Lecture #14: Growth (Last) to Preferences Flashcards
Batch Culture
A population of microbes growing in a closed culture vessel containing a single batch of medium.
Halophiles
Some microbes are adapted to extreme hypertonic environments. These require the presence of NaCl or other salts at a concentration above about 0.2 M. Extreme halophiles have adapted so completely to hypertonic, saline conditions that they require high levels of NaCl to grow.
prefer to live in high salt environments. Modify structure of membranes for hypertonic medium. May stock compatible solutes in the cytoplasm to balance hypertonic medium. Enzymes function in cytoplasm with high concentrations of K.
pH Preference
Each species has a definitive pH growth range and pH growth optimum. Acidophiles have their growth optimum between 0 and 5.5; neutrophiles between 5.5 and 8.0; and alkaliphiles (alkalophiles), between 8.0 and 11.5. Extreme alkaliphiles have growth optima at 10 or higher.
Most known bacteria and protists are neutrophiles. Most fungi prefer more acidic surroundings, about 4 to 6; photosynthetic protists also seem to favor slight acidity. Many archaea are acidophiles.
Organic carbon fermenters (sugar) produce acids. Some are more tolerant of acidic conditions. Some, like Streptococcus (yogurt) poison their own environment! Progression of forms.
Some break down proteins to ammonia and thrive in basic conditions of their own making.
Yogurt Represents a Progression
Streptococcus species ferment the milk, thicken it as they produce lactic acid. Lowers the pH. Their growth slows as pH drops.
Lactobacillus takes over, as it thrives at lower pH.
One species changes the environment, favoring the growth of another.
Psychrophiles
Grow well at 0C and have optimum growth temperature at 15C; the maximum is around 20C. Oceans constitute enormous habitat because 90% of ocean is 5C or colder.
These have adopted to environment in several ways. Their enzymes, transport systems, and protein synthetic machinery function well at low temperatures. The cell membranes of psychrophilic microbes have high levels of unsaturated fatty acids and remain semifluid when cold.
Many begin to leak cellular constituents at 20C+ because of cell membrane disruption.
0 to 16˚C. (Freezing and up). Enzymes, transport systems, metabolism adapted to low temperatures. Cell membranes have different structures to allow fluidity at colder temperatures. Live in Arctic, Antarctic, other cold habitats.
Psychrotrophs
optima 20 to 30˚C but tolerate <10 ˚C and spoil food in your refrigerator. Nasty example is
- Listeria monocytogenes (especially dairy products). Current scare.
Mesophiles
Microbes that grow in moderate temperatures. They have growth optima around 20-45C and often have a temperature minimum of 15-20C and max of about 45C. Most microbes probably fall within this category. Almost all human pathogens are mesophiles, as might be expected because the human body is a fairly constant 37C.
Thermophiles
Grow at temperatures between 55 and 85C. Their growth min is around 45C, and they often have optima between 55 and 65C. The vast majority are members of archaea or bacteria, although few protists and fungi are included. Flourish in many habitats including composts, self-heating hay stacks, hot water lines, and hot springs.
55 ˚C (over 100). Special membrane lipids and enzymes tolerant of heat. Haystacks, compost piles, hot springs.
Hyperthermophiles
Growth optima between 85 and about 113C. They usually don’t grow below 55C.
80-100 ˚C. (200 ish). Hot vents, geothermal pools.
Oxygen Preference
Importance of oxygen to the growth of an organism correlates with its metabolism-in particular, with the processes it uses to conserve the energy supplied by its energy source. Almost all energy-conserving metabolic processes involve the movement of electrons through a series of membrane-bound electron carriers called the ETC. For chemotrophs, an externally supplied terminal electron acceptor is critical to the functioning of the ETC. The nature of the terminal electron acceptor is related to an organism’s oxygen requirement.
Obligate Aerobe
Completely dependent on atmospheric O2 for growth.
Microaerophiles
Damaged by the normal atmospheric level of O2 (20%) and require O2 levels in range of 2-10% for growth.
Clostridium (some), Campylobacter.
Facultative Anaerobes
Do not require oxygen for growth but grow better in its presence.
Aerotolerant Anaerobes
Grow equally well whether O2 is present or not.
Obligate Anaerobes
Usually killed in the presence of O2. Employ other methods to generate energy.
Clostridium (some), Archaea.
Radiation
Radiation behaves as it it were composed of waves moving through space like waves traveling on the surface of water. The distance between two wave crests or troughs is the wavelength.
As the wavelength of electromagnetic radiation decreases, the energy of the radiation increases; gamma rays and X rays are much more energetic than visible light or infrared waves.
- Shorter wavelengths most damaging, i.e. UV light.
- Low levels, causes mutations in DNA; at high levels, lethal (affects bonds, glumps up molecules = polymerizes them, generates ions).
Ionizing Radiation
Radiation of very short wavelength and high energy, which can cause atoms to lose electrons (ionize).
Two major forms of ionizing radiation are X rays (artificially produced) and gamma rays (emitted during radioisotope decay).
Low levels of ionizing radiation may produce mutations and may indirectly result in death, whereas higher levels are directly lethal.
Ionizing radiation causes many changes in cells. It breaks hydrogen bonds, oxidizes double bonds, destroys ring structures, and polymerizes some molecules. Oxygen enhances these destructive effects, probably through generation of hydroxyl radicals (OH.). Although many types of constituents can be affected, the destruction of DNA is probably most important cause of death.
Ultraviolet (UV) Radiation
Can kill microbes due to its short wavelength and high energy. Most lethal UV radiation has wavelength of 260 nm, the wavelength most efficiently absorbed by DNA.
The primary mechanism of UV damage is the formation of thymine dimers in DNA, which inhibit DNA replication and function. Thymine dimers are formed when two adjacent thymines in the same DNA are covalently joined.
The damage caused by UV light can be repaired by several DNA repair mechanisms,. Excessive exposure to UV light outstrips the organism’s ability to repair the damage and death results. Longer wavelengths can also harm microbes because they induce the breakdown of the amino acid tryptophan to toxic photoproducts. It appears these toxic photoproducts plus the near-UV radiation itself produces breaks in DNA strands. The precise mechanism is not known, although it’s different from that seen with 260 nm UV.
UV destroys DNA, use it to kill microbes
260 nm most lethal, targets DNA specifically. Forms thymine dimers. Skin cancer.
Closer to 400 nm, leads to breaks in DNA.
As dose increases (length of time), effects more extensive. Some dimers missed.
In lab, use a UV light. Keep skin covered. Do not look at the light.
Glass, even plastic, are effective shields. Use that to stop the dose.
Repair mechanisms in visible light; photoreactivation.
Radiation from Radioactive Sources
Radiation which does not penetrate well is used in surface sterilization. Beta.
Gamma radiation has good penetration. Effective in wiping out bacteria, used to eliminate the possibility of pathogens in food. Not indicated for viruses.
Sterilization
Process by which all living cells, spores, and acellular entities (viruses, viroids, virusoids, and prions) are either destroyed or removed from an object or habitat. A sterile object is totally free of viable organisms, spores, and other infectious agents. When sterilization is achieved by a chemical agent, the chemical is called a sterilant.
Disinfection
The killing, inhibition, or removal of microbes that may cause disease; disinfection is the substantial reduction of the total microbial population and the destruction of potential pathogens.
Disinfectants are agents, usually chemical, used to carry out disinfection and normally used only on inanimate objects. A disinfectant does not necessarily sterilize an object because viable spores and a few microbes may remain.
Antisepsis
The destruction or inhibition of microbes on a living tissue; it’s the prevention of infection or sepsis.
Antiseptics are chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth; they also reduce the total microbial population. Because they must not destroy too much host tissue, antiseptics are generally not as toxic as disinfectants. The exposure of microbes to increasing biocide concentrations decreases the number of viable organisms.
Chemotherapy
The use of chemical agents to kill or inhibit the growth of microbes within host tissue.