Bacterial Metabolism, Growth, and Nutrition

Question 1

Metabolism

Answer 1

the sum total of all reactions which occur in a cell. Chemical reactions either release or require energy.

Divided into two processes:

Catabolism

Anabolism

Question 2

Catabolism

Answer 2

The process of breaking complex molecules (degredative reactions) into smaller, simpler, molecules with the release of Energy (ATP)

Generally hydrolytic reactions and are exergonic.

Question 3

Anabolism

Answer 3

The process of synthesis of complex molecules from simpler ones to form cell structures.

Process is endergonic, and often reducimg power or electrons.

Energy supplied by hydrolysis of ATP.

Question 4

Energy Production

Answer 4

Catabolic Pathways:

chemical energy released in reactions is conserved primarily in the form of ATP.

Question 5

Respiration

Answer 5

An ATP-generating process in which chemicals are oxidized and the final electron acceptor is inorganic molecules.

Must involve the electron transport chain

Two Types:

Aerobic: Final electron acceptor is oxygen

Anaerobic: Final electron acceptor is an inorganic molecule other than oxygen.

Question 6

Fermentation

Answer 6

Defined as an ATP-generating process in which organic molecules are the electron donors and electron acceptors.

Oxidation of an organic molecule (e- donor) is coupled to hte reduction of organic molecules (e- acceptor) derived form the electron donor.

NO exogenous electron acceptor is involved.

Question 7

Bacterial Growth

Answer 7

Means increase in the Number of cells but not in the size of the cells.

Reproduce asexually (bionary fission)

Question 8

Generation Time

Answer 8

Time required for a cell to divide.

Varies considerably among bacterial species and is also dependent on the growth conditions.

Range from 20 mins to 24 hours

Question 9

Growth Curve:

Lag Phase

Answer 9

Initail period of no visible growth and little or no cell division.

Can be brief to several hours or even days depending on the bacterial species.

Cells are not dormant, but undergoing intense metabolic activity.

Question 10

Growth Curve:

Logarithmic Phase

Answer 10

Cells begin to divide logarithmaically to acheive an exponential growth phase.

Cell division is most active during this phase and cells are metabolically most active.

Most susceptible to adverse conditions (antibiotics)

Question 11

Growth Curve:

Stationary Phase

Answer 11

The exponential growth ceases and the population stabilizes. The number of cells dying is aproximately equal to the number of newly formed celsl.

Reasons for this phase:

• Exhaustion of nutrients
• Accumulation of toxic wast products
• Changes in growth conditions

Question 12

Growth Curve:

Death Phase

Answer 12

Eventually the numbers of dead celsl exceed the numbers of cells formed and the population enters the phase of decline.

Appears to be alomst exponential, but typically slower than the log phase.

Question 13

Dierect Method:

Microscopic Count

Answer 13

The number of cells in a population can be measuresd by placing a measured volume of a sample within a defined area on a glass slide and counting the cells under the micropscope.

Quick way of estimating the number, but counts include both dead and live cells.

Total cell count

Question 14

Direct Method:

Viable Cell Count

Answer 14

Counts only live cells because the method requires cells to divide and grow. This is the most frequently used method.

Determines the number of celsl in a sample that can grow and foram a colony on a suitable agar medium.

Also called plate count or Colony count.

Question 15

Indirect method

Answer 15

A rapid and easier method to estiamte bacterial growth is the measure turbidity. As bacteria multiply in a liquid medium, the medium becomes cloudy or turbid. Requires at least a million cells per ml for growth to be visible.

Turbidity is measured with a spectrophotometer, measured as percentage of transmittance of light.

Question 16

Physical Requirements

Answer 16

Helps explain the distribution of bacteria in nature and makes it possible to devise methods to grow, enhance their activity, or to control them.

• Oxygen
• Cabron Dioxide
• Temperature
• pH
• Ionic Strength/osmotic pressure

Question 17

Aerobes

Answer 17

Species that require oxygen for growth.

They utilize oxygen in their metabolism

Three types:

1. Obligate:
   
   1. Bacteria that have to hace absolute requirements of oxygen
2. Facultative:
   
   1. Can use oxygen, and grow when it is present, but also have the ability to grow when oxygen is not available.
3. Microaerophilic:
   
   1. Bacteria that can only grow in oxygen concentratio lower than in air.

Question 18

Anaerobes

Answer 18

Species that con only grow in the absence of oxygen and do not utilize oxygen in their metabolism.

Two Broad Groups:

1. Obligate Anaerobes:
   
   1. are inhibited or even killed by exposure to oxygen
2. Aerotolerant Anaerobes:
   
   1. Survive short exposure to oxygen, but will not grow in its presence. Most anaerobes of clinical importance

Question 19

Carbon Dioxide

Answer 19

Required for growth of bacteria for normal biosynthetic reactions.

Armospheric levels are sufficient for many bacteria, usually reflective of their habitat.

Bacteria that grow better at higher CO2 concentrationss are called Capnophiles or Carboxyphiles

Question 20

Temperature

Answer 20

Important environmental factro affecting the growth and survival of bacteria.

Three types:

1. Psychrophiles:
   
   1. grow best at 10-15C
2. Mesophiles:
   
   1. grow best 30-37C
3. Thermophiles:
   
   1. Grow best at 55C

Question 21

pH

Answer 21

Most pathogenic bacteria grow best at neutral pH, witha range from 6.8 to 7.2.

Question 22

Ionic Strength/Osmotic Pressure

Answer 22

Pathogenic bacteria usually grow best at osmotic presures equivalant to physiological saline.

Question 23

Iron

Answer 23

plays a major role in cellular respiration, being a key component of cytochromes and iron-sulfur proteins involved in Electron transport.

Pathogenic bacteria produce iron-binding agents called siderophores that bind iron and transport into the cell.

Question 24

Growth Factors

Answer 24

Organinc compounds that are required in small amounts by only some bacteria. They include vitamins, amino acids, purines, and pyrimidines.

Most synthesize these compounds, some require them to be provided by the environment.

Vitamins most commonly required by bacteria are thiamin, biotin, pyridoxine, and cobalamin (B12)