Mikrobio weekly questions

Question 1

What is the typical size range of prokaryotic microorganisms?

Answer 1

0,2 um – 300 um

Question 2

Bakteria’s Genome

Answer 2

Usually circular DNA
Usually one chromosome
Usually lack introns

Question 3

Archaea’s Genome

Answer 3

Usually circular DNA
Usually one chromosome
A few introns

Question 4

Eukayotes Genome

Answer 4

Linear DNA
Multiple chromosomes, in pairs
Most genes have introns

Question 5

Location of DNA in Bacteria

Answer 5

Nucleoid region in cytoplasma

Question 6

Location of DNA in Archea

Answer 6

Nucleoid region in cytoplasma

Question 7

Location of DNA in Eukaryotes

Answer 7

Contained within membrane enclosed nucleus

Question 8

Bakteria’s cell membrane

Answer 8

Straight-chain fatty acids ester-linked to glycerol

Question 9

Archaea’s cell membrane

Answer 9

Branched-chain fatty acids ether-linked to glycerol. Branches limits the movement of the hydrocarbon chains and thereby strengthen the membrane

Question 10

Eukaryotes Cell membrane

Answer 10

Straight-chain fatty acids ester-linked to glycerol

Question 11

Bakteriea Cell wall

Answer 11

Usually present, composed of peptidoglycan

Question 12

Achaea’s cell wall

Answer 12

If present composed of proteins or pseudopeptidoglycan

Question 13

Eukaryotes cell wall

Answer 13

If present composed of cellulose (algae) or chitin (fungi)

Question 14

bakteria internal membranes

Answer 14

May have energy transducing lamellae

Question 15

Achaeaøs internal membranes

Answer 15

uncommon

Question 16

Eukaryotes internal membranes

Answer 16

Extensive membranous organelles

Question 17

How do you determine that a certain bacterium is the causing agent of a disease?

Answer 17

1: Mikroorganismen må nødvendigvis forefindes i rigelige mængder i alle organismer, der lider af sygdommen, men ikke i raske organismer.
2: Mikroorganismen må nødvendigvis isoleres fra den syge organisme og dyrkes i en renkultur.
3: Den kultiverede mikroorganisme bør forårsage sygdom, når den introduceres i en rask organisme.
4: Mikroorganismen må nødvendigvis genisoleres fra den podede, syge testvært og identificeres som værende identisk med den originale specifikke patogen.

Question 18

What is a psychrophile, a mesophile, a hyperthermophile?

Answer 18

Bakterier der kan leve I hendholdsvis koldt miljø(4 grader)(psychrophile) mellemgrader (37 – mesophile) og varmt (80-120 – hyperthermophile)

Question 19

Hvad kaldes bakterier der kan leve ved, lave, middel og høje temperature?

Answer 19

Bakterier der kan leve I hendholdsvis koldt miljø(4 grader)(psychrophile) mellemgrader (37 – mesophile) og varmt (80-120 – hyperthermophile)

Question 20

How can you sterilize the surface of a bench, a solution containing a drug compound, empty glass bottles?

Answer 20

70% ethanol, steril filtration, autoclaves.

Question 21

If you get a culture of an unknown microorganism, how would you start to characterize it?

Answer 21

I would start with two samples: one with oxic conditions, one with anoxic condition. Then I would check for endospores by heating the samples. From this point I would try different medias e.g. lactose, sulfur etc. to narrow down the species. Check their shape and colony size and shape. Motility.

Question 22

How can bacterial cells regulate that they swim towards an attractant?

Answer 22

Bakterier har flagellar, der gør det muligt for dem at svømme. Archaea har også flagellar, men disse er kaldt Archaella.
Andre bakterier kan glide, her er der forskellige mekanismer der gør de kan dette.
Andre bakterier bevæger sig mod lys eller mod ”kemi” dette er kaldt chemotaxis og phototaxis.

Question 23

Hvad er mekanismen bag chemotaxis

Answer 23

A methyl-accepting chemotaxis protein (MCP) is embedded in the bacterias periplasm, cell membrane and cytoplasm. In the cytoplasmic part of the MCP is CheW and CheA kinase located. When there is no attractant present, CheA kinase phosphorylates CheY which then makes the flagellum turn clockwise = tumble. When an attractant is present it will bind to MCP which inactivates CheA, CheZ dephosphorylates CheY-p which makes the rotor turn counter clockwise. CheR methylates MCP which makes it desensitized towards the attractant. CheA is reactivated and the cell tumbles. In the absence of attractant CheB-P resets the rotor be demethylating the MCP.

Question 24

What is a spore and what does it contain?

Answer 24

Meget anderledes celler strukturer der er resistente over for varme, stråling og hårde kemikalier. Endosporer er overlevelses strukturer ved dårlige vækst betingelser.
De indeholder: yderste lag kaldes exosporium som er et tyndt protein, under dette findes der flere spore coats som også består af proteiner. Under spore coaten finds cortex som indeholder cross-linked peptidoglycan. Inde i cortex findes core der indeholder en core væg, cytoplasmic membran, cytoplasma, nucleoid (bakteriers celle kerne) ribosomer. Derudover findes der også dipicolinic syrer. De indeholder meget ca+2, skaber forbindelse med dipicolinic syrer.
Bacillus og clostridium laver begge endosporer

Question 25

How do the cell envelopes of a Gram + and a Gram - bacterium differ?

Answer 25

The gram positive has several layers of peptidoglycan and an S layer – this makes a very thick cell wall. The peptidoglycan monomers are connected by teichoic acids. Attached to the S-layer is glycosyl-chains.
The gram negative has a very thin wall with only 1-2 layers of peptidoglycan. They have two membranes an inner membrane (the cell membrane) and an outer membrane. The outer membrane has porins incorporated and LPS attached. Lippoproteins connect the peptidoglycan to the outer membrane.

Question 26

How is the archaeal cell envelope different from the one found in bacteria? Describe the features/structures that you can find.

Answer 26

I stedet for peptidpglycan har nogle archaeal celler pseudomurein. Andre mangler og har istedet polysacarider. Den mest almindelige celle væg hos archaeal er s-layer. S-layer består af sammenlåsende molekyler af proteiner og glykoprotein.

Question 27

A microbe has only cellulose as organic substrate available. What different processes need to take place so that the microbe can gain energy and produce biomass?

Answer 27

Cellulose needs to be hydrolysed first into oligosaccharides, then to disaccharides and then to monosaccharides which can enter the central catabolic pathways e.g. glycolysis.

Question 28

What are the differences between anaerobic respiration and fermentation?

Answer 28

Fermentation er en form for anarobiske metabolisme hvor organiske componenter både donerer og optager elektroner, og det er dermed ikke nødvendigt med en udfrakommende electron acceptor. Hvorimod ved respiration bliver en organisk eller uorganisk electron doner oxiderert med et andet component.

Question 29

What are the differences between anaerobic respiration and fermentation?

Answer 29

Both reactions begin in the same way as aerobic respiration, they start with the glycolysis yielding 2 ATP from a carbon molecule and producing puryvate. Fermentations end product is either lactic acid or ethanol according to the type of fermentation and do not continue in the TCA or the ETS. Because of the lack of electron acceptor, the electrons need to be placed which they do during the electron shuttle NADH needs to be oxidized to NAD+ to carry electrons. The anaerobic respiration continues in the TCA and the ETS but has a different terminal electron acceptor and the terminal oxidase differs according to the terminal electron acceptor. Thus anaerobic respiration yields more energy than fermentation. Facultative anaerobes mean when oxygen is present, they have aerobic respiration but in lack of oxygen they use anaerobic respiration or fermentation.

Question 30

How does ATP get re-generated?

Answer 30

When one molecule of ATP is used in the contraction process, it is hydrolyzed to ADP, adenosine diphosphate, and an inorganic phosphate. … In the process of regeneration of ATP, creatine phosphate transfers a high-energy phosphate to ADP. The products of this reaction are ATP and creatine.

Question 31

Name different electron acceptors for respirations and where you would find them in e.g. a marine sediment. Why are they distributed in that way?

Answer 31

O2, NO3-, Mn4+, Fe3+, SO42-, they are distributed in that way because of the decreasing reduction potential. strength of the electron acceptors, O2 is the strongest electron acceptor and therefore the affinity for O2 is higher than for the rest of them, when O2 is consumed then NO3- will be next and so on.

Question 32

Which different transport mechanisms do you know? What are the differences?

Answer 32

Passive and active transport. The difference between them are that active transport requires energy from ATP either direct use of the ATP or by secondary use. Passive transport do not require energy and the concentrations and voltage gradient determines which way the transport will occur. Passive transport is always with the gradient whereas active transport is against the gradient.
Active transport: includes symport (two molecules in the same direction) and antiport (two molecules in different direction). ABC transport (ATP binding cassette) transporter (the ATPase activity in the component opens the channel for the solute)
Glycolysis, pentosephosphate pathway and Entner-Doudoroff. Glycolysis yields more energy than the two others (2ATP, 2NADH (EMP) vs ATP, NADH, NADPH (ED) & ATP, 2NADPH (PPP).

Question 33

How is reverse electron transport possible?

Answer 33

To carbon fixate NADPH is necessary, so instead of using NADPH to create a proton gradient they use it to regenerate NADPH to carbon fixate. between the periplasm and the cytoplasm sends H+ to the cytoplasm allowing NAD+ to reduce to NADH. The energy comes from the reverse direction of the electron transport chain.

Question 34

What is bacteriorhodopsin and what is its function?

Answer 34

Bakterierhodopsin er et protein, der findes hos arker og først og fremmest hos halobakterier. Stoffet virker som en protonpumpe, dvs. at det opfanger lysenergi og bruger den til at flytte protoner gennem en membran og ud af cellen. Den protongradient, der opstår på den måde, omsættes i næste omgang til kemisk energi.
Bakterierhodopsin er indbygget i membranen, og det findes mest i nogle todimensionelle krystalfelter, der kaldes ”purpurmembran”, og som kan dække næsten op til 50 % af arkens celleoverflade.

Question 35

Which electron donors can be used in lithotrophic processes?

Answer 35

H2, Fe2+, NH3, NO2-, CH4, CO, HS-.

Question 36

Which different types of phototrophs do you know? How do they differ? Name examples of organisms for each.

Answer 36

Photolithoautotrophs (e.g. cyanobacteria energysource: light, carbon source: CO2, reducing equivalents: H2S or H2O). With H2O both PSI and PS II are used, with H2S are either PSI or PSII used.

Cyanobacteria (H2O), Chlorobiaceae, Chromatiaceae (H2S), Chloroflexus (H2)

photoorganoheterotrophs (e.g. Rhodobacter energy source: light, carbon source: organic, reducing equivalents: organic)

Question 37

Can organisms with a Type II photosystem produce NADPH? If yes then explain how.

Answer 37

Yes some bacteria can. They do it by reverse electron flow which requires energy.

Question 38

Which different types of CO2 fixation pathways do you know? What are the key enzymes involved in these pathways? Which one of them needs the least amount of energy for fixing one molecule of CO2? Why are not all microorganisms using it then?

Answer 38

Calvin cycle: 3CO2 produce 1 glyceraldehyd 3-phosphate (three turns in the cycle), that can enter biosynthesis of amino acids, vitamins etc. Alternatively, 6 CO2 can produce 1 glucose. Enzyme Rubisco

Reductive (reverse) TCA cycle: uses 4-5 ATP to fix 4 molecules of CO2 and generates one molecule of oxaloacetate. The enzymes are the same as for the forward cycle except: ATP citrate lyase, 2-oxoglutarate: ferredoxin oxidoreductase & fumarate reductase. Reducing agent: NADPH. 2CO2 + 2 ATP+8H+ +8e- + H-SCoA +CH3CO-SCoA + 3H2O+2ADP+2Pi.

Reductive acetyl-CoA: anaerobic soil bacteria. Reducing agent H2. 2CO2+ATP+4H2+HSCoA+ CH3CO-SCoA+3H2O+ADP + Pi. This one is slightly more efficient than reverse TCA because it uses one less ATP. This one is linear and not a cycle. Carbon monooxid dehydrogenase

3-Hydroxypropionate cycle: acetyl CoA carboxylase, propionyl-CoA carboxylase.

Question 39

In which organisms can you find the capability to fix N2 gas? Which enzyme do they use for it? How much energy is needed to fix one N2?

Answer 39

Nogle fritlevende aerobe bakterier kan også binde kvælstof, og de må beskytte deres nitrogenase mod ilt ved enten binding af enzymet til specielle stabiliserende proteiner som hos Azotobacter eller ved dannelse af tykvæggede og ilttætte specialceller (heterocytter) som hos blågrønalger (cyanobakterier).

Rhizobium-bakterien får del i den glucose, som planten producerer ved sin fotosyntese, og bakterien ikke selv kan fremstille. Glucosen kan bakterien bruge til sin respiration. Til gengæld fikserer bakterien frit nitrogen fra luften, som planten kan bruge til opbygning af N-holdige stoffer som aminosyrer og DNA. Dermed er planten mindre afhængig af at have adgang til N-forbindelser i jorden.

Enzymet nitrogenase findes hos alle disse bakterier.

det koster 16 ATP

Question 40

Which metabolic and biosynthetic pathways are universally found in nearly all prokaryotic cells?

Answer 40

Glycolyse
TCA og( ETC hvis ilt tilstede, kan også bruge andet end ilt til elektron acceptor)
(PPP -> Ribulose 5 phosphat og NADPH)
Proton gradient til at skabe ATP

Question 41

Which criteria can you use to classically characterize microbial species?

Answer 41

Colony morphology (size, colour, shape), cell morphology (size, shape, gram) motility (flagella, gas vacuoles, gliding, nonmotile), nutrition and physiology (photo-, chemoorgano, chemolithotrophs, aerob vs anaerob, temperature, pH, salt, use of carbon, nitrogen or sulfur, growth factor), spores

Question 42

What is a commonly used molecular marker for the identification of prokaryotic species?

Answer 42

16S rRNA gene

Question 43

What is horizontal gene transfer? What evolutionary impact can it have?

Answer 43

When genes are transferred between groups. That some charateristica of eukaryotes can be seen in prokaryotes or that some species that are not related share some genes. In bacteria and archaea it is transferred with plasmids (pili), transposable elements and bacteriophages. It can be examined by looking at the GC/AT ratio (the base pair) which differ from the different species. It is important for adaptation.

Question 44

Which method of classification would you use to distinguish two closely related bacterial strains?

Answer 44

Multilocus sequence typing: sequencing of multiple genes and combined phylogeny

Question 45

What is a metagenome? Why analyze it instead of isolating and cultivating the organisms and then sequence their genomes

Answer 45

All the genetic material present in an environmental sample consisting of the genomes of many individual organisms. Population can be studied on the environment. The full prokaryotic diversity becomes available.

Question 46

Which types of microbial population growth do you know?

Answer 46

Batch culture: not often found in nature, used in laboratory cultures, maximum growth rate

Chemostat: continuous culture, can be optimized for high or low growth rate, good yields, closer to environmental growth

Environment: sometimes batch like (rare), slow growth rate with long G1 phases.

Question 47

Which methods can you use to determine if a culture is growing? What are the advantages/disadvantages of each?

Answer 47

Total cell count:
Turbidity measurements: the amount of light that hits the detector views the amount of cells. If the amount of light is low then there is many cells. The disadvantage is that the cells can out shadow each other.
Microscopic counts: if the culture is too big, they cannot be counted.
Flow cytometry: separates size and pigment in cells in water sample.

Viable cell count:
Dilution and plating: the sample has to be diluted otherwise there will be way too many cells, but one will have to count a rather big sample to be most precise.

Membrane filtration:
analysis of water sample: if the result of one water sample is not enough then it is placed on an agar plate, but on the other hand there can be too many in one sample.
Most probable number:

Question 48

Which factors control microbial growth

Answer 48

temperature, oxygen

, salinity, PH and nutrient availability.

Question 49

How does temperature control microbial growth?

Answer 49

if the temperature is increased to the optimum the growth will increase but the temperature can be too high too and then the enzymes will denaturate. At low temperatures the growth decrease because of an decrease in membrane fluidity and enzymatic activity. Although there are extreme thermophiles 60 - >100°C.

Question 50

How does Nutrient availability control microbial growth

Answer 50

if there aren’t enough nutrients the bacteria will die

Question 51

How does oxygen control microbial growth

Answer 51

oxic bacteria will thrive in oxic environment and cannot survive without oxygen. Some bacteria facultative anaerobes can shift to anaerob respiration, but the aerobic respiration yields the most energy. Species that growth in oxygenic environments need enzymes to break down O2 to avoid damage to the cell e.g. peroxidase.

Question 52

How does salinity control microbial growth

Answer 52

too high salinity will kill some bacteria but there are some bacteria who thrive at high salinity. Halotolerant (on the skin), halophile and extreme halophiles. Usually higher salt concentration inside the cell to avoid bursting.
Pressure: too high pressure will kill some bacteria but some bacteria will thrive at high pressure. Barosensitive bacteria die as the pressure increases. Barophiles require high pressure but dies if the pressure increases further, same goes for barotolerant – they grow uptil a certain pressure but then dies.

Question 53

How does PH control microbial growth

Answer 53

pH: most bacteria thrive at neutral pH, but some are adapted to acidic environment (acidophiles) e.g. the stomach and some thrive at alkalinic conditions (alkaliphiles).
Waste product: too much waste product can limit the growth.
Inhibitors: limit the growth in different ways.

Question 54

What are the different types of prokaryotic cell division?

Answer 54

Budding, binary fission (, assymetric fission.

Question 55

What are the different growth phases of a bacterial batch culture? What happens in each?

Answer 55

Lag phase: preparing phase: adjust to the conditions, increase metabolism / anabolism, grow in size, synthesize enzymes necessary to growth, start replicating enzymes.

Log phase: exponential growth, balanced growth, every time the cells divide the population doubles. dN/dt=kN, N: population size, k: growth rate constant (time-1), t: time. Integrated: N_t=N_0 e^kt, generation time g=ln⁡(2)/k k is the coefficient of the linear regression with logarithmic results.

Stationary phase: Cell division is equal to death phase, no net increase in population size, growth rate and death rate is at balance, new nutrients come only from lysing cells, waste products increase and limits growth, living cells are smaller, organisms capable of producing endospores do it in this phase.

Death phase: nutrients are used up, waste product accumulates to toxic levels, net decrease in cell numbers, cells die quick but at a constant rate, often similar kinetics as the log phase, not all cells die resistant cells and endospore survives.

Question 56

To be able to survive and grow under oxic conditions, microorganisms use specific enzymes. What are their names? What do they do?

Answer 56

Superoxide dismutase catalyse the breakdown of superoxide.

Catalase or peroxidase catalyse the breakdown of H2O2.

Question 57

What are the different steps in a modern wastewater treatment plant like Ejby Mølle?

Answer 57

First of all, big things are removed. Then the primary treatment occurs. This takes place in large tanks with high retention time. Solids are separated by weight, dense solid goes to the bottom and light solids goes to the top where it is skimmed off. The solids go to an anaerobic digester. In the secondary treatment the dissolved organic compounds are oxidated. 1) lagooning (water runs through a large shallow lagoon, where microbes oxidize waste), 2) trickling filter (tank with rock / stone, where the water runs over, the bacteria produce biofilm on the stones on from time to time some bacteria falls off, from this tank the water flows to settling tank the pieces of biofilm settles in the buttom and is pumped to an anaerobic digester, the effluent which now is low in organic matter is chlorinated and dumped, 3) activated sludge digester (the water is stirred with oxygen, bacteria produce flocs, the water is led to another tank where the flocs settle and the effluent is chlorinated and dumped, the sludge is either pumped back to the aerobic digester or to the anaerobic digester, the activated sludge digeste can shift between oxic and anoxic conditions, during oxic conditions nitrification occur during anoxic conditions denitrification occur. , 4) anammox reacter: anoxic NO2- + NH4+ N2+2H2O

Question 58

Which different microbial processes can be employed for the secondary treatment of wastewater?

Answer 58

Ammonium oxidation, nitrification and denitrification, anammox

Question 59

Why do we work next to the flame of a bunsen burner?

Answer 59

To avoid settling of bacteria, by using a Bunsen burner the microorganisms are reduced because of the movement of air due to the temperature difference.

Question 60

Which two different types of growth can you monitor in a bacterial batch culture?

Answer 60

Batch culture: not often found in nature, used in laboratory cultures, maximum growth rate
Chemostat: continuous culture, can be optimized for high or low growth rate, good yields, closer to environmental growth

Question 61

Which method would you use to monitor the one and which for the other?

Answer 61

Total cell count:
Turbidity measurements: the amount of light that hits the detector views the amount of cells. If the amount of light is low then there is many cells. The disadvantage is that the cells can out shadow each other.

Microscopic counts: if the culture is too big, they cannot be counted.
Flow cytometry: separates size and pigment in cells in water sample.

Viable cell count:
Dilution and plating: the sample has to be diluted otherwise there will be way too many cells, but one will have to count a rather big sample to be most precise.
Membrane filtration: analysis of water sample: if the result of one water sample is not enough then it is placed on an agar plate, but on the other hand there can be too many in one sample.
Most probable number:

Question 62

Which biogeochemical cycles do you know?

Answer 62

The carbon cycle (most important): by photosynthesis CO2 is reduced to CH2O and O2 is released. By fermentation and anaerobic respiration organic molecules are catabolized to other products such as alcohol, acids, CO2 and H+. Pressure, heat and anaerobiosis make fossil fuels. Anaerobic lithotrophy CO2 is reduced to the organic biomass CH2O or CO2 is converted to methan (CH4) by methanogenesis. Methan is oxidized to CH2O by methanotrophy. CH2O is oxidized to CO2 by respiration. CO2 is reduced to organic biomass CH2O by lithotrophy.

The nitrogen cycle: N2 can be fixated to NH4+. Nitrification (oxidation) oxidizes NH4+ and NH3 to NO2- and further to NO3-. Anaerobic ammonia oxidation by NO2- (anammox) Bacterial and archaeal denitrification (anoxic, reduction) reduces NO3- to NO2- further to NO to N2O to N2.
Sulfur cycle: sulfur /sulfid oxidation: H2SS0SO42-, sulfate reduction: SO42-  H2S, sulfur reduction (anoxic): S0H2S.

Phosphate cycle: soluble phosphate is taken up by bacteria and plants (PO43-)
The iron cycle: Fe3+ is reduced by anaerobic respiration to Fe2+which can produce salts or be taken up by bacteria or plants.

Question 63

Which types of symbioses do you know? Which of those are beneficial for both partners?

Answer 63

Syntrophy (metabolic association, both partners need a ∆G<0),
synergism (optional, both benefits but they can live separate),
commensalism (one partner benefits the other is unaffected),
amensalism (one partner is harmed without an association),
parasitism (one partner benefits while the host is harmed)

Question 64

Which selective medium do you know to enrich for Azotobacter? What is making it selective?

Answer 64

I would use mannite agar and a medium without nitrogen hence azotobacter is capable of nitrogen fixation.

Question 65

What special features have clostridia that could help with enriching or isolating them?

Answer 65

They thrive at anoxic conditions.

Question 66

When do we talk of an epidemic disease?

Answer 66

Rapid spread of a disease to a large number of individuals in a population over a short period of time.

Question 67

Where on/”in” a human body do you find microbes? How many (in total/in specific places)?

Answer 67

We find microbes in our teeth, skin (107 cells cm-2), vagina and other openings, intestines (1011 cells mL-1) stomach almost sterile due to the low pH (2).

Question 68

What is an infectious dose?

Answer 68

Infectious dose: number of microbes required to cause disease symptoms in half of an experimental group of hosts.

Question 69

What does an LD50 describe?

Answer 69

The dose where 50 percent of the population are dead.

Question 70

Which types of toxins do you know?

Answer 70

Exotoxins (enterotoxins, neurotoxins, cytoxins, pyrogenic toxins) and endotoxins (lipid A in lipidpolysaccharides – gram negative).

Question 71

What targets for antibiotics do you know? With which mechanisms can bacteria be resistant to antibiotics?

Answer 71

Cell wall synthesis, DNA gyrase (DNA syntese), RNA elongation, DNA-directed RNA polymerase, protein synthesis (50S inhibitors), protein synthesis (30S inhibitors), protein synthesis (tRNA), cytoplasmic membrane structure, folic acid metabolism.

Question 72

Lactic acid bacteria grow under oxic or anoxic conditions?

Answer 72

Lactic acids grow under anaerobically but can grow in oxic conditions and therefore have superoxide dismutase and some peroxidase.
Mælkesyrebakterier er en gruppe af Gram-positive, generelt ikke sporeformede, ikke-respirerende rod eller cocci?. En fælles metabolisk egenskab er deres evne til at producere mælkesyre som et væsentligt metabolisk slutprodukt af kulhydratgæring og deres øgede tolerance til at vokse i et lavere pH-interval. Dette giver mælkesyrebakterier mulighed for delvis at udkonkurrere andre bakterier i naturlig gæring, da de kan modstå den øgede surhedsgrad forårsaget af mælkesyreproduktionen.)

Alle mælkesyrebakterier vokser anaerobt, men i modsætning til de fleste anaerober vokser de i nærværelse af O2 som “aerotolerante anaerober”. Fordi de kun opnår energi fra metaboliseringen af sukker, er mælkesyrebakterier begrænset til omgivelser, hvor sukker er til stede.

Question 73

Which method would you use to disinfect surfaces?

Answer 73

I would use ethanol with 70 %, because it denaturates proteins, in 90 % the cells will loose water which will make them produce endospores.

Question 74

Which shape do Lactococcus cells have?

Answer 74

Cocci shaped.

De er kugleformede og lægger sig typisk sammen i ”kæder” (måske er de i kæder fordi de deler sig hurtigt).

Question 75

Mention and describe the different shapes bacterial colonies can have.

Answer 75

De tre grundlæggende bakterieformer er coccus (spherical), bacillus (rod-shaped) og spiral (snoet), men pleomorfe bakterier kan antage flere former. Cocci (eller coccus for en enkelt celle) er runde celler, nogle gange let flade, når de støder op til hinanden

Question 76

Which types of staining techniques do you know? What do they detect/can be used for?

Answer 76

Grunden til, at vi benytter os af bakteriefarvning, er bl.a. for at kunne tydeliggøre bakteriecellens omrids, altså form, og specifikke strukturer, fx cellevægsopbygningen med mere, og derved bl.a. at hjælpe til at kunne identificere hvilken slags bakterie vi har med at gøre.

Vi kender til:

• Generel farvning med methylenblåt
  Man farver bakterierne på et objektglas med methylenblåt, og når man afskyller det overskydende farvestof, er cellerne (membranen?) i vævsceller og gram-negative og -positive bakterier farvet blåt, mens cytoplasma i vævsceller, syrealkoholfaste bakterier og proteinpræcipitater på objektglas ikke er blevet farvet. Methylenblåt bliver også brugt i mange andre farvningsmetoder (fx Ziehl-Neel-sen farvning, gram-farvning og flagelfarvning m.fl.).
• Ziehl-Neelsen-farvning
  Det er en metode, der er blevet brugt til at identificere syrefaste organismer (også kaldet syrefast farvning), som fx Mycobakterier.
  Måden denne metode bruges på er ved, at man starter med at farve med carbol-fuchsin (som er rødt), hvor-efter man affarver med syrealkohol og til sidst farver man med methylenblåt. Da de syrefaste bakterier ikke affarves med syrealkoholen forbliver de røde, hvor resten bliver blå pga. methylenblåt. På den måde kan man isolere og identificere de syrefaste bakterier.
• Flagelfarvning
  Her farver man svingtråde/flageller.
  Metode til flagelfarvning, som består af, at man bruger en blanding af basisk fuksin i alkohol, Tannin og NaCl i vand til farvningen (har svært ved at finde mere, men tror heller ikke det er noget vi skal kunne).
• Spore- og kapselfarvning