The Microbial World: They rule
1-1 Introduction

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This book will focus on the biology of small things, but what is microbiology? Microbiology could be defined as the study of organisms too small to be seen with the naked eye. Figure 1-14 shows the relative size of microbes compared to other living things. However, the recent discovery of bacteria of near 1 mm in size has made this definition somewhat inaccurate and in the grand tradition of science, a new definition is in order.
Figure 1-14 The relative size of microbes

The relative size of microbes

Microbes for being small, span a large range of sizes from the T4 virus virus that are 0.02 µm to giant bacteria larger than 700 µm.

We will consider microbiology to be the study of organisms that can exist as single cells, contain a nucleic acid genome for at least some part of their life cycle, and are capable of replicating that genome. This broad description encompasses an understandably large group of organisms including Figure 1-15. This definition would also include viruses, which microbiology texts traditionally discuss along with living organisms.
Figure 1-15 Some examples of the types of microbes present in the environment

Some examples of the types of microbes present in the environment

Many different organisms fall under the definition of microorganisms. Shown here are; A, the microorganism Escherichia coli; B, a photosynthetic cyanobacterium (Mike Clayton); C, a fungus (CDC); D, Ebola virus (CDC); E, the malaria parasite (a protozoan) (CDC).

Microbiology also involves a collection of techniques to study and manipulate these small creatures. Because of their size, special instruments and methods had to be developed to allow the performance of interpretable experiments on microorganisms. These methods are not restricted to microbes alone, but have also found utility in working with populations of cells from higher organisms.

With apologies to other small organisms, this book will mostly focus on bacteria (which we will also call microorganisms or microbes) and their impact on the rest of the biosphere. This can be weakly justified by the fact that bacteria have a major impact on the world around us and, because of their perceived importance, more research and knowledge has been accumulated about them.

Microorganisms are everywhere, but why are they worth learning about? The short answer is that they affect your life in many different ways. Before we begin our study of these creatures, we will first take a tour of some of their important habitats and point out why your existence depends upon them. We will then briefly explore the history of microbiology.
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Particles capable of causing disease in animals, plants or bacteria that consist of nucleic acid enclosed in an outer shell made of protein, lipids or both.