation Time

The amount of time required for a bacterial cell or population to undergo one round of cell division and double in number.

Lag Phase

The initial period in a bacterial growth curve characterized by intense metabolic activity and enzyme synthesis with no net increase in cell population.

Log Phase

The period of microbial growth characterized by exponential, logarithmic increases in population as cells divide rapidly via binary fission.

Stationary Phase

A plateau period in a bacterial growth curve where microbial deaths balance the formation of new cells, creating an equilibrium.

Death Phase

The phase of microbial population dynamics where cells die at a logarithmic rate, exceeding the formation of new cells.

Pour Plate Method

A direct plate count method in which bacterial dilutions are mixed into liquid melted agar before pouring, causing colonies to grow both within and on top of the agar.

Spread Plate Method

A plate count technique where a small volume ($0.1\,\text{ml}$) of bacterial dilution is distributed evenly across the surface of a pre-solidified agar plate, restricting growth exclusively to the surface.

Most Probable Number (MPN) Method

A statistical dilution-to-extinction method used to estimate the number of viable microbes in a liquid sample based on positive growth tubes compared against an MPN table.

Petroff-Hausser Cell Counter

A specialized microscope slide etched with a calibrated grid of known area and depth used to directly count bacterial cells in a measured volume of suspension.