Chapter 4: Dynamics of Microbial Growth

Which are considered major elements that primarily make up components of cells in microorganisms and all living things?

Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur Potassium Magnesium Calcium and iron are essential components of proteins, carbohydrates, lipids, and nucleic acids.

Death phase

Due to nutrient depletion and waste accumulation, cells begin to die at an exponential rate

It is sometimes difficult to obtain pure cultures of microbes that grow naturally in mixed communities. T or F

True

Stationary phase

With nutrients depleted, total number of viable cells remains constant, with some dying while others multiply

The presence of microbes in food can be ______. - harmful - beneficial or harmful but not neutral - beneficial, harmful, or neutral - beneficial - neutral

Beneficial, harmful, or neutral. Microbes can do both good and bad things to food, or have no particular effect at all. For example, some microbes can be used to make food products such as cheese, yogurt, and bread, but others can cause food poisoning when ingested.

How would you classify L. methylaminiphilus with regards to pH? - Extremophile - Alkaliphile - Halophile - Acidophile - Neutrophile

Neutrophile. Although L. methylaminiphilus can grow at a pH range of 4.0-9.5, its optimum growth is at 5.0-7.0, ranging from somewhat acidic to neutral. Like many microbes, it can tolerate a pH outside of this range, but growth rates are greatly reduced.

You observe bacteria growing on the surface of a Petri dish of nutrient agar you left on the counter in your lab. You can be confident that your bacteria are NOT which of the following? - Obligate aerobes - Obligate anaerobes - Facultative anaerobes - Microaerophiles - Aerotolerant anaerobes

Obligate anaerobes. Obligate anaerobes cannot multiply if oxygen is present.

biofilms

Polymer-encased community of microorganisms. Biofilm formation begins when planktonic (free-floating) cells move to a surface and adhere. The mesh-like accumulation of these polymers, referred to as extracellular polymeric substances (EPS), gives a biofilm its characteristic slimy appearance.

How would you classify L. methylaminiphilus with regards to temperature requirements? - Psychrophile - Psychrotroph - Hyperthermophile - Mesophile - Thermophile

Psychrotroph. L. methylaminiphilus can grow at a temperature range of 10-35°C, with optimal growth at 28-30°C. This makes L. methylaminiphilus a psychrotroph. This matches its habitat, given that it was isolated from cool sediments 63 meters below the surface.

Which of the following environmental factors is the most important in influencing the growth rate of bacteria? - Chemical inhibitors - Oxygen - Moisture - Temperature - pH - Nutrients

Temperature. The primary factors influencing bacterial growth are temperature, moisture, nutrients, pH, oxygen, and chemical inhibitors. Of these, temperature plays the most important role in the rate of growth. Bacteria grow best at some optimum temperature.

The safe temperature ranges for the storage of foods are determined by - the low temperature at which they die and the high temperature at which they stop multiplying. - the low temperature at which microbes stop multiplying and the high temperature at which they stop multiplying. - the low temperature at which microbes die and the high temperature at which they die. - the low temperature at which microbes stop multiplying and the high temperature at which they die. - the low temperature at which they stop multiplying and the high temperature at which their growth accelerates.

The low temperature at which microbes stop multiplying and the high temperature at which they die. The safe temperature ranges for the storage of foods are determined by the low temperature where microbes stop growing and the high temperature where they physically die. Between these temperatures, bacteria can rapidly multiply. If food is contaminated with pathogens and can support bacterial growth (sufficient moisture, appropriate pH, absence of chemical inhibitors, etc.), pathogens can rapidly reach dangerous levels when food is left out at room temperature.

Which is the best definition of generation time? - The time it takes it takes for a bacterial population to exponentially decrease. - The time it takes for the number of cells in a population to double. - The 24 hours it takes for cells to achieve maximum growth rate. - The time it takes for a bacterial cell to duplicate its DNA. - The time it takes for a bacterial cell to complete one round of mitosis.

The time it takes for the number of cells in a population to double. Generation time is the time it takes for the number of cells in a population time to double (also called doubling time). This time varies among species—it can be as fast as 20 minutes or as slow as 16 hours.

According to the figure, food stored for one to two hours at a temperature of 32 degrees Celsius would be safe to eat.

This is false. Food is safe if it is stored for one to two hours at 32 degrees Fahrenheit (which is equivalent to 0 degrees Celsius). Safe temperatures range from 4 degrees Celsius (40 F) to about 57 degrees Celsius (135 F); 32 degrees Celcius falls within the danger zone.

The type of food-borne infection known as an intoxication is caused by - the buildup of oxidative byproducts such as O- in the food. - toxins produced by microbes as they grow in the food. - the buildup of microbial waste products such as lactic acid. - toxins produced by the microbe in the intestinal tract. - growth of the microbe in the intestinal tract and intestinal lining.

Toxins produced by microbes as they grow in the food. The type of food-borne infection known as an intoxication (such as staphylococcal food poisoning) is caused by toxins produced by microbes as they grow in improperly stored food.

Environmental factors control microbial growth through their effect on enzyme activity. T or F

True. Factors such as pH, temperature, and moisture have an effect on bacterial enzymes, which influence bacterial cell division.

Identify the phases of a bacterial growth curve. (5 phases)

1. Lag 2. Log (Exponential) 3. Stationary 4. Death 5. Decline

Starting from a single bacterium, after six generations of binary fission, how many bacterial cells will be present? - 12 - 127 - 64 - 32 - 6

64. Each division doubles the number of organisms, so 1 becomes 2, 2 becomes 4, 4 becomes 8, 8 becomes 16, 16 becomes 32, and 32 becomes 64 in six generations.

A single species of bacteria grows best at - different temperatures, based on nutrient availability. - a modest range around a minimum temperature. - a modest range around an optimum temperature. - different temperatures, based on the availability of oxygen. - a broad range of temperatures ranging from freezing to boiling.

A modest range around an optimum temperature. Bacteria grow best at an optimum temperature and a relatively modest range above and below the optimum. They fit into five broad categories (psychrophiles, psychrotrophs, mesophiles, thermophiles, and hyperthermophiles) based on that temperature range.

From which of the following would you be most likely to obtain a pure culture? - None - A culture growing in a flask - A single colony growing on a streak plate - A biofilm growing on a surface - A streak growing on an agar slant

A single colony growing on a streak plate. A streak plate is used to obtain a pure culture in the form of a single colony.

Which of the following are examples of biofilms? - Dental plaque - Scum accumulating in toilet bowls - Slipperiness on rocks in stream beds - Capsule formation around Streptococcus pneumoniae - Furry grayish-white growth on old bread or fruit

All except capsule formation around Streptococcus pneumoniae. Bacteria frequently grow in polymer-encased communities called biofilms. These involve the production and release of polysaccharides, DNA, and other hydrophilic polymers, yielding a slimy, mesh-like accumulation of polymers referred to as extracellular polymeric substances, or EPS. .

How common are food spoilage microorganisms? - Rare in milk products but common in dry foods - They are extremely rare - Almost all of our foods contain them - A few of our foods contain them - Almost none of our foods contain them

Almost all of our foods contain them

According to the graph, what is the impact of cold temperatures on E. coli? - As temperatures decrease, the growth rate decreases. - As temperatures increase, the growth rate decreases. - As temperatures drop below 30 degrees celsius, cells begin to die. - There is no impact of cold temperatures on cell growth. - Below 6 degrees celsius, all the cells die.

As temperatures decrease, the growth rate decreases. The rate of reaction decreases at lower temperature. This slows the metabolic activity of cells and leads to slower growth rates. As temperatures reach about 6 degrees celsius, growth of E. coli ceases, and the cells are forced to wait until temperatures increase before growth can resume.

If conditions are favorable, the generation time of bacteria - is remarkably stable, showing little change. - usually exceeds 48 hours. - cannot be measured. - can be as short as 12 hours. - can be as short as 30 minutes.

Can be as short as 30 mins. If conditions are favorable, the generation time of bacteria can be as short as 30 minutes. This contributes to their ability to cause food-borne infections.

Exponential/Log phase

Cells are actively growing, doubling the population with each generation

Lag phase

Cells are not dividing but are synthesizing enzymes required for growth

What happens to bacterial cells when their maximum growth temperature is exceeded? - Cells divide more rapidly as the optimum temperature is exceeded. - All bacteria produce endospores by which they can survive the increased temperature. - Cells begin to die when their maximum growth temperature is exceeded. - Cells achieve their maximum growth rate when the maximum growth temperature is exceeded. - The rate of cell division decreases, but cells survive when the maximum temperature is exceeded.

Cells begin to die when their maximum growth temperature is exceeded. At high temperature, proteins denature. As the maximum growth rate is exceeded, damage to the cell from denatured proteins accumulates, leading to increasing rates of cell death as the temperature increases.

Consider the growth of L. methylaminiphilus on methylamine. How would you classify this species based on its metabolism? - Photoautotroph - Photoheterotroph - Chemolithoautotroph - Chemoorganoheterotroph - Chemoorganoautotroph

Chemoorganoheterotroph. Microbiologists commonly classify microorganisms by their sources of energy and carbon. L. methylaminiphilus demonstrates growth using organic compounds as its source of carbon and electrons, making it a chemoorganoheterotroph.

How do you think the scientists isolated L. methylaminiphilus from the sediments, knowing that a single gram of soil may contain thousands of different species of bacteria? - Gram staining - Microscopy - Metagenomics - PCR and DNA sequencing - Enrichment cultures

Enrichment cultures. Enrichment cultures were set up using methylamine as a sole carbon source to promote the growth of methylotrophic bacteria. After multiple transfers, samples were plated out, and individual colonies were streaked for isolation, leading to the discovery of L. methylaminiphilus.

Both human cells and bacterial cells divide by mitosis. T or F

False. Bacteria divide by binary fission and human cells divide by mitosis. The processes are similar in the fact that both involve the division of one cell into two genetically identical cells.

Production of extracellular polymeric substances (EPS) enables bacteria to - form biofilms - communicate with other cells - make endospores - grow in cold climates such as the Arctic - undergo DNA mediated transformation

Form biofilms. Bacteria frequently grow in polymer-encased communities called biofilms. These involve the production and release of polysaccharides, DNA, and other hydrophilic polymers, yielding a slimy, mesh-like accumulation of polymers refered to as extracellular polymeric substances, or EPS.

Cells must _______________ their DNA prior to cell division. - denature - transcribe - replicate - translate - hydrolyze

Replicate. DNA replication is necessary to ensure each daughter cell receives genetic material.

The CDC estimates that in the U.S., ______ people suffer each year from some form of food-borne infection. - an undetermined number of - several thousand - between 1.5 and 2 billion - roughly 100,000 - several million

Several million. Millions of people each year suffer from food-borne infections in the U.S., a significant number.

Most bacteria reproduce by ______. - mitosis - budding - binary fission - endospores - sexual reproduction

binary fission. Bacteria usually divide into two equal, genetically identical cells through a process known as binary fission.

You have a culture of bacteria in which cells are actively expressing genes and synthesizing enzymes, but cells are not dividing. This culture is most likely in ______ phase. - stationary - prolonged decline - death - log - lag

lag. During stationary phase, the total number of viable cells in the population remains relatively constant. Some cells are dying, while others are multiplying. Nutrient levels are low, and levels of wastes are high.