7.1: Microbial Growth
-
- 7.1.1: How Microbes Grow
- The bacterial cell cycle involves the formation of new cells through the replication of DNA and partitioning of cellular components into two daughter cells. In prokaryotes, reproduction is always asexual, although extensive genetic recombination in the form of horizontal gene transfer takes place, as will be explored in a different chapter. Most bacteria have a single circular chromosome; however, some exceptions exist.
-
- 7.1.2: Oxygen Requirements for Microbial Growth
- Ask most people “What are the major requirements for life?” and the answers are likely to include water and oxygen. Few would argue about the need for water, but what about oxygen? Can there be life without oxygen? The answer is that molecular oxygen is not always needed. The earliest signs of life are dated to a period when conditions on earth were highly reducing and free oxygen gas was essentially nonexistent.
-
- 7.1.3: Temperature and Microbial Growth
- Microorganisms thrive at a wide range of temperatures; they have colonized different natural environments and have adapted to extreme temperatures. Both extreme cold and hot temperatures require evolutionary adjustments to macromolecules and biological processes. Psychrophiles grow best in the temperature range of 0–15 °C whereas psychrotrophs thrive between 4°C and 25 °C. Mesophiles grow best at moderate temperatures in the range of 20 °C to about 45 °C. Pathogens are usually mesophiles.
-
- 7.1.4: The Effects of pH on Microbial Growth
- Bacteria are generally neutrophiles. They grow best at neutral pH close to 7.0. Acidophiles grow optimally at a pH near 3.0. Alkaliphiles are organisms that grow optimally between a pH of 8 and 10.5. Extreme acidophiles and alkaliphiles grow slowly or not at all near neutral pH. Microorganisms grow best at their optimum growth pH. Growth occurs slowly or not at all below the minimum growth pH and above the maximum growth pH.
-
- 7.1.5: Other Environmental Conditions that Affect Growth
- Microorganisms interact with their environment along more dimensions than pH, temperature, and free oxygen levels, although these factors require significant adaptations. We also find microorganisms adapted to varying levels of salinity, barometric pressure, humidity, and light.
Thumbnail: Heavy rains cause runoff of fertilizers into Lake Erie, triggering extensive algal blooms, which can be observed along the shoreline. Notice the brown unplanted and green planted agricultural land on the shore. (credit: NASA)