Microbial metabolism Flashcards
Autotrophic bacteria?
Build their cellular structure using carbon dioxide (CO2)
Such bacteria has probably been formed early in evolution
Heterotrophic bacteria?
Require organic carbon as its carbon source
E.g. chemoorganotrophs
Most nitrogen in nature is available as?
Ammonia (NH3), which can be used by virtually all prokaryotes as nitrogen source
Nitrate (NO3), which can be used by many prokaryotes as nitrogen source
Nitrogen gas (N2), which can only be used by nitrogen-fixing prokaryotes
EDTA?
is often added to bacterial lysis-buffers
Artificially produced acid
Is a chelating agent
Has the ability to “sequester” metal ions such as Ca2+ and Mg2+
Destabilizing the membrane, which requires Mg2+
The result is usually bacterial lysis
Trace elements (trace metals)?
Trace elements typically act as cofactors for enzymes
The main trace element is iron (Fe), which is a key-component of cytochromes
and iron-sulphur proteins, which are of essential function in electron transport
reactions
Growth factors (organic micronutrients)?
Vitamins, which acts as coenzymes
Amino acids
Purines
Pyrimidines
Chemotrophs?
(oxidize chemicals for electrons)
Chemoorganotrops (organic chemicals, such as glucose, acetate etc.)
Chemolithotrophs (inorganic chemicals, such as H2, H2S, Fe2+, NH3 etc.)
Phototrophs?
Contain pigment that allow them to convert sunlight into chemical energy
Oxygenic photosynthesis (O2 is produced)
Anoxygenic photosynthesis (does not yield O2)
The Redox-tower?
Most negative E0 values on the top
Most positive E0 values at the bottom
Reduced substance in redox-couple has greatest tendency to donate electrons
The oxidized substance in a redox couple has the greatest tendency to accept electrons
The further the electrons drop from a donor before they are caught by an acceptor, the
greater the amount of energy released
Fermentation tests?
To grow bacteria in the presence of glucose, sucrose, lactose and mannitol (or other
carbohydrates) with addition of bromothymol blue (BTB)
If the bacteria can ferment the sugar acids will be produced and the pH is lowered in
the medium
SIM-test?
S: Hydrogen sulphide-production
Sulphur is a coproduct from cysteine
If an organism can reduce Sulphur to hydrogen sulfide, the H2S will combine
with iron, which is present in the test tube, to form ferric sulfide
I: Production of indole
Indole is a coproduct of tryptophan, which can form complex with added
Kovack’s reagent, and then turns red
M: Motility
Urease test?
To grow bacteria in the presence of urea with addition of phenol-red
If the bacteria produce urease, ammonia and carbon dioxide will be produced and the pH
is increased in the medium
(NH2)2CO + H2O CO2 + 2NH3
Catabolism?
Glycolysis
Synthesis of acetyl CoA
Kreb’s cycle
Electron transport chain
Three main events are important for electron transport chain’s generation of ATP?
Redox reactions
Creation of proton gradient
Chemiosmosis
Cytochrome c oxidase test?
An enzyme that oxidizes cytochrome c and is thus transformed itself into the
reduced and inactive form
Through transfer of the electrons to molecular oxygen the reduced cytochrome
oxidase is transformed again into the active form
With a commercial kit?
Positive: the bacterium contains cytochrome c oxidase and can therefore use
oxygen for energy production by converting O2 to H2O2 or H2O with an electron
transfer chain
Toxic oxygen?
Anaerobic bacteria are inhibited or killed by oxygen
O2 is converted to toxic oxygen by-products when O2 is reduced to H2O during
respiration
Superoxide anions (O2
-
), hydrogen peroxide (H2O2) and hydroxyl radicals (OH•)
Toxic oxygen molecules must be controlled
Catalase, peroxidase, superoxide dismutase or superoxide reductase
Catalase test?
The presence of catalase enzyme in the test isolate is detected using hydrogen peroxide
If the bacteria possess catalase (i.e. are catalase-positive), when a small amount
of bacterial isolate is added to hydrogen peroxide, bubbles of oxygen are
observed
Anaerobic respiration?
Many anaerobic bacteria can create ATP by using something else than oxygen as electron acceptor Nitrate, NO3 - (reduced to nitrite, NO2 - ) Sulphate, SO4 2- (reduced to hydrogen sulphide, H2S) Carbonate, CO3 2- (reduced to methane or acetate) Less energy is conserved when they are reduced as compared to the reduction of O2 Higher up in the Redox-tower means less ATP-production Electron transport chain is required!
Fermentation?
When no electron acceptor exists in the electron transport chain this cannot happened
Fermentation is an alternative system that allows the glycolysis to proceed without the
other steps of respiration
© Erik Gustafsson 9
Essential function of fermentation
Oxidize NADH into NAD+
Acetic acid bacteria?
Some bacteria can convert ethanol to acetic acid
Can be a problem (Acetobacter spp.) when making wine since the bacteria is
usually abundant in windfall fruit
H2S inhibits growth and is often added as preservative
