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Learning Goals
By the end of this reading you should be able to:
- Describe the process of binary fission in bacteria
- Define the nutritional types of microbes in terms of their sources of carbon, electrons, and energy
- Explain horizontal gene transfer and the three mechanisms by which it occurs in bacteria
- Describe how antibiotics function and explain how some bacteria manage to disarm them
Introduction
The diverse environments and ecosystems on Earth have a wide range of conditions in terms of temperature, available nutrients, acidity, salinity, and energy sources. Prokaryotes are very well equipped to make their living out of a vast array of nutrients and conditions. To live, prokaryotes need a source of energy, a source of carbon, and some additional nutrients. When conditions are favorable prokaryotic populations can grow rapidly because they are asexual. They can also maintain genetic diversity through both mutation and the process of horizontal gene transfer. As a result, prokaryotes are one of the most diverse groups of organisms on Earth.
Microbial Growth
Provided with the right conditions (food, correct temperature, etc) microbes can grow very quickly. Depending on the situation, this could be a good thing for humans (yeast growing in the wort to make beer) or a bad thing (bacteria growing in your throat causing strep throat). It’s important to have knowledge of their growth, so we can predict or control their growth under particular conditions. While growth for multicellular organisms is typically measured in terms of the increase in the size of a single organism, microbial growth is measured by the increase in population, either by measuring the increase in cell number or the increase in overall mass.
Binary fission begins with cell elongation, which requires careful enlargement of the cell membrane and the cell wall, in addition to an increase in cell volume. Once the cell reaches a certain size it will start to replicate its DNA, in preparation for having two copies of its chromosome, one for each newly formed cell.
The starting point (origin) of replication, is close to the binding site of the chromosome to the plasma membrane. Replication of the DNA is bidirectional, moving away from the origin on both strands of the loop simultaneously (Step 1 in Fig. 2). As the new double strands are formed, each origin point moves away from the cell wall attachment toward the opposite ends of the cell. As the cell elongates, the growing membrane aids in the transport of the chromosomes (Step 2 in Fig. 2). After the chromosomes have cleared the midpoint of the elongated cell, cytoplasmic separation begins. The formation of a ring composed of repeating units of a protein called FtsZ directs the partition between the nucleoids (Step 3 in Fig. 2). The formation of the FtsZ ring triggers the accumulation of other proteins that work together to recruit new membrane and cell wall materials to the site. A septum (wall) is formed between the nucl