Environmental Influences on Microbial Growth

Vocabulary practice flashcards covering environmental factors influencing microbial growth, including temperature, hydrostatic pressure, osmolarity, pH, and oxygen requirements.

Psychrophile

An organism with an optimal growth temperature at or below $15\,^\circ\text{C}$, characterized by cold-active flexible enzymes, cryoprotectants like trehalose, and membranes with high concentrations of unsaturated fatty acids to preserve fluidity.

Psychrotolerant

A microorganism capable of growth across a broad temperature range between $0\,^\circ\text{C}$ and $35\,^\circ\text{C}$.

Mesophile

A microorganism that exhibits optimal growth within a moderate temperature range between $15\,^\circ\text{C}$ and $45\,^\circ\text{C}$.

Thermophile

A microorganism capable of growing at elevated temperatures between $45\,^\circ\text{C}$ and $80\,^\circ\text{C}$, possessing heat-stable enzymes resistant to unfolding and membranes enriched in saturated fatty acids.

Hyperthermophile

A microorganism that grows at temperatures exceeding $80\,^\circ\text{C}$, typically an archaeon with ether-linked lipids forming monolayer membranes that resist thermal hydrolysis.

Diglycerol Tetraether

A lipid molecule found in hyperthermophilic archaea produced by the condensation of diethers, forming a monolayer membrane that resists hydrolysis at extreme temperatures and pH levels.

Barophile

An organism that requires high hydrostatic pressure to grow, often inhabiting the deep ocean floor at temperatures around $2\,^\circ\text{C}$ and possessing polyunsaturated fatty acids to maintain membrane fluidity.

Shewanella

A barophilic bacterium capable of surviving under deep-sea pressures, such as at $11{,}035\,\text{m}$ ($1{,}085\,\text{atm}$) in the Mariana Trench.

Barotolerant Organism

An organism that grows up to a certain hydrostatic pressure threshold but ceases growth and dies at higher pressures.

Barosensitive Organism

An organism whose growth rate steadily declines and which dies as hydrostatic pressure increases.

Plasmolysis

The shrinkage and detachment of the bacterial cytoplasmic membrane from the cell wall when cells are exposed to a hypertonic environment due to water moving out of the cell.

Compatible Solutes

Organic molecules (such as glycine betaine, ectoine, proline, sucrose, trehalose, and glycerol) accumulated in the cytoplasm to balance external osmolarity and prevent dehydration without interfering with cellular biochemistry.

Nonhalophile

A microorganism that exhibits optimal growth in environments with low salt concentrations of $\le 0.9\%\,\text{NaCl}$.

Halotolerant

An organism that does not require salt for growth and whose proliferation is inhibited at concentrations exceeding $>3\%\,\text{NaCl}$.

Halophile

An organism adapted to low environmental water activity ($a_w$) that exhibits optimal growth between $3\%$ and $10\%\,\text{NaCl (w/v)}$.

Extreme Halophile

An archaeon with an absolute requirement for high salt concentrations between $15\%$ and $30\%\,\text{NaCl (w/v)}$, adapting by importing $\text{K}^+$ and maintaining surface proteins enriched in acidic amino acids ($\text{Asp}$ and $\text{Glu}$).

Acidophile

An organism that grows optimally below $\text{pH } 5$, maintaining an internal neutral cytoplasmic pH by pumping out protons or using proton-consuming enzymatic reactions.

Neutrophile

An organism that grows optimally within a neutral pH range of $\text{pH } 5$ to $8$, matching intracellular levels compatible with life.

Alkaliphile

An organism that grows optimally above $\text{pH } 8$, maintaining cytoplasmic neutrality by importing protons and often utilizing ether-linked lipids to avoid alkaline hydrolysis of ester bonds.

Thioglycolate Broth

A differential liquid growth medium containing sodium thioglycolate and resazurin used to determine the oxygen requirements of microorganisms based on the location of bacterial turbidity.

Sodium Thioglycolate

A reducing agent that consumes dissolved oxygen in broth media according to the reaction: $2\text{NaSCH}_2\text{COOH} + \frac{1}{2}\text{O}_2 \rightarrow \text{HOOCCH}_2\text{S–SCH}_2\text{COOH} + \text{H}_2\text{O}$.

Resazurin

A redox indicator included in thioglycolate broth that turns pink in the presence of oxygen and remains colorless under anaerobic conditions.

Obligate Aerobe

An organism that strictly requires oxygen as a terminal electron acceptor in cellular respiration, growing only in the oxic top layer of thioglycolate broth ($\sim 300\,\mu\text{M O}_2$).

Obligate Anaerobe

An organism that lacks superoxide dismutase, catalase, or peroxidase, making exposure to molecular oxygen lethal; grows only in oxygen-depleted zones ($\le 5\,\mu\text{M O}_2$).

Facultative Anaerobe

An organism that produces protective detoxifying enzymes and can utilize alternative electron acceptors, but derives maximum energy and grows best in the presence of oxygen.

Aerotolerant Anaerobe

An organism that does not use oxygen in its electron transport chain but produces enzymes that detoxify reactive oxygen species, allowing it to grow evenly throughout media regardless of oxygen presence.

Microaerophile

An organism that requires oxygen at low concentrations ($\sim 50\,\mu\text{M O}_2$) but is killed by atmospheric oxygen levels ($21\%$) due to inefficient radical detoxification or electron transport reduction.

Superoxide Dismutase

An enzyme that detoxifies superoxide radicals by catalyzing the reaction: $2\text{O}_2^- + 2\text{H}^+ \rightarrow \text{H}_2\text{O}_2 + \text{O}_2$.

Catalase

An enzyme that detoxifies hydrogen peroxide by converting it into water and oxygen gas according to the reaction: $2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$.

Peroxidase

An enzyme that decomposes toxic hydrogen peroxide without releasing oxygen gas: $\text{H}_2\text{O}_2 + 2\text{H}^+ \rightarrow 2\text{H}_2\text{O}$.

Catalase Test

A rapid diagnostic assay distinguishing catalase-positive Staphylococcus (which produces bubbles of $\text{O}_2$ upon hydrogen peroxide addition) from catalase-negative Streptococcus.

GasPak

A sealed incubation jar system for culturing obligate anaerobes, using a disposable envelope that generates $\text{H}_2$ and $\text{CO}_2$ alongside a lid catalyst that facilitates $\text{H}_2 + \frac{1}{2}\text{O}_2 \rightarrow \text{H}_2\text{O}$.