At higher temperatures, microbes grow more quickly. For instance, pathogens often grow best at normal body temperature, but slowly at cooler temperatures outside the body or when body temperature increases during a fever. Extremely high temperatures usually denature the components required for the cells to survive and are lethal for many microbes. Nonetheless, a few exceptional microbes actually prefer to grow at very high temperatures or very low temperatures.
These microbes, known as extremophiles , can grow near hydrothermal vents where the temperature is above boiling or surrounded by solid ice. Even when nutrients are available and the temperature is right, many other environmental factors can influence the growth of microbes. These include acidity, availability of water, and atmospheric pressure. Each microbe prefers a range of properties for multiple features of the environment. Overall, microbes typically grow best at a specific set of conditions and less well at other conditions Figure 5.
Specific preferences for growth are as diverse as the types of microbes. Decades of research have developed the current understanding of microbial growth to establish the principles outlined above. Establishing common principles allows us to target broad groups of microbes, while unique requirements for growth allows us to target specific microbes. This knowledge enables the control of microbial growth that facilitates many of our interactions with microbes today.
Many methods of control seek to eliminate harmful microbes from foods or equipment. For example, high temperature is often used to kill microbes during cooking or through processes like pasteurization. In this way, potentially harmful microbes are broadly eliminated from the food product making it safe to consume and store.
Similarly, chemicals in disinfectants can damage or kill microbes broadly on surfaces. Alcohols like ethanol and isopropanol damage the cell membranes. Without this protective structure, microbes cannot control what enters or exits the cell.
Subsequently, microbes cannot retain important nutrients and water. Alternatively, hydrogen peroxide damages structures within the cell. As hydrogen peroxide decomposes, it forms molecules known as free radicals that damage proteins and DNA. Meanwhile, we also use soaps to physically remove microbes from surfaces.
The chemical properties of soaps and physical force applied when wiping a surface dislodges the microbes. When microbes cannot be completely eliminated from a material, such as food products that cannot be heated to high temperatures, measures can be taken to mitigate the growth of microbes.
Recognizing how temperature impacts growth, supports the importance of refrigeration. As mentioned, cold temperatures slow the growth of microbes, so refrigeration can delay the growth of microbes in these food products. As described above, microbes can replicate as quickly as every 20 minutes leading to visible growth within only a few hours.
At a lower temperature, the cells may divide only once every few hours and it will take multiple days to see visible growth. Alternatively, when we want to take advantage of microbes, we try to optimize the conditions for their growth. This is why yeasted dough is left at a warm temperature to allow the yeast to grow rapidly. If the dough is refrigerated, it takes much longer to rise.
Similarly, to use E. The results of each investigation should then be presented as a graph. The horizontal axis of the graph should be the intervals of the different temperatures at which the microbes were grown. The vertical axis should represent the logarithmic value of the generations per hour determined for that sample. This is called a Arrhenius plot. The shape of these graphs or plots is characteristic for each species of microbe, but each organism will show an optimum temperature where growth proceeds most rapidly, and as the temperatures either exceed, or fall below that optimum, growth slows down.
Above or below the maximum and minimum permissive temperatures, all growth stops. Each investigation is carried out under a specific set of growth conditions.
A species of microbe is chosen first. It is then necessary to chose a temperature. Use the thermometer sliding scale to set the chosen temperature. The value chosen will appear in the box. In some investigations you will need to record the entire growth curve data on extreme right , but for most investigations you only need to record the "generations per minute" and "log. Record all the temperatures and all the values where you see that the microbial species could grow at all.
Lag phase The lag phase is an adaptation period, where the bacteria are adjusting to their new conditions. Exponential or Log phase Once cells have accumulated all that they need for growth, they proceed into cell division.
Bacterial Growth Rates. Stationary Phase All good things must come to an end otherwise bacteria would equal the mass of the Earth in 7 days! Death or Decline phase In the last phase of the growth curve, the death or decline phase , the number of viable cells decreases in a predictable or exponential fashion.
Key Words binary fission, multiple fission, budding, spores, cell cycle, closed system, batch culture, growth curve, lag phase, exponential or log phase, generation time g , N, N0, n , t , stationary phase, DNA-binding proteins from starved cells DPS , oligotrophic, secondary metabolites, death or decline phase, viable but nonculturable VBNC.
What are the steps of binary fission? What is happening at each step? Know what the growth curve of an organism grown in a closed system looks like. Know the various stages and what is occurring at each stage, physiologically. What can influence lag phase? What are the 2 differing explanations for cell loss in the death or senescence phase? Understand generation time and how can it be determined on a log number of cells vs. Know the advantage of plotting the log number of cells vs.
What factors affect the generation time of an organism? Practice problem: Six Staphylococcus aureus are inoculated into a cream pie by the hands of a pastry chef. The generation time of S. How could this pose a public health threat? NGSS Performance Expectations: MS-LS Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation. The content and activities in this topic will work towards building an understanding of how aquatic plants and algae grow, develop, and reproduce.
Chromosomes are duplicated. Meiosis begins in a fashion similar to mitosis with chromosome replication. Matched sets of chromosomes pair together. Genes are swapped between matched chromosomes. The process of crossing over, or recombination, exchanges genetic information between chromosomes in a cell. The resulting chromosomes are brand new, unique combinations of genetic information.
First division separates one of each chromosome pair. The parent cell divides in half as in mitosis, producing two cells with a complete amount of DNA although they are not identical because of crossing over. Second division separates each chromosome, leaving one copy of each chromosome per cell. The two new cells divide a second time to produce four new gametes. These gametes contain one-half of the genetic information needed to form a new individual.
Each parent provides one gamete to the process of fertilization, which results in a cell called a zygote with a full compliment of chromosomes.
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