Microbial metabolism

Question 1

Autotrophic bacteria?

Answer 1

 Build their cellular structure using carbon dioxide (CO2)

 Such bacteria has probably been formed early in evolution

Question 2

Heterotrophic bacteria?

Answer 2

 Require organic carbon as its carbon source

 E.g. chemoorganotrophs

Question 3

Most nitrogen in nature is available as?

Answer 3

 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

Question 4

EDTA?

Answer 4

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

Question 5

Trace elements (trace metals)?

Answer 5

 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

Question 6

Growth factors (organic micronutrients)?

Answer 6

 Vitamins, which acts as coenzymes
 Amino acids
 Purines
 Pyrimidines

Question 7

Chemotrophs?

Answer 7

(oxidize chemicals for electrons)
 Chemoorganotrops (organic chemicals, such as glucose, acetate etc.)
 Chemolithotrophs (inorganic chemicals, such as H2, H2S, Fe2+, NH3 etc.)

Question 8

Phototrophs?

Answer 8

 Contain pigment that allow them to convert sunlight into chemical energy
 Oxygenic photosynthesis (O2 is produced)
 Anoxygenic photosynthesis (does not yield O2)

Question 9

The Redox-tower?

Answer 9

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

Question 10

Fermentation tests?

Answer 10

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

Question 11

SIM-test?

Answer 11

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

Question 12

Urease test?

Answer 12

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

Question 13

Catabolism?

Answer 13

 Glycolysis
 Synthesis of acetyl CoA
 Kreb’s cycle
 Electron transport chain

Question 14

Three main events are important for electron transport chain’s generation of ATP?

Answer 14

 Redox reactions
 Creation of proton gradient
 Chemiosmosis

Question 15

Cytochrome c oxidase test?

Answer 15

 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

Question 16

With a commercial kit?

Answer 16

 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

Question 17

Toxic oxygen?

Answer 17

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

Question 18

Catalase test?

Answer 18

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

Question 19

Anaerobic respiration?

Answer 19

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!

Question 20

Fermentation?

Answer 20

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+

Question 21

Acetic acid bacteria?

Answer 21

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