Microbiology, part 27: Growth - Plating Methods

Hi. I'm Cathy with Level Up RN. In this video, I will be discussing binary fission and bacterial growth. At the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on binary fission and bacterial growth so you can follow along with me. And pay close attention to the bold red text on the back of the cards because those are the things that you are likely to get tested on.

Binary fission is the primary method of reproduction used by prokaryotic cells. It is a form of asexual reproduction, and it is much faster and less complicated than cell division in eukaryotic cells. During binary fission, one cell divides into two daughter cells, and each offspring receives a complete copy of the parental genome. Let's now go through the steps involved in binary fission. During the first step, DNA is replicated, starting at the origin of replication. Next, the cell elongates, and the two separate DNA molecules will migrate to opposite sides of the cell. Next, a septum forms in the middle of the cell, and then finally, the cells separate with each daughter cell receiving a complete copy of the parental genome.

The time required for a single cell to divide or a population of bacteria to double is referred to as the generation time or doubling time. The most common bacteria have a generation time of approximately 20 to 60 minutes. When microorganisms are grown in a closed culture, meaning that additional nutrients are not added and waste products are not removed, then growth of those microorganisms will follow a predictable pattern known as a growth curve. Let's take a look at a bacterial growth curve and go over the different bacterial growth phases.

The first phase of the growth curve is the lag phase. During this phase, cells are gearing up for the next phase of growth. They are metabolically active and synthesizing proteins during this time, but the number of new cells present does not change during this phase. During the log phase, cells are actively dividing by binary fission, and there is an exponential increase in the number of cells. So the number of new cells greatly exceeds the number of dying cells in the culture. After a while, however, waste products start to build up in the culture, and nutrients start getting depleted. This, in turn, causes the growth rate to stall. So during the stationary phase, the number of new cells approximately equals the number of dying cells. And then finally, we have the death phase. This is where we have a sharp decrease in the number of bacterial cells. So the number of dying cells is greater than the number of new cells. Our cool chicken hint to help you remember that the lag phase comes before the log phase is to remember that A comes before O in the alphabet.

All right. It's quiz time, and I have four questions for you. Question number one, during binary fission, the location on the chromosome where DNA replication starts is called the blank. The answer is, origin of replication. Number two, the time required for a population of bacteria to double is called the blank. The answer is, generation time or doubling time. Number three, which phase of the bacterial growth curve is characterized by an exponential increase in the number of cells? The answer is, the log phase. And number four, the number of dying cells exceeds the number of new cells during the blank phase of the bacterial growth curve. The answer is, the death phase. All right. That's it for this video. Hope you did great on that quiz. Take care, and good luck with studying.