Hello my name is Peder Worning I work at Hvidovre Hospital as bioinformatician, in this presentation I will give you an introduction to the incredibly diverse world of bacteria. Bacteria are unicellular microorganisms. That means that they are extremely small, invisible to the naked eye, and that contrary to multicellular organisms, such as oak trees or tigers, each bacterium consists of just one cell. Bacteria live in vast numbers in all places where there is life on this planet. They are not categorized as plants or animals, but are in a way below that level of categorization, being made of cells that are much simpler than those that make up plants or animals. Like other scientific disciplines, bacteriology – the study of bacteria – is characterized by technical and specialized language, much of it of Greek and Latin origin. At first encounter this may seem confusing. In this presentation I will introduce you to the great diversity of bacteria on Earth, including some basic classification and examples of bacteria, and a certain amount of jargon is unavoidable. I will, however, try to remember to always give a definition when a new concept is introduced. I started out by saying that bacteria a unicellular, and that a bacteria cell is simpler than cells that make up multicellular organisms. One difference is that the cells of plants, animals and fungi are organized by membranes, while bacterial cells only have one space inside the cell. The multi-room cells are called eukariots and the bacterial one-room cells are called procariotes. Prokaryotes are divided into two large groups called Bacteria and Archaea. I will not differentiate between Bacteria and Archaea in this lecture, although they are very different on the phylogenitic level. When I say Bacteria I mean prokaryotes. Bacterial cells can have many shapes, a few of them is shown in this picture The spherical bacteria are called coccus, the elongated are called bacillus and the long spiral ones are called spirochetes. Many bacteria have a flagell - a protein tail that they can use to move around, like the tail of a tadpole. It is estimated that there are about a thousand billion billion billion or 1030 bacterial cells on Earth. This is a very large number that can be difficult to imagine. It is like the number of atoms in 10.000 liters of water or about ten million times the number of stars in the universe. All these bacteria weigh a million billion kilograms or 2.000 times as much as the 7 billion people on Earth. The reason that there are so many of them is that they are extremely adaptive and very small. Bacteria are between 0.1 and 5 micrometer long. In the lab we normally see bacteria as colonies on a petri dish. A colony, so small that it is barely visible, can contain a million bacteria, and a colony one millimeter across contains a billion. Bacteria can grow very fast. The fastest growing organism known to man is Clostridium perfringens. Given the right conditions it has a generation time of 6 minutes and twenty seconds. This means that one cell can become a thousand in one hour and 3 minutes, a million in two hours and 7 minutes and a billion in three hours and ten minutes. Clostridium perfringens is an extremly fast species, but bacteria as Escherichia coli and Staphylococcus aureus can grow with a generation time of about twenty minutes, so things move fast in the bacterial world. The Nitrogen Cycle - Bacteria makes the world go around Nitrogen is one of the most important elements for all life. The amino acids in our proteins and the nucleotides in our DNA and RNA contain nitrogen. There is a lot of nitrogen on Earth, 80 % of our atmosphere is nitrogen in the form of N2. But N2 is chemically a very stable molecule that cannot be used by plants, fungi or animals to make amino acids or nucloetides. The nitrogen in the air must be converted to ammonium so plants can use it as fertilizers and build it into proteins and nucleotides. Bacteria are the only living organisms that can bind N2 from the air and convert it into ammonium, so it can be used by other living organisms. It is called nitrogen fixation and it is a very important process for the continuation of life here on Earth. If bacteria were not able to fixate nitrogen from the air all the nitrogen in living organisms would eventually end as N2 in the air, and life on Earth would die out. Plants of the Legume family - such as peas, beans and lentils - can fixate nitrogen from the air. They can do this because they have a symbiotic relationship with the nitrogen fixating Rhizobia bacteria that live in the roots of the plant. The picture shows Rhizobia nodules at the roots of a bean plant. Bacteria can also convert ammonium to nitrate and nitrate to free nitrogen N2. In that way the nitrogen cycle is completed. The process where nitrogen is extracted from solution, converted to free nitrogen and released into the air is called denitrification. We use bacteria with this dentrification ability to remove nitrogen from wastewater, when we process our sewage in treatment plants before leading it out in nature. Bacteria are everywhere.Wherever there is life on this planet, there are also bacteria. They live on their own or on and within plants and animals. The Rhizobia bacteria living in the roots of Legume plants is only a single example of their symbiosis with multicellular organisms. In fact, all animals with a gut have bacteria living in the gut that help them digest the food. In many ways bacteria are absolutely necessary for our utilization of the food we eat. They make vitamins in our gut, regulate our immune system and keep pathogenic bacteria away. For cows and other grass eating mammals the bacteria in the gut play a very important role. Grass is mostly made of cellulose - a polysaccharide that no mammal enzyme can break down. This is also known as dietary fiber. Diatary fibers are good for our digestion, but they don't contribute to our nutrition. You won't get fat by eating grass, but cows do. The bacteria living in a cow’s gut can break down the cellulose into simple sugars that the cows can use as nutrition. In other words: it is the gut bacteria that make it possible for grass eating animals to utilize the energy of the grass. Bacteria are highly adaptive, and they can live in the most extreme environments. Some bacteria can survive in hot springs at 120° Celcius and grow above 100° C. Bacteria living at very high temperatures are called thermophiles. In the 80° C hot water of the hot springs in Yellowstone National Park you can find the bacteria Thermus aquaticus. The picture shows the Grand Prismatic Spring, the largest hot spring in Yellowstone. The bright colors are due to bacteria living at different temperatures in the hot spring. The temperature is highest in the middle of the spring and falls towards the shore. This type of bacteria has become kind of a celebrity among molecular biologists, because it has revolutionized all work with DNA. The wonder of this enzyme, is that it withstands the repeated heatings to 80° C, that is needed to separate the DNA strands to melt DNA for duplication. A very well-known application of this is the DNA test on crime scenes made by the police. This would not have been possible without the thermophilic bacteria. There are even bacteria living in the radioactive waste from nuclear power plants. The bacteria Deinococcus radiodurans can stand extremely high amounts of radioactivity. For a cell the greatest threat from radiation is that it can break the DNA. As a defense mechanism the D. radiodurans has four copies of its DNA in each cell, and the ability to use the other copies to repair a broken chromosome. The water in the Dead Sea is a saturated salt brine in which neither fish, nor shellfish nor plants can live. Some bacteria however, have evolved to be able to live in this extremely salty environment. They are called halophiles. That means ‘salt lovers’. As these examples show, Bacteria are the forefront of life on our planet, they live in the most extreme environments and they were the very first forms of life on this planet. In the first 2 billion years of life they were in fact the only kind of life on the planet. Cyanobacteria is a large group of bacteria that can make photosynthesis. They do not need organic material for life, but can make all they need from sun light, water, CO2 and inorganic salts. The cyanobacteria make up the first step in the global food chain. The photosynthesis we know from plants is an evolutionary descendant from cyanobacteria. Bacteria that can live using only inorganic material and sunlight are called photoautotrophs. But the opposite also exists. Deep in the Earth and on the ocean floor you can find bacteria that do not even need light to survive. These forms of bacteria extract energy from inorganic chemical reactions like oxidating Fe2+ to Fe3+, oxidating Mangan or Sulfur. They can even build new cells from inorganic material alone. This kind of bacteria are called chemoautotrophs. We normally consider oxygen as a prerequisite for life – but there are some bacteria to which oxygen is toxic. These organisms are called anaerobic bacteria – or anarobes. Anarobes come in two kinds – the obligate anarobes, to whom oxygen is toxic, and the facultative anarobes, which can tolerate oxygen, but grow better without it. Bacteria that grow best with Oxygen are called aerobes. There are many ways to charaterise bacteria and one of the most important methods, when it comes to pathogenic bacteria, was invented in 1884 by the Danish medical doctor Hans Christian Gram as a coloring technique used to visualize bacterial cells in the microscope. The method is called Gram staining and it divides bacteria into two large groups: the Gram-positive that become purple and the Gram-negative that becomes pink. The picture shows Gram staining of the Gran-positive Staphylococcus aureus and the Gram-negative E. coli. The difference between Gram-positive and Gram-negative cells is determined by the way the cell wall is arranged relative to the cell membrane. The Gram-positive cell has the cell wall outside the membrane, while the Gram-negative cell has two membranes and the cell wall is located between the two membranes. The Gram stain shows a very fundamental difference between bacterial cells. A difference that determines which type of antibiotic that can be used to combat a bacterial infection. The Gram stain is fairly easy to make and it is almost always the first step in the identification of a bacterial infection. To summarize: Bacteria are small unicellular organisms with very simple cells, that are extremely adaptive. They can grow in very hostile environment above 100 C in high radiation, in very dry and in very salty environment. Bacteria are absolutely necessary for life on Earth. But they are also very dangerous , because they are the reason for some of our most severe diseases. Bacteria are the fastest growing organisms on Earth, and they exist in enormous numbers everywhere on this planet. When they cause infection, they are normally characterized by a staining technique called Gram stain, that divide them into two groups Gram-negative and Gram-positive bacteria. This difference is very fundamental and it is determined by the way the cell wall are arranged relative to the cell membrane. Gram-positive and Gram-positive bacteria are normally treated with different kind of antibiotics.
