In this video, we're going to begin our lesson on endospores. Recall from way back in our previous lesson videos that a scientist named John Tyndall discovered a heat-resistant form of bacterial cells, which were later termed endospores. Endospores can be defined as a dormant cell that is only produced by some bacteria and is highly resistant to damaging conditions. Because endospores are resistant to damaging conditions, they are able to survive in conditions where most normal cells would not be able to survive. Since endospores are dormant, they have lowered activity and are not able to perform the same functions as normal cells would. However, they are highly resistant to damaging conditions such as extreme amounts of heat, toxic chemicals, and nutrient depletion.
Endospores are able to survive many conditions where most normal cells would not be able to survive. It is important to note that endospore formation starts and ends with a single cell; it does not form more cells and is not a form of replication. Instead, endospore formation is a form of survival, allowing cells to survive damaging conditions where they might not otherwise survive. Another important concept is that a vegetative cell is the scientific term for a normal cell that is replicating and is not dormant. Vegetative cells can form endospores when nutrients are depleted.
Observe in the image below, on the left-hand side, we have a vegetative cell under normal conditions with nutrients available. Nutrients in the environment are indicated by hexagons that represent glucose. When nutrients are absent, the vegetative cell can undergo a process called sporulation, which leads to the formation of an endospore. Thus, the endospore, though still alive, is a dormant cell with reduced activity, unable to perform the same functions as the vegetative cell. However, it can survive conditions with no nutrients. Once nutrients become available again, the endospore can undergo a process called germination, reverting back into a vegetative cell that can perform more normal functions.
It is important to note that endospores are usually only produced by gram-positive cells. Examples of bacteria that are gram-positive and produce endospores include Bacillus and Clostridium. A helpful memory tool to remember that it is gram-positive cells that typically form endospores is to think of endospores as being dormant like winter clothes during the summer in the back of your closet. When the temperature is positive Celsius (warm like in the summer), your winter clothes are in a dormant state in the back, rarely used. This can remind you that gram-positive cells are the ones that form endospores.
This concludes our brief introduction to endospores. We will be able to apply the concepts that we have learned here as we move forward. I'll see you all in our next video.
