Bio 2051- Chapter 4 Dynamic Study Modules

What is the best way to maintain a bacterial culture in the exponential growth phase?

- chemostat *what you need to know: The best way to maintain a bacterial culture in the exponential growth phase is to use a chemostat. A biofilm forms when bacteria attach to a surface and interact, forming a complex structure with bacteria that grow at different rates depending on their locations. A batch culture passes through the exponential phase relatively quickly as bacteria rapidly consume nutrients and produce wastes. Semisolid cultures are not used in continuous culture systems.

Which important molecules contain iron that is important for their function?

- cytochromes *what you need to know: Important molecules that contain iron that is important for their function are cytochromes. Cytochromes are essential components of electron transport chains. Thiamine is a B vitamin. Carotenoids and chlorophyll are pigment molecules that are important in many photosynthetic cells.

A researcher carefully combines 10 grams of glucose, 8 grams of buffer components, and 4 grams each of six specific nutrients before adding them to 900 mL of distilled water. This medium is best described as a __________.

- defined medium *what you need to know: A medium containing 10 grams of glucose, 8 grams of buffer components, and 4 grams each of six specific nutrients mixed with 900 mL of distilled water is best described as a defined medium. In a defined (or synthetic) medium, the exact amounts of each component are known. Selective media are used to encourage the growth of bacteria of interest while inhibiting the growth of other types of bacteria. Differential media are used to distinguish between specific types of bacteria. A complex medium contains ingredients such as yeast or beef extract, so the exact composition is unknown.

A microbe that lives in a hydrothermal vent at 109°C is a __________.

- hyperthermophile *what you need to know: A microbe that lives in a hydrothermal vent at 109°C is a hyperthermophile. As shown in the following figure, the optimal temperatures for psychrophiles are relatively cool temperatures. Mesophiles thrive at intermediate temperatures, and thermophiles prefer warm temperatures.

What happens if an obligate anaerobe such as Clostridium is exposed to air?

- it cannot grow, although it may survive *what you need to know: If an obligate anaerobe such as Clostridium is exposed to air, it cannot grow but may survive. Some species are more sensitive than others, but oxygen does not necessarily kill them. Obligate anaerobes require an oxygen-free environment for growth, so they are not able to grow even slowly in atmospheric oxygen.

A researcher obtains a microbe from a very hot environment with an average temperature of about 101°C. What can he be most confident is true?

- it is classified in domain Archaea *what you need to know: If a researcher obtains a microbe from a very hot environment with an average temperature of about 101°C, he can be confident that the cell is classified in domain Archaea. Some bacteria thrive at high temperatures, but none are known to have an upper temperature limit of growth above 99°C. It is possible that an unknown species may have a higher upper temperature limit of growth, but that is not the most likely scenario. Only bacterial cells, and not archael cells, have peptidoglycan cell walls. Monolayer membranes are common in Archaea, but not all hyperthermophiles have monolayer membranes. This cell should be examined to determine its membrane structure. Cells have an optimal temperature that is close to their maximum growth temperature and quickly die once above their maximum growth temperature. Because the highest maximum growth temperature known for bacteria is 95°C, this cell is not a bacterial cell that is just at a higher temperature than is optimal for its growth.

Human pathogens are generally __________.

- mesophiles *what you need to know: Human pathogens are generally mesophiles because these bacteria have optimal temperatures for growth around human body temperature. The optimal temperatures for thermophiles are higher than human body temperature. Psychrophiles thrive at relatively cool temperatures that are lower than human body temperature. Hyperthermophiles have optimal temperatures higher than those of thermophiles.

A microbial sample is unable to grow in a normal batch culture but does not grow in an anaerobic environment either. This organism is a(n) __________.

- microaerophile *what you need to know: A microbial sample that is unable to grow in a normal batch culture or an anaerobic environment contains a microaerophile. These are organisms that require low concentrations of oxygen, less than the concentration of oxygen in the atmosphere, to grow. They require special culture medium to maintain a region with the correct oxygen concentration. Aerotolerant anaerobes grow equally well with or without oxygen and do not require oxygen. Facultative anaerobes can grow with or without oxygen but can grow more quickly in the presence of oxygen because this allows them to use aerobic respiration. Obligate aerobes require oxygen to survive and die if moved to an anoxic environment.

A thioglycolate broth culture that contains a thin band without growth, a thin band with growth, and then a large region without growth that extends to the bottom of the tube contains a(n) __________.

- microaerophile *what you need to know: A thioglycolate broth culture that contains a thin band without growth, a thin band with growth, and then a large region without growth contains a microaerophile. These microbes can't grow in the oxic zone near the top, which contains oxygen and cannot grow in the anoxic zone beneath. They can only grow in the narrow zone where the oxic and anoxic zones meet, which contains a low concentration of oxygen. Obligate aerobes grow near the top in the oxic zone. Obligate anaerobes grow in the anoxic zone. Facultative anaerobes can grow throughout the tube.

Why do defined culture media often contain the components of a buffer, such as K2HPO4 and KH2PO4?

- microbes are sensitive to pH *what you need to know: Defined culture media often contain the components of a buffer, such as K2PO4 and KH2PO4, because microbes are sensitive to pH and buffers help to maintain a relatively constant pH.These components are used to stabilize the pH and not because microbes need to metabolize them.Microbes are sensitive to temperature and require sufficient water, but these are not reasons that buffer components are needed

A bacterial culture has accidentally been left for more than a year in the back of an incubator. Is it sterile?

- no, because a few bacteria may have survived even though it is in the decline phase *what you need to know: A bacterial culture that has been accidentally left for more than a year in the back of an incubator is not sterile because a few bacteria may have survived even though it is in the decline phase. The culture will probably have few nutrients and considerable accumulation of wastes, but often some cells survive for an extended time in the decline phase.

A test tube of bacteria is allowed to sit undisturbed in the lab for an extended time, and then the growth is estimated using turbidity measurements. Do you predict that this estimate will be accurate?

- no, because it is likely that a biofilm has formed *what you need to know: If a test tube of bacteria is allowed to sit undisturbed in the lab for an extended time before growth is estimated using turbidity measurements, then the measurements may not be accurate as it is likely that a biofilm has formed. Turbidometric measurements are a well-accepted method of estimating bacterial density that can be reliable, but the cultures should be shaken or stirred to inhibit biofilm formation. The tube has been given an opportunity to grow but should not have been left undisturbed prior to the measurement.

The term for eliminating or killing all microbes present is __________.

- sterilization *what you need to know: The term for eliminating or killing all microbes present is sterilization. Disinfection is the term for killing or removing pathogens. Antisepsis is the term for killing microbes to reduce the risk of infection on living tissue. Sanitization is the process of making something safe by public health standards.

Which is one of the major elements that is required by cells, making up most of their dry weight?

- sulfur (S) *what you need to know: One of the major elements that is required by cells, making up most of their dry weight, is sulfur (S ). This element is an important component of the amino acids cysteine and methionine. Bromine (Br) is metabolized but not essential. Sodium (Na) is essential but present in smaller quantities. Radon (Rn) is not metabolized by cells.

Most organisms that live in aerobic environments require catalase and __________.

- superoxide dismutase *what you need to know: Most organisms that live in aerobic environments require catalase and superoxide dismutase. These enzymes and other enzymes with similar functions are important to react with potentially harmful reactive species produced by oxygen metabolism. Catalase reacts with hydrogen peroxide, a potentially harmful molecule , to produce water and oxygen. Cytochromes are important in the electron transport chain. Hydroxyl radicals are potentially harmful molecules produced by oxygen metabolism.

What is true of the cardinal temperatures?

- the optimal temperature is closer to the maximum temperature than the minimum temperature *what you need to know: The cardinal temperatures show a pattern in which the optimal temperature is closer to the maximum temperature than to the minimum temperature.Enzyme activity increases with temperature but then drops rapidly once denaturation occurs. Denaturation occurs when bonds break, and the protein loses its normal shape, which is necessary for function.

One of the most common methods for sterilization, which uses moist heat, is __________.

- using an autoclave *what you need to know: One of the most common methods for sterilization, which uses moist heat, is using an autoclave. This effectively kills microbes and spores. Germicides kill some microbes but do not sterilize. Pasteurization is an approach to reduce the number of microbes in a liquid and is important for food safety. However, it does not sterilize liquids. Halogenation means the addition of halogens, such as chlorine, to a substance. Chlorine is often added to water to reduce the microbial load and make it safer to drink. This approach does not involve heat.

Microbes that can survive in extremely dry environments are called __________.

- xerophilic *what you need to know: Microbes that can survive in extremely dry environments are called xerophilic. These organisms need only low water activity (aw) to survive. It is important to realize that dissolved solute concentration affects aw. Water with a high solute concentration has low aw. Barophilic organisms grow best in a high-pressure environment, and hydrophilic organisms grow best when water is readily available. Halotolerant organisms can survive in environments with a high solute concentration but grow better when the solute concentration is lower.

The number of cells in a bacterial culture at any given time during the exponential growth phase can be calculated as Nt = N02n, so how many cells are present if there were originally two cells and there have been two generations since exponential growth began?

- 8 *what you need to know: The number of cells in a bacterial culture at any given time during the exponential growth phase can be calculated as Nt = N02n, so the number of cells present if there were originally two cells and have been two generations since exponential growth began would be 8. Nt = 2 × 22 = 8.

What is one way in which microbes in a biofilm may differ based on their location?

- Access to nutrients may vary by location. *what you need to know: One way in which microbes in a biofilm may differ based on their location is that access to nutrients may vary by location. Microbes on the outside may have more access to oxygen and nutrients than those deeper within, which may have less oxygen availability and a reduced growth rate.

Do disinfectants work the same when used in standard, real-world situations as they do in the laboratory?

- No, because organic material may protect microbes from exposure. *what you need to know: When disinfectants are compared in the real world and in the laboratory, they often do not work as well in the real world for multiple reasons, including the fact that organic material may protect microbes from exposure. The concentration may vary between the laboratory and real-world use, but different concentrations can be compared in the laboratory to predict what will happen. The chemical composition is the same in both settings, but this does not necessarily mean that the disinfectant will work the same. Although researchers attempt to determine how disinfectants will work in the real world by testing them in different ways, it is difficult to examine all of the complex factors that affect how a disinfectant will work in any particular real-world situation.

A researcher realizes that the cytoplasm of a microbe has a pH of 6.0. Knowing that a microbe is an acidophile, she injects acid into the cytoplasm to lower the pH to 4.0. What do you predict will happen?

- The microbe will probably die because its internal pH is too low. *what you need to know: If acid is injected into the cytoplasm to lower the pH to 4.0, you can predict that the microbe will die because its internal pH is too low. Acidophiles require an external environment that is acidic amd not an acidic intracellular environment. The injected acid will denature proteins and cause damage, killing the microbe. Microbes have ways to maintain their intracellular pH, and this microbe would attempt to adjust its pH higher if it survived long enough. Because the acid lowered the pH beyond the correct range, the microbe would become less (not more) metabolically active. The original intracellular pH of 6.0 was probably optimal; damage would have resulted only after the pH was lowered and not before.

Why do facultative anaerobes grow better when oxygen is present?

- They can use aerobic respiration, which produces more adenosine triphosphate (ATP) than fermentation or anaerobic respiration. *what you need to know: Facultative anaerobes grow better when oxygen is present because they can use aerobic respiration, which produces more adenosine triphosphate (ATP) than fermentation or anaerobic respiration. Microbes switch from aerobic respiration to fermentation or anaerobic respiration as needed. Using both at once would be inefficient because molecules that could be used to produce more ATP through aerobic respiration would produce less ATP if other pathways were used.

If you transfer an old culture of bacteria to a new experimental medium with a very distinctive composition, when should you take a sample if you want to study them during the exponential growth phase?

- You should leave the bacteria a little longer than usual before sampling as the lag phase will be long due to the unusual medium and the age of the culture. *what you need to know: If you transfer an old culture of bacteria to a new experimental medium with a very distinctive composition, you sho uld leave the bacteria a little longer than usual before sampling as the lag phase will be relatively long due to the unusual medium and the age of the culture. As shown in the following figure, the exponential growth phase occurs after a lag phase. The length of the lag phase depends on how much the bacteria need to adjust to the new medium. Bacteria use up nutrients and begin to run low by the end of the exponential growth phase. Older cultures have a longer lag period.

An organism that thrives at a pH of 2 is called a(n) __________.

- acidophile *what you need to know: An organism that thrives at a pH of 2 is called an acidophile. These organisms grow best in an acidic environment. The pH of the environment is important to growth because it affects electrostatic interactions. Proteins denature if the pH is too far from optimal, meaning that important enzymatic reactions cease. Alkaliphiles grow best in alkaline environments with a pH above 8. Barophiles are microbes that grow best at high pressure. Neutrophiles grow best in a pH that is close to neutral (between 5.5 and 7.9).