Chapter5 Nurtution of Microbes

第5章 微生物的营养

CHEMICAL REQUIREMENTS         

1.     Microorganisms require a carbon source; chemoheterotrophs use an organic molecule, and autotrophs typcally use carbon dioxide.

2.     Nitrogen is needed for protein and nucleic acid synthesis. Nitrogen can be obtained from decomposition of proteins or from NH4+ or NO3-; a few bacteria are able to fix N2.

3.     Water is also necessary to the growth of all microorganisms.

4.     Other chemicals required for microbial growth include iroganic salt(sulfur, phosphorus, and some trace elements), and, for some microorganisms, organic growth factors.

MOVEMENT OF MATERIALS ACROSS MEMBRANES

1.      1Movement across the membrane may be by passive processes, in which materials move from higher to lower concentration and no energy is expended by the cell.

2.      In simple diffusion, molecules and ions move until equilibrium is reached.

3.      In facilitated diffusion, substances are transported by permeases across membranes from high to low concentration.

4.      Osmosis is the movement of water from high to low concentration across a selectively semipermeable membrane until equilibrium is reached.

5.      In active transport, materials move from low to high concentrations by permeases, and the cell must expend energy.

6.      In group translocation, energy is expended to modify chemicals and transport them across the membrane.

Culture Media

1.      A culture medium is any material prepared for the growth of bacteria in a laboratory.

2.      Microbes that grow and multiply in or on a culture medium are known as a culture.

3.      Agar is a common solidifying agent for a culture medium.

CHEMICALLY DEFINED MEDIA

A chemically defined medium is one in which the exact chemical composition is known.

COMPLEX MEDIA

1. A complex medium is one in which the exact chemical composition is not known.

ANAEROBIC GROWTH MEDIA AND METHODS

1.    Reducing media chemically remove molecular oxygen

2.    Petri plates can be incubated in an anaerobic jar or an­aerobic glove box.

SPECIAL CULTURE TECHNIQUES

1.      Some parasitic and fastidious bacteria must be cultured in living animals or in cell cultures.

1.      CO2 incubators or candle jars are used to grow bacteria requiring an increased CO2 concentration.

SELECTIVE AND DIFFERENTIAL MEDIA

1.    By inhibiting unwanted organisms with salts, dyes, orother chemicals, selective media allow growth of only the desired microbe.

2.          Differential media are used to distinguish between different organisms.

ENRICHMENT CULTURE              

An enrichment culture is used to encourage the growth of a particular microorganism in a mixed culture.

Trace Elements

Microbes require very small amounts of other mineral elements, such as iron, copper, molybdenum, and zinc; these are referred to as trace elements. Most are essential for activity of certain enzymes, usually as co-factors. Although these components are sometimes added to a laboratory medium, they are usually as­sumed to be naturally present in tap water and other components of media. Even most distilled waters con­tain adequate amounts, but tap water is sometimes specified to ensure that these trace minerals will be present in culture media.

 ●What advantages do solid media offer for the culture of microorganisms?

●What is the enrichment culture technique and why was it a useful new method in microbiology?