Microbial Metabolism

A. Basic Concepts Definitions

Metabolism: The processes of catabolism and anabolism

Catabolism: The processes by which a living organism obtains its energy and raw materials from nutrients

Anabolism: The processes by which energy and raw materials are used to build macromolecules and cellular structures (biosynthesis)

Overview of cell metabolism

What are nutrients that bacteria want?

C Sugar, Lipid Energy, Biosynthesis

N Protein Biosynthesis

O Air Energy

BreakdownProteins to Amino Acids, Starch to Glucose

SynthesisAmino Acids to Proteins, Glucose to Starch

Bacterial Metabolism ☺ 

  Exoenzymes: Bacteria cannot transport large polymers into the cell. They must break them down into basic subunits for transport into the cell. Bacteria therefore elaborate extracellular enzymes for the degradation of carbohydrates to sugars (carbohydrases), proteins to amino acids (proteases), and lipids to fatty acids (Lipases).

– After Sugars are made or obtained, they are the energy source of life.

– Breakdown of sugar(catabolism) different ways:

• Aerobic respiration• Anaerobic respiration • Fermentation

Energy Generating Patterns

Aerobic respiration– Most efficient way to extract energy from

glucose.– Process: Glycolysis

Kreb Cycle

Electron transport chain– Glycolysis: Several glycolytic pathways– The most common one:

glucose-----> pyruvic acid + 2 NADH + 2ATP

B. Glycolytic Pathways 4 major glycolytic pathways found in different

bacteria: Embden-Meyerhoff-Parnas pathway

“Classic” glycolysis Found in almost all organisms

Hexose monophosphate pathway Also found in most organisms Responsible for synthesis of pentose sugars used in

nucleotide synthesis

Entner-Doudoroff pathway Found in Pseudomonas and related genera

Phosphoketolase pathway Found in Bifidobacterium and Leuconostoc

Formation of intermediates of the Embden– Meyerhof–Parnas (EMP) and Entner–Doudoroff (ED) pathway

from carbohydrates other than glucose

BIOCHEMICAL REACTIONS OF RESPIRATION

Carbohydrate Metabolism

4. TCA cycle

Anaerobic respiration– Final electron acceptor : never be O2 Sulfate reducer: final electron acceptor is sodium

sulfate (Na2 SO4) Methane reducer: final electron acceptor is CO2 Nitrate reducer : final electroon acceptor is

sodium nitrate (NaNO3)

O2/H2O coupling is the most oxidizing, more energy

in aerobic respiration.

Therefore, anaerobic is less energy efficient.

C. Fermentation Features of fermentation pathways

Pyruvic acid is reduced to form reduced organic acids or alcohols.

The final electron acceptor is a reduced derivative of pyruvic acid

NADH is oxidized to form NAD: Essential for continued operation of the glycolytic pathways.

O2 is not required. No additional ATP are made. Gasses (CO2 and/or H2) may be released

Fermentation Glycosis:Glucose ----->2 Pyruvate + 2ATP + 2NADH

Fermentation pathwaysa. Homolactic acid F.

P.A -----> Lactic Acideg. Streptococci, Lactobacilli

b.Alcoholic F.P.A -----> Ethyl alcoholeg. yeast

Nutrition

Table 27.1

Alternative energy generating patterns(3)

Alternative energy generating patterns(4)

Energy/carbon classes of organisms

Fig. 5-12

Overview of Metabolism