Chapter 6 Elements of Microbial Nutrition, Ecology, and Growth
一. Microbial Nutrition
Nutrition is a process by which chemical substances called nutrients are acquired from the environment and used in cellular activities such as metabolism and growth. In general, all living things require a source of elements such as carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium, chlorine, magnesium, and certain other elements. But the ultimate source of a particular, its chemical form, and how much of it the microbe needs are all points of variation between different types of organisms. Any substance, whether in elemental or molecular form that must be provided to an organism is called an essential nutrient.
1 Six kinds of essential nutrient for microbes
Two categories of essential nutrients are macronutrients and micronutrients. Macronutrients are required in relatively large quantities and play principal roles in cell structure and metabolism. Micronutrients, or trace elements, such as manganese, zinc, and nickel are present in much smaller amounts and are involved in enzyme function and maintenance of protein structure. What constitutes a micronutrient can vary from one microbe to another. Several important features of cell composition can be summarized as follows: water content is the highest of all the components; proteins are the next most prevalent chemical; about 97% of the dry cell weight is composed of organic compounds; about 96% of the cell is composed of six elements (represented by C H N O P S); bioelements are needed in the overall scheme of cell growth, but most of them are available to the cells as compounds and not as pure elements.
Carbon Sources:
The majority of carbon compounds involved in the normal structure and metabolism of all cells are organic. It provides the carbon element for organic molecules.
Nitrogen Sources:
Regardless of the initial form in which the organic nitrogen enters the cell. It must first be converted into NH3, the only form that can be directly combined with carbon to synthesize amino acids and other compounds.
Energy Sources:
Autotrophs derive energy from one of two possible nonliving sources: sunlight (photoautotrophs) and chemical reactions involving simple inorganic chemicals (chemoautotrophs). Photoautotrophs are photosynthetic: that is, they capture the energy of light rays and transform it into chemical energy that can be used in cell metabolism. The majority of heterotrophic microorganisms are chemoheterotrophs that derive both carbon and energy from organic compounds.
Phosphorus (Phosphate) Sources
The main inorganic source of phosphorus is phosphate (PO43-), derived from phosphoric acid (H3PO4) and found in rocks and oceanic mineral deposits. Phosphate is a key component of nucleic acids and is thereby essential to the genetics of cells and viruses.
Growth Factors: Essential Organic Nutrients
An organic compound such as an amino acid, nitrogen base, or vitamin that cannot be synthesized by an organism and must be provided as a nutrient is a growth factor.
Other Nutrients Important in Microbial Metabolism
The remainder of important elements are mineral ions Potassium is essential to protein synthesis and membrane function. Sodium is important for certain types of cell transport. Calcium is a stabilizer of the cell wall and endospores of bacteria. It is also combined with carbonate (CO32-) in the formation of shells by foraminiferans and radiolarians. Magnesium is a component of chlorophyll and a stabilizer of membranes and ribosomes. Iron is an important component of the cytochrome pigments of cell respiration. Zinc is an essential regulatory element for eucargotic genetics. It is a major component of "zinc fingers"--binding factors that help enzymes adhere to specific sites on DNA. Copper, cobalt, nickel, molybdenum, manganese silicon, iodine, and boron are needed in small amounts by some microbes but not others.
二、Main nutrition type of microbes
A hetemtroph* is an organism that must obtain its carbon in an organic form because organic carbon originates from the bodies of other organisms, heterotrophs are dependent on other life forms. Among the common organic molecules that can satisfy this requirement are proteins, carbohydrates, lipids, and nucleic acids In most cases, these nutrients provide several other elements as well. Some organic nutrients available to heterotrophs already exist in a form that is simple enough for absorption (for example, monosaccharides and amino acids) but many larger molecules must be digested by the cell before absorption. Moreover, heterotrophs vary in their capacities to use various organic carbon sources. Some are restricted to a few substrates, whereas others (certain Pseudomonoas bacteria, for example) are so versatile that they can metabolize more than 100 different substrates.
An autotroph* is an organism that uses CO2, an inorganic source. Because autotrophs have the special capacity to convert CO2 into organic compounds, they are not nutritionally depending on other living things. Enlarge on the topic of nutritional types as based on carbon and energy sources.
Autotrophs derive energy from one of two possible nonliving sources: sunlight (photoautotrophs) and chemical reactions involving simple inorganic chemicals (chemoautotrophs). The majority of heterotrophic microorganisms are chemoheterotrophs that derive both carbon and energy from organic compounds. These include saprobic microorganisms and parasitic microorganisms. Saprobes occupy a niche as decomposers of plant litter, animal matter, and dead microbes. Parasitic microorganisms live in or on the body of a host. Which usually harm to some degree?
三、MOVEMENT OF MATERIALS ACROSS MEMBRANES
1. Movement 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.
四、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.
1. 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 an-aerobic 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 as-sumed to be naturally present in tap water and other components of media. Even most distilled waters con-tain 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？
§2 Microbial Ecology
Microbial ecology：
The study of microorganisms in their natural environments, with a major emphasis on physical conditions, processes, and interactions that occur on the scale of individual microbial cells.
1、Microorganisms in natural environment
1.2 Microorganisms in aquatic environment
1.4 Microorganisms in extreme environments
1.5 Microorganisms in other organisms
2 Microbial interactions
3 Nutrient cycling interactions
Biogeochemical cycling
The oxidation and reduction of substances carried out by living organisms and/or abiotic processes that results in the cycling of elements within and between different parts of the ecosystem (the soil, aquatic environment, and atmosphere)
3.1Carbon cycle：
3.2 Nitrogen cycle
3.3 Sulfur cycle
3.4 Other cycles
4 Microorganisms and microenvironment
Biofilms and microbial mats
Biofilm:
Organized microbial systems consisting of layers of microbial cells associated with surfaces, often with complex structural and functional characteristics.
5 Wastewater treatment
5.1 Measuring water quality
COD
BOD
5.2 Water treatment processes
Primary treatment
Secondary treatment
Tertiary treatment
Major steps in primary, secondary, and tertiary treatment of wastes
Step | Processes |
Primary | Removal of insoluble particulate materials by settling, screening, addition of alum and other coagulation agents, and other physical procedures |
Secondary | Biological removal of dissolved organic matter: Trickling filters/Activated sludge/ Lagoons/Extended aeration systems/Anaerobic digesters |
Tertiary | Biological and/or chemical removal of inorganic nutrients; Virus removal/inactivation; Trace chemical removal |
5.3 Bioremediation in soils
§3 Microbial Growth and growth control
1. Overview of Cell Growth
2 Population Growth
The growth curve
Batch culture:
A culture of microorganisms produced by inoculating a closed culture vessel containing a single batch of medium
Growth curve
A curve that describes the growth of microorganisms reproducing by binary fission, and it is plotted as the logarithm of the number of viable cells versus the incubation time. It has four distinct phases.
lag phase: adapeatation
logarithmic phase: most rapid reproduction
Stationary phase: rate of reproduction rate of deed
Decline phase: rate of dead > rate of reproduction.
3 Measurement of Growth
(1）Measurement of biomass
Direct approach
Indirect approach
(2) Measurement of cell numbers
Direct counting
Indirect counting
4 Continuous Culture: The Chemostat
Microorganisms are grown in an open system, in which constant environmental conditions were maintained through continual provision of nutrients and removal of wastes. The microorganism population can be maintained in exponential growth phase.
Turbidostat:
A continuous culture system which has a photocell that measures the absorbance or turbidity of the culture in the growth vessel and the flow rate of media through the vessel is automatically regulated to maintain a predetermined turbidity or cell density.
Chemostat:
A continuous system in which sterile medium is fed into the culture vessel at the same rate as the media containing microorganisms is removed.
5 Effect of Environment on Growth
Temperature
pH value
Oxygen concentration
Pressure
Radiation
6 Heat Sterilization
(1)Definition of frequently used terms
Sterilization
The process by which all living cells, viable spores, viruses, and viroids are either destroyed or removed from an object or habitat.
Disinfection
The process that kill, inhibit, or remove microorganisms that may cause disease.
Antisepsis
Control of the growth of microorganisms on living tissue with chemical or physical agents.
Chemotherapy
The use of chemical substances to treat various aspects of disease.
(2) Conditions influencing the effectiveness of antimicrobial agent activity
Population size
Population composition
Concentration or intensity of antimicrobial agent
Duration of exposure
Temperature
Local environment
Categories:
Dry heat sterilization
Moist heat sterilization
Boiling
Pasteurization
Autoclaving
7 Filter Sterilization
Depth filters
Membrane filters
8 Chemical Growth Control
MIC : (minimum inhibitory concentration)
LD50: (50% lethal dose)
MLD: (minimum lethal dose)
9 Antibiotics from Prokaryotes
A microbe- or other organism-producing metabolite or its derivative that kills susceptible organisms or inhibits their growth
Kirby-Bauer method
