The first person to see a bacteria was probably van Leeuwenhoek, who made the first microscopes in the late 17th century. His single lens microscope magnified an amazing 300x, enough to see bacteria as well as protozoa in pond water. From these humble beginnings, the science of bacteriology emerged. ‘Ology’ means study of and bacteria are single celled organisms that have no nuclei. When I first went to university there was only one kingdom for the bacteria. Now there are two: Eubacteria and Archaebacteria.
The Archaebacteria are the oldest living organisms in the world and the most primitive. They evolved when the Earth was hot and its atmosphere was poisonous. Modern archaebacteria continue to inhabit some of the most extreme environments on earth. They are found in poisonous hot springs and volcanic vents and extra-salty lakes or enduring the crushing pressures and of the ocean depths, so they are called ‘extremophiles’ or extreme condition lovers. What they cannot endure is oxygen, having evolved before there was oxygen in the atmosphere, so they are obligate anaerobes.
There are three groups of archaebacteria. The first group are methanogens, converting hydrogen and carbon dioxide to methane and gaining energy from that reaction. They are found in anaerobic swamps and in the guts of ruminants, which is why cows can digest such rough food and why they produce so much methane in the process.
The second group are the extreme halophiles, found in the Great Salt Lake, the Dead Sea and other highly saline environments. Normal cells die quickly in such environments as the liquids are sucked out of their bodies, but halophiles have a large amount of salt in their cells and so can survive where others cannot.
The third group of archaebacteria are the thermophiles, first identified from volcanic vents. The conditions in these vents resemble those of the early earth: hot, acidid and poisonous. They give us clues to how life evolved billions of years ago.
The other kingdom consists of the Eubacteria or true bacteria. These creatures, like the Archaebacteria, all have a very simple cellular structure with no nucleus and no mitochondria. They are also very small, only one tenth the size of normal cells. They have a protective cell wall and often slime around that to help them stick to surfaces. Some have a whiplike flagellum for movement but many have no means of moving themselves. Their DNA is contained in a single circular chromosome. Some are anaerobes but many are aerobic.
Beyond these basics, bacteria are as diverse as the plant and animal kingdoms. Bacteria are the most widespread of the kingdoms, being found virtually everywhere and in every condition. They have been found in soil, water, air, dust and as parasites in the bodies of all higher plants and animals. They have been found alive 2500 meters below the earth’s surface, in the depths of the oceans and up to 8 kilometers high in the atmosphere. They can endure freezing cold and boiling temperatures as well as acidic, basic and anaerobic conditions. When conditions get too tough, bacteria form endospores which endure until conditions improve. Then they come back to life.
Eubacteria are classified by their shapes. Cocci are round bacteria. Bacilli are rod shaped and spirilli are twisted or coiled rods. No one knows how many species of bacteria there are since the only way to tell is to analyze their genetic sequences to see if they are different. One study estimated that there were 20,000 species of bacteria in a single liter of seawater, while another study of soil bacteria estimated that there could be a million species in a gram of soil!
Bacteria are of great importance to humans for many reasons. Many are decomposers, breaking down dead bodies and so are important in natural ecosystems as recyclers of materials and energy. Many species are necessary for our survival, helping us to digest our food or break down waste products. Many others are parasites and cause disease. Until the invention of the microscope, diseases were believed to be caused by bad air, witches, curses or God’s wrath. The discovery of ‘germs’, many of which are bacteria, led to the development of modern bacteriology and the curing of many previously fatal illnesses.
The battle is never ending though, because bacteria evolve so quickly. Already many strains of antibiotic-resistant bacteria are causing resurgences in diseases we once thought we had conquered. Bacteria reproduce quickly, by simple cellular division known as binary fission. When bacteria are exposed to antibiotics, most die, but the survivors then reproduce quickly, dividing as often as every twenty minutes. Any genetic variation that improves survival and gives them resistance to the antibiotics are passed on to the daughter cells, so we are, in effect, selecting for antibiotic resistant forms.
So the study of bacteria must continue, both because there is still so much to learn and because we are only just keeping up with them now. For something so small, they are enormously important in both positive and negative ways. The science of Bacteriology is on the frontline of our own battle for survival.
References: Snedden, R.2002. The World of the Cell: Life on a Small Scale. Heinemann Library.
http://www.essortment.com/all/archaebacteriae_rmkr.htm
http://www.wisegeek.com/how-many-species-of-bacteria-are-there.htm
