Growth and Cultivation of Microorganisms - Bacterial Growth Curve & Environmental Factors

A comprehensive set of vocabulary-style flashcards covering the bacterial growth curve, generation time, nutrient needs, metabolic energy sources, environmental factors (pH, temperature, osmotic stress), and related microbial physiology concepts from the notes.

Growth

Increase in the number of cells (population) of a microorganism, not the size of individual cells.

Microbial Growth

Increase in the number of microbial cells.

Binary Fission

Asexual reproductive process by which a single bacterial cell divides into two daughter cells.

True Growth

Increase in population/number of cells, not just increases in cell size or mass.

Exponential Growth

Growth pattern where the population increases at a constant doubling rate (2^n) during the exponential phase.

Generation Time (Doubling Time)

Time required for a bacterial population to double in number.

E. coli Generation Time

Approximately 15 minutes (shortest generation time cited in notes).

Mycobacterium tuberculosis Generation Time

Slow generation time (example of slower-growing bacterium).

Generation Time Formula

N = N0 × 2^n, where N0 = initial cell count, N = count after n generations.

n in the Generation Time Formula

n = t / generation time (number of generations in time t).

Lag Phase

Phase with little or no cell division as cells adapt to environment; high metabolic activity.

Log/Exponential Phase

Phase of rapid, exponential cell division; cells are most metabolically active.

Stationary Phase

Phase where deaths equal new cells; growth ceases due to nutrient depletion and waste accumulation.

Death Phase

Phase of decline where microbial deaths exceed new cell formation; viability may decrease.

VBNC (Viable but Not Culturable)

Cells are alive but cannot be cultured under standard conditions, often due to stress.

Incubation Period

Time from acquisition of microorganism to appearance of first symptoms.

Incubator

Device that provides the proper environmental conditions (temperature, atmosphere) for growth.

Fermentation

Metabolic process producing energy via substrate-level phosphorylation; involves transfer of a phosphate to ADP by a phosphorylated intermediate.

Respiration

Energy production via oxidation-reduction reactions with electron transport and a proton motive force; oxygen is a common terminal electron acceptor.

Oxygen as Oxidant (Aerobic Respiration)

O2 commonly used as the terminal electron acceptor in aerobic respiration.

Alternative Electron Acceptors

Other oxidants used by some organisms: CO2, sulfate (SO4^2-), nitrate (NO3^-).

Photosynthesis

Light-driven reduction of an oxidant via electron carriers; generates reductant photochemically; requires light.

Autotroph

Organism that uses CO2 as its carbon source (does not require organic carbon).

Heterotroph

Organism that requires organic carbon for growth.

Photoautotroph

Energy from light; carbon from CO2.

Photoheterotroph

Energy from light; carbon from organic compounds.

Chemoautotroph (Lithotroph)

Energy from inorganic substrates; carbon from CO2.

Chemoheterotroph

Energy and carbon from organic compounds.

Siderophores

Iron-chelating compounds that promote iron uptake by bacteria.

Growth Factor

Organic compound required for growth that the cell cannot synthesize.

Nitrogen Sources

NO3^-, NO2^-, NH3, NH2, and amino acids used by various microbes.

Nitrogen Cycle

Biogeochemical cycle transforming nitrogen among forms in the environment.

Nitrogen Fixation

Conversion of N2 to NH3 by prokaryotes, making nitrogen available for biosynthesis.

Ammonification

Production of NH3 from deamination of amino acids.

Nitrification

Conversion of ammonia (NH3) to nitrite (NO2^-) and nitrate (NO3^-).

Assimilation (Nitrogen)**

Reduction of nitrate/nitrite to NH3 by microorganisms for incorporation into biomolecules.

Denitrification

Conversion of NH3 to gaseous N2 under anaerobic conditions.

Sulfur in Biology

Sulfur is in proteins and coenzymes; sources include sulfate (SO4^2-) and hydrogen sulfide (H2S).

Coenzymes Containing Sulfur

Sulfur-containing coenzymes found in various enzymes.

Phosphorus

Component of ATP, nucleic acids, and coenzymes; essential in cell structures.

Magnesium (Mg) & Ferrous (Fe) Ions

Mg in chlorophyll; Fe in cytochromes and peroxidases; important cofactors.

Magnesium & Potassium (Mg & K) in Ribosomes

Essential for ribosome structure and function.

Calcium (Ca)

Constituent of Gram-positive cell walls; not required for all Gram-negative bacteria.

Sodium (Na) in Microbes

High Na requirements in some marine organisms; variable essentiality.

Trace Elements

Minerals required in small amounts (Mn, Mo, Co, Zn, Cu, etc.) essential for enzyme function.

Siderophores (revisited)

Iron-chelating compounds that enhance iron acquisition from the environment or host.

Growth Factor (Revisited)

Organic compound required for growth that cannot be synthesized by the organism.

Neutralophiles

Microorganisms that grow best at pH 6.0–8.0.

Acidophiles

Organisms that thrive at acidic pH, as low as pH 3.0.

Alkaliphiles

Organisms that thrive at alkaline pH, up to around pH 10.5.

Psychrophiles

Microorganisms that prefer very cold temperatures; optimum well below 20°C (−5 to 15°C in notes).

Psychrotrophs

Organisms that grow at refrigeration to mild temperatures (typical range up to ~30°C).

Mesophiles

Moderate-temperature-loving microbes; optimum around 30–37°C; common among many pathogens.

Thermophiles

Heat-loving microbes with optimum growth around 50–60°C.

Hyperthermophiles

Extreme thermophiles with optimum growth at very high temperatures (often >80°C).

Optimum Temperature

Temperature at which growth rate is highest for a given organism.

Minimum/Maximum Temperature

Lowest and highest temperatures at which a microbe can grow.

Heat Shock Response

Transient production of heat-shock proteins to protect cells from sudden temperature increases.

Cold Shock

Cell death caused by rapid cooling (e.g., exposing cells to sudden temperature drop).

Aerobic Metabolism Byproducts

Reactive oxygen species such as hydrogen peroxide (H2O2) and superoxide (O2−) produced during metabolism.

Catalase

Enzyme that decomposes hydrogen peroxide to water and oxygen.

Superoxide Dismutase (SOD)

Enzyme that converts superoxide radicals to hydrogen peroxide and oxygen.

Oxygen Requirements

Categories describing how microbes use oxygen: Aerobic, Anaerobic, Facultative, Microaerophiles, Aerotolerant, Obligate.

Obligate Aerobes

Organisms that require oxygen as the terminal electron acceptor.

Facultative Anaerobes

Organisms that can grow with or without oxygen; prefer oxygen but can use other electron acceptors.

Microaerophiles

Organisms that require only small amounts of oxygen and lack full detoxifying enzymes.

Aerotolerant Anaerobes

Do not use oxygen but can tolerate its presence.

Oxygen as Electron Acceptor (Summary)

O2 serves as the main electron acceptor in aerobic metabolism; other acceptors exist in some species.

Halophiles

Organisms that require or tolerate high salt concentrations.

Osmophiles

Organisms that thrive in high sugar concentrations.