(click here for help navigating the site and for misc site info)

 

Index | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16  

BIO 341 Lecture Topic 16: 

For best results in printing, download the PDF version of this page 

Corresponding Readings:
  • TBA 
Printed Notes, Main Points:

(click on the main point headings to jump to the selected location in the notes)


Metabolic Relationships of Fungi with Oxygen

 

Majority        =          obligate aerobes

 

Many                        =          facultative anerobes

 

Some                       =          obligately fermentative

 

Few*                        =          obligately aneroblic

 

* Only recently discovered among animal gut organisms.  Therefore, may be many that yet need to be discovered.

447

(Back to main points)


Major Respiratory Pathways Associated with Obligately Aerobic Fungi

 

1.      Glycolytic/Embden, Meyerhoff, Parnas (EMP) pathway

 

2.      Pentose phosphate (PP) pathway

 

3.      Entner Doudoroff (ED) pathway

 

4.      Tricarboxylic acid (TCA) or Krebs cycle pathway*

 

* Operates in conjunction with an electron transport chain that dictates that oxygen acts as the final electron/hydrogen acceptor.  (see pp. 14 and 15 of handouts)

448b

(Back to main points)


Aqualinderella fermentans

 

1.      [O2] does not affect amount of lactate produced

 

2.      [O2] does not affect amount of glucose consumed

 

3.      [O2] does not affect amount fungus grows or at rate it grows*

 

*no concentration dependency of biomass production on [O2*] as seen with other fungi.

 

Thus, obligate fermentative fungus, as Leucosporidium (Candida) stoffii & RD mutants of S. cereviseae & N. crassa

453

(Back to main points)


Stage I Events   Conversion of C-6 compounds to appropriate forms and their subsequent phosphorylation.

                     a.  ATP requiring step.

 

Stage II Events -   Degradation of the phosphorylated C-6 compounds to C3 compounds by various pathways.

                     a.         These degradation steps can result in the release of no more than  1/3 of the original          free energy of the hexose.

454

(Back to main points)


Stage III Events -  Degradation of the C-3 compounds to the C-1 compound CO2

                     a.         These events (Stage III) bring about the     formation of numerous intermediates                                                      which can be used as substrates for anabolic processes or they can accumulate; e.g., citric acid.

 

                     b.         Release of most of remaining free energy of the original hexose molecule.

455

(Back to main points)


Stage 1 Phosphorylation

Hexokinase*

 

                                

* Constitutive in yeast & probably other (all?) fungi having enzyme - S. cereviseae 2 isoenzymes

 

* Specificity low = will phosphorylate D-fructose, 5-beta-D-fructose, 2 deoxy-D-glucose, mannose, D-glucosamine

456a

(Back to main points)


Primary Accumulated Metabolism

("overflow metabolism")

 

Caused by metabolic lesions (disruptions in normal enzyme system caused by mutation or abnormal growing conditions with strain having selected enzymes)

                                                                                                                     stressed

                                                                                                  enzyme

A                              B                                 C                                                                     D

                                                                                                 (low Km)

 

                                                                                                         trapped inside of

                                                                                 C overflow      cell or released

                                                                                                         into medium

 

*examples   ethanol, citric acid, phenylalanine, etc., etc., etc.

470

(Back to main points)


Conditions for Citrate Production

 

1.      high glucose (15 - 20%)

2.      low pH (  2- 4.5)

3.      high aeration

4.      NH4 NO3 [ ] of 2-2.5 g/l

 

Main agent of production*

 

Aspergillus niger

 

world wide 1978  175,000 tons/year

 

*see handout p. 30

471

(Back to main points)


Secondary Metabolites*

("shunt metabolites")

Compounds produced by microorganisms having no known function in cells and little or no known economy for cells.

 

* Production often has little or no taxonomic relevance

 

Examples:  penicillins, cephalosporins, cytochalasins, aflatoxins, griseofulvin, etc.

472

(Back to main points)


Why 20 Metabolites Arise?

 

 

1.      Biochemical pathway lesions

 

2.      Biosynthesis of waste products

 

3.      Biosynthesis of detoxifying agents from deleterious products

 

4.      Biosynthesis of compounds, which are products of chance events

 

5.      Biosynthesis of regulators produced in excess

 

6.      Biosynthesis of unusual compounds produced in excess, which are important in development

 

7.      Virus or plasmid-mediated products of metabolism

473

(Back to main points)


Tropophase

 

1.      The exhaustion of an essential nutrient which leads to the termination or near termination of cellular proliferation (balanced phase)

 

Idiophase

 

2.      The accumulation of primary intermediates of metabolism (storage phase)

 

3.      The triggering of the induction of enzymes necessary for secondary biosynthesis by these intermediates, or the          activation of enzymes formed during tropophase, which lead to product formation (maintenance phase)

475

(Back to main points)


Types of Fungal Culture Media

 

1.      Natural - medium represents essentially unmodified plant or animal material

 

         a.  complete - seeds, fruit, twigs, vegetable slices, pollen, dung, hair, exoskeleton, etc.

 

         b.  partially processed - malt or yeast extract, potato extract, tomato juice, cornmeal, peptone, corn steep.

 

2.      Semisynthetic - media with mixtures of      partially processed plant &/or animal products & known pure chemicals -     e.g., YPG, CMDP, Subaurauds, etc.

 

3.      Synthetic - media with all ingredients chemically defined - e.g., Vogals synthetic, Westegard's synthetic cross,       Czapeks Dox, etc.

480

(Back to main points)

(Back to top of page)

 

Home | Syllabus | Lectures | Exams | Links | Help

For questions, comments, or suggestions,
please send e-mail to:
pluong@mail.utexas.edu

The University of Texas at Austin

Hit Counter