Microbiology Exam 1

What is a microbe?

Generally, organisms that require a microscope to be seen

What is the size of a microbe?

Generally, 0.2 microns to a few millimeters

*Caulerpa taxifolia* is an exception (invasive species that can be a few meters long)

What type of cells are microbes?

Prokaryotes and eukaryotes

Single-celled or multicellular

How diverse are microbes?

Populous

300-400 species on the hands alone, 15% shared among people

Where are microbes found?

Everywhere: deep sea thermal vents to Mt. Everest

How do microbes help society/environment?

Source of nutrients and can carry out photosynthesis

Aid in the production of food, beverages, antibiotics, and vitamins

What can microbes cause in plants and animals?

Disease

What historical events did microbes play a large role in?

The plague

Civil War (and war in general)

What were the earliest hints of microbes?

As early as 10,000 BCE

\-fermentation, copper recovery, disease

\-fossil records place microbes on the planet 4 billion years ago

What century introduced microscopes?

17th century

What century connected microbes to disease?

19th century

Robert Hooke

Compound microscope (2 lenses)

Magnification of 25x

Cork = cells

Unable to see microbes

Antony van Leeuwenhoek

First person to observe and describe microorganisms accurately

Refined the lenses to be more accurate

Observed pond water, feces, teeth scrapings

Experimented about control of bacteria (hot coffee experiment)

Spontaneous generation

The theory that living creatures could arise without parents

Vitalists

Believed that a vital life force was required for the spontaneous generation of life

Francesco Redi

Need to have life to create more life

Redi experiment

Three containers with a steak in each. The one left uncovered led to flies and maggots on the steak, the flask sealed with a cork had no flies, and the flask covered with gauze lead to flies and maggots but on the gauze

John Needham (experiment)

Mutton broth in flasks → boiled → sealed

Needham results

Broth became cloudy (turbid) indicating the growth of microbes

Contamination, exposed to air for too long

Lazzaro Spallanzani (experiment)

Mutton broth in flasks → sealed → boiled

Spallanzani results

Broth remained clear (free of microbes)

Louis Pasteur

Observed yeast cells in wine

Demonstrated microorganisms carried out fermentations, helping French wine industry

Developed pasteurization (killing bacteria) to avoid wine spoilage by microbes

Swan neck flask experiments

Nutrient solution in flask

Created flask with long, swan neck

Boiled the solutions

Left solutions open to air

Results: no growth

John Tyndall

Broth (hay infusion-from soil) sometimes gave rise to microbes, no matter how long it was sterilized by boiling

His experiment-repeated cycles of boiling and resting

Lead to endospores

Endospores

A tough heat resistant structure that forms around bacteria, takes time to break through and kill off bacteria

Scientific method

Make several observations

Make a hypothesis

Conduct experiments to support or not support the hypothesis

Accept, reject, or modify

Ignaz Semmelweis

Observed puerperal fever that led to death in patients that had just given birth (mid wives did not have this problem)

Microbes can be transferred from person to person

Stressed the importance of hand washing-lost his job

Joseph Lister

Observed death in surgical patients due to infections after surgery

Microorganisms in the air could be responsible

Developed chemical methods for disinfection of tools and for skin

John Snow

Cholera epidemic in London

Interviewed healthy and sick people and plotted cholera on the map

Linked cholera to the contaminated water pump

Importance of water cleanliness

Germ theory of disease

Many diseases are caused by microbes

Robert Koch

Founder of the scientific method of microbiology

Applied methods to numerous lethal diseases

Koch’s postulates

What important principle of epidemiology did Koch demonstrate?

Chain of infection

What is needed to prove a particular bacterium caused a specific disease

Pure culture

Angelina and Walther Hesse

Solid medium using agar

Julius Petri

Double-dish container

Koch’s postulates

Criteria for establishing a causative link between an infectious agent and a disease

\-Microbe is always present in the diseased host

\-Microbe is grown in pure culture

\-Introduce pure microbe into healthy host

\-Same microbe re-isolated from now-sick individual

When will Koch’s postulates not work?

Viruses

Diseases that are not caused by microbes

Mary Montagu introduced what practice?

Smallpox inoculation in 1717

What did Edward Jenner do?

He deliberately infected patients with matter from cowpox lesions

Administered cowpox to 8 yr old boy, 2 weeks later exposed the boy to smallpox and was safe

What did Dmitri Ivanosky study?

Tobacco mosaic disease-agent of transmission could pass through a porcelain filter that blocked all known microbes

Martinus Beijernick

The agent of tobacco mosaic disease is not a bacterium, because it passes through a filter that retains bacteria

What did Wendell Stanley do?

Purified and crystallized filterable agent-Tobacco mosaic virus (TMV)

Sergei Winogradsky and Martinus Beijernick

Studied soil microorganisms and discovered numerous interesting metabolic processes

Pioneered the use of enrichment cultures and selective media

Kingdoms and domains

Trying to make sense of the taxonomic relationships

Ernest Haeckel

Microbes are neither plants nor animals, they are a third kind of life called Monera

Herbert Copeland

Divided monera into two groups: eukaryotic protists (protozoa and algae) and prokaryotic bacteria

Robert Whittaker

Added fungi as a fifth kingdom of eukaryotic microbes

Five kingdom system

Implies an evolutionary lineage

Includes more characterization than the three-kingdom system

Monophyletic relationship

Start simple and evolve into something more complex

Lynn Margulis

Serial endosymbiosis theory

Carl Woese

Studied recently discovered prokaryotes in hot springs that produced methane

What did Woese analyze and reveal?

Analyzed the 16S rRNA which revealed a distinct form of life called archaea

16S rRNA

Part of the 30S ribosome

Associates with about 21 proteins

The gene that codes for 16S rRNA is \~1550bp

Highly conserved

Misconception of prokaryotes

That they are only unicellular-99% exist as a community

Misconception of eukaryotes

That they are multicellular

Examples of unicellular eukaryotes: algae, protists, fungi

Biofilm

A “multi-cellular state” where survival requires chemical communication and cooperation between cells

Are bacteria simple or complex

Complex

What makes bacteria so complex (5 things)

Complex gene control (DNA, genetic material)

Complex biochemical processes for growth and metabolism

Complex responses to the environment (can adapt to)

The ability to reproduce

Complex cellular organization

Bacterial plasma membrane is an…

Absolute requirement

Some bacteria also have internal membrane systems

Functions of bacterial plasma membrane (three things)

Encompass the cytoplasm

Selectively permeable barrier (gases, uncharged molecules)

Houses proteins with functions ranging from biosynthesis to sensing the environment

Membrane lipids

Phospholipid bilayer

**Fluidity**

Consistent thickness

Membrane proteins (6 things)

Comprised of hydrophobic and hydrophilic regions

Structural support

Detect environmental signals

Secretion of virulence factors

Communication with other cells (own species or different)

Ion transport and energy storage

Virulence factors

Make a pathogen more dangerous

Membranes also contain______ and what do they do

Planar molecules; fill gaps between hydrocarbon chains (hopanoids or hopanes in bacteria)

Transport across the membrane

Cell membrane is semi-permeable: nutrients go in, toxins and waste out

Mechanisms of transport

Passive diffusion and facilitated diffusion (with the concentration gradient)

Coupled transport and energy-driven transport systems (against gradient)

Cell wall characteristics (5 things)

Prokaryotes: tough and protective external shell

Protects cell from injury

Maintains cell shape

Maintains water balance

May contribute to pathogenicity (turns organism into pathogens)

Atypical cell walls

Eukaryotic microbes possess their own structures to avoid osmotic shock

Algae form cells walls of cellulose

Fungi form cell walls of chitin

Paramecium possess a contractile vacuole to pump water out of the cell

Mycoplasma lack a cell wall

Archaeal cell wall composition differs-most lack peptidoglycan, pseudopeptidoglycan NAM is replaced by NAT (N-acetylalosamineuronic acid)

The cell wall is…

A single molecule

Peptidoglycan

Mesh like polymer of identical subunits forming long strands

Two alternating sugars (NAG & NAM)

NAM lactate group is linked to 4-6 amino acids (Alanine and Glutamic acid)

Additional envelope layers provide what

Structural support and protection

Envelope composition defines:

Gram-positive bacteria (thick cell wall/peptidoglycan layer)-dark purple

Gram-negative bacteria (thin cell wall/peptidoglycan layer)-pink

Gram-positive cell walls

Composed primarily of peptidoglycan

Teichoic acids (negatively charged)-help maintain cell envelope, protect from environmental substances, may bind to host cells

Periplasmic space-thinner in gram-positive. enzymes aid in nutrient breakdown

Gram-negative cell walls

More complex than gram positive

Consist of a thin layer surrounded by an outer membrane

Outer membrane composed of lipids, lipoproteins and lipopolysaccharides

No teichoic acids

Larger periplasmic space filled with many enzymes, transport proteins, etc

Lipopolysaccharides (LPS)

Consists of three parts-lipid A (embedded w/in phospholipid bilayer) core polysaccharide, O side chain

Core polysaccharide, O side chain extend out from cell

Importance of LPS (6 things)

Contributes to negative charge on cell surface

Helps stabilize outer membrane structure

May contribute to attachment to surfaces and biofilm formation

Creates permeability barrier

Protection from host defenses

Can act as an endotoxin

Gram-negative outer membrane permeability

More permeable than plasma membrane due to presence of porin proteins and transporter proteins

Porin proteins form channels to let small molecules pass

Glycocalyx characteristics (7 things)

Protection

Prokaryotes secrete this adhering layer of polysaccharides

Encapsulate the cell, provide an extra layer

Slime layer=thin versions, capsule = thick layer

Colonies appear moist and look shiny

High water content protects cells from desiccation

Virulence factor-aids in attachment to cells, may interfere with phagocytosis

Capsules characteristics (4 things)

Usually composed of polysaccharides

Well organized and not easily removed from cell

Visible in light microscope

Protective advantages-resistant to phagocytosis, protect from desiccation, exclude viruses and detergents

S-layer

Surface

Regularly structured layers of protein or glycoprotein that self-assemble

In gram-negative bacteria the S layer adheres to outer membrane

In gram-positive bacteria it is associated with the peptidoglycan surface

S-layer functions

Protect from ion and pH fluctuations, osmotic stress, enzymes, and predation

Maintains shape and rigidity

Promotes adhesion to surfaces

Protects from host defenses potential use in nanotechnology-s-layer spontaneously associates

Thylakoids

Photosynthetic bacteria

Maximize light collection

Lamellae packed with chlorophylls and electron carriers

Photon absorption and energy storage

Carboxysomes-protein covered bodies, CO2 fixation

Storage granules and gas vesicles

Utilized as a nutrition source (digested)

Glycogen source-some bacteria are capable of using other polymers (PHB and PHA)

Found in phototropic and non-phototropic soil bacteria

Gas vesicles-buoyancy

Pili and nanotubes

Pili (fimbriae)-adherence, conjugation (DNA transfer)

Nanotubes-connect bacteria or different species, contribute to biofilm formation, transmit materials from one cell to the next

Why do bacteria move?

Bacteria and archaea have directed movement

Chemotaxis (chemical gradient)-move towards chemical attractants such as nutrients, away from harmful substances, can be applied to temperature, light, oxygen, osmotic pressure, and gravity

How do bacteria move?

Flagellar motility-swimming, swarming

Spirochete motility

Twitching motility (not smooth, pili polymerize → reach out and extend → move forward)

Gliding motility

Sliding motility (product of reproduction)

Flagellar motility

Flagellum rotates like a propeller-very rapid rotation up to 1100rev/sec

Counterclockwise (CCW) rotation causes forward motion (run)

Clockwise (CW) rotation disrupts run causing cell to stop and tumble

Two types: swimming and swarming

Swimming vs Swarming

Swimming-individual cell movement, liquid environment

Swarming-multicellular bacterial surface movement, requires increased flagellar biosynthesis, cell-cell interactions and the presence of a surfactant, peritrichous flagella arrangement

Transition from swimming to swarming results in an increase in the number of flagella on the cell

The benefits of swarming

Enhanced resistance to antibiotics

Enhanced resistance to phagocytosis

Enhanced nutrition and competitiveness from secreted surfactants

Spirochete motility

Multiple flagella form axial fibril which winds around the cell

Flagella remain in periplasmic space inside outer sheath

Corkscrew shape exhibits flexing and spinning movements

Twitching motility

Pili at ends of cell short, intermittent, jerky motions

Cells are in contact with each other and surface

May involve slime

Gliding motility

Gliding-in the absence of flagella, some species can “glide” across a surface

Exact mechanism not clear-slime excretion, surface ratcheting

Promotes movement through environments and social interactions with other cells

Sliding motility

Passive form of surface spreading

Does not require an active motor

Relies on surfactants to reduce surface tensions

Movement is away from the origin (during cell growth)

Chemotaxis

Chemotaxis is the movement of a bacterium in response to chemical gradients

Attractants cause CCW rotation-flagella bundle together, push cell forward, “run”

Repellents cause CW rotation-flagellar bundle fall apart, “tumble”-bacterium briefly then changes direction

Chemotaxis: runs and tumbles

In presence of attractant tumbling frequency is intermittingly reduced and runs in direction of attractant are longer

Behavior of bacterium is altered by temporal concentration of chemical

Chemotaxis away from repellent involves similar but opposite responses

Biofilms

In nature, many bacteria form specialized, surface-attached communities called biofilms-single or multiple species, form on a range of organic or inorganic surfaces

Bacterial biofilms form…

When nutrients are plentiful

Bacterial biofilm formations

Once nutrients become scarce, individuals detach from the community to forage for new sources of nutrients

Biofilms in nature can take many different forms and serve different functions for different species

The formation of biofilms can be cued by different environmental signals in different species

Biofilm formation…

dependent on signals

pH

Iron concentration

Temperature

Oxygen availability

Presence of certain amino acids

Biofilm formation (5 things)

Attachment to monolayer by flagella

Microcolony formation

Exopolysaccharides production

Mature biofilm

Dissolution and dispersal