Microbiology Lecture 22

Reduction tower order of things

Right: Reduced form. Substance has been through gaining electrons and now has available electrons ready to donate.

Left: Oxidized form. Substance has been through losing electrons. Now is ready to accept electrons.

Reduced form will donate electrons to the oxidized form under it in the redox tower.

Metabolic wise; Bacteria can be separated into 2 cateogies:

Energy Source

Carbon Source

Energy Source

Bacteria can use both organic and inorganic compounds. Humans can only use organic compounds.

Consists of Electron acceptors and Electron donors. Usable Energy is released when electrons are transferred between electron donors and acceptors.

Shewanella oneidensis

MnO2 is going to accept electrons and is reduced to soluble Mn2+

Relationship between bacteria and antibiotics

Bacteria can eat antibiotics

Energy Source

Photo: Energy from light

Chemo: Energy from chemical reactions.

Electron donor

Organotroph: Electron donor is organic and has C-H bonds.

Lithotroph: Electron donor is inorganic. H2S, NH4+, Fe2+

Carbon Source

Heterotroph: Organic. Carbon source is not CO2

Autotroph: Carbon source is CO2

Glycolysis

-Process of breaking down glucose into smaller molecules.
-Commonly refers to the EMP pathway.

-A common pathway for catabolism of glucose.

-No oxygen is required.

-ATP is generated by substrate level phosphorylation.

-Generates 2 ATP, 2 NADH, and 2 pyruvates.

Glycolysis pathway

-We start with 1 glucose molecule.

-ATP donates a phosphate group making it ADP, and the glucose molecule becomes glucose 6P.

-Glucose 6P is rearranged into fructose 6P.

-Another ATP donates its phosphate group to become Fructose 1,6 biphosphate. (now has 2 phosphate groups)

-We now have used 2 ATP’s.

-That fructose 1,6 biphosphate molecule splits into 2 molecules, each containing 3 carbons.

-Both molecules eventually become glyceraldehyde-3-phosphate (G3P molecules).

-Each G3P molecule becomes oxidized and loses electrons.

-NAD+ accepts those electrons and become NADH. Since we have 2 G3P molecules, 2 NADH’s are produced.

-Each 3 carbon molecule (G3P) produces 2 ATP. Since we have 2, 4 ATP’s are produced. But we end up with 2 because 2 are used in this process.

-At the end, our 3 carbon molecules become 2 pyruvate molecules.

Multiple glycolysis?

There is more than 1 glycolysis.

Glucose can be oxidized by several pathways.

Pentose Phosphate pathway (PP) pathway generates NADH and precursors for anabolic pathways.

Entner-Doudoroff Pathway (ED)

Required for gluconate utilization. Gluconate is a nutrient compound.

Plays an important role in the E.Coli growth in human intestines.

Absent from humans.

Lactic Acid Fermentation

Carried out by lactic acid bacteria. Gram + bacteria can only ferment. Bacteria use lactic acid fermentation to regenerate NAD⁺ so glycolysis can continue producing ATP.

Step 1) Glycolysis breaks down glucose.

Step 2) Remember that NAD⁺ accepts electrons and becomes NADH.

But here's the problem: glycolysis needs NAD⁺ to keep running.

If all the NAD⁺ becomes NADH and we don't regenerate NAD⁺, glycolysis will eventually stop. So bacteria need a way to turn NADH back into NAD⁺.

Step 3) Lactic Acid solves this problem. NADH will donate electrons to pyruvate. Because NADH loses electrons, it is oxidized to NAD+. This way glycolysis can continue.

What is produced in lactic acid fermentation? What happens chemically?

1 glucose molecule forms 2 lactic acid molecules.

Keto group is reduced to a hydroxyl (alcohol) group.

Ethanol Fermentation

Carried out by Yeast, Zymomonas (proteobacteria) and other organisms like E.Coli that produce ethanol.

Step 1) Glycolysis

Step 2)The 2 pyruvate molecules are converted into 2 acetaldehyde molecules. During this process, 2 CO₂ molecules are released.

Step 3) Acetaldehyde acts as the electron acceptor. 2 acetaldehyde molecules accept electrons from 2 NADH, regenerating 2 NAD+ and producing 2 ethanol.

Zymomonas are used to make

pulque. It also provides an archaeological signature.

Fermentation

The main purpose of fermentation is to regenerate NAD⁺ so glycolysis can keep producing ATP.

There is an enormous diversity in fermentation reactions. It is of high importance in the food industry.

Streptococcus mutans

-A bacterium found in your mouth that contributes to cavities.

-This bacterium uses glucose as an energy source.

-Goes through glycolysis and lactic acid fermentation.

-The production of lactic acid lowers the pH in your mouth, creating an acidic environment that damages tooth enamel and promotes tooth decay

Sucrose in Streptococcus mutans

Helps Streptococcus mutans bacteria form biofilms, allowing bacteria to remain on the surface of the tooth. Bacteria can then undergo glycolysis and lactic acid fermentation. Lactic acid lowers pH, and an acidic environment damages the enamel quality, leading to cavities.

Dental Plaque experiment

Volunteers were implanted with pH microelectrodes in partial dentures which measured plaque pH in caries-free patients (without cavities) and caries active patient (with cavities)

Lactic Acid Bacteria use sugar (metabolizing) to produce lactic acid. (They also produce biofilms)

The critical pH for enamel dissolution is 5.3

Citric Acid Cycle

-A highly conserved metabolic cycle.

-Required by many anabolic processes

as intermediates can be used for

biosynthesis

-Required for catabolism by many

heterotrophs

Citric Acid Cycle

1) Glucose goes through glycolysis to produce 2 ATP Net, 2 pyruvate, and 2 NADH.

2) Pyruvate oxidation: Before entering the citric acid cycle, the 2 pyruvate molecules are converted into 2 acetyl-CoA molecules. This releases 2 CO2 molecules. Electrons removed from pyruvate are accepted by 2 NAD⁺ molecules. Those 2 NAD⁺ molecules are reduced to 2 NADH.

3)Citric acid cycle: The 2 acetyl-CoA molecules enter the cycle, producing a total of:

Each acetyl-CoA produces:

• 2 CO₂

• 3 NADH

• 1 FADH₂

• 1 ATP

That gives you 4 CO₂, 6 NADH, 2 FADH₂, and 2 ATP from the citric acid cycle.

What happens to the NADH made from citric acid cycle?

Goes through electron transport chain to produce 34 ATP.