Bacterial Growth, Nutrition, and Environmental Limits

Comprehensive vocabulary flashcards covering microbial nutrition, culture media, metabolic classes, the nitrogen cycle, quantification methods, bacterial growth kinetics, environmental stress tolerances, biofilms, and endospore formation.

Macronutrients

Essential chemical elements needed in large quantities to construct cell structures, including Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S), Potassium ($\text{K}^+$), Magnesium ($\text{Mg}^{2+}$), Ferrous Iron ($\text{Fe}^{2+}$), and Calcium ($\text{Ca}^{2+}$).

Trace Elements

Essential micronutrients required by bacteria in tiny amounts, specifically cobalt, copper, manganese, molybdenum, nickel, and zinc.

Growth Factors

Specific organic compounds that fastidious bacteria cannot synthesize on their own and must acquire directly from their environment to grow (e.g., vitamins, specific amino acids, Hemin, or NAD).

Synthetic Medium (Minimal Medium)

A strictly defined culture medium where every single ingredient—including water, salts, carbon, nitrogen, and energy sources—is known in precise, measured quantities.

Complex Medium (Rich Medium)

A nutrient-rich culture medium composed of poorly defined organic extracts and digests, such as yeast extract, beef extract, peptides, and pancreatic digests of casein.

Enriched Medium

A medium formulated for fastidious microbes by supplementing a complex nutrient base with blood or intact red blood cell components.

Selective Media

Culture media formulated to favor the growth of one specific group or type of microbe while actively inhibiting the growth of others.

Differential Media

Culture media designed to produce visible biochemical differences, such as distinct colony colors or media color changes, between two species growing on the same plate.

MacConkey Lactose Agar

A selective and differential agar containing bile salts and crystal violet to inhibit Gram-positive bacteria, as well as lactose and the pH indicator neutral red to identify lactose fermenters by their pink/red color.

Chocolate Agar

A culture medium made with lysed (broken) red blood cells that releases essential growth factors Hemin and NAD, required for the growth of organisms like Haemophilus influenzae.

Autotroph

An organism that captures inorganic atmospheric carbon dioxide ($\text{CO}_2$) using light energy or mineral oxidation to build complex organic cell molecules.

Heterotroph

An organism that relies on consuming preformed organic molecules for carbon, breaking them down into simpler components and releasing $\text{CO}_2$ or fermentation products.

Phototroph

An organism that absorbs and converts light energy from the sun to power cellular processes.

Chemotroph

An organism that extracts energy from oxidation-reduction reactions by removing electrons from high-energy chemical compounds.

Lithotroph

An organism that extracts electrons from inorganic chemical donors such as hydrogen ($\text{H}_2$), hydrogen sulfide ($\text{H}_2\text{S}$), ammonium ($\text{NH}_4^+$), nitrite ($\text{NO}_2^-$), or ferrous iron ($\text{Fe}^{2+}$).

Organotroph

An organism that harvests electrons exclusively by oxidizing organic compounds such as sugars.

Nitrogen Fixation

The enzymatic conversion of gaseous atmospheric nitrogen ($\text{N}_2$) into bioavailable ammonium ions ($\text{NH}_4^+$).

Nitrogenase

The key microbial enzyme responsible for catalyzing the reduction of atmospheric $\text{N}_2$ gas into usable ammonium ($\text{NH}_4^+$).

Nitrification

The microbial process where nitrifying bacteria biologically convert ammonium ($\text{NH}_4^+$) into nitrate ($\text{NO}_3^-$).

Denitrification

The biochemical process carried out by denitrifying bacteria that converts nitrate ($\text{NO}_3^-$) back into atmospheric dinitrogen gas ($\text{N}_2$).

Pure Culture

A laboratory population comprising a single, genetically uniform strain of a single microorganism isolated from a mixed population.

Colony Forming Unit (CFU)

A single viable cell or group of attached cells that lands on a solid medium and divides to form a visible distinct colony.

Isolation Streaking

A technique using an inoculation loop to spread and dilute cells across an agar surface in multiple steps, reflaming the loop between quadrants to obtain single colonies.

Spread Plate Technique

A quantification method in which serial tenfold dilutions of a liquid culture are spread onto agar plates to determine viable bacterial concentrations.

Hemocytometer (Petroff-Hausser Chamber)

A specialized glass microscope slide etched with a calibrated volume grid, used to directly count the total number of bacterial cells in a sample.

Fluorescence-Activated Cell Sorter (FACS)

An instrument that uses lasers, fluorescent dyes, and high-voltage deflection plates ($\pm 3,000\text{ volts}$) to count and physically sort individual bacterial cells based on fluorescence and scattering properties.

Optical Density

An indirect measure of bacterial culture density and growth determined by measuring the amount of light scattered (turbidity) using a spectrophotometer.

Binary Fission

The standard asexual reproductive process in bacteria where a single parent cell divides into two equal daughter cells.

Generation Time (Doubling Time)

The constant time period required for a bacterial population to double in number during unrestricted exponential growth.

Lag Phase

The introductory period of a batch culture growth curve during which cells do not divide but adapt to their environment and synthesize necessary cellular machinery.

Log Phase (Exponential Phase)

The phase of the bacterial growth curve characterized by maximal, constant doubling rates, appearing as a straight line when plotted on a logarithmic scale.

Stationary Phase

The plateau phase in a batch culture where cell division halts due to nutrient exhaustion and accumulation of toxic metabolic by-products, prompting stress response adaptations.

Death Phase

The final stage of the closed growth curve where cells die at an exponential rate due to severe nutrient deprivation and toxic environmental conditions.

Extremophile

Any organism evolutionary adapted to grow optimally in extreme physical environments (such as extreme temperature, hydrostatic pressure, salinity, or pH) outside normal human physiological limits.

Psychrophile

A cold-adapted organism that grows at temperatures below $15^\circ\text{C}$, has an optimum growth temperature of around $14^\circ\text{C}$, and can grow at temperatures down to $0^\circ\text{C}$.

Mesophile

An organism adapted to moderate temperatures, exhibiting a growth range of $15^\circ\text{C}$ to $45^\circ\text{C}$ and an optimum between $20^\circ\text{C}$ and $40^\circ\text{C}$, which includes human pathogens.

Thermophile

An organism adapted to high heat, thriving in temperatures between $50^\circ\text{C}$ and $80^\circ\text{C}$ with an optimum of $55^\circ\text{C}$ or above.

Hyperthermophile

An organism adapted to extreme heat that thrives at temperatures ranging from $80^\circ\text{C}$ up to $121^\circ\text{C}$.

Barophile (Piezophile)

An organism specifically adapted to survive only under very high hydrostatic pressures, requiring pressures greater than $380\text{ atm}$ to grow.

Barotolerant

An organism that can tolerate elevated hydrostatic pressures between $10\text{ atm}$ and $500\text{ atm}$, but does not strictly require them for survival.

Halophile

An organism that strictly requires high salt concentrations ($> 2\text{ M}$ or $3.4\text{--}5.1\text{ M}$, representing $20\text{--}30\%\text{ NaCl}$) to grow.

Halotolerant

An organism that can grow over a wide salinity range, surviving in either low salt or high salt conditions ($0\text{--}30\%\text{ NaCl}$).

Acidophile

An organism that thrives in acidic environments below $\text{pH } 3$ (spanning $\text{pH } 0\text{--}5$), frequently producing sulfuric acid via mineral oxidation.

Neutralophile

A microorganism that grows optimally between $\text{pH } 5$ and $\text{pH } 8$, encompassing the majority of human microbial pathogens.

Alkaliphile

A microorganism adapted to grow optimally in basic or alkaline conditions ranging from $\text{pH } 9$ to $\text{pH } 11.5$.

Strict Aerobe

An organism that requires molecular oxygen ($\text{O}_2$) as a terminal electron acceptor for respiration and possesses enzymes (SOD, peroxidase, catalase) to neutralize reactive oxygen species.

Strict Anaerobe

An organism that cannot survive in the presence of oxygen because it lacks reactive oxygen species detoxifying enzymes, relying on fermentation or alternative electron acceptors.

Facultative Anaerobe

An organism capable of growing in both the presence and absence of oxygen by switching between aerobic respiration, anaerobic respiration, and fermentation.

Aerotolerant Anaerobe

An anaerobic organism that only ferments and does not utilize oxygen for respiration, but can survive in oxygen-rich environments because it possesses protective enzymes like SOD and catalase/peroxidase.

Microaerophile

An organism that requires low concentrations of oxygen for survival and has decreased levels of reactive oxygen species detoxifying enzymes.

Superoxide Dismutase (SOD)

An essential antioxidant enzyme that protects cells by catalyzing the destruction of toxic superoxide radicals into hydrogen peroxide and molecular oxygen.

Catalase

An enzyme found in aerobes and facultative anaerobes that detoxifies harmful hydrogen peroxide ($\text{H}_2\text{O}_2$) into water and oxygen gas.

GasPak Anaerobe Jar

A sealed container used to culture anaerobic bacteria where a water-activated foil sachet produces $\text{H}_2$ and $\text{CO}_2$, and a lid catalyst combines $\text{H}_2$ with free $\text{O}_2$ to form $\text{H}_2\text{O}$.

Biofilm

A specialized, structured bacterial community adhering to an organic or inorganic surface enclosed within a self-produced protective extracellular matrix.

Endospore

A dehydrated, highly resilient, dormant structure formed by certain Gram-positive bacteria (such as Bacillus and Clostridium) to survive extreme heat, desiccation, UV radiation, and chemical exposure.

Small Acid-Soluble Proteins (SASPs)

Specialized proteins synthesized during sporulation that bind directly to endospore DNA to protect it from damage caused by heat, radiation, and harsh chemicals.

Dipicolinic Acid

A spore-specific compound that complexes with calcium inside the bacterial endospore core to dehydrate the interior and provide heat resistance.

Germination

The developmental reactivation process triggered by favorable environmental cues in which a dormant endospore sheds its protective coat and emerges as a metabolically active vegetative cell.