Lecture #10: Nutrition, Media & The Enterics Flashcards
Nutrition
Powers cell.
Provides macronutrients and micronutrients cells need for biosynthesis, energy conversion (food to ATP).
Specific metabolic needs of specialists.
Macroelements
Needed in relatively large amounts.
C, H, O, and to a lesser amount N, P, S.
Why? C, H, O for all 4 classes of the ‘Molecules of Life;’ Carbohydrates,
Fats,
Proteins,
Nucleic Acids.
N, P, S—especially for Proteins, NA’s.
Macroelement Cations
Potassium, Calcium, Magnesium, and iron exist as cations and play a variety of roles.
activate enzymes, work with carrier proteins and cofactors, set up charge differentials, stabilize molecules and ribosomes and membranes, shuttle across membranes to assist uptake.
In essence, to drive metabolism.
Microelements
Nutrients required in small amounts by microorganisms. Also called trace elements.
The micronutrients-manganese, zinc, cobalt, molybdenum, nickel, and copper-are needed by most cells.
Micronutrients are a part of certain enzymes and cofactors, and they aid in the catalysis of reactions and maintenance of protein structure.
Required in tiny amounts for specialized structures or compounds, many are metals and are the central molecule in molecules designed for energy transfer.
Specific Needs for Specific Physiologies
Some microorganisms have particular requirements that reflect their specific morphology or metabolic capabilities. But no matter what their nutritional requirements, microbes require a balanced mix of nutrients. If an essential nutrient is in short supply, microbial growth will be limited regardless of the concentrations of other nutrients.
Specific structural needs for forms that live in high heat, high salt, low temperature, soils with high metal concentrations, or forms that have variant metabolisms.
Trace elements needed vary!
Growth Factors
Organic compounds needed for growth that cells can not make. Can’t grow unless they get it from outside source. Vitamins, amino acids, nitrogen rings for nucleotides.
Heterotroph
An organism that uses reduced, preformed organic molecules as its principal carbon source.
Uses reduced compounds (i.e., sugars) for C source, as well as for electrons to make energy (ATP).
Autotroph
An organism that uses CO2 as its sole or principal source of carbon.
Uses CO2 for C source and inorganic molecules for electrons to make energy (ATP).
Symbionts & Parasites
For symbionts and parasites, dependence on host or partner such that genes have been lost. Streptococcus pyogenes and 3 key amino acids. Growth factors.
Limiting Nutrients
Just as in Chemistry, limiting reactant limited the amount of product; limiting nutrient will set the limits on growth even if the others are abundant.
General Nutrition Need
All organisms require carbon, hydrogen, oxygen, and a source of electrons.
Carbon is needed to synthesize the organic molecules from which organisms are built. Hydrogen and oxygen are also important elements found in many organic molecules.
Electrons needed for two reasons. The movement of electrons through ETCs and during other oxidation-reduction reactions can provide energy for use in cellular work. Electrons are also needed to reduce molecules during biosynthesis.
- Why? Electrons power cells—they are used to generate ATP, the energy currency for the cell.
- The most common source is H. In biological systems, reduced is equivalent to having stored energy = having H.
Reduced & Oxidized
Reduced – Has Energy to Give.
Oxidized – Energy Poor.
For living organisms, reduced means having hydrogen.
Are Bacteria Strict in their Diet?
Not typically. Most bacteria are versatile, and can utilize a number of different substances for food.
Can find bacteria to degrade most anything; rubber, flesh, crude oil, styrofoam, soap scum…
One man’s junk is another man’s treasure; waste from one bacterium may be the ‘want’ for another and this seems to structure many natural communities.
Phototrophs
Use light as their energy source.
Chemotrophs
Obtain energy from the oxidation of chemical compounds (organic or inorganic).
Lithotrophs
Use reduced inorganic substances as their electron source.
Organotrophs
Extract electrons from reduced organic compounds.
Nutritional Types
You are used to autotroph or heterotroph. That qualifier goes at the end. Refers to carbon source.
Determine energy source (Photo or Chemo) for first qualifier.
The electron source goes between. Lithotrophs get e-from inorganic sources (water, carbon dioxide, hydrogen sulfide, etc.), organotrophs from organic compounds.
Photo-Litho-Autotroph
Photo-Organo-Heterotroph
- the non-Sulfur bacteria, purple and green bacteria. Specialized.
Chemo-Litho-Autotroph
- the forms that extract their energy from things like iron, nitrogen, or sulfur compounds. Ecologically specialized.
Chemo-Litho-Hererotroph
- rare. Use reduced inorganics for energy and electrons, and organics for C. Cycling of nutrients (nitrogen, sulfur).
Chemo-Organo-Heterotroph
Photolithoautotrophs
Use light energy and have CO2 as their carbon source.
Photosynthetic protists and cyanobacteria employ water as the electron donor and release oxygen.
Other photolithoautotrophs, such as the purple sulfur bacteria and the green sulfur bacteria, cannot oxidize water but extract electrons from inorganic donors such as hydrogen, hydrogen sulfide, and elemental sulfur.
Photoautotrophs are important primary producers in ecosystems. That is, they convert light energy into chemical energy that can sustain the chemoorganoheterotrophs that share their habitats.
Chemoorganoheterotrophs
Use organic compounds as sources of energy. Frequently the same organic nutrient will satisfy all these requirements.
Chemoorganotrophs contribute to biogeochemical cycles such as the carbon cycle and nitrogen cycle, in which elements are converted into different forms.
In addition, they’re of considerable practical importance. Many are used to make foods, medical products, and beverages.
Nearly all pathogenic microbes are these.
Prokaryotes Grow on Media
Recipes typically include beef extract or another protein source. Nutrient Agar has beef extract and Tryptic Soy Agar has soy protein (‘vegetarian version’). Could be a sugar instead, or a sugar in addition—the logical sugar is glucose. All the necessary macroelements, and microelements.
Liquid form is a broth. Solid gels due to the presence of agar.
Agar
Most commonly used solidifying agent. Well suited as a solidifying agent.
Melts at about 90 degrees Celsius but, once melted, does not harden until it reaches about 45 degrees Celsius. Thus after being melted in boiling water, it can be cooled to a temperature that is tolerated by human hands as well as microbes.
Furthermore, microbes growing on agar medium can be incubated at a wide range of temperatures.
Finally, agar is an excellent hardening agent because most microbes cannot degrade it.
Agar Dissolves in Boiling Water, Becomes Solid at Room Temperature, and is Inert. At least more so than gelatin. Use the presence of gelatinase as an identifier for soil microbes. A few things do digest agar. A very few.
Defined Medium
Medium in which all chemical components are known.
Complex Media
Media that contain some ingredients of unknown chemical composition. Useful due to fact they may be sufficiently rich to meet all the nutritional requirements of many different microbes. Also often needed if nutritional requirements of microbe are unknown.
The Common Media We Use Are Complex
Natural source media.
–Nutrient Agar contains extract of beef, a digest.
–Tryptic Soy Agar contains soy isolates, largely proteins.
–Blood Agar contains sheep blood which is red blood cells (already complex) along with any associated material.
Minimal to Enriched
Degree of enrichment.
Minimal contains only what is needed for growth. Minimal media vary depending upon the organism—whatever is the minimal level to support growth. For one organism that may be a mixture of salts (for N, P, S) plus glucose, while another may need a specific vitamin or amino acid.
General media is the ‘intermediate level’ here.
Enriched media has extra nutrients to favor growth. Blood Agar is an enriched media (it has beef digest and salts, to which blood is added). NA + 1% Glucose is enriched.
Enriched Media
Media such as tryptic soy broth and tryptic soy agar are called general purpose or supportive media because they sustain the growth of many microbes. Blood and other nutrients may be added to supportive media to encourage the growth of fastidious microbes. These fortified media (e.g., blood agar) are called enriched media.
Selective Media
Favor the growth of particular microbes. Bile salts or dyes such as basic fuchsin and crystal violet favor the growth of gram- bacteria by inhibiting the growth of gram+ bacteria; the dyes have no effect on gram- organisms.
Endo agar, eosin methylene blue agar, and MacConkey agar are three media widely used for the detection of E. coli and related bacteria in water supplies and elsewhere. These media contain dyes that suppress the growth of gram+ bacteria. MacConkey agar also contains bile salts. Bacteria also may be selected by incubation with nutrients that they specifically can use.
A medium containing only cellulose as a carbon and energy source is quite effective int he isolation of cellulose-digesting bacteria from samples such as soil. Thus selective media are useful as media for enrichment cultures.
Differential Media
Media that distinguish among different groups of microbes and even permit tentative identification of microbes based on their biological characteristics.
Blood Agar
Blood agar is both a differential medium and an enriched one. It distinguishes between hemolytic and nonhemolytic bacteria. Some hemolytic bacteria produce clear zones around their colonies because of red blood cell destruction. Blood agar is an enriched growth medium in that blood (usually sheep blood) provides protein, carbohydrate, lipid, iron, and a number of growth factors and vitamins necessary for the cultivation of fastidious organisms.
MacConkey Agar
Both differential and selective. Because it contains lactose and neutral red dye, bacteria that catabolize lactose by fermenting it release acidic waste products that make colonies appear pink to red in color. These are easily distinguished from colonies of bacteria that don’t ferment lactose.
Mannitol Salt Agar
Selective and differential. A concentration of 7.5% NaCl selects for the growth of staphylococci. Pathogenic staphylococci can be differentiated based on the release of acidic products when they use mannitol as a carbon and energy source. The acidic products cause a pH indicator (phenol red) in the medium to turn yellow.
Characteristic Media
Screen for a particular characteristic.
We use as diagnostic tests.
Urea broth - + of urease.
Iron Compounds – production of sulfides.
Citrate Agar – identifies G.I. tract bacteria as can break down citrate.
Streak Plate
If cells from a mixture of microbes can be spatially isolated from each other, each cell will give rise to a completely separate colongy, a macroscopically visible cluster of microorganisms in or on a solid medium.
Because each colony arises from a single cell, each colony represents a pure culture. One method for separating cells is the streak plate. In this technique, cells are transferred to the edge of an agar plate with an inoculating loop or swab and then streaked out over the surface in one of several patterns. After the first sector is streaked, the inoculating loop is seterilized and an inoculum for the second sector is obtained from the first sector. A similar process is followed for streaking the third sector, except that the inoculum is from the second structure. It’s essentially a dilution process.
Eventually very few cells will be on the loop, and single cells will drop from it as it’s rubbed along the agar surface. These develop into separate colonies.
Spread Plate
A small volume of a diluted mixture containing around 30-300 cells is transferred to the center of an agar plate and spread evenly over the surface with a sterile bent rod. The dispersed cells develop into isolated colonies.
small amount of liquid media with cells is spread across the top of the agar to generate a continuous, dense growth of cells called a lawn. Problem is to avoid ‘drowning the cells.’
Pour Plate
Extensively used with bacteria, archaea, and fungi.
The original sample is diluted several times to reduce microbial population sufficiently to obtain separate colonies when plating. Then small volumes of several diluted samples are mixed with liquid agar that has been cooled to about 45 Celsius, and the mixtures are poured immediately into sterile culture dishes.
Most microbes survive a brief exposure to the warm agar. Each cell becomes fixed in place to form an individual colony after the agar hardens.
Like the spread plate, the pour plate can be used to determine the number of cells in a population. For both methods, the total number of colonies equals the number of viable microbes in the sample that are capable of growing in the medium used.
Colonies growing on the surface also can be used to inoculate fresh medium and prepare pure cultures.
introduce cells from a loop into molten agar at 45° C. The cells can tolerate it for a brief period. Mix and pour into a plate. Cells will produce colonies. If well mixed, and sufficiently diluted, should make a nice even growth.
Proteobacteria, A Phylum
All GN rods.
Several groups within it.
One group contains Pseudomonas. It lives in soil and water and is not a normal member of a healthy gut biota.
Another group contains the enterics.
Enterobacteriaceae
Large family of facultative anaerobes. Rods. Forty or so genera.
Some live in soil or water, though enterics live in vertebrate G.I. tracts*.
Lactose fermenters are the human coliforms (live in the colon) and are natural human residents while non-lactose fermenters are not natural in humans and cause disease. Salmonella and Yersinia are in this family.
*Cow, racoon, cat—many non-dairy consumers.
