Microbial Growth Lecture Review

Vocabulary flashcards covering microbial growth phases, physical and chemical requirements, quantification methods, and biochemical metabolism tests.

Microbial Growth

The increase in the number of cells, which occurs by cell division, rather than an increase in cell size.

Lag Phase

A period of high metabolic activity and preparation for cell division where growth begins only after a period of time.

Log or Exponential Phase

The phase where the cell population doubles at regular intervals (generation time), achieving the maximum growth rate with uniform chemical and physiological properties.

Stationary Phase

A phase where growth rate slows as nutrients deplete and waste accumulates, causing some cells to grow while others die, often triggering a switch to survival mode or secondary metabolite production.

Decline or Death Phase

The final phase of the growth cycle where growth ceases and some cells undergo lysis (breakdown).

Cardinal Temperature

The range of temperatures (minimum, optimum, and maximum) within which a specific microbe can grow.

Psychrophiles

Cold-loving microbes that can grow at $0\,^{\circ}\text{C}$.

Psychrotroph

A variant of psychrophile that displays an optimum temperature in the mesophile range.

Mesophiles

Moderate-temperature-loving microbes that grow best between $25$-$40\,^{\circ}\text{C}$; they are the most common type of microbe.

Thermoduric Microbes

Microbes that can withstand short periods of exposure to high temperatures.

Thermophiles

Heat-loving microbes with an optimum temperature between $50$-$60\,^{\circ}\text{C}$.

Hyperthermophiles

Microbes with an optimum growth temperature of $80\,^{\circ}\text{C}$ or higher.

Extreme Thermophiles

Microbes capable of growth at temperatures of $121\,^{\circ}\text{C}$ and above.

Planococcus halocryophilus

The microbe reported to live at $-15\,^{\circ}\text{C}$, which is the coldest temperature ever reported for bacterial growth.

Acidophiles

Acid-loving microbes that grow in a pH range of $0.1$ to $5.4$, such as Lactobacillus.

Neutrophiles

Microbes that grow in a neutral pH range of $5.4$ to $8.0$.

Alkaliphiles

Base-loving microbes that grow in a pH range of $7.0$ to $11.5$, such as Vibrio cholerae and Bacillus firmus.

Water activity ($a_w$)

A measure of available moisture ranging from $0$ (no water) to $1$ (pure $H_2O$).

Matric water activity

A measure of water bound to a surface, with the limit for growth being $0.61\,a_w$.

Xerophiles

Microbes that are able to survive in dry environments.

Osmolarity

The number of particles of solute per liter of solution.

Compatible Solute

Highly water-soluble organic molecules (sugars, alcohols, amino acid derivatives) that do not inhibit biochemical processes; Archaea use $KCl$ as a compatible solute.

Halophiles

Microbes that grow only in the presence of $NaCl$, typically between $1$-$4\%$, including extreme halophiles in salty environments.

Halotolerant

Microbes that grow best in the absence of added solute but can tolerate some level of dissolved solutes.

Osmophiles

Microbes that grow in environments with high sugar concentrations.

Obligate Aerobes

Organisms that require oxygen for survival and only live by aerobic respiration.

Obligate Anaerobes

Organisms for which oxygen is toxic; they live by fermentation, anaerobic respiration, photosynthesis, or methanogenesis.

Facultative Anaerobe

Organisms that can grow with or without oxygen, utilizing aerobic respiration in aerobic conditions and fermentation or anaerobic respiration in anaerobic conditions.

Microaerophiles

Organisms that require oxygen levels lower than atmospheric concentration.

Aerotolerant Anaerobes

Organisms that are indifferent to oxygen and do not use it for growth, living only by fermentation.

Capnophiles

Carbon dioxide-loving microbes.

Barophiles

Bacteria that live at high hydrostatic pressures exerted by standing water.

Deinococcus radiodurans

A microbe that can survive $10,000\,\text{Grays (Gy)}$ of radiation due to efficient DNA repair systems.

Trace Elements

Micronutrients like iron, magnesium, zinc, and copper required in small amounts as cofactors for enzymes.

Organic Growth Factors

Essential organic compounds like vitamins, amino acids, purines, and pyrimidines that an organism cannot synthesize and must obtain from the environment.

Singlet Oxygen ($^{1}O_2$)

A higher-energy, extremely reactive state of normal molecular oxygen ($O_2$).

Superoxide Dismutase (SOD)

An enzyme produced by bacteria to neutralize superoxide radicals ($O_2^{-}$) by converting them into molecular oxygen ($O_2$) and hydrogen peroxide ($H_2O_2$).

Catalase

An enzyme used to neutralize the peroxide anion ($O_2^{2-}$) by converting it into water and oxygen.

Peroxidase

An enzyme that breaks down hydrogen peroxide without producing oxygen as a byproduct.

Hydroxyl Radical ($\cdot OH$)

The most reactive intermediate form of oxygen, transiently formed in the cytoplasm by ionizing radiation.

Phototrophs

Microbes that derive their energy from light.

Chemotrophs

Microbes that obtain energy from chemical compounds through the oxidation of organic or inorganic substances.

Generation Time Equation

$g = \frac{t}{n}$, where $g$ is generation time, $t$ is time, and $n$ is the number of generations.

Specific Growth Rate ($k$ or $\mu$)

$k = \frac{0.693}{g}$ or $\mu = \frac{\ln(2)}{g}$.

Petroff-Hausser Chamber

A counting chamber used for direct microscopic counting of cells.

Coulter Counter

An instrument used for electronic cell counting.

Most Probable Number (MPN)

A statistical estimation of microbial cell numbers based on dilution series and turbidity, involving presumptive, confirmatory, and completed tests.

Turbidity

An indirect method of measuring microbial growth by checking the cloudiness of a culture using a spectrophotometer to determine Optical Density.

Methyl Red (MR) Test

A biochemical test that identifies stable acid producers through mixed acid fermentation, indicated by a red color at pH $< 4.4$.

Voges-Proskauer (VP) Test

A test detecting acetoin production from glucose fermentation using Barritt's reagents ($\alpha$-naphthol and $KOH$).

Citrate Utilization Test

A test determining if citrate is used as the sole carbon source on Simmons' citrate agar, with a positive result being a blue color.

Indole Test

A test for the production of indole from tryptophan using Kovac's reagent; a red layer at the top indicates a positive result.

Urease Test

A test detecting urease activity where ammonia production raises the pH, turning the Phenol Red indicator pink.

Hydrogen Sulfide ($H_2S$) Production

A test where $H_2S$ gas reacts with iron salts in Peptone Iron Agar (PIA) to produce a black precipitate.

Oxidase Test

A test identifying bacteria with cytochrome c oxidase, where the reagent turns purple within $30$ seconds.

Catalase Test

A test detecting the enzyme that breaks down hydrogen peroxide into water and oxygen, visible through bubble formation.