Bacteria



Bacteria 2795
Photo by: Michal Kowalski

Bacteria are very small organisms, usually consisting of one cell, that lack chlorophyll (a green pigment found in plants that allows for the production of food). Except for viruses, they are the smallest living things on Earth. Many bacteria are so small that a million of them, laid end-to-end, would measure no more than about five centimeters (two inches). The term bacteria is the plural form of the word bacterium, which represents a single organism.

Bacteria are found everywhere, in the air, soil, water, and inside your body and on your skin. They tend to multiply very rapidly under favorable conditions, forming colonies of millions or even billions of organisms within a space as small as a drop of water.

The Dutch merchant and amateur scientist Anton van Leeuwenhoek (1632–1723) was the first person to observe bacteria and other microorganisms. Using single-lens microscopes of his own design, he described bacteria and other microorganisms (calling them "animalcules") in a series of letters to the Royal Society of London between 1674 and 1723.

Today, bacteria are classified in the kingdom Procaryotae. This term refers to the fact that bacteria consist of prokaryotic cells, cells that do not contain a nucleus. (A nucleus is a structure that controls a cell's functions and contains genes. Genes carry the deoxyribonucleic acid [DNA] that determines the characteristics passed on from one generation to the next.) The genetic material of bacteria is contained, instead, within a single, circular chain of DNA.

Characteristics of bacteria

Bacteria are generally classified into three groups based on their shape. They are described as spherical (coccus), rodlike (bacillus), or spiral or corkscrew (spirochete [pronounced SPY-ruh-keet] or spirilla). Some bacteria also have a shape like that of a comma and are known as vibrio.

Words to Know

Aerobic bacteria: Bacteria that need oxygen in order to live and grow.

Anaerobic bacteria: Bacteria that do not require oxygen in order to live and grow.

Bacillus: A type of bacterium with a rodlike shape.

Capsule: A thick, jelly-like material that surrounds the surface of some bacteria cells.

Coccus: A type of bacterium with a spherical (round) shape.

Decomposers: Bacteria that break down dead organic matter.

Fimbriae: Short, hairlike projections that may form on the outer surface of a bacterial cell.

Fission: A form of reproduction in which a single cell divides to form two new cells.

Flagella: Whiplike projections on the surface of bacterial cells that make movement possible.

Pasteurization: A process by which bacteria in food are killed by heating the food to a particular temperature for some given period of time.

Pili: Projections that join pairs of bacteria together, making possible the transfer of genetic material between them.

Prokaryote: A cell that has no distinct nucleus.

Spirilla: A type of bacterium with a spiral shape.

Spirochetes: A type of bacterium with a spiral shape.

Toxin: A poisonous chemical.

Vibrio: A type of bacterium with a comma-like shape.

As the drawing of the anatomy of a typical bacterium shows, the cytoplasm of all bacteria is enclosed within a cell membrane that is itself surrounded by a rigid cell wall. Bacteria also produce a thick, jelly-like material on the surface of the cell wall. When that material forms a distinct outside layer, it is known as a capsule.

Many rod, spiral, and comma-shaped bacteria have whiplike limbs, known as flagella, attached to the outside of their cells. They use these flagella for movement by waving them back and forth. Other bacteria move simply by wiggling their whole cell back and forth. Some bacteria are unable to move at all.

Two other kinds of projections found on bacterial surfaces include fimbriae and pili. Fimbriae (pronounced FIM-bree-ay) are tiny bristles that allow bacteria to attach themselves to other objects or to surfaces.

A scanning electron micrograph of the aerobic soil bacterium Pseudomonas fluorescens. The bacterium uses its long, whiplike flagellae to propel itself through the water layer that surrounds soil particles. (Reproduced by permission of Photo Researchers, Inc.)
A scanning electron micrograph of the aerobic soil bacterium Pseudomonas fluorescens . The bacterium uses its long, whiplike flagellae to propel itself through the water layer that surrounds soil particles. (Reproduced by permission of
Photo Researchers, Inc.
)

Pili are tiny whiskers that allow bacterial cells to exchange genetic material with each other.

Bacterial growth

The term bacterial growth generally refers to the growth of a group of bacteria rather than a single cell. Single cells generally do not get larger in size, so the term growth refers to the reproduction of cells.

Bacteria most commonly reproduce by fission, the process by which a single cell divides to produce two new cells. The process of fission may take anywhere from 15 minutes to 16 hours, depending on the type of bacterium.

A number of factors influence the rate at which bacterial growth occurs, the most important of which are moisture, temperature, and pH. Bacteria

The anatomy of a typical bacterium. (Reproduced by permission of The Gale Group.)
The anatomy of a typical bacterium. (Reproduced by permission of
The Gale Group
.)

are about 80 to 90 percent water. If too much water passes into or out of a bacterial cell, the cell dies. The bacterial cell wall provides protection against the gain or loss of water in most ordinary circumstances. But conditions may be such as to produce an unusually large gain or loss of water.

For example, if a bacterial cell is placed in a highly concentrated solution of salt water, water begins to pass out of a cell and into the salt water. The cell begins to shrink and is unable to carry on normal life functions. It cannot grow and will eventually die. On the other hand, an excess of water can be harmful to bacteria also. If water flows into a bacterial cell, the cell begins to swell and may eventually burst, resulting in the death of the cell.

All bacteria have a particular temperature range at which they can survive. For a specific type of bacteria, that range can be very high, very low, or somewhere in between, although it is always a narrow range. Most bacteria thrive at temperatures close to that of the human body (37°C or 98.6°F). But some bacteria prefer cold temperatures as low as freezing (0°C or 32°F), and others require very hot temperatures such as those found in hot springs (50°C to 90°C or 120°F to 200°F). The most extreme conditions in which bacteria have been found are around the hydrothermal vents near the Galapagos Islands. The temperatures near these cracks in the ocean floor is about 350°C (660°F), an environment just right, apparently, for the bacteria that live there.

Another factor affecting bacterial growth is pH, the acidity of a solution. Most bacteria require a pH of 6.7 to 7.5 (slightly more or less acidic than pure water). Other bacteria, however, can survive at a pH more severe than that of battery acid.

Finally, bacteria may or may not require oxygen to grow. Those that do need oxygen are called aerobic bacteria, while those that do not are known as anaerobic bacteria. Anaerobic bacteria have evolved ways of using substances other than oxygen, such as compounds of nitrogen, to obtain the energy they need to survive and grow.

Harmless, beneficial, and harmful bacteria

Bacteria can also be classified according to the effects they have on human life. Some bacteria are used to supply products that improve human life, others cause disease, while still others have no overall affect at all on human life.

Helpful bacteria. Bacteria make possible the digestion of foods in many kinds of animals. Cows, deer, sheep, and other ruminants, for example, have a large organ known as the rumen in which bacteria live and help break down cellulose fibers and other tough plant materials. In humans, bacteria known as Escherichia coli ( E. coli ) occur everywhere in the digestive system, aiding in the breakdown of many kinds of foods. Bacteria are also responsible for the production of vitamin K and certain B vitamins.

Certain kinds of bacteria are also essential in the decay and decomposition of waste materials. Such bacteria are known as decomposers. Decomposers attack dead materials and break them down into simpler forms that can be used as nutrients by plants.

Finally, bacteria are involved in the production of many foods eaten humans. For example, bacteria that cause milk to become sour are used in the production of cottage cheese, buttermilk, and yogurt. Vinegar and sauerkraut are also produced by the action of bacteria on ethyl alcohol and cabbage, respectively.

Harmful bacteria. It seems likely, however, that most people know bacteria best because of the diseases they cause. Some of these diseases are produced when bacteria attack directly the tissues in a plant or animal. For example, fruits and vegetables that become discolored as they are growing may be under attack by bacteria.

Bacteria also attack organisms by releasing chemicals that are poisonous to plants and animals. Such poisons are known as toxins. A familiar toxin-producing bacterium is Clostridium tetani , responsible for the disease known as tetanus. Tetanus is a condition in which one's muscles are paralyzed, explaining its common name of lockjaw. A related bacterium, Clostridium botulinum , releases a toxin that causes the most severe form of food poisoning, botulism.

Some forms of dangerous bacteria live on the human skin, but cause no harm unless they are able to enter the blood stream through a break in the skin. Among these bacteria is Staphylococcus , responsible for the potentially fatal toxic shock syndrome. And although E. coli is helpful within the digestive system, if it is ingested and enters the bloodstream it causes severe cramping, diarrhea, and possibly even death.

Most forms of food preservation, such as freezing and drying, are designed to kill or inactivate bacteria that would otherwise damage food or cause disease. One of the most common methods of destroying bacteria in foods is pasteurization. Pasteurization is the process of heating a food product to a particular temperature for some given period of time. The temperature and time are selected to be sure that all bacteria in the food are killed by the process. The pasteurization of milk has made it possible to insure safe supplies of one of the most popular of all human foods.

Hardy survivors

In October 2000, a team of biologists claimed to have revived a bacterium that existed 250 million years ago, well before the age of the dinosaurs. They found the bacterium in a drop of fluid trapped in a crystal of rock salt that had been excavated from an air duct supplying a radioactive waste dump 1,850 feet (564 meters) below Earth's surface near Carlsbad, New Mexico. When the biologists drilled into the pocket of fluid in the crystal and mixed nutrients with the fluid, bacteria soon appeared. However, other scientists quickly suggested that the bacteria that grew was simply modern bacteria that had infected the crystal sample. The questioning scientists also pointed out that it would be impossible for the bacterium's DNA (a complex molecule that stores and transmits genetic information) to have survived more than a few thousand years, at best.

Regardless of the debate, bacteria have been around since the dawn of life on Earth, and they have continued to evolve. A major problem facing the medical community today is the ability of disease-causing bacteria to develop a resistance to antibiotics and other antibacterial drugs. These types of bacteria have been able to change their forms or have even been able to secrete enzymes that destroy the antibiotics. Since the

A scanning electron micrograph of a T4 bacteriophage virus. (Reproduced by permission of Photo Researchers, Inc.)
A scanning electron micrograph of a T4 bacteriophage virus. (Reproduced by permission of
Photo Researchers, Inc.
)

development and use of antibiotics in the 1940s, most known bacterial diseases have developed a resistance to at least one type of antibiotic.

[ See also Antibiotics ; Antiseptics ; Fermentation ]



User Contributions:

1
praveen kumar
this website is very usefull to study about the bacteria. its usefull nto give lecture to students
2
Elizabeth
I think this website provides very useful information if anyone needs to research on bacteria, and different types of bacteria too. thank you!
3
xxx
ooh this website helpzzz really!!
i had to do a project on the nutrition in bacteria it wazz helpfull!!
4
mark
this is a good website. it really helped me with my school work thanks fo the site
5
sophie :)
thanks for the great website it helped alot with my school project. It has some very useful things
6
good.one
thanks so much very informative and just the info i was looking for.
7
Berline
wow This web site is so amazing. it just answered the answers to my report..wow
8
mohamed nour
good topic . although i know all of this but i still reading
bacteria may called the first enemy of human
thanks
9
Alisha
This website was JUST what I was looking for! It really really helped me for my school project!
THANKS A LOT!!
10
anoynomous
I think this website is very neat,but does anyone know what is the process that changes milk into yoghurt called?
11
Rahul
This site gives some of the basic idea of the bacteriology.
it is good for the primary knowledge of bacteriology.
12
lucero
THIS WEB SITE PROVIDES VERY INTERESTING INFO ABOUT BACTERIA AND HELPFULL TOO THANKS
13
Anonymous
Thanx for helping me with my biology 2 homework! This gave me everything I needed.
14
yolanda
This website really helped me in a biology project seriously auch thanks




*student*
15
jonald
Thats so nice because all i want to know is here already
so Very Very thank you so much
16
Nancy
I just want to point out that viruses are not living things as stated in the opening paragraph. Thank you.
17
Jacob
OMG this website wus sooo helpful. My sciencefair project was a breeze after this :DD
18
danny
thank you soo much this website was easy to understand and gave me lots of information so i could complete my assignment =] thnx again
19
Rilla
it was great for a science project i had to do, thanks!:
20
charlieXchokehold
very good site, helped a lot, my projects are now complete (scholl work) ;]

X
21
Cyndi
This is a good overview, and was somewhat helpful on my research paper covering beneficial uses of bacteria. Though not all information is entirely correct (bacteria are nonliving, not living), it will be helpful to those who are not looking for in-depth, extreme detailed information.
22
Cyndi
I am correcting myself. I meant to say that viruses are nonliving, not bacteria. Bacteria are living. Sorry about that.
23
justice nealy
this website is awesome i love it i had to do a reasearch paper and it had everything it rocks!!!!!!!!!
24
LA Paulino
thanks for the infos. This site is very useful. Hope you'll continue to serve the best interest of the students :)
25
donna
THANK YOU SO MUCH FOR THIS BLOG, IT REALLY HELPS ME A LOT....GOD BLESS
26
Jasmine
this website was very helpful for my formal lab report for anatomy
27
paigee
this was a great help with my homework xx!! :)it was
28
Tariq Hussain
IT'S VERY NICE AND FRUITFUL.THERE IS ALOT OF INFORMATION IN THIS ADDRESS
29
anju sharma
TODAY FIRST TIME I OPEN THIS WEBSITE .I AM IMPREESED .IN THIS WE GET ALL INFORMATION ABOUT MY MICROBIAL STUDY
30
lahjan
this is e very interesting web i have increased my knowledge on microbes
31
S.Q.
hey
i need help on this question for homework
so plz help if you can
32
marlee
omggg, this was such a great help for my science fair research paper. alot of great accurate information. thankss
33
Abayomi
I just stumbled on this website today. It's quite helpful for my assignments.
34
aty
help me to find the example of microorganism life in different temperature {low, normal and high temperature}..im so blur to search this..
35
Zaid
The last picture looks like a spectacular insect !
36
ReG
this is a good website for school project...helps me alot ...
37
xxxxxxxxxxxxxxx
Thanks! This was really helpful! I had 2 do research for a science fair, and this was extremely helpful! Thanks again!
This website was very helpful to me thanks a bunch!
The information is useful as it helps me in my science project.=)
This was very helpful!! It helped a lot with my report on bacteria. It answered all my questions. Thanks a bunch =)
this helped a little cause i have a project for my science class due soon so i need the characteristics
Good information. could you help me,i want some information about characterize of marine actinomycetes.
Thanks for the article, it educated my knowledge and helped with my GCSE Biology.
I totally agree... scientific Bacteria has cleared up to me aftre reaading this article... Thank You!!!
well this web site helped me out a lot so i think this page is a good website to get good data about bacteria.
This is alot of information!!Thanks for posting this I now have some info for my paper!!!
Please help, I need to know the bacteria associated with food that inhabit the water (salt & fresh), soil & other organisms by their names
48
miasxtery
woah . this is great . thanks a lot :) I can now easily finish my assignments because of this .I hope that other research things would be like this too :))
49
sam
how exactly are harmful bacteria able to survive in the human body?
50
dr. mariam
thx alot i was need w website like this
i take the introduction from u and i use it 0n my report
51
K3nzKi
thanks for this site... i learn more .. and i have done my assignments with great GRADES!
This website is very useful. Has an excellent overview and description.
This website doesnt help me and my other classmates.
This website is very helpful to study or have a research about bacteria .
55
Anna
this is a great site for someone who has a lot of time on their hands to come look at this stuff, but if you have the time, it will SO pay off!
56
kiana
i love this website it helped so much because it helped my group with so much and now i got an a+ thanks
57
Matt Baker
I'm in school right now in my Biology class and this website is very very helpful thank god or else i would be failing this class
58
Beverly
Best resource I've found for understanding bacteria. Very informative and easy to understand. =)
59
JONSTINA
i'm so amazed while watching this website. thankyou.
60
sasha
This website has been a lot of help to me.I breeze through my project very fast:-)
61
ibstudent
This site has been such a great help!
I would like to site it for my extended essay in MLA format but who is the author and when was this created or last revised?
62
kellygirl 2552
I would like to site it for my extended essay in MLA format but who is the author and when was this created or last revised?
63
zaegai
thank you from your information i have found and lunar more thank you
64
Mussie
Very helpful thanks now I know more things about bacterias.
65
ahmad
Thank you 4 ur great contributions in an educational pedagogy,i realy apreciate dis helpfull website.
66
Isaac
I love this article it explains bacteria nicely and it helped me on my schoolwork
HELP ME ON MY SCHOOLWORK AND DO MY HOMEWORK,COOL=,PROJECT
68
Ali Agharokh
A-dd B is a component that used for wast-water treatment. This probably solution made of bacteria. May I have some information about it?
69
luie luie
good job, whoever wrote this did a good job with it :).
70
anonymous
Thank you so much. I am doing a science fair project on bacteria, and this was so helpful. I hope you guys make another page with helpful information for science fairs, and school projects. My teacher is picky, so she was really pleased to see how well written and thought out my project was. If you are reading this people, this information was great. So thank you so much to whom ever wrote this. Thanks! Please put more on bacteria in water.
71
Mahmood
Thank you . I want a report about Alga ,please ,I hope you have a nice time .
72
md shaif ali
it is best website.it helps me to know about.biology.
The site have really helped me, but I still have a problem I need like 20 importance of micro organisms in human and its environment.
74
dianna
that was very helpful i am learning about bacteria which i am intrested in
75
Abaa Elizabeth
It has given me a very much better understanding than the lecture I attend.Thanks to you all and a very good job!!!.
76
Kelly Salvatore
what are the steps of bacteria being created? plz help i need it for a school project.
77
Malilwe
Lovely site! What other environmental factors affect the types of microbes in and on the body other than the moisture and temperature? Thanks in advance.
78
shimhanda elias-mazzo
this site is simply best of the best, it helped me a lot now! I appreciated it.
79
jhgjhgvkiufyvgj
Great site! Gave me a lot of info for a project! Other people who wish to succeed, visit this site!
80
Abhinandan
This is very useful Information. I want to know more about Pro-biotic. (Useful biodegradable) bacteria. Kindly arrange information on my e-mail ASAP.

Comment about this article, ask questions, or add new information about this topic: