Unit 3. Bacterial Metabolism

• substrates as a carbon source

• specific end products

• acid or alkaline pH

Diagnostic schemes analyse each unknown microorganism for: (3)

Acetamide Utilization Test

• Pseudomonas aruginosa

• uses acetamide as its carbon

• Escherichia coli

• uses acetate as its carbon

Example of (1) utilization of various substrates as a carbon source

Voges–Proskauer (VP) Test

• acetoin & 2,3-butanediol

• Enterobacteriaceae

Example of (production of specific end products from various substrates)

1. Fermentation

2. Respiration (oxidation)

Bacteria use biochemical pathways to catabolize (break down) carbohydrates and produce energy by two mechanisms:

FERMENTATION

is an anaerobic process in which bacteria break down carbohydrates to produce ATP (energy) without using oxygen.

Obligate anaerobes

Facultative anaerobes

what type of organisms can carry out FERMENTATION?

organic compound

what is the final electron acceptor in fermentation?

FERMENTATION

this process is less efficient in energy generation---beginning substrate is not completely reduced

• Lactate (lactic acid)

• Butyrate (butyric acid)

• Ethanol

• Acetoin

[BELA]

ENUMERATE

Common end products of fermentation.

(These products accumulate in the culture medium and are detected by biochemical tests.)

1. Voges-Proskauer (VP) Test

2. Methyl Red Test

Tests utilized in detecting fermentation

Acetoin

Voges-Proskauer (VP) fermentation test detects _________.

Voges-Proskauer (VP)

dects microorganisms that are capable of converting acid products of fermentation of 23-butanediol and acetoin

red

positive VP test will yield what color?

red

positive methyl red test will yield what color?

No red color (often remains copper/brown depending on the reagent reaction).

negative VP test will yield what color?

IMVC Test

• Indole

• Methyl Red

• VP

• Citrate

VP and Methyl Red tests are a part of which test commonly for enterobacteriaceae

Methyl Red Tests

Detects the production of mixed acid fermentation

yellow

negative methyl red test will yield what color?

molecular oxygen (O₂)

what is the final electron acceptor in aerobic respiration?

inorganic forms of oxygen

• Nitrate (NO₃⁻)

• Sulfate (SO₄²⁻)

what is the final electron acceptor in anaerobic respiration?

RESPIRATION

is process wherein bacteria produce ATP, which is efficient energy-generating process

• Obligate aerobes

• facultative anaerobes

what type of organisms can carry out RESPIRATION?

1. Embden-Meyerhof-Parnas (EMP) Glycolytic pathway

2. Pentose Phosphate Pathway

3. Entner-Doudoroff Pathway

Three major biochemical pathways bacteria use to break down glucose to pyruvic acid are:

EMBDEN-MEYERHOF-PARNAS (EMP) GLYCOLYTIC PATHWAY

Major pathway in conversion of glucose to pyruvate (90%)

Enterobacteriaceae

• Escherichia coli

• Salmonella

• Shigella

• Klebsiella

example of bacteria that uses EMP pathway

EMBDEN-MEYERHOF-PARNAS (EMP) GLYCOLYTIC PATHWAY

An anaerobic pathway that generates reducing power in the form of NADH2 and energy in the form of ATP

NADH2

EMBDEN-MEYERHOF-PARNAS (EMP) GLYCOLYTIC PATHWAY

• Generates reducing power in the form of

ATP

EMBDEN-MEYERHOF-PARNAS (EMP) GLYCOLYTIC PATHWAY

• Generates energy in the form of

PENTOSE PHOSPHATE PATHWAY

An alternative pathway that converts glucose into ribulose-5-phosphate → 3-, 4-, 5-, 6-, and 7-carbon sugars → glyceraldehyde-3-phosphate

Ribulose-5-phosphate.

First major intermediate in PPP

• Lactobacilli

• Brucella abortus.

Example of bacteria using PPP

Heterolactic fermentation

what metabolic process is being used by Lactobacilli

Brucella abortus

this bacteria lacks some of the enzymes used required in the EMP pathway, thus it utilizes PPP

PENTOSE PHOSPHATE PATHWAY

• Provides pentoses for nucleotide synthesis

• Produces glyceraldehyde-3-phosphate, which can be converted to pyruvate

• May be used to generate ATP

NADPH

PENTOSE PHOSPHATE PATHWAY

• Generates _______, which provides reducing power for biosynthetic reactions

ENTNER-DUODOROFF PATHWAY

An alternative pathway that converts glucose-6-phosphate into pyruvate and glyceraldehyde-3-phosphate while producing NADPH.

ENTNER-DUODOROFF PATHWAY

this pathway generates one NADPH per molecule of glucose but uses one ATP

Glucose-6-phosphate.

Starting molecule of ED pathway

• Pseudomonas

• Alcaligenes

• Enterococcus faecalis

• Other bacteria lacking certain glycolyticenzymes

Example of bacteria using ED pathway

Alcoholic fermentation

Fermentation in which pyruvate is converted mainly into ethanol and CO₂

yeasts

Alcoholic fermentation example

Homolactic fermentation

Fermentation that produces almost exclusively lactic acid

• All members of the Streptococcus genus

• Members of the Lactobacillus genus

example of bacte. that utilizes Homolactic fermentation:

Heterolactic fermentation

Fermentation that produces lactic acid, CO₂, alcohols, formic acid, and acetic acid;

some Lactobacillus.

Heterolactic fermentation examples

• Lactic acid

• CO2

• Alcohols

• Formic acid

• Acetic acid

[CAFAL]

ENUMERATE

Heterolactic fermentation end products

Propionic acid fermentation

Fermentation whose major end product is propionic acid. characteristic of Propionibacterium acnes.

• Propionibacterium acnes

• Some anaerobic non–spore-forming, gram-positive bacilli

example of bacte. that utilizes Propionic acid fermentation:

Mixed acid fermentation

Fermentation that produces lactic, acetic, succinic, and formic acids; characteristic of Escherichia, Salmonella, and Shigella.

• Lactic acid

• Acetic

• Succinic

• Formic acid

[LAFS]

ENUMERATE

Mixed acid fermentation end products

• Escherichia

• Salmonella

• Shigella

example of bacte. that utilizes Mixed acid fermentation:

Butanediol fermentation

Fermentation producing acetoin and 2,3-butanediol with relatively little acid; typical of Klebsiella, Enterobacter, and Serratia.

• Klebsiella,

• Enterobacter

• Serratia

example of bacte. that utilizes Butanediol fermentation:

Butyric acid fermentation

Fermentation producing butyric acid, along with acetic acid, CO₂, and H₂; common in Clostridium, Fusobacterium, and Eubacterium.

• Clostridium

• Fusobacterium

• Eubacterium

example of bacte. that utilizes Butyric acid fermentation:

True

T or F

Organisms that have a positive VP reaction usually have a negative reaction on the methyl red test, and vice versa.

KREBS OR TRICARBOXYLIC ACID (TCA) CYCLE

The major aerobic pathway that completely oxidizes pyruvate, generates electron carriers (NADH and FADH₂), releases CO₂, and supplies intermediates for biosynthesis.

a. low (acidic)

during fermentation, pH is

a. high

b. low

β-galactoside permease

Membrane protein that transports lactose into the bacterial cytoplasm.

β-galactosidase

enzyme that break the galactoside bond, releasing glucose, which can be fermented

False

All lactose fermenters can ferment glucose, but not all glucose fermenters can ferment lactose.

T or F

All lactose fermenters can ferment glucose and vice versa

Glucose

_______ must not be present if the ability to ferment another sugar is being tested

• acid production

CARBOHYDRATE UTILIZATION AND LACTOSE FERMENTATION

• Fermentation is usually detected by ____________ and a concomitant change of color resulting from a pH indicator present in the culture medium

1. biosynthesis of new cell components

2. Maintenance of the physical and chemical integrity of the cell

3. Activity of the locomotor organelles

4. Transport of solutes across membranes

5. heat production

ENUMERATE

reasons for energy utilization of bacte.