SB6e. Bacteria and Viruses Bacteria are classified into two Kingdoms – Archaebacteria are the earliest monerans – this kingdom has three types of bacteria that are all found in extreme environments Eubacteria can be Heterotrophs, which must get their energy from other organisms Photosynthetic Autotrophs, which get their energy through photosynthesis of sunlight Chemosynthetic Autotrophs, which get their energy from the breakdown of inorganic substances

SB6e. Bacteria and Viruses Structure of Bacteria Bacteria are the smallest and simplest of living things They are prokaryotes They have a plasma membrane surrounded by a cell wall They have a single DNA molecule that is found as a circular chromosome and it is NOT inside a nucleus

SB6e. Bacteria and Viruses Structure of Bacteria Bacteria are often classified by the shapes of their cells: coccus = round, spirillum = spiral-shaped bacillus = rod-shaped They can also be classified by their arrangements: diplo- = cells are paired, staphylo- = grape-like clusters strepto- = long chains

SB6e. Bacteria and Viruses A virus is made of DNA or RNA and a protein coat. non-living pathogen can infect many organisms including Plants Animals Bacteria NOT considered to be a living organism

Why are viruses NOT considered to be a living organism? SB6e. Bacteria and Viruses Why are viruses NOT considered to be a living organism? Living things are made up of cells and are able to live independently of other organisms By this definition viruses are NOT alive They share many characteristics of living things but cannot function without infecting a living cell

SB6e. Bacteria and Viruses Cells Viruses Reproduce through cell division (sexual/asexual) Reproduce only inside of host cell Genetic code is DNA Genetic code can be DNA or RNA Use energy Do not use energy Respond to environment Do not respond to environment Change with time (evolve) Develop and Grow Do not develop or grow

SB6e. Bacteria and Viruses Bacteriophage Most common virus Infect bacteria cell by attaching their “legs” to the bacterium Injecting their genetic material into it Virus takes control of cell and produces more viruses. New viruses are released when the cell bursts and then they are free to infect other cells

SB6e. Bacteria and Viruses Bacteriophages infect bacteria. capsid DNA tail sheath tail fiber PROTEIN COAT

SB6e. Bacteria and Viruses Viruses enter cells in various ways. bacteriophages pierce host cells colored SEM; magnifications: large photo 25,000; inset 38,000x

SB6e. Bacteria and Viruses What happens next? Two different processes that occur once genetic material of the virus is inside the host cell Lytic infection Lysogenic infection

SB6e. Bacteria and Viruses Lytic Infection Injects DNA directly into the cell. Host cell is unable to tell the difference between viral DNA and its own. Host cell begins to make viral mRNA Translated into viral proteins that destroy the cell DNA Cell then makes thousands of copies of virus’s DNA Cell bursts and releases the new viruses.

SB6e. Bacteria and Viruses A lytic infection causes the host cell to burst. host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

SB6e. Bacteria and Viruses Lysogenic Infection Does not destroy host cell right away Insert DNA into host’s DNA Called a prophage Exists in cell for many generations without becoming active Once active it enters in to the lytic cycle and behaves just like lytic infection

SB6e. Bacteria and Viruses A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

SB6e. Bacteria and Viruses VACCINES Vaccines have been developed for viruses such as measles, mumps and polio. Usually a piece of the antigen (the foreign substance or part that the body reacts to) is injected into the body. The immune system then produces antibodies against it. That way if you later come in contact with the pathogen, your body will have a defense against it.

SB6e. Bacteria and Viruses Natural Selection in Viruses Because viruses are composed of genetic material, DNA & RNA, they can evolve. Short generation times and large population sizes allow rapid evolution When two viruses infect a cell at the same time, they may swap genetic material to make new, "mixed" viruses with unique properties. For example, flu strains can arise this way Heritable traits that help a virus reproduce (such as high infectivity for influenza, or drug resistance for HIV) will tend to get more and more common in the virus population over time.

SB6e. Bacteria and Viruses What is a “super bug?” Bacterial strand that is resistant to treatment from antibiotics Evolved from: Unnecessary use of prescription antibiotics Overdose of antibiotics

SB6e. Bacteria and Viruses What are Antibiotics? Compound that kills or limits the growth and reproduction of bacteria They cannot be used to treat viral infections only bacterial. Penicillin- discovered by Alexander Fleming in 1928. Substance secreted by a certain fungus Lead to the creation of numerous antibiotics used to treat several different bacterial diseases Pneumonia, tuberculosis

Applications of Antibiotics SB6e. Bacteria and Viruses Applications of Antibiotics Used to treat human illness Prevent infection in healthy livestock Found in commercial feed that is given to chickens and other farm animals Over $20 Billion is spent worldwide on antibiotics each year

Natural Selection in Bacteria SB6e. Bacteria and Viruses Natural Selection in Bacteria Increase in antibiotic use leads to decrease in effectiveness in treating bacterial infections. Some bacteria have the genetic ability to survive in the presence of an antibiotic. These bacteria survive and reproduce Passing this trait to their offspring Result: Population of disease causing bacteria that are resistant to antibiotics More we use antibiotics, increase number of resistant strands

Limit effects of biological resistance SB6e. Bacteria and Viruses Limit effects of biological resistance Limit the non-medical and unnecessary use of antibiotics Take antibiotics as they are prescribed and for the full duration. Stop taking prematurely resistant bacteria thrive and reproduce Creation of new antibiotics Use of combination drugs

Other Biological Resistance SB6e. Bacteria and Viruses Other Biological Resistance Insects and other pests have become resistant to certain pesticides Some widely used pesticides have become ineffective Population of insects is not longer affected by the pesticide Example: DDT