Microbiology Lecture Notes

Comprehensive practice flashcards covering the nature, diversity, physiology, and applications of microorganisms based on the Biology resource book.

Microbiology

The study of small organisms that cannot be clearly observed with the naked eye or without visual aids, usually smaller than $0.1\,mm$.

Microorganisms

Organisms such as bacteria, archaea, cyanobacteria (Blue Green Bacteria - BGB), fungi, and protists, as well as mollicutes ($mycoplasmas$ and $phytoplasmas$), viruses, viroids, and prions.

Micrometer ($\mu m$)

A unit of measurement for microorganisms and their structural components equal to $10^{-6}\,m$.

Nanometer ($nm$)

A unit of measurement for microorganisms and their structural components equal to $10^{-9}\,m$.

Bio-aerosols

Microorganisms suspended in the atmosphere that can travel long distances via air currents and potentially spread diseases.

Extremophiles

Microorganisms that live in extreme environments lethal or unsuitable for other organisms, such as deep seas with high pressure, extreme acidic or alkaline conditions, and hydrothermal vents.

Thermophiles

Extremophiles that exist in high-temperature conditions.

Psychrophiles

Extremophiles that exist in low-temperature conditions.

Acidophiles

Extremophiles that exist in acidic $pH$ conditions.

Alkaliphiles

Extremophiles that exist in alkaline/basic $pH$ conditions.

Halophiles

Extremophiles that require $NaCl$ (salt) to exist.

Barophiles / Piezophiles

Extremophiles that exist under high-pressure conditions.

Generation Time

The relatively short time taken for a microbial population to double, facilitated by a high surface area to volume ratio which increases metabolic rate.

Coccus

A spherical-shaped bacterium.

Bacillus

A rod-shaped bacterium.

Spirillum

A spiral-shaped bacterium with a rigid, corkscrew-like body.

Streptococci

Cocci bacteria that divide in a single plane and remain attached in chain-like patterns.

Staphylococci

Cocci bacteria that divide in multiple planes and form grape-like clusters.

Sarcina

Cocci bacteria that divide in three planes and remain attached in groups of eight.

Vibrio

A spiral-shaped bacterium that appears as a curved rod.

Spirochete

A spiral-shaped bacterium that is flexible.

Hyphae

Fine, tube-like, branched thread-like structures in fungi that together form a mycelium.

Coenocytic Hyphae

Fungal hyphae that do not contain septa (cross-walls) and consist of long continuous cells with many nuclei.

Prions

Small proteinaceous infectious particles that lack nucleic acids.

Mollicutes

Pleomorphic (various shaped) prokaryotes belonging to the Domain Bacteria that typically lack cell walls.

Chemoautotrophs

Microorganisms that use inorganic chemicals as an energy source and inorganic carbon ($CO_2$) as a carbon source.

Photoheterotrophs

Microorganisms that use light as an energy source and organic carbon as a carbon source.

Obligate Aerobes

Microorganisms that require oxygen for survival and produce energy through oxidative phosphorylation.

Obligate Anaerobes

Microorganisms that cannot exist in the presence of oxygen and produce energy through fermentation.

Facultative Anaerobes

Microorganisms that prefer to grow in oxygen using oxidative phosphorylation but can survive in anaerobic environments using fermentation.

Microaerophiles

Microorganisms that live only in oxygen concentrations lower than that found in the air.

Heterocysts

Specialized thick-walled cells in cyanobacteria where nitrogen fixation occurs via the enzyme nitrogenase, protected from oxygen.

Akinetes

Inactive, thick-walled spores in cyanobacteria containing food reserves that are resistant to drought and high temperatures.

Icosahedral

One of the basic morphological symmetries of viruses based on the architecture of the protein capsid.

Bacteriophages

A typical group of viruses that can infect bacteria, multiplying through the lytic or lysogenic cycles.

Lytic Cycle

A viral replication cycle that ends with the lysis (breakdown) and death of the host cell.

Lysogenic Cycle

A viral replication cycle where the viral $DNA$ is incorporated into the host $DNA$ and multiplies without lysing the host.

Viroids

Small pieces of naked $RNA$ without a protective protein coat that infect plants.

Sterilization

The process of destroying or removing all forms of microbial life, including endospores.

Autoclave

An instrument used for moist heat sterilization using steam at $121^\circ\text{C}$ and $15\,\text{psi}$ (1 atmosphere) for $15\,\text{minutes}$, effective against all microbes except prions.

Pasteurization

The use of mild heat to kill pathogens and reduce microbial numbers to prolong the quality of products like milk without damaging taste/texture.

HTST Pasteurization

High-Temperature Short-Time pasteurization which maintains at least $72^\circ\text{C}$ for $15\,\text{seconds}$.

UHT treatment

Ultra-High-Temperature treatment where milk is heated to $140^\circ\text{C}$ for less than $5\,\text{seconds}$ using flashing steam.

Probiotics

Live beneficial bacterial cultures, such as those found in yogurt, that help prevent colonization by pathogens like $Salmonella\,enterica$.

Opportunistic Pathogens

Microorganisms that are usually harmless but cause infection when they move to different body parts or when host conditions change (e.g., $E.\,coli$ causing urinary tract infections).

Pathogenicity

The ability of a pathogen to cause disease by overcoming the host's defense mechanisms.

Virulence

The degree or intensity of pathogenicity of a microorganism.

Endotoxins

Heat-stable lipopolysaccharides ($LPS$) found in the cell walls of Gram-negative bacteria that are released when the bacteria die.

Exotoxins

Heat-labile proteins, mostly enzymes, produced inside bacteria and secreted or released following lysis; highly toxic even in small amounts.

Enterotoxins

Exotoxins that abnormally stimulate cells in the gastrointestinal tract, such as the toxin produced by $Vibrio\,cholerae$.

Antiseptics

Chemicals used to kill or reduce microbial populations that are safe for direct application on living tissues like skin.

Disinfectants

Chemicals used to destroy microbes on inanimate surfaces (sinks, drains, etc.) and are not safe for use on living tissue.

Broad-spectrum Antibiotics

Antibiotics that are effective against a wide range of bacterial species.

Vaccine

A suspension of weakened pathogens or microbial parts used to induce immunity/protection against a disease.

Single Cell Protein (SCP)

Protein-rich microbial cells grown on a large scale as food supplements, such as $Spirulina\,sp.$ and $Chlorella\,sp.$

Acetobacter

A genus of bacteria used in the second step of vinegar production to aerobicly oxidize ethanol into acetic acid.

Leaching

The process of using microorganisms to extract metals (like copper, uranium, or gold) from low-grade ores.

Reting

The process of loosening plant fibers (like coir) by immersing plant material in water, involving bacteria that secrete pectinase.

Bioremediation

The technology of using organisms (mostly microbes) to remove, degrade, or detoxify environmental pollutants.

Bio-fertilizers

Inoculated microorganisms used to increase the bioavailability of nutrients like nitrogen ($N$) and phosphorus ($P$) in agricultural systems.

Myco-insecticides

Entomopathogenic fungi formulated to infect and kill a broad range of insects.

Bt toxin

A protein crystal produced by $Bacillus\,thuringiensis$ that is toxic to insect larvae upon ingestion by breaking down their gut tissues.

Mineralization

The decomposition of plant and animal remains by microbial extracellular enzymes, breaking complex organic matter into simple inorganic substances like $CO_2$ and $H_2O$.

Ammonification

The process by which microbes decompose proteins into amino acids and then convert the amine groups into ammonia ($NH_3$) or ammonium ions ($NH_4^+$).

Nitrification

The two-step process of oxidizing ammonium ions into nitrate ($NO_3^-$) by bacteria like $Nitrosomonas$ and $Nitrobacter$.

Denitrification

The reduction of nitrates into nitrogen gas ($N_2$) by microbes like $Pseudomonas\,sp.$ in anaerobic conditions, such as waterlogged soil.

Rhizosphere

The dynamic micro-environment in the soil within a few millimeters of plant roots where symbiotic interactions occur between plants and microbes.

Mycorrhiza

A symbiotic association between plant roots and fungi (myco = fungus, rhiza = root) that helps the plant absorb water and immobile nutrients like phosphorus and zinc.

Coliform Bacteria

Aerobic or facultatively anaerobic, Gram-negative, non-endospore-forming, rod-shaped bacteria that ferment lactose with gas production within 48 hours at $35^\circ\text{C}$; used as indicators of fecal contamination in water.

Algal Blooms

Excessive growth of cyanobacteria and algae in water bodies caused by nutrient enrichment (eutrophication).

Activated Sludge System

A secondary wastewater treatment method using mechanical aeration to promote the growth of aerobic bacteria and rapid microbial oxidation.

Putrefaction

The breakdown of proteins in food by proteolytic microbes into amino acids, amines, ammonia, and hydrogen sulfide ($H_2S$), leading to spoilage.

Rancidity

Food spoilage where lipolytic microorganisms break down lipids into fatty acids and glycerol.