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Microbes are the Foundation of Life What Is A Microbe? Microbe is a term for tiny creatures that individually are too small to be seen with the unaided eye. Microbes include bacteria, archaea, fungi and protists Archaea are bacteria-like creatures Protists include primitive algae, amoebas, slime molds and protozoa They may live as individuals or cluster together in communities Size of Micorbes So how small are microbes? Well, let's say we could enlarge an average virus, the smallest of all microbes, to the size of a baseball An average bacterium would then be the size of the pitcher's mound. And just one of the millions of cells that make up your body would be the size of the ballpark! Bacteria Bacteria consist of only a single cell They're an amazingly complex and fascinating group of creatures They can live in temperatures above the boiling point and in cold that would freeze your blood They "eat" everything from sugar and starch to sunlight, sulfur and iron Classification Bacteria fall into a category of life called the Prokaryotes Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment called the nucleus Eukaryotes, creatures whose cells have nuclei Early Origins Bacteria are among the earliest forms of life that appeared on Earth billions of years ago Scientists think that they helped shape and change the young planet's environment – Oxygen Many believe that more complex cells developed as once free-living bacteria took up residence in other cells - Mitochondria What They Look Like Some are rod- or stick-shaped and called bacilli Others are shaped like little balls and called cocci Others still are helical or spiral in shape Some bacterial cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings Where They're Found Bacteria live on or in just about every material and environment on Earth from soil to water to air Each square centimeter of your skin averages about 100,000 bacteria A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria How They Move Some bacteria move about their environment by means of long, whip-like structures called flagella Other bacteria secrete a slime layer and ooze over surfaces like slugs Others are fairly stationary What They Eat Some bacteria are photosynthetic Other bacteria absorb food from the material they live on or in Some of these bacteria can live off unusual "foods" such as iron or sulfur The microbes that live in your gut absorb nutrients from the digested food you've eat Archaea The archaea very much resemble bacteria, so much so that they were once thought to be a weird group of bacteria. However, by studying archaeal cells on a molecular level, scientists have now come to think that these "weird bacteria" actually are a separate category of life altogether. In fact, in some ways, archaea are more like you than they are like bacteria! Classification Archaeans are single-celled creatures that join bacteria to make up a category of life called the Prokaryotes However, while archaeans resemble bacteria and have some genes that are similar to bacterial genes, they also contain other genes that are more like what you'd find in eukaryotes Furthermore, they have some genes that aren't like any found in anything else Early Origins Archaeans are among the earliest forms of life that appeared on Earth billions of years ago Archaea and bacteria developed separately from a common ancestor nearly 4 billion years ago Millions of years later, the ancestors of today's eukaryotes split off from the archaea Life at the Extreme Many archaeans thrive in conditions that would kill other creatures -extremophiles How do these extremophiles do it? - They make a variety of protective molecules and enzymes Many live in more ordinary temperatures and conditions What They Eat Archaeans dine on a variety of substances for energy, including hydrogen gas, carbon dioxide and sulfur One type of salt-loving archaean uses sunlight to make energy, but not the way plants do it This pigment, called bacteriorhodopsin, reacts with light and enables the cell to make ATP, an energy molecule Types of Archaea Crenarchaeota, which are characterized by their ability to tolerate extremes in temperature and acidity Euryarchaeota, which include methaneproducers and salt-lovers Korarchaeota, a catch-all group for archaeans about which very little is known Subtypes – Methanogens, Halophiles, Thermophiles, Psychrophiles Fungi Fungi come in a variety of shapes and sizes and different types. They can range from individual cells to enormous chains of cells that can stretch for miles Classification Fungi are eukaryotic organisms—their DNA is enclosed in a nucleus. Many of them may look plant-like, but fungi do not make their own food from sunlight like plants do What They Look Like Fungi include single-celled creatures that exist individually—the yeasts—and multicellular bunches, such as molds or mushrooms Yeast cells look like little round or oval blobs under a microscope. They're too tiny to see as individuals, but you can see large clusters of them as a white powdery coating on fruits and leaves Molds are described as filament-like, or filamentous, because they form long filament-like, or thread-like, strands of cells called hyphae They also form the fleshy body, or mushroom, that some species grow Where They're Found Fungi usually grow best in environments that are slightly acidic (a pH measurement of 5 or so; a pH of 7 is neutral). They can grow on substances with very low moisture. Fungi live in the soil and on your body, in your house and on plants and animals, in freshwater and seawater. A single teaspoon of topsoil contains about 120,000 fungi How They Spread Fungi are basically static But they can spread either by forming reproductive spores that are carried on wind and rain or by growing and extending their hyphae What They Eat Fungi absorb nutrients from living or dead organic matter (plant or animal stuff) that they grow on. They absorb simple, easily dissolved nutrients, such as sugars, through their cell walls. They give off special digestive enzymes to break down complex nutrients into simpler forms that they can absorb Friendly Fungi Some fungi are quite useful to us. We've tapped several kinds to make antibiotics to fight bacterial infections. These antibiotics are based on natural compounds the fungi produce to compete against bacteria for nutrients and space. We use Saccharomyces cerevisiae, aka baker's yeast, to make bread rise and to brew beer. Fungi break down dead plants and animals and keep the world tidier. We're exploring ways to use natural fungal enemies of insect pests to get rid of these bugs Fungal Enemies There are some nasty fungi that cause diseases in plants, animals and people. One of the most famous is Phytophthora infestans, which caused the Great Potato Famine in Ireland in the mid-1800s that resulted in a million deaths. Fungi ruin about a quarter to half of harvested fruits and vegetables annually Protists The category of Protists includes many widely ranging microbes, including slime molds, protozoa and primitive algae. They are all eukaryotic creatures, meaning their DNA is enclosed in a nucleus inside the cell Algae Here we'll focus on the microscopic algae Algae are found in bodies of fresh and salt water They can also grow on rocks and trees and in soil when enough moisture is available Most algae are able to make energy from sunlight, like plants do However, at some stages of their lives, some algae get their nutrients from other living things Dinoflagellates Pfiesteria belongs to a type of algae called the dinoflagellates Some dinoflagellates make their own energy from sunlight, like plants The Piesteria then feed on the fish blood and fluids This microbe has at least 24 different forms it cycles through during its life Pfiesteria produce toxic substances Diatoms They have hard shells made out of silica, or glass Diatoms come in all sorts of shapes— some, like the one pictured here, are round and others are oval. Some look like leaves and others like fat commas Protozoa The word protozoa means "little animal.“ Protozoa mainly feed on bacteria, but they also eat other protozoa, and sometimes fungi Some protozoa absorb food through their cell membranes. Others, like the amoebas <ahme-buhs>, surround food and engulf it. Others have openings called mouth pores into which they sweep food. All protozoa digest their food in stomach-like compartments called vacuoles Protozoa range in size from 1/5,000 to 1/50 of an inch in diameter Ciliates They are generally the largest protozoa. They have hair-like projections called cilia and they eat the other two types of protozoa as well as bacteria. You can just see the thin cilia poking out around the edges of the protozoan in the image to the right Amoebae which can be subdivided into the testate amoebae, which have a shelllike covering, and the naked amoebae, which don't have this covering Flagellates They are generally the smallest of the protozoa and have one or several long, whip-like projections called flagella poking out of their cells Moving of protozoa Amoebas ooze about by extending parts of their cells as pseudopods or "false feet." Many ciliates swim along by beating their cilia in a rhythmic pattern, like so many tiny oars Flagellates swim by waving their flagella, using them much like a fish uses its tail push itself through water Protozoa & human The vast majority of protozoa do us no harm. But, yes, there are a few that cause disease. One type of amoeba can live in human intestines. It feeds on red blood cells and causes a disease known as dysentery . The parasitic protozoan Cryptosporidium parvum sickened around 400,000 people in Milwaukee in 1993 when it got into the tap water. Perhaps the best-known protozoal menace is Plasmodium, the parasite that causes malaria. This terrible disease leads to about 800,000 deaths each year worldwide Slime Molds They have very complex life cycles involving multiple forms and stages During good times, they live as independent, amoebalike cells, dining on fungi and bacteria Conditions become uncomfortable—not enough food available, the temperature isn't right, etc.— individual cells begin gathering together to form a single structure Viruses Viruses are strange things that straddle the fence between living and nonliving A virus is basically a tiny bundle of genetic material— either DNA or RNA—carried in a shell called the viral coat, or capsid, which is made up of bits of protein called capsomeres. Some viruses have an additional layer around this coat called an envelope. What They Look Like There are thousands of different viruses that come in a variety of shapes Many are polyhedral, or multi-sided Other viruses are shaped like spiky ovals or bricks with rounded corners Some are like skinny sticks while others look like bits of looped string Some are more complex and shaped like little lunar landing pods Single-Minded Mission Viruses exist for one purpose only: to reproduce To do that, they have to take over the reproductive machinery of suitable host cells.
