Microbial Metabolism, Growth, and Control

Comprehensive vocabulary flashcards covering microbial metabolism, growth requirements, culture techniques, and physical and chemical control methods.

Metabolism

The sum of all chemical reactions that occur within a living organism.

Catabolism

Degradative chemical reactions that release energy by breaking down large, complex molecules into simpler ones, frequently involving hydrolysis.

Anabolism

Biosynthetic chemical reactions that build complex molecules from simpler ones, requiring energy input and often involving dehydration synthesis.

ATP Coupling

The energetic linking where catabolic reactions drive the synthesis of ATP from ADP and inorganic phosphate ($\text{ADP} + \text{P}_i + \text{Energy} \rightarrow \text{ATP}$), while anabolic reactions utilize energy released by ATP hydrolysis ($\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$).

Enzyme

A highly specific protein molecule that acts as a biological catalyst, speeding up chemical reactions by lowering their activation energy up to 10 billion times without being consumed.

Turnover Number

The number of substrate molecules that an individual enzyme molecule converts into product each second, generally ranging from 1 to 500,000.

Energy of Activation

The minimum amount of energy required to trigger a chemical reaction.

Apoenzyme

The inactive protein portion of an enzyme that requires an activating cofactor to become functional.

Cofactor

The nonprotein component of an enzyme, which may be an inorganic metal ion (such as $Mg^{2+}$ or $Ca^{2+}$) or an organic molecule.

Coenzyme

An organic cofactor molecule, frequently derived from vitamins, such as $NAD^+$ (derived from niacin) or Coenzyme A (derived from pantothenic acid).

Holoenzyme

The complete, catalytically active whole enzyme consisting of an apoenzyme combined with its cofactor.

Active Site

The specific localized region on an enzyme's surface that binds directly and specifically to substrate molecules.

Oxidoreductases

The class of enzymes that catalyze oxidation-reduction reactions, including dehydrogenases and oxidases.

Transferases

The class of enzymes that transfer functional chemical groups (such as amino or phosphate groups) from one molecule to another.

Hydrolases

The class of enzymes that catalyze hydrolysis reactions by breaking chemical bonds using water.

Lyases

The class of enzymes that remove groups of atoms from substrates without involving hydrolysis.

Isomerases

The class of enzymes that catalyze the geometric or structural rearrangement of atoms within a single molecule.

Ligases

The class of enzymes that join two chemical molecules together, typically coupled to energy released by ATP hydrolysis.

Denaturation

The loss of a protein's functional three-dimensional tertiary structure due to breakage of hydrogen and noncovalent bonds caused by extremes in temperature or pH.

Saturation Point (Enzymatic)

The substrate concentration at which the active sites on all enzyme molecules are constantly occupied, resulting in the maximum possible reaction velocity.

Competitive Inhibitor

A chemical agent that mimics the substrate and binds directly to the enzyme's active site, preventing substrate binding (e.g., sulfa drugs, AZT).

Noncompetitive Inhibitor

An inhibitor that binds to an allosteric site on an enzyme rather than the active site, altering the active site's conformation so the substrate cannot react effectively (e.g., cyanide, fluoride).

Feedback Inhibition

A metabolic control mechanism (also known as end-product inhibition) in which the final product of an enzymatic pathway allosterically inhibits an early enzyme in the pathway.

Ribozymes

Catalytic RNA molecules discovered in 1982 that contain substrate-binding active sites and specifically cut and splice RNA substrates.

Oxidation

The loss of electrons or hydrogen atoms, or the addition of oxygen, which is accompanied by a loss of chemical potential energy.

Reduction

The gain of electrons or hydrogen atoms, or the loss of oxygen, which is accompanied by a gain of energy.

Cellular Respiration

An ATP-generating catabolic process wherein substrate molecules are oxidized, an electron transport chain is used, and the final electron acceptor is an inorganic molecule.

Glycolysis

The cytoplasmic oxidation of one glucose molecule into two molecules of pyruvic acid ($3\text{C}$), yielding a net of $2\text{ ATP}$ via substrate-level phosphorylation and $2\text{ NADH}$ without requiring oxygen.

Krebs Cycle

An eight-step cyclical series of redox reactions where acetyl CoA ($2\text{C}$) combines with oxaloacetic acid ($4\text{C}$) to form citric acid ($6\text{C}$), releasing $2\text{ CO}_2$ and producing $2\text{ ATP}$, $8\text{ NADH}$, and $2\text{ FADH}_2$ per glucose.

Chemiosmosis

The generation of ATP by ATP synthase as protons ($H^+$) flow down a concentration gradient across a membrane, driven by a proton gradient established by the electron transport chain.

Aerobic Respiration

A cellular respiration pathway in which molecular oxygen ($O_2$) serves as the terminal electron acceptor, generating $38\text{ ATP}$ per glucose in prokaryotes and $36\text{ ATP}$ in eukaryotes.

Anaerobic Respiration

A form of cellular respiration that uses an inorganic molecule other than oxygen (such as nitrate, sulfate, or carbonate) as the final electron acceptor, yielding less ATP ($2\text{ ATP}$ per glucose) than aerobic respiration.

Fermentation

An anaerobic catabolic process that extracts energy from sugars without using the Krebs cycle or an electron transport chain, using an organic molecule as the final electron acceptor and producing $1\text{ or }2\text{ ATP}$.

Lactic Acid Fermentation

A fermentation pathway carried out by organisms like Lactobacillus and Streptococcus where pyruvic acid is reduced to lactic acid, used in making yogurt, sauerkraut, and pickles.

Alcohol Fermentation

A fermentation process carried out by yeasts and some bacteria that converts pyruvic acid into ethanol and $CO_2$.

Phototrophs

Organisms that utilize light as their primary source of energy.

Chemotrophs

Organisms that obtain energy through the oxidation of organic or inorganic chemical compounds.

Autotrophs

Organisms that use carbon dioxide ($CO_2$) as their principal carbon source.

Heterotrophs

Organisms that require organic compounds as their source of carbon.

Chemoheterotrophs

Organisms that use organic compounds as both their energy and carbon sources, including most bacteria, all fungi, protozoans, and animals.

Chemoautotrophs

Organisms that obtain energy from inorganic chemicals (such as $H_2S$, $NH_3$, $S$, $H_2$, or $Fe^{2+}$) and utilize $CO_2$ as their carbon source.

Photoheterotrophs

Organisms that use light as their energy source and organic compounds as their carbon source, such as green and purple nonsulfur bacteria.

Photoautotrophs

Organisms that use light as their energy source and carbon dioxide ($CO_2$) as their carbon source, including photosynthetic bacteria, algae, and plants.

Microbial Growth

The increase in the number of microbial cells in a population over time, rather than an increase in the physical size of individual cells.

Binary Fission

The standard asexual division method of bacteria in which a cell elongates, replicates its DNA, forms a cross-wall, and divides into two daughter cells.

Psychrophiles

"Cold-loving" microbes capable of growth at $0^\circ\text{C}$, including true psychrophiles (optimum $\le 15^\circ\text{C}$) and psychrotrophs (optimum $20\text{ to }30^\circ\text{C}$, which cause low-temperature food spoilage).

Mesophiles

"Middle-loving" bacteria that grow best between $25\text{ and }40^\circ\text{C}$ (optimum commonly $37^\circ\text{C}$), including most human pathogens and common spoilage organisms.

Thermophiles

"Heat-loving" microorganisms that have optimum growth temperatures between $50\text{ and }60^\circ\text{C}$, including hyperthermophiles with optima at $80^\circ\text{C}$ or above.

Danger Zone (Food Spoilage)

The temperature range between $15^\circ\text{C}\text{ and }52^\circ\text{C}$ ($60^\circ\text{F}\text{ to }130^\circ\text{F}$) characterized by rapid bacterial multiplication and possible toxin production.

Acidophiles

Organisms that grow optimally at very low pH levels ($0.1\text{ to }5.4$), such as Lactobacillus.

Neutrophiles

Organisms that grow optimally in the pH range of $5.4\text{ to }8.5$, encompassing the majority of human pathogenic bacteria.

Alkaliphiles

Organisms that grow optimally at alkaline pH values between $7\text{ and }12$ or higher, such as Vibrio cholerae and Alcaligenes faecalis.

Plasmolysis

The osmotic shrinkage of a cell's plasma membrane away from its cell wall that occurs when placed in a hypertonic environment.

Halophiles

Organisms requiring elevated salt concentrations for growth; obligate halophiles require $20\text{ to }30\%\text{ NaCl}$, whereas facultative halophiles tolerate $2\%\text{ or more}$ without requiring it.

Obligate Aerobes

Organisms that strictly require molecular oxygen ($O_2$) to survive and grow (e.g., Pseudomonas).

Facultative Anaerobes

Microbes that utilize oxygen when present for aerobic respiration but can continue growing via fermentation or anaerobic respiration in its absence (e.g., E. coli, Staphylococcus).

Obligate Anaerobes

Microbes that cannot use oxygen and are inhibited or killed by toxic oxygen forms because they lack protective enzymes (e.g., Clostridium).

Aerotolerant Anaerobes

Bacteria that cannot use oxygen for growth but tolerate its presence because they possess protective enzymes such as superoxide dismutase (SOD) (e.g., Lactobacillus).

Microaerophiles

Aerobic organisms that require oxygen to grow but only at low concentrations, being damaged by standard atmospheric levels (e.g., Campylobacter).

Agar

A complex polysaccharide solidifying agent isolated from red algae that melts above $95^\circ\text{C}$, solidifies at $40^\circ\text{C}$, and is not degraded by most microbes.

Chemically Defined Media

A culture medium whose exact chemical composition and specific nutrient quantities are precisely known.

Complex Media

A culture medium made of nutrient-rich extracts from yeasts, meats, or plants (peptones) whose exact chemical composition is unknown and may vary slightly.

Reducing Media

Culture media containing chemical agents (such as sodium thioglycolate) that bind and deplete dissolved oxygen, used to culture obligate anaerobes.

Capnophiles

Microbes that grow best under conditions of elevated carbon dioxide ($CO_2$) and reduced oxygen levels.

Selective Media

Culture media formulated to suppress the growth of unwanted microbes while encouraging the growth of desired organisms (e.g., Sabouraud's Dextrose Agar, Brilliant Green Agar).

Differential Media

Culture media designed to distinguish colonies of a specific target microbe from others based on a visible diagnostic reaction (e.g., Blood Agar showing hemolysis).

Enrichment Culture

A liquid medium designed to selectively increase very small numbers of a specific organism to detectable levels without necessarily suppressing all other microbes.

Streak Plate Method

A dilution technique where an inoculum is streaked across solid agar with an inoculating loop to isolate individual bacterial cells that grow into discrete pure colonies.

Generation Time

The time required for an individual bacterial cell to divide or for an entire bacterial population to double in number.

Lag Phase

The initial period in a bacterial growth curve characterized by intense metabolic activity and cell growth without an increase in population number.

Log Phase

The period of exponential bacterial growth during which cells divide at a constant minimum generation time and are most metabolically active and vulnerable to antibiotics.

Stationary Phase

The phase of the bacterial growth curve where the rate of cell division equals the rate of cell death, resulting in a stable total population count.

Death Phase

The final phase of a bacterial growth curve (logarithmic decline) where the rate of cell mortality exceeds the rate of new cell production.

Most Probable Number (MPN)

A statistical dilution-to-extinction method that estimates bacterial population numbers based on positive and negative growth in multiple liquid broth tubes.

Turbidity

The cloudiness of a liquid bacterial culture, measured using a spectrophotometer to estimate cell density without requiring an incubation period.

Sterilization

The destruction or complete removal of all forms of microbial life, including bacterial endospores, from a material or object.

Commercial Sterilization

A limited heat treatment intended to destroy endospores of Clostridium botulinum in canned foods without destroying endospores of nonpathogenic thermophiles.

Disinfection

The reduction of pathogenic microorganisms on inanimate objects to a level where they no longer pose a disease threat, targeting vegetative pathogens.

Antisepsis

The chemical destruction or inhibition of vegetative pathogens on living tissue.

Degerming

The mechanical removal of microbes from a limited area, such as swabbing human skin with an alcohol pad prior to injection.

Sanitization

The treatment of food-handling equipment to reduce microbial populations to safe public health levels, such as using hot soap and water.

Asepsis

The absence of significant microbial contamination; achieved via aseptic techniques designed to prevent infection in surgery and medicine.

Bacteriostatic Agent

A biological or chemical agent that stops or inhibits bacterial growth without killing the organisms.

Thermal Death Point (TDP)

The lowest temperature at which all microorganisms in a liquid suspension are killed within exactly 10 minutes.

Thermal Death Time (TDT)

The minimal length of time required to kill all bacteria in a liquid culture at a specified temperature.

Decimal Reduction Time (DRT)

The time in minutes required to kill $90\%$ of a bacterial population at a specified temperature.

Autoclave

A sterilization apparatus that utilizes moist steam under pressure ($121^\circ\text{C}$ at twice atmospheric pressure) to kill all vegetative organisms and endospores within 15 minutes.

Pasteurization

A controlled heating method (e.g., flash pasteurization at $72^\circ\text{C}$ for 15 seconds) that reduces microbial counts in beverages to prevent spoilage without damaging flavor.

High-Efficiency Particulate Air (HEPA) Filter

A specialized air filter designed to remove microorganisms from the air in clinical environments such as operating rooms and burn units.

Lyophilization

A preservation method (freeze-drying) that combines rapid freezing with water removal under a vacuum to preserve microbial cultures indefinitely.

Ionizing Radiation

Short-wavelength radiation ($< 1\text{ nm}$, e.g., gamma rays and X-rays) that dislodges electrons to create reactive ions and lethal DNA mutations, used to sterilize pharmaceuticals and medical supplies.

Nonionizing Radiation

Radiation with wavelengths longer than $1\text{ nm}$ (specifically ultraviolet light) that damages DNA by forming thymine dimers, inhibiting transcription and replication.

Oligodynamic Action

The antimicrobial capability of tiny amounts of heavy metal ions (such as silver, copper, mercury, and zinc) to denature proteins.

Quaternary Ammonium Compounds (Quats)

Cationic surface-active detergents that disrupt cellular membranes, effective against Gram-positive bacteria, fungi, and enveloped viruses.

Glutaraldehyde

A chemical aldehyde sterilizing agent (commonly $2\%$ Cidex) that cross-links proteins, acting as a bactericide in 10 minutes and a sporicide in 3 to 10 hours.

Ethylene Oxide

A gaseous chemical sterilant that replaces protein functional groups with alkyl groups, killing all microbes and endospores in closed chambers over 4 to 18 hours.

Peracetic Acid

A liquid peroxygen sterilant that destroys bacteria and fungi in under 5 minutes and endospores within 30 minutes without leaving toxic residues.

Disk Diffusion Method

A standard laboratory method to assess disinfectant effectiveness by applying chemical-soaked filter paper disks to an inoculated agar plate and measuring the resulting clear zone of inhibition.