By: Sela Miller
Antrax a type of Bacteria (MP) (20)
Antrax a type of Bacteria (MP) (20)

Diagnostic Characteristics
Bacteria are prokaryotic cells, so they have no membrane-bound organelles. There is no nuclear envelope. Also, bacteria have one double-stranded, circular piece of DNA which is found in the nucleoid region.
Bacteria respond to gaseous oxygen in one of three ways: Aerobic, anaerobic, or facultative anaerobes. Aerobic bacteria require oxygen to growth and will die without it. Anaerobic bacteria cannot use oxygen in its gas form. These bacteria normally live in underwater sediments or those that cause bacterial food poisoning. Facultative anaerobes are able to grow without gaseous oxygen but, they prefer to grow with oxygen in its gas form. (14)(MF)

Bacteria are found all over the place. For example, they can be found on mountains, in the stomachs of animals, or even in the water. Most bacteria cannot live in extreme conditions (ex. extremely salty places); however, there are a few kinds that can.

Bacteria are found in many symbiotic relationships. For example, there are bacteria that live in our intestines to help in digestion and in destroying harmful organisms that may enter our digestive tract. Intestinal bacteria also produce some vitamins required by the human body. (DB) (27)

Bacteria exist in marine ecosystems, freshwater ecosystems, terrestrial ecosystems. (SR)

Bacteria that can be found on land is responsible for mainting our enviornment. For example, rhizobium helps in the nitrogen fixation which is what allows plants to acquire the nitrogen they need. (GR)(15)

One way bacteria can be grouped is based on their response to oxygen, which would define their habitat as well. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Other bacteria are anaerobic, and cannot utilize oxygen, such as those bacteria which live in deep underwater vents, or those which cause bacterial food poisoning. The third group are the facultative anaerobes, which prefer growing in the presence of oxygen, but can continue to grow without it. (RG) (22)

Rhizobium, a kind of nitrogen-fixing bacterium. (NI)
Rhizobium, a kind of nitrogen-fixing bacterium. (NI)

Rhizobium, a kind of nitrogen-fixing bacterium. (NI) 19

Major Types
Proteobacteria - The second largest phylum of bacteria. They are all gram negative, but are otherwise very diverse. (KL)(1) Gram negative bacteria are called gram negative because they cannot be detected by Gram's Test. Gram negative cells have thin cell walls (compared to gram positive) made of lipopolysaccharide and proteins, with a lack of lipoproteins. The lipopolysaccarides form a side chain that chemically distinguishes gram negative cells from other types of bacteria. The composition of this cell wall does not hold the violet dye used in Gram's Test.(CSR, 13)
o Alpha Proteobacteria
§ Mostly found in eukaryotic hosts as either mutual symbionts or as parasites
§ Mitochondria evolved from an anaerobic alpha proteobacteria that inhabited a larger host cell (endosymbiosis)
o Beta Proteobacteria
§ Contains Nitrosomonas which are soil bacteria that recycle nitrogen
o Gamma Proteobacteria
§ Photosynthetic or heterotrophic
§ Some are enterics (bacteria that inhabit the intestines of animals)
o Delta Proteobacteria
§ Some form the most elaborate colonies of all the prokaryotes
§ Some are predators that attack other bacteria
o Epsilon Proteobacteria
§ Closely related to Delta Proteobactereia
o Parasites that can only survive within animal cells
o Their cell walls lack peptidoglycan
o Because chlamydia is unable to make its own ATP it must survive off of its host cell. The bacteria uses adhesins in its own cell wall to bind to the receptors on host cells. These adhesins make the chlamydia very difficult to physically remove. Next, invasins act as the battle front and penetrate into the host cell. The parasite tricks the host cell to accept it into an endocytic vacuole, where it grows, divides by binary fission, is released by the host cell, and spreads. (NG)(2)

external image life%20cycle%20of%20chlamydia.gif(NG)(3)
o They are too thin to be seen without a microscope
o Internal flagellum-like filaments produce a corkscrew-like movement
o Many are free-living
o Some are pathogens
o Spirochetes are long, slender, tightly curled bacteria and resemble wound telephone cords.Their axial filaments make them unique among bacteria, as they run along the outside of the protoplasm while still remaining inside and outer sheath. These filaments allow the bacterium to move by rotating in place. (ZXU)(7)
Gram-Positive Bacteria
o Very diverse category
o Contain free-living species that help decompose organic litter in soil
o Some are solitary species
o Contains the only bacteria that do not have a cell wall
o Characterized by having peptidoglycan as well as polysaccharides and/or teichoic acids. Peptidoglycans are also called murein are heteropolymers of glycan strands cross linked through short peptides. Murien is basically a chain of alternating residues of N-acetylglucosamine and N-acetyl muramic acid which are Beta-1,4 linked. Muamic acid is a substance associated with bacterial walls. The chains are cross-linked by short polypeptide chains consisting of L- and D- aminoacids. (MC)

“There are several major differences between gram positive bacteria and gram negative bacteria that are used to determine which is which. The first is the number of layers in the cell wall. Gram positive bacteria have more peptidoglycan layers in their cell wall than gram negative bacteria: this means gram positive bacteria have stronger cell walls, and gram negative bacteria are more prone to mechanical breakage. In addition to the cell wall, gram positive bacteria utilize techoic and lipotechoic acids to transport nutrients while gram negative bacteria utilize porins, which are proteins. Lastly, gram negative bacteria have their cell membrane on the outside of their cell wall in addition to inside their cell wall, while gram positive bacteria have their membrane only within their cell wall like most cells we have learned about.” (SD) (23)
o Photoautotrophic
o The only prokaryotes with plant-like photosynthesis
o Chloroplasts evolved from a cyanobacteria that lived within a larger cell as a symbiont
o They can be solitary or colonial
o They live in the water
o Some colonies have cells that are specialized for nitrogen fixation
o Cyanobacteria have been around for over 3.5 billion years, they are one of the largest and one of the most important groups of bacteria on earth. The oxygen atmosphere we depend on today is thanks to numerous Cyanobacteria from the Archaean and Proterozoic Eras. Cyanobacteria is also known for their residency in certain eukaryote cells, during the late Proterozoic Era or the early Cambrian Era, known as Endosymbiosis, the origin of Eukaryotic Mitochondria. (MLK)(24)

Basic Anatomy
Bacteria have three common shapes - spheres, rods, and helices. Their cell walls contain peptidoglycan which is a modified sugar cross-linked by polypeptides. Gram-positive bacteria have simple walls with large amounts of peptidoglycan, and gram-negative bacteria have less peptidoglycan. Gram-negative bacteria are more complex than gram-positive bacteria. Outside of the cell wall is a protective layer called the capsule. This layer helps the bacteria to stick to things. Along with the capsule, some bacteria have pili which also help it attach to things. To move, some bacteria have flagellum. Inside of the nucleoid region is the DNA of the bacteria. Some bacteria contain plasmids, smaller rings of DNA. Some bacteria also contain endospores which are resistant cells that help the bacteria live in extreme conditions. Also found within bacteria are ribosomes and in some bacteria there are storage granules. Storage granules are membrane bound vesicles used to store energy and organic materials. (RL) (4,5,6)


Transport of Materials
Saproboes are decomposers that absorb nutrients from dead organisms. Parasites absorb nutrients from the body fluids of living hosts.
Materials enter through the bacteria’s selectively permeable membrane, across the phospholipid bilayer. Small neutral molecules go though the membrane though diffusion. Large or charged molecules are transported through channel proteins in facilitated diffusion. These are both passive transport mechanisms and require the molecules to travel along the concentration gradient. Active transport using ATP and transfer proteins carries materials across against the gradient. Necessary materials enter and waste products exit through the membrane.(ORS 16)

The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy, but these traits often do not correspond with modern genetic classifications. Bacterial metabolism of bacteria is classified into nutritional groups on the basis of three major criteria: source of energy used for growth, the source of carbon, and the electron donors used for growth. Additional criterions of respiratory microorganisms are the electron acceptors used for aerobic or anaerobic respiration. Carbon metabolism in bacteria is either heterotrophic, where organic carbon compounds are used as carbon sources, or autotrophic, where cellular carbon is obtained by fixing carbon dioxide. Heterotrophic bacteria include parasitic types. Typical autotrophic bacteria are phototrophic cyanobacteria, green sulfur-bacteria and some purple bacteria, but also many chemolithotrophic species, such as nitrifying or sulfur-oxidizing bacteria. Energy metabolism of bacteria is either based on phototrophy, the use of light through photosynthesis, or on chemotrophy, the use of chemical substances for energy, which are mostly oxidized at the expense of oxygen or alternative electron acceptors (aerobic/anaerobic respiration).

Source of energy
Source of carbon
Organic compounds (photoheterotrophs) or carbon fixation (photoautotrophs)
Cyanobacteria, Green Sulfur Bacteria, or Purple Bacteria
Inorganic compounds
Organic compounds (lithoheterotrophs) or carbon fixation (lithoautotrophs)
Organic compounds
Organic compounds (chemoheterotrophs) or carbon fixation (chemoautotrophs)

All bacteria asexually reproduce by binary fission. They synthesize DNA almost continuously. Bacteria have two ways of transferring genes - transformation (taking genes from the surrounding environment) and conjugation (direct transfer of genes). Mutation is the major source of genetic variation among bacteria. In perfect conditions, bacterial growth is geometric (one cell --> two cells. two cells --> four cells).
The process of binary fission is a method of asexual reproduction employed by most prokaryotes. It begins when the DNA is replicated. Each circular strand of DNA then attaches to the plasma mebrane. The cell elongates, causing the two chromosomes to separate. The plasma membrane then invaginates (grows inward) and splits the cell into two daughter cells through a process called cytokinesis.Conjunction involves the direct joining of two bacteria, which allows their circular DNA to undergo recombination. Bacteria can also undergo transformation by absorbing remnants of DNA from dead bacteria and integreating these fragments into their own DNA. Bacteria can also exchange genetic material through a process called transduction, in which genes are transported into and out of the cell by bacterial viruses, called bacteriophages or plasmids. (LW) (8)

An awesome picture of bacteria reproducing through binary fission. (CC) (18)

Environmental Adaptations
One of bacteria's environmental adaptations are endospores which help the bacteria to live in extreme conditions. The best way for bacteria to adapt to the environment is by mutations which occur during reproduction.
Not only do endospores help bacteria survive in unfavorable conditions, but the formation of endospores also makes it more difficult for humans to kill bacteria. (AK) (21)
Ancestors of bacteria were the first forms of life to develop on Earth.
Generations of bacteria can be created in a few hours and minutes, so mutations can spread to a large number of offspring. Bacteria are able to adapt to their environments very quickly as natural selection processes new mutations. (SR) (26)
Bacteria have learned to adapt very well to their environments and survive through different conditions. Humans have had a hard time trying to kill different bacteria that infects our bodies. Bacteria becomes resistant to antibiotics by mutations within its DNA that can remove the targeted protein or prevent the antibiotic from binding. Genetic change in the bacterium's DNA can produce enzymes to counteract the antibiotic or alter the permeability of its own membrane. (CW)(25)
Bacteria are adaptable; the genetic information in the surrounding layers of bacteria are capable of alteration. Some of these changes are reversible, meaning they go back to their normal state after an environmental pressure is removed. Other changes are irreversible and may even be passed onto following generations of bacteria. In 1929, the antibiotic, a bacteria fighting medication, was discovered. Since then, an adaptation of bacteria has been resistance to antibiotics. Resistance can occur in two ways, inherent (natural) and acquired resistance. Bacteria can also adapt to changes in temperature, pH, and concentration of ions. (SI) (10)

Bacteria are constantly adapting to the nutritional and physical environment. Bacteria can react to changes by altering the patterns of structural proteins, changing the behavior of transport proteins, controlling enzymes or toxins, etc. For example, when E. Coli lives in a planktonic (free-floating) environment, it does not produce fimbriae. If E. Coli is fed glucose and lactose, it will metabolize the glucose first because it takes less enzymes to use glucose than it does to use lactose. These changes help adapt the bacteria to their particular ecological environment and ensure that the organism does not waste energy. Bacteria have also developed mechanisms for regulating catabolic (“breaking down”) and anabolic (“building up”) pathways. Bacteria will avoid synthesizing catabolic enzymes if the substrates for the enzymes are absent in the environment. Likewise, bacteria have developed mechanisms to control anabolic pathways by shutting down biosynthetic pathways when the product is easily obtained from the environment or is not needed. The bacteria can conserve energy through metabolic adaptation. (MT)

Review Questions
How are Bacteria and Protists different, morphologically? Would you say they're more similar or different? Explain. (TM)
Compare and contrast the processes of prokaryotic binary fission and eukaryotic meiosis. (LW)
Describe the different types of bacteria and their specific characteristics. (AK)
What makes the cells of bacteria different from cells of eukaryotic organisms? (JS)
How do bacteria adapt to their environment?

Main source: Campbell, N.C., Reece, J.R. (2002). Biology. (Sixth Edition). San Francisco: Benjamin Cummings
1. (KL)
2. (NG)
3. (NG)
4. (RL)
5. (RL)
6. (RL)
7. (ZXU)
8. (LW)
11. (MT)
12. (ZS)
13. (CSR)
14. (MF)
15. (GR)
17. (MC)
19. (NI)
20. (Antrax photo) MP
21. (AK)
22. (RG)
24. (MLK)
26. (SR)