Growing a Pure Culture: Study with Video Lessons, Practice Problems & Examples

In microbiology, a pure culture is a population of cells containing only one species, typically initiated from a single colony of approximately 1,000,000 cells. This process begins with an inoculum, which is a colony added to a culture medium to grow the pure culture. Understanding these concepts is crucial for studying bacterial and archaeal cells, as they allow for the isolation and examination of specific microorganisms in a controlled environment.

Growing a Pure Culture

In this video, we're going to begin our lesson on growing a pure culture. And so in a scientific lab or a microbiology lab, bacterial and archaeal cells are generally isolated, grown, and studied in what's known as a pure culture. And so a pure culture can be defined as a population of cells containing only one single species. And typically, these pure cultures are grown starting from a single colony. Now, a colony is a scientific term that's used to describe a group of approximately 1,000,000 cells or so. And colonies are going to be required to start a pure culture. And these pure cultures are again typically grown in a lab. And so if we take a look at our image down below over here at this pure culture, notice that we're starting with just a single bacterial cell over here. And this single bacterial cell will divide and replicate in order to create many more cells of the same exact species. And so we have a population of cells here, but this population of cells consists of just one single species. And because we have a lot of cells here, if we had about 1,000,000 cells or so, we would have ourselves a colony of cells or a group of cells that are all the same species. And so this is an example of a pure culture because it is a population of cells containing only one species. And so, notice here that this old guy over here saying, 'Look at all my children' and these guys are saying 'We form a colony together' and all cells are going to be descended from a single cell in a pure culture. That is what allows for the population of cells to only contain 1 single species. Now, there is another term here that might be important to keep in mind if you're in a microbiology lab and that is the term inoculum. And so an inoculum is really just a colony of cells that are added to a culture medium in order to start a pure culture. And so if we wanted to create a pure culture, what we would typically do is start with a colony of cells that are all of a single species, and then we would use that colony as an inoculum to inoculate growing a pure culture, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

A pure culture of bacteria is made of…

• A. Around 1 million viable bacteria cells that are all of the same species.
• B. Around 1 million viable bacteria cells that are all descended from a single parent cell.
• C. Around 1 million viable bacteria cells that are a mixture of different bacterial species.
• D. Both A and B.
• E. Both A and C.
• F. Both B and C.

A bacterial culture grown in a _________________ will not continue to grow exponentially forever, but will stop once the limited nutrients have been consumed.

• A. Open system.
• B. Secure system.
• C. Closed system.
• D. Extended system.

Here’s what students ask on this topic:

What is a pure culture in microbiology?

A pure culture in microbiology is a population of cells that contains only one single species. This is typically achieved by starting with a single colony, which is a group of approximately 1,000,000 cells. The colony is used as an inoculum to inoculate a culture medium, allowing the cells to grow and replicate. The result is a controlled environment where only one species of microorganism is present, making it easier to study specific bacterial or archaeal cells without contamination from other species.

How is a pure culture initiated in a lab?

A pure culture is initiated in a lab by starting with a single colony of cells, which contains about 1,000,000 cells of the same species. This colony is used as an inoculum, which is added to a culture medium. The inoculum allows the cells to grow and replicate, forming a population of cells that all belong to the same species. This process ensures that the culture remains pure and uncontaminated by other microorganisms, facilitating accurate study and analysis.

What is an inoculum in the context of growing a pure culture?

An inoculum in the context of growing a pure culture is a colony of cells that is added to a culture medium to start the growth of a pure culture. The inoculum typically consists of about 1,000,000 cells of a single species. By using an inoculum, scientists can ensure that the resulting culture contains only one species of microorganism, which is crucial for accurate study and experimentation in microbiology.

Why is it important to use a pure culture in microbiology studies?

Using a pure culture in microbiology studies is important because it ensures that only one species of microorganism is present in the culture. This eliminates the risk of contamination from other species, allowing for more accurate and reliable results. Pure cultures are essential for studying the characteristics, behavior, and interactions of specific microorganisms, as well as for developing antibiotics and other treatments. They provide a controlled environment that is crucial for scientific research and experimentation.

What is a colony in microbiology?

In microbiology, a colony is a group of approximately 1,000,000 cells that originate from a single cell. Colonies are visible to the naked eye and are used to start pure cultures. Each colony consists of cells that are genetically identical, making them ideal for studying specific species of microorganisms. Colonies are essential for isolating and growing pure cultures, as they provide a starting point for the inoculum used in the culture medium.