Bacterial Metabolism & Growth Flashcards
(49 cards)
Biochemical reactions bacteria use to break down organic compounds and reactions they use to synthesize new bacterial parts from the resulting carbon skeleton
Bacterial metabolism
Biochemical processes of metabolism by which molecules are broken down.
Catabolism
Synthesis of complex molecules in living organisms from simpler ones together with the storage of energy; constructive metabolism.
Anabolism
Diagnostic schemes analyze each unknown microorganism for:
- Utilization of various substrates as a carbon source
- Production of specific end products from various substrates
- Production of an acid or alkaline pH in the test medium
Breakdown of chemical substrate through the degradative process of catabolism coupled with oxidation reduction reactions
Energy Production
Bacteria use biochemical pathways to catabolize (break down) carbohydrates and produce energy by two mechanisms:
- Fermentation
- Respiration (oxidation)
• Anaerobic process carried out by both obligate and facultative anaerobes
• Electron acceptor is an organic compound less efficient in energy generation beginning substrate is not completely reduced
• A mixture of end products lactate, butyrate, ethanol, and acetoin accumulates in the medium identification of anaerobic bacteria
FERMENTATION
• Efficient energy generating process
• Molecular oxygen is the final electron acceptor
• Obligate aerobes and facultative anaerobes
RESPIRATION (OXIDATION)
True or false:
Certain anaerobes can carry out anaerobic respiration, in which inorganic forms of oxygen, such as nitrate and sulfate act as the final electron acceptors
True
Three major biochemical pathways bacteria use to break down glucose to pyruvic acid:
Embden Meyerhof Parnas (EMP) Glycolytic pathway
Pentose Phosphate Pathway
Entner-Doudoroff Pathway
• Major pathway in conversion of glucose to pyruvate
• Generates reducing power in the form of NADH 2
• Generates energy in the form of ATP
• Anaerobic does not require oxygen
o Example:
▪ Enterobacteriaceae
Embden Meyerhof Parnas (EMP) Glycolytic pathway
• Alternative to EMP pathway
• Glucose to ribulose 5 phosphate, which is rearranged into other 3 4 5 6 and 7 carbon sugars
• Provides pentoses for nucleotide synthesis
• Produces glyceraldehyde 3 phosphate, which can be converted to pyruvate
• Generates NADPH, which provides reducing power for biosynthetic reactions
• May be used to generate ATP
Pentose Phosphate Pathway
• Glucose 6 phosphate (rather than glucose) to pyruvate and glyceraldehyde phosphate
• Generates one NADPH per molecule of glucose but uses one ATP
Entner-Doudoroff Pathway
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• Major end product is ethanol
• Example: yeasts
Alcoholic Fermentation
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• End product is almost exclusively lactic acid
• Example
o All members of the Streptococcus genus
o Members of the Lactobacillus genus
Homolactic Fermentation
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• In addition to lactic acid, the end products include carbon dioxide, alcohols, formic acid, and acetic acid
• Example: Some lactobacilli
Heterolactic Fermentation
Anaerobic Utilization of Pyruvic Acid (Fermentation):
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• Propionic acid is the major end product of fermentations
• Example:
o Propionibacterium acnes
o Some anaerobic non spore forming, gram positive bacilli
Propionic Acid Fermentation
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• Produce a number of acids as end products lactic, acetic, succinic, and formic acids
• Strong acid produced is the basis for the positive reaction on the methyl red test
o Example: Members of:
▪ Escherichia
▪ Salmonella
▪ Shigella
Mixed Acid Fermentation
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• End products are acetoin (acetyl methyl carbinol) and 2,3-butanediol
• Detection of acetoin is the basis for the positive VP reaction
• Little acid is produced by this pathway
Butanediol Fermentation
True or false:
Organisms that have a negative VP reaction usually have a negative reaction on the methyl red test, and vice versa
False. Organisms that have a POSITIVE VP reaction usually have a negative reaction on the
methyl red test, and vice versa
Anaerobic Utilization of Pyruvic Acid (Fermentation):
• Involves the conversion of pyruvate to butyric acid along with acetic acid, CO2 and Hydrogen
• Example:
o Clostridium
o Fusobacterium
o Eubacterium
Butyric Acid Fermentation
- Most important pathway for the complete oxidation of a substrate under aerobic conditions
- Pyruvate is oxidized, carbon skeletons for biosynthetic reactions are created, and the electrons donated by pyruvate are passed through an electron transport chain and used to generate energy in the form of ATP
- Results in the production of acid and the evolution of carbon dioxide
Krebs or Tricarboxylic acid (TCA) Cycle
• Use of various sugars (carbohydrates)
• Fermentation is usually detected by acid production and a concomitant change of color resulting from a pH indicator present in the culture medium
Carbohydrate Utilization and Lactose Fermentation
