Kingdom Prokaryota
What Are Bacteria?
Bacteria consist of only a single cell—but don't let their small size and seeming simplicity fool you. They are an amazingly complex and fascinating group of organisms. Bacteria have been found that can live at temperatures above the boiling point and in those that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There is even a species of bacteria that can withstand blasts of radiation 1,000 times greater than those that would kill a human being.
Clostriduimbotulinum causes botulism in humans. Where Are They Found?
Bacteria live on or in just about every material and environment on Earth from soil to water to air, from inside your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000 bacteria.
Some microbes live on our skin and protect us from harmful agents. The drier areas, like the back, have few microbes; moist areas, such as the armpit, have many more.
What Do They Eat?
C
ha
p
te
r
Some bacteria are photosynthetic—they can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. 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 food you've digested.
A structure that is vital to bacterial survival is its unique cell wall. It defines the shape of the bacterium, gives it mechanical strength and protects it from environmental changes. Bacteria are classified according to the single cell's shape and size, and the way in which the cells organized.
Some bacteria have unique additional structures:
Capsule—protects the bacterium from phagocytic cells, which are part of the host’s defense mechanism. Pili—cilia that enable pathogenic bacteria to attach to the body and cause disease.
Flagellum—a structure used for locomotion
Endospore creation—a thick envelope that surrounds the bacterium when the spore is
hibernating, i.e. its metabolism is at a minimal level. The process of
creating the spore takes place when the environmental conditions are not suitable for the bacterium's
proliferation (extremely low humidity, high temperature, presence of antibacterial substances, radiation). bacteria can survive for long periods of time in the spore state. When the conditions are right for development, the envelope is dismantled.
Only a small number of bacteria have the ability to form spores: among them are bacteria that cause severe disease.
Review Questions
1. List some of the conditions that bacteria can live in. 2. Describe the structure of a bacterium.
Friendly Bacteria
We are used to thinking of bacteria as disease-causing agents. Indeed, bacteria are at the origin of various worrisome diseases. However, it is important to point out that, in contrast to popular opinion, only a small number of the thousands of bacterial species are pathogenic, meaning disease-causing. Most bacteria do not harm humans at all, and many species of bacteria are even beneficial and vital to our health.
The bodies of humans and animals serve as a natural environment for bacteria. The bacteria that live in our bodies produce and provide us with different vitamins.
For instance:
In the human digestive system, there are different species of friendly bacteria, which take part in an important and inseparable way. These bacteria are vital to the
metabolism of food, the production of enzymes and vitamins (e.g., bacteria that
manufacture vitamin B or vitamin K), the demolition of disease-causing microorganisms including fungi, and the regulation of intestinal acidity. These bacteria play a decisive role as symbionts (help out themselves as well as the host) in most multicellular organisms. Bacteria that live in ruminants' digestive system break down cellulose to its monosaccharide components, releasing usable energy in the process.
Not only do the bacteria located at the entrances to the body (for example the mouth, skin ) not cause damage, they also do not allow disease-causing microorganisms to settle there or to invade our bodies through these entrance points.
The essential uses of bacteria for humans can be seen in the environmental protection arena:
Sewage-disposal facilities are aided by bacteria in the breakdown of many waste products (not only organic) and in the neutralization of some of the toxic substances that make their way into sewage.
Bacteria play an important role in the biological view of pest control—as the natural enemies of different organisms that damage food crops and the agricultural industry.
Psuedomonas putida An oil eating bacteria
Several bacteria play a major role in modern genetic-engineering techniques: by inserting specific genes into the bacterial cell, the bacteria can be induced to produce the protein, which these genes encode. These proteins can then be used to produce medicines and other vital substances, such as hormones. Another use of bacteria is in the making of food, especially dairy products. Special fermentation bacteria convert milk to products such as cheese, cultured milk and yogurt, the manufacture of which would be impossible without them.
This is an 'ugly' one.
Cholera is a word that most Americans have never heard, or perhaps only in antiquated stories of our forefathers. For most people in industrialized nations, clean water is something taken for granted. Because water comprises such a large part of our bodies, we constantly need to replenish ourselves through constant water drinking. No one expects that water will make them sick, in fact they assume the
opposite. However, for those who are denied basic human rights, water can be lethal.
Pathology: Cholera is acquired through the contraction of the bacteria
Vibrio cholerae. This bacteria lives in feces, so one can contract this through direct fecal contact or through eating contaminated food or drinking contaminated water. Thus, in areas where there is a lack of proper sanitation or a clean water source, it is very easy to spread the bacteria.
The bacterium has an incredibly short incubation period- anywhere from a couple of hours to five days. For someone who is already immuno-compromised (such as with an HIV infection), the bacteria can kill a person within hours of contact. In fact, it is considered the most rapidly fatal illnesses. This short incubation period also contributes to its
catastrophic nature- many people can develop and spread this quickly, leading to a cholera outbreak.
The Bad ...
So what is bad about bacteria? The bad news is that sometimes bacteria cause diseases in plants and animals that sicken or even kill them. Disease-causing bacteria can infect organisms in two different ways. Most attack the body's cells directly. Others produce chemicals called TOXINS (poisons). Either way, the bacteria destroy or damage cells within the plant or animal.
Anthrax (Bacillus anthracis)
Anthrax is a deadly type of bacteria that infects animals, especially cattle and sheep. Plants can be infected as well with a number of dangerous bacteria. Fire blight is plant disease that occurs in apple trees and pear trees.
... and the Ugly
Humans also have to deal with bacterial disease on a daily basis. Around the world, hundreds of thousands of people die every year from bacterial infections, which can invade the body in several ways.
Some bacteria enter the body through the intestines. This occurs by eating or drinking contaminated food or liquids. Cholera (see previous page), for example, is a disease caused by bacteria in unsanitary drinking water. Eating food contaminated with bacteria such as salmonella and E.coli brings on food poisoning. Other bacteria enter the body through the lungs. Breathing in airborne bacteria causes tuberculosis and pneumonia. Bacteria can also get inside the body from puncture wounds (such as tetanus) or insect or animal bites and cause a variety of diseases.
Most strains of E.coli are harmless to humans and are found in your intestines. One strain pictured here, the 0157:H7 strain is a major cause of severe food poisoning and may even cause death.
One particularly ugly episode in human history was due to a rod-shaped bacterium called Yersinia pestis, otherwise known as the bubonic plague or the Black Death (so named because of the dark discoloration in the victim's face after death).
The 'Black Death' caused millions of deaths in the Europe and around the world, unknown to people at the time it is caused by a bacteria species that lived in fleas that infested all types of animals.
The Black Death, transmitted by bacteria-carrying fleas, caused millions of deaths in 14th-century Europe. During the 14th century, this tiny organism killed millions of people — more than half the population of Europe. Transmitted by flea bites, the plague was spread across the continent by flea-carrying animals such as mice and rats.
Even now, the bubonic plague still occurs in parts of the world. But it is treatable with antibiotics and does not cause the mass epidemics it once did.
The bacterium Yersiniapestis
.
This rod shaped bacteria that lived in fleas caused half of the
population of tEurope to perish in the mid 1300's.
Review questions
5. What is meant by the term 'pathenogenic'?
6. Explain three instances wher bateria are useful for humans. 7. What is Cholera? How do you get it? What does it do to you? 8. Are all species of E.coli harmful? Explain
