Question

22) During conjugation, the bacterial chromosome is usually not exchanged. Describe a situation where the bacterial chromosome could be exchanged between microbes? (10 points) 23) List and fully describe how microbes display antibiotic resistance and how these mechanism originate from the genome? (15 points)

Answer 1

A-Bacteria do not have an obligate sexual reproductive stage in their life cycle, but they can be very active in the exchange of genetic information. The genetic information carried in the DNA can be transferred from one cell to another; however, this is not a true exchange, because only one partner receives the new information. In addition, the amount of DNA that is transferred is usually only a small piece of the chromosome. There are several mechanisms by which this takes place. In transformation, bacteria take up free fragments of DNA that are floating in the medium. To take up the DNA efficiently, bacterial cells must be in a competent state, which is defined by the capability of bacteria to bind free fragments of DNA and is formed naturally only in a limited number of bacteria, such as Haemophilus, Neisseria, Streptococcus, and Bacillus. Many other bacteria, including E. coli, can be rendered competent artificially under laboratory conditions, such as by exposure to solutions of calcium chloride (CaCl2). Transformation is a major tool in recombinant DNA technology, because fragments of DNA from one organism can be taken up by a second organism, thus allowing the second organism to acquire new characteristics.

Transduction is the transfer of DNA from one bacterium to another by means of a bacteria-infecting virus called a bacteriophage. Transduction is an efficient means of transferring DNA between bacteria because DNA enclosed in the bacteriophage is protected from physical decay and from attack by enzymes in the environment and is injected directly into cells by the bacteriophage. However, widespread gene transfer by means of transduction is of limited significance because the packaging of bacterial DNA into a virus is inefficient and the bacteriophages are usually highly restricted in the range of bacterial species that they can infect. Thus, interspecies transfer of DNA by transduction is rare.

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Exchange of genetic information
Discover how genetic material is exchanged between bacteria via conjugation and transduction
Discover how genetic material is exchanged between bacteria via conjugation and transduction
Bacterial DNA can pass from one cell to another through the processes of conjugation and transduction.
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Bacteria do not have an obligate sexual reproductive stage in their life cycle, but they can be very active in the exchange of genetic information. The genetic information carried in the DNA can be transferred from one cell to another; however, this is not a true exchange, because only one partner receives the new information. In addition, the amount of DNA that is transferred is usually only a small piece of the chromosome. There are several mechanisms by which this takes place. In transformation, bacteria take up free fragments of DNA that are floating in the medium. To take up the DNA efficiently, bacterial cells must be in a competent state, which is defined by the capability of bacteria to bind free fragments of DNA and is formed naturally only in a limited number of bacteria, such as Haemophilus, Neisseria, Streptococcus, and Bacillus. Many other bacteria, including E. coli, can be rendered competent artificially under laboratory conditions, such as by exposure to solutions of calcium chloride (CaCl2). Transformation is a major tool in recombinant DNA technology, because fragments of DNA from one organism can be taken up by a second organism, thus allowing the second organism to acquire new characteristics.

Transduction is the transfer of DNA from one bacterium to another by means of a bacteria-infecting virus called a bacteriophage. Transduction is an efficient means of transferring DNA between bacteria because DNA enclosed in the bacteriophage is protected from physical decay and from attack by enzymes in the environment and is injected directly into cells by the bacteriophage. However, widespread gene transfer by means of transduction is of limited significance because the packaging of bacterial DNA into a virus is inefficient and the bacteriophages are usually highly restricted in the range of bacterial species that they can infect. Thus, interspecies transfer of DNA by transduction is rare.

Conjugation is the transfer of DNA by direct cell-to-cell contact that is mediated by plasmids (nonchromosomal DNA molecules). Conjugative plasmids encode an extremely efficient mechanism that mediates their own transfer from a donor cell to a recipient cell. The process takes place in one direction since only the donor cells contain the conjugative plasmid. In gram-negative bacteria, donor cells produce a specific plasmid-coded pilus, called the sex pilus, which attaches the donor cell to the recipient cell. Once connected, the two cells are brought into direct contact, and a conjugal bridge forms through which the DNA is transferred from the donor to the recipient. Many conjugative plasmids can be transferred between, and reproduce in, a large number of different gram-negative bacterial species. Plasmids vary in size, from a few thousand to more than 100,000 base pairs; the latter are sometimes called megaplasmids.

Thebacterial chromosome can also be transferred during conjugation, although this happens less frequently than plasmid transfer. Conjugation allows the inheritance of large portions of genes and may be responsible for the existence of bacteria with traits of several different species. Conjugation also has been observed in the gram-positive genus Enterococcus, but the mechanism of cell recognition and DNA transfer is different from that which occurs in gram-negative bacteria.

B-What are antibiotics?

Antibiotics are drugs used to treat bacterial infections. They are among the most commonly prescribed drugs for people. They target bacteria by inhibiting or stopping their growth, or by killing the bacteria.

Penicillin was the first antibiotic discovered. Alexander Fleming discovered it in 1928. It was used widely during World War II. However, the sulfonamides were the first antibiotic class used clinically (in the 1930's). The discovery of antibiotics revolutionized medicine by making once-deadly infections treatable. There are now hundreds of antibiotics, classified into several categories. These antibiotic classes include:

Penicillins
Cephalosporins
Carbapenems
Aminoglycosides
Tetracyclines
Macrolides
Fluoroquinolones
Sulfonamides
Antibiotics work in different ways. For example, penicillin works by indirectly causing the bacterium's cell wall to weaken and burst, so it dies. Tetracyclines, on the other hand, do not kill bacteria but inhibit their growth by stopping the bacteria from making proteins.

Some antibiotics can be used to treat a broad range of infections, while others are used to treat infections caused by specific types of bacteria. Most antibiotics can cause some side effects (e.g., stomach upset, diarrhea), though some have a higher risk of causing serious side effects (e.g., hearing damage, kidney damage).

What is antibiotic resistance in bacteria?
Antibiotic resistance is when bacteria are able to survive and grow in the presence of one or more antibiotics. When this occurs, the resistant bacteria continue to cause infection.

Bacterial antibiotic resistance is a specific type of antimicrobial drug resistance. Other microbes, like viruses and fungi, can also become resistant to antimicrobial drugs used to treat infections with these microbes, but this article focuses on bacteria that are resistant to antibiotics.

The development of resistance commonly occurs in nature. However, because of the routine use of antibiotics, bacterial exposure to antibiotics is more frequent and resistance develops at a faster rate. Without effective antibiotics, common infections such as bacterial pneumonia, would become life-threatening once again. Complex procedures, such as open-heart surgery, would become much more dangerous and deaths from infection more common.

How do bacteria become resistant?
There are several ways for bacteria to become antibiotic-resistant. The main one is through selective pressure. Selective pressure happens when not all the bacteria are susceptible to the antibiotic used to treat the infection, and the surviving bacteria can continue to multiply. This creates a bacterial population that is resistant to the antibiotic to which the bacteria was exposed. Selective pressure is a natural process that can be slowed but not stopped. Antibiotic overuse helps speed up selection for resistant bacteria.

Bacteria can also acquire resistance when they pass genetic material back and forth from one bacteria to another. One way they can do this is through plasmids. Plasmids are pieces of bacterial DNA that can be transferred between bacteria. Some plasmids enable the bacteria to produce an enzyme that can make antibiotics useless. When the plasmid is inserted into other bacteria, antibiotic resistance can spread easily and quickly among bacteria.

Additionally, when a bacterium's genetic material spontaneously changes, or mutates, those genetic changes can create resistance. Over time, bacteria can acquire more than one type of resistance through different mechanisms. This can lead to so-called "superbugs" that are resistant to multiple antibiotic classes. Antibiotic resistant bacteria can spread from one person to another (e.g., through touching contaminated surfaces, coughing or sneezing), resulting in the spread of hard-to-treat or untreatable infections.