Microorganisms Flashcards
Brief history of microbes
Hooke: microscope
Nothing 150 years
Pasteur : disproved spontaneous generation…discovered germs
- Sterilised equipment
Koch: link between micro orgs and disease..wash hands
- Koch postulates
What are koch’s postulates
- Koch postulates
○ Diseased animal will have bacteria not present in healthy animal
○ If reinfect healthy animal with that bacteria they will get same disease And same bacteria will be seen in the blood
What are the different ways to observe microorganisms
- bright field microscopy
- fluorescent microscopy
- differential interface contrast microscopy
- atomic force microscopy
- confocal scanning laser microscopy
- electron microscopy (transmission and scanning)
Bright field microscopy
- staining can improve but kills cells
- phase contrast and dark field = 2 different filters that may allow to see more easily
Fluorescent microscopy
- visualise cells that fluoresce e.g. chlorophyll, DAPI stain
- stains dna of the cell
Differential interface contrast microscopy
- form of light microscopy
- uses polarised light (light in a single plane)
- cellular structures appear more 3D
Confocal scanning laser microscopy
- couples laser source to fluorescent microscope
- focuses through specimen = reconstructs layers into 3D image
- cells stained with fluorescent dye to make them distinct
Electron microscopy
- uses electrons instead of visible light
- electromagnets function as lenses
- whole system operates in a vacuum
Split into transmission and scanning
Transmission electron microscopy
- high mag
- high res
- see structures at molecular level
- have to make very thin sections of specimen (electrons don’t penetrate into tissue well)
- tissue has to be dead
Scanning electron microscope
- shows external surfaces of cells
- specimen coated in film of heavy metal e.g gold
- electrons scatter from metal coating are collected/processes to form image
Why study microbes
- fight disease
- food preservation
- agriculture e.g. nitrogen fixing bacteria
- animal husbandry
- fermentation in food
- biofuels
- biotechnology
Why microbes are useful in studies
- all cells very similar = discoveries of microbes could be transferred to other organisms
- don’t take up too much space
- grow rapidly
- easily manipulated
What are the different types of microorganisms
- bacteria
- archaea
- Protozoa
- algae
- viruses
- fungi
Different shapes of microorganisms cells
○ Coccus ○ Spirochete ○ Rod ○ Spirilla ○ Stalk and hypha ○ Filamentous bacteria
Why is morphology useful
- Useful to identify species
- Differences between people
However: - shape of cell doesn’t tend to predict properties of cell
- Many species of bacteria look identical
- Differences between people
Advantages of cells being small
- Small cells = larger SA:V ratio
○ Faster nutrient exchange per unit cell volume
○ Can grow faster
○ Support a larger population- Faster evolution
○ DNA replicated as cells divide
○ DNA replications cause mutations
○ High rate of division = higher rate of mutation (mutations are ‘raw material’ for evolution)
○ Allows for rapid adaptation to changing environments
- Faster evolution
What is the minimum cell size limit
0.15 micrometers
Otherwise cant fit everything inside
Describe a gram stain
- Gram stain separates bacteria into positive or negative
- Positive = purple
- Negative = red/pink
- Used as starting point for identifying bacteria
Procedure: - Place bacteria on slide
- Flood slide with crystal violet
- Add iodine solution (stain pos purple)
- Add ethanol briefly (too long will pop cells) (neg cells decolourised)
- Add counterstain safranin (stains neg cells red)
What is a gram positive cell wall
Contains peptidoglycan layer
What is a negative gram cell wall
Cell wall, thin peptidoglycan and second membrane
- Second outer membrane prevents purple staining inner membrane which is why it goes red instead
What are endospores
- Highly specialised
- Only with certain species of bacteria
- Highly resistant to heat, harsh chemicals, radiation etc.
- Enable species to survive in very harsh conditions: produce one that survives until conditions good again
Describe sporulation
- Vegetative cell = average cell (no reproduction or specialisation etc)
- An essential nutrient is exhausted e.g. carbon or nitrogen
- Vegetative cell stops growing
- Triggers development of endospore within vegetative cell and is released once matured
- Spores can remain dormant for years
- Germinates into a vegetative cell once conditions stabilise
Terminal endospore
Develops at very end of vegetative cell
Subterminal endospore
Endospore not quite at end but not at middle
Central endospore
Develop right in the centre of the cell
Describe endospore structure
- Strongly refractive and impermeable to almost all dyes
- More layers than in vegetative cell
- Exosporium: thin protein covering
- Spore coat: layers of spore specific proteins
- Cortex: loosely cross-linked peptidoglycan
- Core: core wall, cell membrane, cytoplasm, nucleotide, ribosomes etc.
Fimbriae
- Enables cells to stick to surfaces and each other
Assist disease process
Pilli functions
- Conjugation: genetic exchange between cells
- Plasmid copied and sent to recipient cell
2. Adhesion of pathogens to specific host tissues and subsequent invasion
3. Can also be used in mobility
- Plasmid copied and sent to recipient cell
What a re the 2 main types of bacteria cell locomotion
- Swimming
- needs flagellum
- in gram pos or neg - Gliding
- slow
- needs contact with solid surface
- bacteria will have ragid edge
What are the 3 different attachments of flagella
Polar = attached atone or both ends
Tuft
Peritrichous = flagella all over
How does gliding locomotion
- Cell connects with surface and slime pulls along
2. Pilli reach out along surface and pull
Describe flagella structure
- Helical
- Wavelength is characteristic for given species
- Composed of many copies of a protein called flagellin
- Molecular motor that drives rotation of flagellin filament is embedded in cell membrane
Describe the proton turbine model for flagella
○ motor Contains central rod Passed through a series of rings
○ Mot proteins line lower rings = acts as stators
○ Rod and rings rotate while the mot proteins stay still
- Proton turbine model:
○ Proton movement across membrane through mot complex
○ Protons flow through channel
○ Exert electrostatic forces on helically arranged charges on rings (spirals of alternating positive and negative charges: positive will attract negative proton and repelling negative atttractions = spinning motion)
○ Attraction between charges cause rotation
Taxis
Movement towards something that will aid growth/growth away from toxins
Chemotaxis
Responding to chemicals
Photo taxis
Responding to light
Why do cells have locomotion
To aid with taxis
Gives evolutionary advantage
Myxobacteria and myxospores
○ Form multicellular structures = fruiting bodies
○ Fruiting body creates mysxospores (resistant to bad conditions, similar to endospores but not the same.) mysxospores related and germinate ( gram neg ). Wait till favourable conditions then turn vegetative
○ Fruiting bodies often colourful and morphologically elaborate
○ Vegetative cells release slime trails for gliding
○ Under favourable conditions vegetative cells aggregate. Do this via slime trails, that can identify and follow = radiating pattern of established slime trails. Slime trail gets thicker and more join. End up in big circle.
○ Aggregated myxobacteria differentiate into fruiting body
Autotroph
Org that grows with co2 as sole carbon source
Chemolithotrophs
Org that gets energy from oxidation of inorganic compounds
Only in prokaryotes
No competition from chemoorganotrophs (many compounds used are the waste products from chemoorganotrophs) : often live close together
Chemoorganotrophs
Org that obtains energy from oxidation of organic compounds
Can be aerobic or anaerobic or both
Heterotrophs
Org that requires organic carbon as carbon source
Phototrophic
Orgs that obtain energy from light
Symbiotic mutualities
Cooperative relationship between microbe and host
Parasitic microbe
Antagonistic to host
Takes carbon and gives nothing back
Saprotrophic
Host is dead
What are the 3 types of prokaryotic photosynthetic orgs
Cyanobacteria, plants and algae
Purple and green bacteria
Uses oxygenic photosynthesis
Inorganic compounds used instead of water as reducing power in photosynthesis
What types of bacteria can fix nitrogen
Free living = require no host
Symbiotic
(Eukaryotes CANT)
Why is nitrogen fixation important
Used for sewage and wastewater treatment
Removes toxic amines and ammonia
What 2 groups of bacteria are fixing nitrogen
Nitrosomonas
Nitrobacter
What’s humus
Mixture of organic materials that have resisted rapid decomposition
Mainly plants and microorganisms
What is the most important contributor of CO2 to atmosphere
Microbial decomposition of dead organic materials and humus
