Microbiology Lecture 1

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Questions and Answers

What is the main function of flagella?

Protein synthesis

Reproduction

Locomotion (correct)

Sensory organelle

What is the composition of the filament of flagella?

Flagellin

Gliding motility is faster than swimming.

False

Flagellar biosynthesis involves the growth of the filament from the __________.

tip Signup and view all the answers

Match the following terms with their descriptions:

Biofilms = Adhered bacterial cells enclosed in an adhesive matrix Pseudomonas aeruginosa = Forms biofilms in Cystic Fibrosis lungs Quorum sensing = Intra- and interspecies signaling in biofilms Anaerobic microorganisms = Grow in environments with low oxygen levels Signup and view all the answers

Who was the first to describe bacteria, also known as animalcules?

Antoni van Leeuwenhoek Signup and view all the answers

Louis Pasteur developed the concept of spontaneous generation.

False Signup and view all the answers

What is the function of pure culture in microbiology?

obtaining only a single kind of microbe Signup and view all the answers

Gram-positive bacteria appear violet/purple and gram-negative bacteria appear ____ after staining.

red Signup and view all the answers

Match the microbial structure with its description:

Cytoplasmic Membrane = Stabilized by hydrogen bonds and hydrophobic interactions Cell walls = Contain up to 90% peptidoglycan Capsules and Slime Layers = Polysaccharide or protein layers Fimbriae = Enable organisms to stick to surfaces or form pellicles Endospores = Highly differentiated cells resistant to heat, harsh chemicals, and radiation Signup and view all the answers

What is pasteurization?

Quick process of using precisely controlled heat to reduce the microbial load in heat sensitive liquids Signup and view all the answers

What does Ultra High Temp pasteurization involve?

Heating at 140°C for 2-5 seconds Signup and view all the answers

Ionizing Radiation can be used for sterilization in the medical field and food industry.

True Signup and view all the answers

Chemical ________ can be categorized as Bacteriostatic, Bacteriocidal, and Bacteriolytic.

Antimicrobials Signup and view all the answers

What is the consequence of abrupt changes in an animal's diet in terms of rumen acidification?

Rumen acidosis Signup and view all the answers

We have more bacterial cells than human cells in our body.

True Signup and view all the answers

What type of culture is characterized by a fixed volume and shows four distinct phases of growth?

batch culture Signup and view all the answers

______ is defined as the time per generation in microbial growth.

Generation time Signup and view all the answers

Match the environmental factor with its effect on microbial growth:

pH = Can range from acidophiles to neutrophiles Temperature = Exhibits psychrophiles, mesophiles, thermophiles, and hyperthermophiles Osmotic effects = Influence water activity and ability to grow in solute-rich environments Oxygen = Affects growth of aerobes, anaerobes, and facultative organisms Signup and view all the answers

Study Notes

Microorganisms and Their Importance

Microorganisms make up the largest mass of living material on Earth
The first cells appeared between 3.8 and 3.9 billion years ago, and life was exclusively microbial until ~1 billion years ago
Microorganisms play a crucial role in cleaning up pollutants (bioremediation)

Macronutrients and Micronutrients

Macronutrients:
- Carbon: required by all cells, makes up ~50% of a typical bacterial cell, and is a major element in all classes of macromolecules
- Nitrogen: makes up ~13% of a typical bacterial cell, and is a key element in proteins, nucleic acids, and other cell constituents
- Phosphorus: necessary for the synthesis of nucleic acids and phospholipids
- Sulfur: found in sulfur-containing amino acids, vitamins, and coenzyme A
- Magnesium: stabilizes ribosomes, membranes, and nucleic acids, and is required for many enzymes
- Calcium: helps stabilize cell walls in microbes, and plays a key role in heat stability of endospores
Micronutrients:
- Trace elements: boron, chromium, cobalt, iron, manganese, nickel, zinc, and molybdenum
- Growth factors: organic compounds required in small amounts by certain organisms, such as vitamins, amino acids, purines, and pyrimidines

Culture Media

Selective media: contains compounds that selectively inhibit the growth of some microbes, but not others
Differential media: contains an indicator that detects particular chemical reactions occurring during growth
Pure culture: a liquid culture or a plate containing only a single kind of microbe

Microscopy

Light microscopy:
- Bright-field: specimens are visualized due to differences in contrast between the specimen and surroundings
- Positively charged dyes can be used to stain cells and improve their contrast
- Differential stains: separate bacteria into groups, such as Gram-positive and Gram-negative
3D microscopy:
- DIC (differential interference contrast) microscopy: gives structures a 3D appearance
- AFM (atomic force microscopy): can image and measure the size of material at the nanoscale
- CSLM (confocal scanning laser microscopy): applications include thick biofilms and microbial ecology

Microbial Metabolic Diversity

Chemoorganotrophs: obtain energy from the oxidation of organic molecules
Chemolithotrophs: obtain energy from the oxidation of inorganic molecules
Phototrophs: contain pigments that allow them to use light as an energy source
Autotrophs: use CO2 as their carbon source
Heterotrophs: require one or more organic molecules for their carbon source
Extremophiles: inhabit extreme environments, such as boiling hot springs and high-pH environments

Microbial Structure and Function

Cytoplasmic membrane: embedded proteins, stabilized by hydrogen bonds and hydrophobic interactions
Cell walls:
- Gram-positive bacteria: contain up to 90% peptidoglycan
- Gram-negative bacteria: outer membrane with porins and periplasm
Cell surface structures:
- Capsules and slime layers: polysaccharide or protein layers that assist in attachment to surfaces
- Fimbriae: filamentous protein structures that enable organisms to stick to surfaces
- Pili: filamentous protein structures that facilitate genetic exchange between cells

Microbial Inclusions

Polyphosphates: accumulations of inorganic phosphate
Sulfur globules: composed of elemental sulfur
Magnetosomes: magnetic storage inclusions
Gas vesicles: confer buoyancy in planktonic cells
Endospores: highly differentiated cells resistant to heat, harsh chemicals, and radiation

Locomotion

Flagellum: structure that assists in swimming and motility
Gliding motility: flagella-independent motility

Microbial Ecology

Microbes account for ~50% of all biomass on Earth
Commensalism: one species benefits, and the other is neither harmed nor helped
Ammensalism: one species doesn't benefit, but the other is harmed
Most microbial growth takes place on the surfaces of soil particles
Geosmin: formed by certain bacteria that gives a characteristic earthy aroma when rain falls after a dry spell of weather

Biofilms

Assemblages of bacterial cells adhered to a surface and enclosed in an adhesive matrix
Initiated by attachment of a cell to a surface followed by expression of biofilm-specific genes
Formation of AHL (acylated homoserine lactones) and matrix formation
Both intra- and interspecies signaling likely occur in biofilms (quorum sensing)
Biofilms resist physical forces, phagocytosis, and penetration of toxins
Allows cells to remain in a favorable niche and provides a consistent source of nutrients

Mutualistic Interactions

Legume–root nodule symbiosis: mutualistic relationship between leguminous plants and nitrogen-fixing bacteria
Microbe-insect symbiosis: horizontal and vertical transmission of symbionts
Epibionts consortia: microbial mutualisms in freshwaters
Lichens: mutualistic relationship between a fungus and an alga (or cyanobacterium)### Symbiotic Relationships
Primary symbionts: required for host reproduction, restricted to specialized region bacteriome, and found in bacteriocytes
Secondary symbionts: not required for host reproduction, not always present in every individual, can invade different cells and live extracellularly, and must provide a benefit such as nutrition, protection from environment stresses, or protection from pathogens

Microbial Interaction with Termites

Termites decompose cellulose and hemicellulose
Termite gut consists of foregut, midgut, and hindgut
Posterior alimentary tract of higher termites (Termitidae) contains a diverse community of anaerobes, including cellulolytic anaerobes
Lower termites contain anaerobic bacteria and cellulolytic protists

Marine Invertebrates at Hydrothermal Vents and Gas Seeps

Association is mostly mutualistic
Bacteria supply organic compounds, while animals supply electron donors for energy metabolism and a safe place to live

Symbiosis with Leeches

Leeches are parasitic annelids (segmented worms) that feed on vertebrate blood and secrete anticoagulants and vasodilators
In the digestive tract, the crop has Aeromonas and a Rikenella-like bacterium, while the bladder is packed with Ochrobactrum

Reef Building Corals

Coral skeleton is a very efficient light-gathering structure
Large surface area of animal body is well-suited to capture light
Found in clear tropical waters (low nutrient condition for animals)
Phototrophic symbionts include cyanobacterium, rhodophytes, chlorophytes, dinoflagellates, and diatoms
Most ecologically significant symbiosis is between stony coral and the dinoflagellate Symbiodinium
Bleaching is the loss of color caused by lysis of symbiont, which can be triggered by high temperature and high light, impairing the photosynthetic apparatus of the dinoflagellate

Microbes in Mammalian Gut

Microbial associations with certain animals led to their ability to catabolize plant fibers
Plant fibers are composed of insoluble polysaccharides, with cellulose being the most abundant component
Two digestive plans: foregut fermentation and hindgut fermentation
Ruminants, such as cows, sheep, and goats, possess a special digestive organ (the rumen) that contains a diverse community of microbes, including cellulolytic microbes

Human Microbiome

We are more microbes than human, with 10-100 times more bacterial cells than human cells
Important for proper maturation of the immune system, preventing growth of pathogenic bacteria in the mucosa, reducing predisposition to allergies, lactose, and gluten insensitivities
Atherosclerosis is associated with the metabolism of L-carnitine by the intestinal microbiota

Bacterial Growth

Increase in number of cells, rather than size
Accumulate in colonies on solid medium
Cell division: each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell
Binary fission: cell division following enlargement of a cell to twice its minimum size
Growth: increase in the number of cells
Generation time: time required for microbial cells to double in number
Budding division results in a totally new daughter cell

Batch Culture

A closed-system microbial culture of fixed volume
Typical growth curve for population of cells grown in a closed system is characterized by four phases: lag, exponential, stationary, and death
Exponential growth: growth of a microbial population in which cell numbers double within a specific time interval
Generation time (G) is defined as the time (t) per generation (n = number of generations): G=t/n

Continuous Culture

Constant working volume, open-system microbial culture
In bioreactor, affluent and effluent flows have the same volume/hr rate
Maintain proper pH conditions, and can connect acid and base inputs to regulate pH with a sensor
Find growth rate first to maintain steady-state, and low dilution rate corresponds to higher growth

Chemostat

Most common type of continuous culture device
Both growth rate and population density of culture can be controlled by adjusting the flow of fresh medium/limiting nutrient
Dilution rate: rate at which fresh medium is pumped in and spent medium is pumped out
Chemostat cultures are sensitive to the dilution rate and limiting nutrient concentration

Chemostat Variations

Turbitostat: feedback is between the turbidity of the culture vessel and the dilution rate
Auxostat: measurement taken from growth vessel to control the media flow rate (pH, oxygen tension, metabolite concentration, etc.)
Retentostat: use biomass, mainly for anaerobic conditions
Fed-batch: measuring major C or N sources and using that information to feed culture, more manual method

Microbial Growth Measurements

Microscopic counts: Petroff-Hausser counting chamber with grids
FACs: flow cytometer using laser-based technology to count and sort cells
Viable counts: measurement of living, reproducing population
Spread-plate method: measurement of living, reproducing population
Turbidimetric method: measurement of microbial growth based on the optical density of the culture

Environmental Factors Affecting Microbial Growth

Temperature: can grow in many different temperatures, with optimal temperature for growth
Psychrophile: low temperature (cold lovers), permanently cold environments
Psychrotolerant: can grow at 0 degrees but optimum is a little higher, adapted due to evolution
Mesophile: midrange temperature optima, warm-blooded animals, human intestinal and gut microflora
Thermophile: high temperature (heat lovers), 45-80°C
Hyperthermophile: very high temperature (above 80°C)

pH

Some organisms have evolved to grow best at low or high pH, but most organisms grow best between pH 6 and 8 (neutrophiles)
Acidophile: organisms that grow best at low pH
Pectinase enzymes can digest pectin, a major component of fruit, and are activated at low pH

Osmotic Effects

Range between 0-1, water activity
Halotolerant: organisms that can tolerate some reduction in water activity of the environment but generally grow best in the absence of the added solute
Halophile: organisms that grow best at reduced water potential, with a specific requirement for some NaCl to grow
Osmophile: organisms that live in environments high in sugar as solute (high osmotic pressure)
Xerophile: organisms able to grow in very dry environments (less than 0.75 aw)

Oxygen

Aerobe: requires oxygen to live
Anaerobe: does not require oxygen and may even be killed by exposure
Facultative organism: can live with or without oxygen
Aerotolerant anaerobe: can tolerate oxygen and grow in its presence even though they cannot use it
Microaerophile: can use oxygen only when it is present at levels reduced from that in air

Microbial Growth Control

Sterilization: the killing or removal of all viable organisms within a growth medium
Inhibition: effectively limiting microbial growth
Decontamination: the treatment of an object to make it safe to handle
Disinfection: directly targets the removal of all pathogens, not necessarily all microorganisms

Heat Sterilization

The most widely used method of controlling microbial growth
Denature macromolecules like enzymes and proteins
Amount of time required to reduce viability tenfold is called the decimal reduction time

Radiation Sterilization

Microwaves, UV, and X-rays can reduce microbial growth
UV is useful for decontamination of surfaces
Ionizing radiation: electromagnetic radiation that produces ions and other reactive molecules

Filter Sterilization

Filtration to avoid the use of heat on sensitive liquids and gases
Pores of filter are too small for organisms to pass through
HEPA (High efficiency particulate air) filters for biosafety applications

Chemical Antimicrobials

Bacteriostatic: inhibit growth, but cells can survive if concentration is low
Bacteriocidal: can kill bacteria, dead cells are not destroyed and can interfere with Optical Density
Bacteriolytic: kill by lysing bacteria, cytoplasmic contents are released

Chemical Growth Control

Minimum inhibitory concentration (MIC) is the smallest amount of any chemical agent needed to inhibit growth of a microorganism
Disc diffusion assay (Kirby-Bauer method): tiny small paper disks, put antibiotics on it, look for areas of inhibition

Antimicrobials in vivo

Antimicrobial drugs are classified on the basis of mechanism of action, spectrum of antimicrobial activity, molecular structure### Quinolones
Interfere with DNA gyrase, preventing supercoiling of DNA
Active against both Gram-positive (G+) and Gram-negative (G-) forms of bacteria
Examples: Ciprofloxacin, Moxifloxacin used to treat UTI, Anthrax, TB, and Respiratory diseases in animals

Fungal Cell Walls

Major component of fungal cell walls is chitin, which can be targeted by drugs

Antibiotics

Naturally produced antimicrobial agents, with less than 1% being clinically useful
Can be modified to enhance efficacy (semisynthetic antibiotics)
Susceptibility of microbes to different antibiotics varies greatly
Broad-spectrum antibiotics are effective against both G+ and G- bacteria (e.g., Tetracycline)

Antibiotic Targets

Ribosomes (inhibiting protein synthesis)
Cell wall
Cytoplasmic membrane
Lipid biosynthesis
DNA replication and transcription

β-Lactam Antibiotics

One of the most important groups of antibiotics
Examples: Penicillins, Cephalosporins, Cephamycins
Over half of all antibiotics used worldwide
Target cell wall synthesis

Penicillin

Discovered by Alexander Fleming in 1929
Primarily effective against Gram-positive bacteria
Some synthetic forms are effective against some Gram-negative bacteria
Penicillin G is naturally occurring, while others are synthetic

Cephalosporins

Produced by fungus Cephalosporium
Same mode of action as Penicillins
Commonly used to treat Gonorrhea
Example: Ceftriaxone has a 6-member dihydrothiazine ring, making it resistant to most β-lactamases

Antibiotics from Prokaryotes

Aminoglycosides: contain amino sugars bonded by glycosidic linkage
Inhibit protein synthesis
Target 30S subunit of ribosome
Clinically effective against Gram-negative bacteria
Not commonly used today due to serious side effects

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This quiz covers the introduction to microbiology, including the history of microorganisms, their evolution, and the discovery of microbes by Robert Hooke and Antoni van Leeuwenhoek.