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电子讲义- 第二章 Nutritional Types and Enery production

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Chapter 2 Nutritional Types and Enery production

1Nutritional Requirements

1.1 Source of Energy

All microorganisms require a source of energy. Some rely on chemical compounds for their energy and are designated as chemotrophs. Others can utilize radiant energy (light) and are called phototrophs.

1.2 Source of electrons

All microorganisms require a source of electrons for their metabolism. Some can use reduced inorganic compounds as electron donors and are termed lithotrophs. Others use organic compounds as electron donors and are called organotrophs.

1.3 Carbon source

All microorganisms require carbon in some form for use in synthesizing cell components. All require at least small amount of CO2. However, some can use CO2 as their major, or even sole, source of carbon; such microorganisms are termed autotrophs. Others require organic compounds as their carbon source and are termed heterotrophs.

1.4 Nitrogen source

All microorganisms require nitrogen in some form for cell components. Bacteria are extremely versatile in this respect. Unlike eucaryotes, some bacteria can use atmospheric nitrogen. Others thrive on inorganic nitrogen compounds such as nitrate, or ammonium salts, and still others derive nitrogen from organic compounds such as amino acids.

1.5 Oxygen sulfur and phosphorus

All microorganisms require oxygen, sulfur and phosphorus for cell components. Oxygen is provided in various forms, such as water, component atoms of various nutrients, or molecular oxygen. Sulfur is needed for synthesis of certain amino acids. Some bacteria require organic sulfur compounds, some are capable of utilizing inorganic sulfur compounds, and some can even use elemental sulfur. Phosphorus, usually supplied in the form of phosphate, is an essential component of nucleotides, nucleic acids, phospholipids, and other compounds.

1.6 Mineral elements

All microorganismsrequire metal ions, such as K+, Ca2+, Mg2+, and Fe2+ for nomal growth. Other metal inos are also needed but usually only at very low concentrations, such as Zn2+, Cu2+, Mo6+, and Co2+. These are often termed trace elements. Not all the biological functions of metal ions are known, but Fe2+, Mg2+, Zn2+, Ca2+, Mo6+, and Cu2+, are known to be cofactors for various enzymes. Most bacteria do not require Na+, but certain marine bacteria, cyanobacteria, and photosynthetic bacteria do require it. For those members of archaeobacteria known as the “ extreme halophiles”, the requirement is astonishing. They can not grow with less than 12~15% NaCl. They require this high level of NaCl for maintenance of the integrity of their cell walls and for the stability and activity of their certain enzymes.

1.7 Vitamins

All microorganisms need vitamins and vitaminlike compounds. Some bacteria are capable of synthesizing vitamins from other compounds in the culture media, but others can not do so and will not grow unless the required vitamins are supplied in the media.

1.8 Water

All microorganisms require water. Nutrients must be in aqueous solution before they can enter the cells. Water is to dissolve and disperse nutrients and to provide a suitable milieu for the various metabolic reactions of a cell. Moreover, the high specific heat of water provides resistance to sudden, transient temperature changes in the environment.

2Nutritional Types of Microorganisms

Although microorganisms have great diversity of nutritional requirement, they can be divided into four major groups on the basis of their utilization of energy and carbon sources.

2.1 Photolithotroph or photoautotroph

They utilize light as energy source, and CO2 as major or even sole source of carbon.

2.2 Photoorganotroph or photoheterotroph

They require light as energy source and organic compounds as carbon source.

2.3 Chemolithotroph or Chemoautotroph

They rely on inorganic chemical compounds for their energy and use CO2 as their major, or even sole source of carbon.

2.4 Chemoorganotroph or Chemoheterotroph

They utilize organic compounds as their energy and carbon Source. Most bateria and all fungi belong to this group.

3 Medium, Media or culture mediaum, culture media

3.1 definition: an aqueous solution containing various nutrients suitable for the growth of microorganisms.

3.2 Types of media

3.2.1 Based on the chemical composiion

● Synthetic media

The chemical composition of every ingredients in the medium is clear.

Medium for cultivation of Actinomycetes

Starch 20gKNO31.0gK2HPO40.5g

MgSO4?7H2O0.5gNaCl0.5gFeSO4?7H2O0.01g

d-H2O1000ml

● Natural media

The media containing complex natural raw materials surch as peptones, meat broth, yeast extract, plants and animal materials.

Medium for cultivation of fungi

Potato200gsucrose 20gH2O1000ml

Medium for cultivation of bacteria

Beef extract5.0gpeptone10.0gNaCl5.0g

H2O1000ml

3.2.2 Based on physical status

● Broth media: liquid media

● Solid media: The solidifying agent is added to the liquid media. The solidifying agent is usually agar, which at concentrations of 1.5~2.0% forms firm, transparent gels that are not degraded by most bacteria. Silica gel is sometimes used as an inorganic solidifying agent for cultivation of autotrophic bactoria.

● Semisolid media: Agar concentration: 0.2~0.5%

3.2.3 Based on special purpose

● Selective media

These media provide nutrients that enhance the growth of a particular type of microorganism and do not enhance (and may even inhibit) other types of microorganisms that may be present. For instance, nitrogen-free medium (Ashby) will specifically select the growth of nitrogen-fixing bacteria.

● Enriched media

These media contain a certain nutrient that promotes and enriches a special type of microorganism. For example, a medium in which cellulose is the only carbon source will enrich the growth of cellulose-utilizing microorganism. During the process of cultivation, the noncellulose-utilizing microorganisms are eliminated gradually. This is especially useful for isolation of a bacterium when the number is very low in the sample.

● Differential media

The media that contain some kinds of ingredients which can differentiate various kinds of microorganisms. For example, if a mixture of bacteria is inoculated onto a blood-containing agar medium, some of the bacteria may hemolyze the red blood cells; others do not. Thus one can distinquish between hemolytic and nonhemolytic bacteria on the same medium.

3.3 Preparation of media

3.3.1 The principles

●The nutrients in the medium with suitable concentration and ratia must satisfy the normal growth of microorganisms.

● Optimum pH for growth

● In large scale protuction, the source and price of the ingredients in the medium must be considered.

3.3.2 The procedures

● Each ingredient with correct amount is dissolved in the appropriate volume of distilled H2O;

●The pH of the fluid medium is determined with a pH meter and adjusted if necessary;

● If a solid medium is desired, agar is added and the medium is boiled to dissolve the agar;

●The medium is sterilized, generally by autoclaving. Some specific ingredients that are heat-labile are sterilized by filtration.

4Transport of nutrients

4.1 Passive diffusion

Passive diffusion is the process that solute molecules cross the membrane as a result of a difference in concentration of the molecules across the membrane. The difference in concentration ( higher outside the membrane than inside) governs the rate of inward flow of the solute molecule. With time, this concentration gradient diminishes until equilibrium is reached.

Except for water and some lipid-soluble molecules, few compounds can pass through the cytoplasmic membrane by passive diffusion. In passive diffusion, no substance in the membrane interacts specifically with the solute molecule, and energy is not needed.

4.2 Facilitated diffusion

This process is similar to passive diffusion in that the solute molecule also flows from a higher to lower concentration. But it is different from passive diffusion because it involves a specific protein carrier molecule called permease located in the cytoplasmic membrane. The carrier molecule combines reversibly with the solute molecule, and the carrier-solute complex moves between the outer and inner surfaces of the membrane, releasing one solute molecule on the inner surface and returning to bind new one on the outer surface.

This type of transportation is common in eucaryotic cells. Sugars enter them by this way.

No ATP is needed. There is specific interactions between the solute and protein carrier in the membrane.

4.3 Group translocation

Group translocation is the process in which the solute is chemically altered in the course of passage across the membrane.

4.4 Active transport

Almost all solutes are taken up by cells through active transport. The three steps of active transport are:

● Binding of solute to a receptor site on a membrane-bound carrier protein.

●Translocation of the solute-carrier complex across the membrane.

● Carrier protein release solute to the cell interior

● Group translocation and active transport require energy and accumulate substrates against concentration gradient.Solutes can be concentrated within the cell several thousand times greater than outside the cell. There is specific interaction between the solute and protein carrier in the membrane.

5Energy production(ATP)

5.1 Energy production by aerobic process

● Substrate-level phosphorylation: production of ATP by the direct transfer of a high-energy phosphate molecule from a phosphorylated organic compound to ADP.

● Oxidative phosphorylation: production of ATP at the process of electron transport.

5.2 Energy production by anaerobic process

● Fermentation

Fermentation is a process of anaerobic oxidation of organic compounds. Neither gaseous oxygen nor respiratory chain is involved in this energy-yielding process. ATP is produced by substrate-level phosphorylation. An organic compound is the electron acceptor.

The lactic fermertation is a typical example. Streptococcus lactis, the bacterium responsible for the souring of milk, dissimilates glucose to lactic acid, which accumulates as the sole fermentation product.

5.3 Energy production by photosynthesis

● Photophosphorylation: Synthesis of high-energy phosphate bonds as ATP, using light energy.

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