Gram-stain-negative Bacteria Flashcards
What is the process of gram staining?
Crystal violet oxalate (blue-violet) is applied in the presence of triiodide (I3-) which helps trap the stain inside of cells.
[at this stage all cells are violet]
Cells are washed with ethanol.
[some cells retain the violet dye, some do not]
Cells are counterstained with either Bismarck brown (red-brown) or safranin O (crimson/pink).
[cells that retained the violet dye still look violet; cells that lost the violet dye will now appear the colour of the counterstain used]
Cells are examined.
Cells that retained the violet dye are termed Gram-stain-positive.
Cells that lost the violet dye (and thus appear pink or brown) are termed Gram-stain-negative.
Label and explain the structure of a cell wall in Gram-stain-negative
*Outer membrane =a phospholipid bilayer with channel proteins.
-Lipopolysaccharides in outer membrane which are phospholipids with chains of sugar attached involved in recognition and immune response.
*Inner membrane (a phospholipid bilayer with channel proteins and Cytoplasm (or cytosol) respiratory chain (if present)
*In between there is space =Periplasm which contains peptidoglycan (murein) (chains linked by tetrapeptide linker), which is anchored by proteolipids to the outer membrane (the polypeptides are linked to the lipid by a cysteine residue.)
ORDER
N-acetylglucosamine (GlcNAC)
N-acetylmuramic acid (MurNAC)
tetrapeptide linker (variable sequence)
Label and explain the structure of a cell wall in Gram-stain-positive
(resistant to heat and drying out due to wall)
*Single membrane (a phospholipid bilayer with channel proteins and respiratory chain (if present))
*Sometimes an S-layer and polysaccharides outside of wall
*Peptidoglycan layer – contains teichoic acids, unlike in Gram-stain-negative walls
-Teichoic acids are backbones of repeating sugar alcohols alternating with phosphate groups. Backbones are crosslinked by D-alanine and/or D-lysine. (sugar alcohols are usually glycerol (C3) and D-ribitol (C5).
ORDER
sugar monomers
S-layer protein
teichoic acid
N-acetylglucosamine (GlcNAC)
N-acetylmuramic acid (MurNAC)
What is the rank in the Bacteria and the Archaea.
We do not use the rank of Kingdom.
Domain > Phylum > Class > Order > Family > Genus > Species [ > Subspecies]
Individual isolates of a species are strains and each one has a strain code
How are species defined in the Bacteria and the Archaea.
Species are defined currently based only on whole-genome studies
What is;
N.L
M.L
E.L
Neo Latin (made up sounding Latin)
medieval Latin
church Latin
Describe what Escherichia coli look like, where they are found and its negatives and positves.
- Gram-stain-negative rods, dividing by binary fission. Some strains are motile by flagella in a peritrichous arrangement (hairy all over).
- found in colon of most Mammalia.
- widely used model organism in genetics because it grows
fast and is relatively easy to handle. - some species are pathogenic, causing food poisoning, UTIs, meningitis in neonates, (Crohn’s disease)
- E. coli O157:H7 produces shiga toxin – causes bloody diarrhea, destruction of gut wall and of erythrocytes and usually kidney failure (and often death).
- gut strains in most Homo sapiens L. are beneficial and produce one form of vitamin K2 (menaquinone-8, MK-8) which we take up through gut wall
Escherichia coli what do they do (divide) and how do they grow?
- cells dividing by binary fission elongate, duplicate the
genomic DNA and then a septum forms, dividing the long
cell into two new ones. - some E. coli strains divide every 20 min in complex
media at 37 °C (that’s not what they do in the gut/in food
in the refrigerator). - can respire molecular oxygen (O2 , yielding H2O) or nitrate
(NO3, yielding N2), or grow by fermentation if either are
lacking. - grows on sugars, amino acids, intermediates of Krebs’
cycle etc. - ferments sugars by mixed acid fermentation in absence
of O2 or NO3- producing lactate, succinate, acetate,
ethanol, CO2, H2 – produces a lot of gas e.g in
the gut. This allows them to make their ATP by substrate-level
phosphorylation.
Acidithiobacillus thiooxidans (acid-loving sulfur rod) (sulfur oxidation)
- Gram-stain-negative rods, dividing by binary fission. Motile by long, single flagella at one pole (monotrichous).
- found in acid-mine drainage, spoil heaps, on coal.
- extreme acidophile, growing at pH 0.5 to 6.0 – some strains grow at pH -0.6!
- can only respire molecular oxygen (O2).
- obligate chemolithoautotroph – uses CO2 at the expense of inorganic sulfur species e.g. elementary sulfur (S8), thiosulfate (S2O32-), molecular hydrogen (H2) – these are oxidised to sulfuric acid (H2SO4) or water (H2O), respectively.
- takes up CO2 into biomass using the Calvin cycle like the Viridiplantae (albeit a different RuBisCO isoenzyme).
- grows very slowly and has to oxidise a huge amount of sulfur to make a small amount of biomass.
What is Acidithiobacillus thiooxidans used for?
production of huge amounts of acid but very little
biomass so used in biohydrometallurgy
* used commercially to extract mostly copper, nickel, vanadium, manganese and uranium from low grade ores.
* e.g. Cu2S (chalcocite) leaching:
Desulfovibrio vulgaris (sulfur reduction)
- Gram-stain-negative rods, dividing by binary fission. Some strains are motile by single flagella at one pole.
- ubiquitous in water-logged soils, river sediments etc.
- obligate anaerobe – cannot use molecular oxygen for respiration. Instead, it uses sulfate (SO42-) as terminal electron acceptor in respiration, yielding hydrogen sulfide gas (H2S). This is called sulfate reduction, it is a ‘sulfate-reducing bacterium’ (SRB).
- uses amino acids, fatty acids etc as carbon source and energy sources.
- sediments it is in tend to look green-black as pyrrhotite (FeS) forms as a result of iron in the soil reacting with H2S.
- minor member of the Homo sapiens L. gut flora.
Candidatus Electrothrix aarhusiensis
- Gram-stain-negative cables – the cable Bacteria.
- live across the oxic:anoxic interface – the bottom end of the filament is oxidising an electron donor, the other end is reducing oxygen as an electron acceptor – electrons travel from bottom to top along ‘cables’ in the periplasmic space.
- discovered in 2010 – visible with the naked eye as cotton-like threads across the oxic:anoxic interface.
- periplasmic ridges are probably the site of electron transduction up the filament.
Magnetospirillum magnetotacticum
capable of orienting with respect to a magnet.
* Gram-stain-negative spirilla, dividing by binary fission. Flagella on each pole.
* ubiquitous in iron-rich shallow sediments and freshwater
* obligate aerobe – cannot grow without O2 for respiration, but needs to live at a low concentration of it as poisoned by it (1-3%).
* have a chain of magnetosomes inside the cell – each one is about 20 crystals of magnetite (Fe3O4) inside of a lipid bilayer.
* allows the cell to orient itself to magnetic north, which allows them to turn and find up/down so they can move towards microxic sediments.
* spiral shape aids ‘drilling’ into sediments.
* magnetosomes can also be made of griegite (Fe3S4) in some species.
Myxococcus xanthus
- Gram-stain-negative rods that change morphology a lot.
- have a full life-cycle and a type of (primitive) behaviour.
- found in soils and on leaf-litter but colonies are only just visible with the naked eye.
- forms multicellular masses (sing. grex, pl. greges) that act a bit like a single organism.
- yellow colouration is from DKxanthene (DK = Dale Kaiser)
- forms fruiting bodies and disperses itself via myxospores.
