Mesophiles Microbes that grow at optimal temperatures in the range 20 o C to 40 o C, are called mesophilic. Important members of this group are those that live in and on warm blooded creatures, such as humans.
Pathogenic bacteria and included here, as are symbiotic bacteria that live in the human body without harming it. Thermophiles Certain bacteria can live and grow at temperatures that exceed 50 o C. These are thermophilic microbes that can tolerate the very harsh conditions decomposing organic material, the hot springs at Yellowstone National Park where temperatures are at least 80 o C to 85 o C , or deep in the oceans by thermal vents bubbling up from the hot rocks just below the earth's crust.
Tools of the Trade. In these investigations, a tiny group of each microbe species are placed into a liquid, nutrient filled broth that has been sterilized so no other bacteria will compete! Usually this is in a special flask called an "Erlenmeyer flask" , which is slowly shaken to keep the microbes and nutrient at uniform distributions. Each growing culture is carefully kept at the appropriate, and constant, temperature for the length of the experiment.
At regular intervals of time, small samples of the growing culture are taken from the flask and all reproduction of the microbes stopped by some poison or inhibitor they can also be chilled or frozen.
The size of the population at each time point is then determined. M endel's M other shows you -- how bacteria grow. The results of each of your investigations should be recorded as a table a Table of Results. Some microbes are also surrounded by a cell wall. The wall provides a structure to enclose the internal components of the cell.
Within its interior, each cell carries the DNA encoding its genome. Other structures in the cell perform metabolic functions that are essential for life. Microbial growth refers to an increase in number of cells rather than an increase in cell size. Many microbes including Escherichia coli, Salmonella enterica, and Listeria monocytogenes are unicellular, meaning they are made of only one cell. The size of any unicellular microbe is limited by the capacity for the essential components of the cell to support its survival.
For example, the integrity of the cell wall is impaired when cells become too large. The solution to growing despite limits on cell size is for cells to divide or produce new cells from the original cell.
Therefore, the population grows although the size of the individual members of the population remains stable. Most commonly, a single-cellular microbe divides into two identical new cells during one growth cycle Figure 3a. The original cell, called the parent cell, makes a copy of its DNA and generates enough material to build the membrane, wall, and molecular machines for two cells. The parent cell slightly increases in size to accommodate these additional materials.
Then, the parent cell begins to contract at the middle and a new piece of cell wall is assembled at the site of contraction. This process continues until the parent cell is split into two cells with complete cell walls. The resulting cells are called the daughter cells. Because both daughter cells are identical, cell division is also called replication. Replication in this manner leads to a rapid increase in the number of cells as each daughter cell begins the cycle again by acting as a parent cell.
Cell division can look slightly different for microbes with different shapes Figure 3b , but the key principles remain the same. As long as the conditions are favorable, one cell produces two new cells in a continuous cycle. Every cycle doubles the number of cells in the population. This is known as exponential growth. Depending on the conditions, the division cycle of E.
This rapid division leads to a rapid increase in the population size Figure 3c. Eventually, the population is large enough to have an impact we can detect, such as formation of a physical structure. You might notice this as plaque on your teeth. It takes over a million bacteria to form a visible structure, but this can occur in only about eight hours when conditions are optimal for E.
Some microbes produce new cells asymmetrically. In this situation, one parent cell produces a single daughter cell by a process called budding. During budding the parent cell develops a small protrusion known as the bud. The materials necessary to support a new cell are sent into the bud, which eventually splits from the parent cell to form a new daughter cell. The parent cell continues to make buds, but the budded daughter cells do not divide. Buds can remain connected in a chain or separate into individual cells Figure 4.
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Set your location: Set Cancel. Phosphorus is an essential element for nucleic acid synthesis and for the construction of phospholipids. Oxygen is used by aerobic bacteria during the process of cellular respiration as a final electron acceptor. For aerobic organisms, oxygen is an absolute requirement for their energy-yielding properties.
Certain microorganisms grow in oxygen-free environments and are described as anaerobic. Organisms such as these produce odoriferous gases in their metabolism, including hydrogen sulfide gas and methane. Certain pathogenic species, such as Clostridium species, are anaerobic. Certain species of microorganisms are said to be facultative. These species grow in either the presence or absence of oxygen. Some bacteria species are microaerophilic , meaning that they grow in low concentrations of oxygen.
In some cases, these organisms must have an environment rich in carbon dioxide. Organisms such as these are said to be capnophilic.
Other chemical requirements for microbial growth include such trace elements as iron, copper, and zinc. These elements often are used for the synthesis of enzymes.
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