Hello, and welcome to this video. We will try to answer a question, could humans live without bacteria? Bacteria have lots of benefits. We can classify beneficial bacteria into groups; bacteria that live in soil and water and bacteria that are in the human body or other animals bodies. Bacteria that are present in soil and water are beneficial for human life because they can decomposed organic matter and they can also recycle chemical elements. Bacteria that are present in the human body are also beneficial because they can decompose also organic matter and they can supply essential vitamins and they help in the immune system. In all these benefits, we don't include essential cell organelles, such as mitochondria and chloroplast. But we should because they were once primitive bacteria. This was described by Lynn Margulis, who developed that theory called the Endosymbiotic theory. According to this theory, mitochondria and chloroplasts were primitive bacteria that ended up inside of other cells and established with them a symbiotic relationship. Eventually, they became essential cell organelles. Therefore, life with no mitochondria or chloroplasts would mean that animals and plants would be dead in one minute. Now we will talk about the benefits of bacteria that are present in soil and water and later, we will talk about bacteria that are in the human body. Ann Maczulak from US has studied a lot the relationship between bacteria and environment, and she's the author of 14 books. One of them is Allies and Enemies. How the world depends on bacteria. She says that bacteria are invisible mysterious and essential organisms, and yet we fear them. As we mentioned before, bacteria participate in the decomposition of organic matter. It is well-known that bacteria can release enzymes that oxidize organic compounds that are present in organic matter. As a result, we obtain energy, carbon, and mineral nutrients which are essential for plants to grow and to live. Bacteria participate also in recycling chemical elements. For example, they participate in the carbon cycle. Bacteria take part in the photosynthesis, and they fix carbon as organic matter. Bacteria take part also in the decomposition of that organic material obtaining from this CO_2. Bacteria can participate also in the nitrogen cycle. They take part in the fixation of nitrogen to ammonia. They take part also in the nitrification from ammonia to nitrites and nitrides, which are essential for plant growth. They can participate also in the denitrification, obtaining nitrogen. Johanna Döbereiner from Brazil dedicated 50 years of her career to study the nitrogen fixation by bacteria.Thanks to her work, now we know that nitrogen fixing bacteria can promote plant growth, and this was used to improve production of bio fuel in Brazil. Bacteria participate also in the water cycle. They can take part in the precipitation, and these bacteria are called rainmaking bacteria. Now we will talk about the bacteria that are present in the human body. First, we will introduce a bit about human microbiota, which are all the bacteria that live in our bodies. In this slide, you can see the estimated number of bacteria and the estimated number of human cells for our reference female body of 63 kilograms. As you can see, you have 2.2 times more bacteria than human cells. These bacteria weight approximately 0.2 kilograms, and it is known that 95 percent of our microbiota is located in the gastrointestinal tract. Abigail Salyers from University of Illinois in US was the mother of microbiota research. During her career, she changed the way how we think about the microbiota. She made major contributions on carbohydrate metabolism and also on the transfer of antibiotic resistance. As we said, bacteria can decompose organic matter. They do that also in our bodies. In our bodies there are some substrates that are indigestible, and bacteria, the gut microbiota can release enzymes that decompose these indigestible dietary fibers. Therefore, we obtain from that observable nutrients and energy. There are other benefits also from the bacteria that live in our bodies. They supply essential vitamins such as vitamin B7 and vitamin K. They help in the development of the immune system and therefore, the immune system will respond better to pathogens. Finally, they prevent also colonization of pathogens by producing antimicrobial compounds, especially on the skin and on the gastrointestinal tract. Therefore as a conclusion, could humans live without bacteria? As we said, most plant and animal life would cease instantly in the absence of mitochondria and chloroplasts. But if we don't include them, then we would say that life would remain possible in the absence of bacteria, but with a drastic reduction in both the quantity and quality of life.
