Christine Muise
Diagnostic Characteristics
Bacteria are prokaryotic, and make up the majority of most known prokaryotes. Bacteria have no nuclear envelope, membrane enclosed organelles, or histones for DNA. Unlike archaea, the other prokaryotic domain, Bacteria have peptidoglycan in their cell walls, and only have one kind of RNA polymerase. Bacteria have unbranched hydrocarbons, and unlike archaea, have Formylmethionine as the interior start amino acid for protein synthesis, instead of methionine. Bacteria also have circular chromosomes, like archaea, but cannot grow in temperatures above 100 degrees C and have growth inhibited in response to the antibiotics streptomycin and chloramphenicol. Lastly, bacteria rarely have introns in their genes, like archaea and eukarya do.
Some bacteria contain mitochondria, which also differentiates them from other prokaryotes. (AM)


A few strains of bacteria that can be found in food and water (ZJ)

Bacteria can be found almost anywhere. Bacteria live in almost all habitats except the most extreme areas, where the other type of prokaryote archaea are found instead.

Bacteria are often found in aquatic environments, like ponds, streams, lakes, rivers and seas. In these environments, bacteria are often in the form of cyanobacteria, and serve as important primary producers as they contain chlorophyll. Cyanobacteria are usually closer to the surface, but bacteria that live lower and are producers are chemotrophs. Bacteria love organic matter so they are often found in soils when in terrestrial biomes. (JP- 2)

Bacteria are abundantly present in terrestrial areas as well. They are crucial to preparing area for future colonization by plantlife. Cyanobacteria exist in mutualistic relationships with fungi in the form of lichens, a key organism in primary succession. In addition, due to their necessity in the nitrogen cycle, bacteria can be found in soil. Some bacteria are capable of turning atmospheric nitrogen into forms that are usable by plants through the processes of ammonification and nitrification. (Matt B - Source 5)

Major Types

Proteobacteria is a large roup of bacteria that contains five subgroups. These subgroups are Alpha Proteobacteria, which are either mutual symbionts or parasites, Beta proteobacteria, which are important to recycling nitrogen by oxidizing ammonium and producing nitrite, Gamma Proteobacteria, such as sulfer bacteria and Escherichia coi, Delta Proeteobacteria, such as the myxobacteria that are known for secreting substratum so that they can move around, and Epsilon Proteobacteria, which are related to the delta group and are seen in bacteria such as Helicobacter pylori.

Alpha Proteobacteria are the largest group within bacteria, including phototropgs, chemolithotrophs, chemoorganotrophs, and photoheterotrophs. One type, the Pelagibacter oblique, is the smallest known bacteria. They’re believed to be the most abundant bacteria on Earth, making up 25% of the microbial cells in the ocean! Whoa! Scientists are zeroing in on studying Proteobacteria genomes, hoping some of their DNA can be used in medicine. (LPE)

Another group of bacteria is the Chlamydias. This is a group of parasites that only live in animal cells. They depend on the cell for everything they need to survive. The third group is Spirochetes. A lot of these types of bacteria are free living, and some are pathogens. Spirochetes are helical in shape and are heterotrophic. The forth group is Gram-Positive bacteria. This group also contains subgroups, such as actinomycetes, which are important in medicine and are known to form colonies with branched chains of cells, and spore forming groups like Bacillus and Clostridium. Another subgroup is the mycroplasmas, which are usually soil bacteria or pathogens. The last group is Cyanobacteria. This group contains photoautotrophs, and they are the only prokaryotes with photosynthesis that is plantlike and oxygenic.
Cyanobacteria are usually found where there is lots of water. They are unicellular and although they lack flagella, they are still able to move. They are easily distinguishable because of their blue-green color and are often called “Blue-Green Algae”. Cyanobacteria also contain heterocysts which are large sized thick walls. This thick wall is permeable to nitrogen but impermeable to oxygen. (AP)

Gram staining is one of a few major ways of further classifying bacteria and involves studying the behavior of bacteria in when presented with a series of colored dyes. It generally refers to the structure of a bacterium’s cell wall. (MR; Source 17)

Basic Anatomy
The basic anatomy of a bacterium consists of a cell wall and cell membrane on the outside, which contains the bacterium. This is all contained in a protective layer called a capsule, which is located outside the cell wall. Also in the bacteria’s outer layer are pili, which are surface appendages that help the bacterium adhere to surfaces. A flagellum is also commonly found on bacteria, and is used for movement. Inside of the bacteria, structures such as DNA, which are found in the nucleoid region, and plasmids, which are smaller rings of DNA. Bacteria also sometimes have specialized membranes for things such as respiration for an aerobic bacterium, or thylakoid membranes for photosynthetic bacteria.

Pilli are made of proteins, and are hairlike and hollow. Some pilli are sex pilli, which transfer DNA between cells. Bacteria can also have multiple flagella, which are made of proteins. (PS Source 12)

external image 494px-Average_prokaryote_cell-_en.svg.png(AR)

Transport of Materials
The transport of materials in bacteria occurs through passive transport as well as active transport, which requires ATP to move the substance across the membrane. Material transport often uses proteins that are specifically for moving substances across.
Passive transport is a way to transport materials from areas of high concentration to areas of low concentration using the concentration gradient. This doesn't need energy because the concentration gradient provides the movement of molecules, and it's easy. Active transport is the opposite, it moves materials from low concentration to high concentration. However, this means that the materials go against the concentration gradient that is created from the differences in concentrations, so energy is needed. (MM)

Reproduction for bacteria is asexual, which means that the bacterium is the only parent for its offspring and therefore passes on all of it genes directly, usually through binary fission. Binary fission is where the offspring are all identical to their parent, because the parent passed on genes that are identical to its own.

Binary fission is a process that causes reproduction of a living cell by dividing into identical two parts that are able to grow to the size of the original cell. The original cell is called the parent cell and the two off spring are called daughter cells. Binary fission starts with the replication of DNA. Cell division in bacteria is controlled by proteins that collect around where the cell is going to divide. The cell wall and plasma membrane grow from the middle of the dividing cell and eventually separates the parent cell into two equal daughter cells, each with their own nuclear body. The cell membrane then grows inward and splits the cell into two separate daughter cells. (CP source 3)

Some bacteria do carry out a process called conjugation, which is the direct transfer of DNA from one bacterial cell to another. Through this direct contact, bacteria can exchange and incorporate new DNA into their plasmids. Conjugation is often thought of as the bacterial equivalent to sex, allowing new genetic combinations to be created.


Environmental Adaptations
A major adaptation that some bacteria have is endospores. An endospore is a resistant cell that is for withstanding harsh conditions that the bacterium may be in, such as boiling water. Endospores are formed by the original cell replicating its chromosome and one copy is surrounded by a wall. The endospore is then revealed by the outer cell disintegrating.

Endospore (JS 14)
Endospore (JS 14)

Endospores are mainly characteristic of a phylum of bacteria called the Firmicutes – not all bacteria produce endospores. Other extreme situations in which endospores may be useful include “high temperature, high UV radiation, desiccation, chemical damage, and enzymatic destruction.” Endospores are dormant yet highly resistant cells that preserve the original cell’s genetic material in extreme environments or situations in which the original cell may not survive. The diagram below show how endospores are formed. (MR; Source 18)

Above is a diagram of the general formation of an endospore in given bacterial families. The following link or the link in the citation for source 19 at the bottom of this page provides a longer, more detailed explanation of this process for those interested. (MR; Source 19)
Above is a diagram of the general formation of an endospore in given bacterial families. The following link or the link in the citation for source 19 at the bottom of this page provides a longer, more detailed explanation of this process for those interested. (MR; Source 19)

Bacteria are exposed to a variety of environments changing physically and chemically. Bacteria can react to their environment by changing their patterns of proteins, toxins and enzymes, adapting the organism to a specific ecological situation. One example is that E. Coli does not produce fimbriae for colonization when living in a planktonic environment. Another example is that the bacteria, Vibrio cholerae does not produce the cholera toxin that causes diarrhea until it is in the human intestinal tract. (AR)

An adaptation exhibited by Vibrio parahaemolyticus, and a great many other bacteria as well, is the formation of adherent populations on solid surfaces. This mode of growth is called a biofilm. Adoption of a biofilm mode of growth induces a myriad of changes, many involving the expression of previously unexpressed genes. In addition,de-activation of actively expressing genes can occur. Furthermore, the pattern of gene expression may not be uniform throughout the biofilm. Bacteria within a biofilm and bacteria found in other niches, such as in a wound where oxygen is limited, grow and divide at a far slower speed than the bacteria found in the test tube in the laboratory. Such bacteria are able to adapt to the slower growth rate. (RW)

Bacteria eating Uranium (MS 15))
Bacteria eating Uranium (MS 15))

Review Questions
1. Does a bacterium have histones in the DNA? (RK)
2. What is the function of certain groups of bacteria to the human body?
3. Explain the process of reproduction in bacteria through Binary Fission? (VN)
4. What are endospores and how are they formed? What is their function? Bonus: Form a simile with this definition in the form: An endospore is like a _, because ___. (MB)
5. What aspects of the bacterial anatomy differ from the anatomy of eukaryotes, and how do bacteria use these different features to compensate for the eukaryotic organelles etc. that they don't have? (PS)
6.Explain what the pili is and the function? (MP)
7. Explain the adaptations of bacteria and how they are beneficial to the organism? (RW)
8. How are new genetic combinations sometimes created in bacteria when bacteria reproduce asexually? (IL)

1.Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.
3. (CP)
4. Todar, Kenneth. "Regulation of Bacterial Metabolism." Online Textbook of Bacteriology. The Online Textbook of Bacteriology, 2011. Web. 29 Oct. 2011. <>. (AR) (LPE)
5. (Matt B)
6. (AM)
7. (TB)
8. Passive Transport vs 06. Nov 2011 (MM)
9. (RJ)
10. (picture) (AR)
11."What Are Cyanobacteria And What Are Its Types?" Web. 12 Nov. 2011. <>. (AP)
13. (ZJ)
14. (JS)
Bacteria Eating Uranium. Digital image. Web. 13 Nov. 2011.
16. (RW)
17. "Bacterial Cell." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2009. Gale Science In Context. Web. 30 Nov. 2011.
18. "Bacterial Endospores." Cornell U: Department of Microbiology. Cornell U, n.d. Web. 30 Nov. 2011.
19. Endospore Development. N.d. Cornell University: Department of Microbiology. Cornell University, n.d. Web. 30 Nov. 2011. < endo2.cfm>.