Microbiology: Microbial Death, Environmental Microbiology, and Industrial Microbes

Comprehensive vocabulary flashcards covering microbial death, physical and chemical antimicrobial control, environmental microbial ecology and biogeochemical cycles, water/sewage treatment, and industrial biotechnology applications.

Biofilm

A structured community of microorganisms that adhere to a surface and secrete a protective extracellular matrix (slime layer) that shields them from antimicrobial agents and immune cells.

Quorum Sensing

The mechanism by which bacteria coordinate gene expression and community behaviors in response to local population density through the production and release of chemical signaling molecules called autoinducers.

Bactericidal

An agent, drug, or process that kills bacterial cells outright (such as penicillin).

Bacteriostatic

An agent, drug, or environmental condition that inhibits the growth and reproduction of bacteria without killing them (such as tetracycline or low temperatures).

Sterilization

The complete destruction or removal of all viable forms of microbial life, including vegetative cells and bacterial endospores (with the possible exception of prions); commonly achieved using steam under pressure or sterilizing gases like ethylene oxide.

Commercial Sterilization

A heat treatment protocol designed to eliminate endospores of $Clostridium\text{ }botulinum$ in canned foods without destroying food quality; more heat-resistant thermophilic endospores may survive, but they will not germinate at normal storage temperatures.

Disinfection

The destruction or removal of vegetative pathogens on inanimate surfaces or objects using physical or chemical methods.

Antisepsis

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

Degerming

The mechanical removal of microbes from a limited localized area, such as cleaning the skin around an injection site using soap and water or an alcohol-soaked swab.

Sanitization

Treatment intended to lower microbial numbers on eating and drinking utensils to safe public health levels, typically accomplished through high-temperature washing or immersion in a chemical disinfectant.

Autoclave

A specialized chamber that uses moist heat as pressurized steam—typically operating at $121\,^{\circ}\text{C}$ at $15\,\text{psi}$ for $15\,\text{min}$—to coagulate and denature proteins, successfully killing all vegetative organisms and endospores.

High-Temperature Short-Time (HTST) Pasteurization

A pasteurization treatment applying $72\,^{\circ}\text{C}$ for $15\,\text{sec}$ to substantially lower microbial counts and eliminate pathogens without destroying product quality.

Ultra-High-Temperature (UHT) Treatment

A heat sterilization method that exposes liquid food to $140\,^{\circ}\text{C}$ for $4\,\text{sec}$, rendering products shelf-stable for months without refrigeration.

Hot-Air Sterilization

A dry heat sterilization protocol carried out in an oven by maintaining a temperature of $170\,^{\circ}\text{C}$ ($338\,^{\circ}\text{F}$) for $2\,\text{hours}$.

High-Efficiency Particulate Air (HEPA) Filter

A screen-like filtration matrix configured to remove all airborne particulate matter and microorganisms larger than $0.3\,\mu\text{m}$ in diameter.

Membrane Filter

A porous synthetic filter typically with a pore size of $0.22\,\mu\text{m}$ (or down to $0.01\,\mu\text{m}$ to retain viruses and large proteins), employed to sterilize heat-sensitive liquid solutions.

Desiccation

The removal or absence of moisture from microbial cells, inhibiting cellular metabolic reactions and vegetative proliferation.

Ionizing Radiation

High-energy radiation (such as X-rays and gamma rays) that ionizes water molecules to produce reactive hydroxyl radicals and directly shatters microbial DNA; applied to sterilize heat-sensitive pharmaceuticals, single-use medical supplies, spices, and meats.

Nonionizing Radiation

Shortwave ultraviolet radiation (specifically near $260\,\text{nm}$ and $254\,\text{nm}$) that damages microbial DNA by forming covalent bonds between adjacent thymine bases (thymine dimers), blocking transcription and replication.

Disk-Diffusion Method

A standardized assay in which absorbent paper filter disks impregnated with defined concentrations of antimicrobials are placed on a bacterial lawn to evaluate chemical efficacy by measuring the resulting clear zone of inhibition.

Phenolics

Chemical derivatives of phenol that kill microbes by injuring lipid-rich plasma membranes and denaturing proteins, causing cytoplasmic leakage.

Triclosan

A bisphenol antibacterial agent previously incorporated into approximately $75\%$ of antibacterial soaps and consumer products that disrupts bacterial fatty acid synthesis and damages plasma membranes.

Biguanides

A class of broad-spectrum chemical antimicrobials (such as chlorhexidine) that disrupt microbial plasma membranes, commonly used for surgical hand scrubs and clinical skin disinfection.

Bacteriocins

Antimicrobial peptides or proteins produced by one bacterial strain that inhibit or kill other closely related bacteria.

Plate Count

A direct enumeration method in which a sample is serially diluted, plated, and incubated; viable cells produce visible colonies on plates showing $30\text{--}300\,\text{CFUs}$, calculated by multiplying colony count by the reciprocal of the dilution factor.

Most Probable Number (MPN) Method

A statistical direct measurement method estimating bacterial density in liquid samples (especially coliforms) by inoculating multiple tubes of broth across decimal dilutions, tallying positive growth tubes, and consulting an MPN index table.

Direct Microscopic Count

A direct cell-counting technique in which a measured volume of bacterial suspension is loaded onto a calibrated ruled counting chamber (cell counter/Petroff-Hausser chamber) and cells are enumerated visually under a microscope.

Biogeochemical Cycles

Natural cyclical pathways in which inorganic and organic forms of vital chemical elements (including carbon, nitrogen, sulfur, and phosphorus) are alternately oxidized and reduced by microorganisms to fulfill their metabolic and energy requirements.

Ammonification

The decomposition stage of the nitrogen cycle during which microbial decomposers break down proteinaceous organic matter into amino acids and subsequently release ammonia ($NH_3$) or ammonium ($NH_4^+$).

Nitrification

The biological two-step oxidation of ammonium ($NH_4^+$) first to nitrite ($NO_2^-$) by bacteria such as $Nitrosomonas$, and then to nitrate ($NO_3^-$) by bacteria such as $Nitrobacter$, yielding a nitrogen compound assimilable by plants.

Denitrification

An anaerobic respiratory process performed by soil bacteria (such as $Pseudomonas$ and $Bacillus\text{ }licheniformis$) that reduces nitrate ($NO_3^-$) to nitrite ($NO_2^-$) and ultimately to nitrogen gas ($N_2$), which escapes into the atmosphere.

Nitrogen Fixation

The enzymatic conversion of free atmospheric nitrogen gas ($N_2$, which constitutes $80\%$ of the atmosphere) into ammonia ($NH_3$), carried out by free-living rhizosphere microbes (fixing $30\%$) or symbiotic root nodule bacteria (fixing $70\%$).

Root Nodule

A specialized swelling on the root of a leguminous plant that houses symbiotic nitrogen-fixing bacteria ($Rhizobium$ or $Bradyrhizobium$) that enter via an infection thread and differentiate into bacteroids.

Lichen

A mutualistic symbiotic organism composed of a fungus and a photosynthetic partner (an alga or a nitrogen-fixing cyanobacterium).

Freshwater Lake Zones

Distinct ecological divisions of a freshwater lake: the nearshore littoral zone with rooted plants; the open sunlit limnetic zone dominated by algae; the deep profundal zone with low oxygen; and the anaerobic benthic zone in bottom sediments.

Littoral Zone

The shallow freshwater zone along the shoreline where sunlight penetrates completely to the sediment, allowing the growth of rooted aquatic vegetation.

Limnetic Zone

The sunlit, open water surface layer of a freshwater body situated away from the shoreline, characterized by abundant dissolved oxygen and photosynthetic algae.

Profundal Zone

The deeper water region located beneath the limnetic layer in freshwater systems, characterized by diminished light penetration and low dissolved oxygen levels.

Benthic Zone

The bottom sediment layer of an aquatic ecosystem with minimal light and oxygen, populated by anaerobic purple and green photosynthetic bacteria, sulfur-reducing bacteria ($Desulfovibrio$) that metabolize $H_2S$, and methanogens.

Eutrophication

An overabundance of nutrients (such as nitrates and phosphates) in bodies of water that prompts massive algal blooms; subsequent microbial decomposition of dead algal biomass consumes and exhausts dissolved oxygen, suffocating aquatic life.

Coliforms

Aerobic or facultatively anaerobic, gram-negative, non-endospore-forming rod-shaped bacteria (predominantly $Escherichia\text{ }coli$) that ferment lactose with acid and gas production within $48\,\text{hours}$ at $35\,^{\circ}\text{C}$, used as indicator organisms to monitor fecal contamination in water.

Flocculation

A municipal water purification step in which chemical flocculants are added to raw water to cause colloidal particles, bacteria, and suspended debris to aggregate and settle out of suspension.

Biochemical Oxygen Demand (BOD)

A quantitative measurement of the biodegradable organic matter present in water, expressed as the amount of dissolved oxygen required by aerobic microorganisms to biologically oxidize the organic pollutants.

Primary Sewage Treatment

The initial physical phase of wastewater treatment in which sewage is screened, skimmed, and placed in sedimentation tanks to separate settleable solids (sludge) from primary effluent, removing $25\text{--}35\%$ of BOD.

Secondary Sewage Treatment

The biological stage of wastewater treatment that harnesses aerobic microbial communities to metabolize dissolved organic matter, achieved via activated sludge systems, trickling filters, or rotating biological contactors.

Activated Sludge System

A secondary sewage treatment process in which air is actively bubbled through primary effluent in aeration tanks to foster a high density of suspended, sewage-metabolizing aerobic microbes, eliminating $75\text{--}95\%$ of BOD.

Trickling Filter

A secondary sewage treatment design where primary effluent is intermittently sprayed over a packed bed of coarse rocks or plastic honeycomb coated with a complex biofilm of aerobic microbes, eliminating $80\text{--}85\%$ of BOD.

Anaerobic Sludge Digester

A sealed, airless tank where anaerobic bacteria ferment and decompose concentrated primary and secondary sewage sludge into stabilized organic matter, $CO_2$, and methane gas ($CH_4$).

Retort

An industrial-scale pressure vessel utilizing pressurized steam—analogous to a giant autoclave—used to commercially sterilize canned foods by destroying heat-resistant endospores of $Clostridium\text{ }botulinum$.

Thermophilic Anaerobic Spoilage

Spoilage occurring in low-acid canned foods held at elevated temperatures caused by thermophilic $Clostridium$ species; characterized by gas production that visibly swells or bulges the can, a lowered pH, and a sour odor.

Flat Sour Spoilage

Thermophilic food spoilage caused by $Bacillus\text{ }stearothermophilus$ whose endospores germinate when canned goods are stored warm; it acidifies and sours the food without producing gas, leaving the can ends flat.

Mesophilic Spoilage

Microbial spoilage occurring in room-temperature canned goods caused by leaks or defective seam sealing that allow external environmental bacteria (such as mesophilic $Clostridium$ or $Bacillus$) to enter during cooling.

Pascalization

A non-thermal food preservation method in which prepackaged foods are submerged in water chambers under extreme hydrostatic pressure ($87{,}000\,\text{psi}$) to inactivate vegetative pathogens and preserve flavor.

Curd

The solid, casein-rich coagulum formed during cheese manufacturing by treating milk with the enzyme rennin and lactic acid-producing bacteria.

Whey

The watery liquid residue that separates from the curd during the enzymatic and acidic coagulation of milk proteins in cheese production.

Malting

The brewing process of steeping, germinating, and kilning cereal grains (typically barley) to synthesize endogenous amylase enzymes that convert insoluble starches into fermentable sugars.

Recombinant DNA (rDNA) Technology

A suite of molecular genetic techniques by which scientists join DNA sequences from disparate sources and introduce them into a host organism to modify its genome and express novel products.

Restriction Enzyme

A site-specific bacterial endodeoxyribonuclease that cuts double-stranded DNA at palindromic recognition sequences, frequently generating staggered single-stranded complementary cohesive ends ("sticky ends").

Vector

A self-replicating DNA molecule, such as a circular bacterial plasmid, used in genetic engineering to carry a targeted foreign gene into a recipient host cell.

Blue-White Screening

A molecular cloning screening procedure where bacteria carrying non-recombinant vectors produce an active enzyme metabolizing substrate to yield blue colonies, whereas bacteria containing the inserted recombinant gene have disrupted operons, resulting in white colonies.

Isolation Chip (iChip)

A high-throughput cultivation device housing hundreds of individual diffusion chambers (approximately 400) that allows researchers to grow and isolate novel environmental bacteria in their native soil habitats to discover new antibiotics.