Please enable JavaScript.
Coggle requires JavaScript to display documents.
Biol 243 End of year exam BACTERIAL GROUPING - Coggle Diagram
Biol 243 End of year exam BACTERIAL GROUPING
Bacterial cell structure
No
nucleus
Has a
nucleoid
which is:
irregularly shaped
contains most of the genetic material
circular piece of DNA that has folded
varies in size between different species.
Contains
plasmids:
small, circular DNA
can be linear
vary in copy number (1-50)
can vary in length (2.3-1354 kbp)
exist seperately to chromosome and not required for growth.
can carry selective advantage, for example drug resistance.
Inclusions
within the cell which are storage products of organic or inorganic molecules.
reserved for future use
glucose stored as glycogen
lipid stored as poly-b-hydroxybutrate.
phosphate stored as polyphosphate.
sulphur stored but only released when bacteria eaten by preditor.
Cytoplasmic membrane:
Typically a phospholipid bilayer.
there are integral and peripheral membrane proteins.
Cell wall:
can be either gram positive or gram negative
gram positive purple after gram test due to thick peptidoglycan.
Gram positive cell wall:
has thick layer of peptidoglycan which makes up 90%.
120% is teichoic acid which is used by phagocytes for recognition.
has lipoteichoic acid which allows it to go through peptidoglycan???
Gram negative cell wall:
peptidoglycan gap known as periplasm.
crystal violet difficult to get through peptidoglycan to stain it.
porins which fill with water and allow hydrophillic products to come in and waste out.
soluble molecules such as phosphate and nitrates go in.
last bit of outer membrane is the LPS. Important molecule because made up of: lipid A which is hydrophobic and ancors LPS to other membrane and is non toxic. A chain of sugars and O polysaccharide which differs between bacteria.
if GN bacteria dies, LPS is released and acts as a toxin.
Capsule:
made of polysaccharides
there to evade host defences.
protection from phagocytosis
protection from harsh conditions such as extreme dryness (desiccation)
can aid with attachment to surfaces.
S layer: rare in hetrotrophic bacteria (cant produce its own food, takes food from sources of organic carbon).
present in all arachae
its a monolayer of identical proteins or glycoproteins.
function is for adhesion or for anti-phagocytosis.
Flagella:
Flagella are used for swimming and attachment
polar flagella: flagellum at one end of cell.
monotrichous= one flagellum.
amphitirichous: one flagellum at each end
lophotrichous: cluster of flagella at one or both ends.
Petririchous: spread over entire surface.
Fimbrae and Pili:
Fimbrae are short, hair like, protein containing and allow for recognition and attachment.
Pili are longer and thicker than F and less numerous. They are required for mating (conjugation pilus) and attachment to surfaces.
Bacteria identification:
-
16S rRNA sequences
16s rRNA gene highly conserved.
Universal PCR primers designed to target the conserved regions of 16S and make it possible to amplify the gene
16s sequence is approximately 1500bp long with 9 variable regions. Its variable regions are used for identification.
16s RNA is responsible for making the 30S subunit in prokaryotic ribosomes (the 30S subunit). It comes together with the 50S subunit which is conserved between bacteria so not much different between bacteria.
Programme looks for differences then plots a phylogenic tree.
Bacteria taxonomy
For every species, there are many strains.
Each of these strains are deposited in culture collections.
Different bacterial strains all behave differently.
Class 1 strain are very tame and non-pathogenic.
class 2 can cause disease but will be mild and treatable.
class 3 definitely cause disease and are toxigenic but still a cure.
no known class 4 strain of bacterium
Classical taxonomy uses a decision tree to get identification to at least genus level. CLASSICAL TAXONOMY
we look at shape, gram positive and gram negative.
Can test with oxygen tolerance:
growth at top is obligate anaerobe
growth at bottom is anaerobe
growth all throughout is facualtive anaerobe
microaerophile can tolerate low levels of oxygen. Form distinct growth line somewhere down from top.
aerotolerant anaerobe: also growth throughout whole tube.
Can identify based on prescense of endospores:
they are survival mechanism of certain gram positive bacteria.
can survive 100s of years
resistant to heat, drying, radiation and chemicals.
contain calcium dipicolinate.
very low water content
special proteins protect DNA.
long and tedious process to get rid of endospores.
CELL MOTILITY: Looking at whether cells can swim. Cant just be done under slide due to movement just created between water, slide and coverslip. Looks as if bacteria moving.
Instead, a hanging drop is done so no chance of artifacts. You put cover slip with drop of culture suspended. Then can observe under microscope. On market is also a motility test which uses growth medium and a dye to stain the bacterial cells.
Taxonomy based on Catalase activity.
when bacteria metabolise, one of the waste products is hydrogen peroxide so they use catalyse to break it down into water and oxygen.
have drop of hydrogen peroxide, take culture and pop in. If oxygen bubbles then catalase positive.
Oxidase test: cytochrome C oxidase:
uses a dye called kovaks reagent. Colourless when reduced and purple when oxidised.
You can look at the G-C base content. To join a G and a C, you need three hydrogen bonds. Stronger than AT. Higher GC content, more energy required to seperate.
estimated by looking at temperature required to separate two strands into one strand.
Can use a lactose test. If ferments lactose to lactic acid, PH change from red to yellow and production of gas.
Hydrogen sulfide test. Production of ferrous sulfide which is insoluble and black. These small tests are time consuming so strips are now on the market.
Use of selective media:
MacConkey agar has bile salts which inhibits gram positive growth and therefore enterobacteriaacae can grow. Then seperated based on ability to ferment lactose.
blood agar used to see if bacteria can breakdown blood. Can show beta hemmolysis, alpha and gamma
chocolate agar is the same but uses heated blood which releases haem. Bacteria that require haem will grow, such as nisseria.
Chromogenic Brilliance E.coli agar will give pink coliforms and purple e.coli.
Listeria selective agar will give no halo around Non pathogenic listeria colony but halo around pathogenic Listeria colony.
Selective medium such as Mannitol salt. If mannitol is fermented, hydrogen ions so red to yellow. Need POSITIVE and NEGATIVE control.
Classing bacteria by nutrition:
96% of the biomass is made up of chnops which are the 6 key elements that allow for growth and reproduction.
These are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P) and sulphur (S)
bacteria need correct PH
correct salinity as it could affect osmosis (concentration of salts).