General Microbiology

Introduction to Microbiology

Welcome to the wonderful world of microbiology! Yay! So. What is microbiology? If we break the word down it translates to “the study of small life,” where the small life refers to microorganisms or microbes. But who are the microbes? And how small are they?

Generally microbes can be divided into two categories: the cellular microbes (or organisms) and the acellular microbes (or agents). In the cellular camp we have the bacteria, the archaea, the fungi, and the protists (a bit of a grab bag composed of algae, protozoa, slime molds, and water molds). Cellular microbes can be either unicellular, where one cell is the entire organism, or multicellular, where hundreds, thousands or even billions of cells can make up the entire organism. In the acellular camp we have the viruses and other infectious agents, such as prions and viroids.

In this textbook the focus will be on the bacteria and archaea (traditionally known as the “prokaryotes,”) and the viruses and other acellular agents.

Characteristics of Microbes

Obviously microbes are small. The traditional definition describes microbes as organisms or agents that are invisible to the naked eye, indicating that one needs assistance in order to see them. That assistance is typically in the form of a microscope of some type. The only problem with that definition is that there are microbes that you can see without a microscope. Not well, but you can see them. It would be easy to dismiss these organisms as non-microbes, but in all other respects they look/act/perform like other well-studied microbes (who follow the size restriction).

So, the traditional definition is modified to describe microbes as fairly simple agents/organisms that are not highly differentiated, meaning even the multicellular microbes are composed of cells that can act independently– there is no set division of labor. If you take a giant fungus and chop half the cells off, the remaining cells will continue to function unimpeded. Versus if you chopped half my cells off, well, that would be a problem. Multicellular microbes, even if composed of billions of cells, are relatively simple in design, usually composed of branching filaments.

It is also acknowledged that research in the field of microbiology will require certain common techniques, largely related to the size of the quarry. Because microbes are so small and there are so many around, it is important to be able to isolate the one type that you are interested in. This involves methods of sterilization, to prevent unwanted contamination, and observation, to confirm that you have fully isolated the microbe that you want to study.

Microbe Size

Since size is a bit of theme in microbiology, let us talk about actual measurements. How small is small? The cellular microbes are typically measured in micrometers (μm). A typical bacterial cell (let us say E. coli) is about 1 μm wide by 4 μm long. A typical protozoal cell (let us say Paramecium) is about 25 μm wide by 100 μm long. There are 1000 μm in every millimeter, so that shows why it is difficult to see most microbes without assistance. (An exception would be a multicellular microbe, such as a fungus. If you get enough cells together in one place, you can definitely see them without a microscope!)

When we talk about the acellular microbes we have to use an entirely different scale. A typical virus (let us say influenza virus) has a diameter of about 100 nanometers (nm). There are 1000 nanometers in every micrometer, so that shows why you need a more powerful microscope to see a virus. If a typical bacterium (let us pick on E.coli again) were inflated to be the size of the Statue of Liberty, a typical virus (again, influenza virus works) would be the size of an adult human, if we keep the correct proportions.

http://learn.genetics.utah.edu/content/cells/scale/