Imagine you are a scientist investigating a mysterious animal in a rainforest. The animal is so secretive that no one has ever seen it. You suspect that it exists because it leaves clues behind, like a bad smell coming from a hole in the ground, or another animal with a strange wound. How do you study this invisible creature? What tests do you run to determine how it reproduces, or what it eats?
Before the invention of the microscope, this is what it was like to study microbes. No one had ever seen a microbe before, because they are too small to observe with the human eye. The microscope, however, enabled scientists to finally see the unknown creatures that left marks on the world in the form of diseases, decomposition and even strange smells. The microscope was only the first of many techniques developed to study microbes that live throughout the world. Without these tools, much of what we know about microbes, diseases and even genetics may never have been discovered.
The first step to studying microbes is collecting them. Obviously, microbes are difficult to collect because they are so small. That is only one of the challenges. Very rarely do microbes grow in isolation. If you run a moist cotton swab along any surface in your home, you will pick up many types of microbes, including bacteria, fungi and viruses. Some of these were already on the surface, but others are floating in the air, or may have come from your nose as you exhaled. Unless you are careful, your cotton swab may have already been contaminated with microbes.
Microbes are everywhere. That is why scientists developed special methods for collecting them from the environment. These procedures ensure that the microbes brought back to the lab actually came from the pond, toilet or back of your throat, and were not picked up along the way. These methods involve using tools that are sterilized, with the use of alcohol, fire, heat or ultraviolet radiation.
Only a fraction of microbes on the planet grow in a laboratory. Microbes have evolved so they grow best in the conditions of their environment. When moved elsewhere, they may die, or go dormant. Some environments are easy to recreate in a laboratory, because they are stable and predictable. The human body is an excellent example of this, because the body’s temperature, acidity and other factors stay within narrow ranges.
Most environments, however, fluctuate. Even within a single habitat, such as a pond or a grass field, the conditions change from one end to the other. Microbes are also extremely small. For a bacterium, which is less than five millionths of a meter long, a spoonful of water or dirt is enormous. The conditions in the pond or field are likely to change from one location to the next. Microbes living in each tiny location grow best in that spot, making it very difficult to recreate the best conditions for all of the microbes.
Given the right conditions and an unlimited amount of food, most microbes will continue to reproduce. While this is useful when growing microbes in the laboratory, sometimes you want to keep them from multiplying. When microbes grow out of control, they can overwhelm other microbes that you are trying to grow, and they can throw off your experimental results.
Scientists have developed many methods for controlling how fast, or long, microbes grow. The techniques depend upon the type of microbe. Viruses behave very differently than bacteria. Some common techniques for controlling the growth of microbes includes limiting the amount of food available, using drugs or chemicals to kill the microbe or make them dormant, or changing the temperature. In some cases, the microbes are killed, but in others they go dormant and can be grown again later.
Direct observation of microbes is impossible without a microscope. Since their invention in the late seventeenth century, microscopes have changed dramatically. The first ones were single, hand-held lenses with limited magnifying power. Magnification is the ability of a lens to make an object appear larger. By combining two lenses, scientists increased the magnification power of the microscope. These lens-based microscopes use light that either passes through the sample of microbes, or reflects off its surface. Hence, they are called light microscopes.
Viewed with a powerful light microscope, many microbes look identical. Scientists, therefore, use other techniques along with the microscope to enable them to identify the microbe, or view details of the microbe. Various stains are used that make certain microbes, and not others, visible. These stains can also be used to make structures inside the cell stand out, like the cell nucleus or DNA. In some cases, a fluorescent tag is used that is specific for the microbe, or its DNA. This enables scientists to quickly find these microbes on a slide filled with many types of organisms.
Recently, the use of genetic techniques has become an important part of microbiology. Each microbe has its own distinct DNA sequence. This information can be used to accurately identify microbes. Genetic tests like this are very sensitive, so scientists can identify microbes more quickly than with other methods. This has been used during disease outbreaks, such as with the H1N1 influenza virus.
Microbial genetics involves more than just identifying the type of microbe. A DNA sequence provides instructions for how an organism looks and functions. Scientists also study specific parts of microbial DNA to understand activities of the microbe, like how it converts carbon dioxide to energy, or how it builds its cell wall. They also study how DNA controls the reproduction of microbes. The techniques learned with microbes have been applied to other organisms, as well, enabling scientists to modify the genetic sequences of plants and animals. This changes how they look, or the activities of their cells.