Question

Shortly after your graduation from FSCJ, you were hired by NASA to design experiments to study bacterial/prokaryotic genetics on specimens which they obtained from Antarctica here on Earth. Their ultimate goal in hiring you is to study and explore not only the Moon but also Mars and other extra-terrestrial locations. Describe here known bacterial chromosome (size, shape, genomic DNA, plasmid DNA) and genetic diversity (mutations, conjugation, transformation, transduction) we discussed and then suggest experiments to investigate the NASA samples. What roles might Quorum sensing play in your research? Your budget seems to be very large so money is no object with respect to technology and staffing needs. You're the boss.

Answer 1

A circular chromosome is a chromosome in bacteria, archaea, mitochondria, and chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromosome of most eukaryotes.

Most prokaryote chromosomes contain a circular DNA molecule – there are no free ends to the DNA. Free ends would otherwise create significant challenges to cells with respect to DNA replication and stability. Cells that do contain chromosomes with DNA ends, or telomeres (most eukaryotes), have acquired elaborate mechanisms to overcome these challenges. However, a circular chromosome can provide other challenges for cells. After replication, the two progeny circular chromosomes can sometimes remain interlinked or tangled, and they must be resolved so that each cell inherits one complete copy of the chromosome during cell division.The circular bacteria chromosome replication is best understood in the well-studied bacteria Escherichia coli and Bacillus subtilis. Chromosome replication proceeds in three major stages: initiation, elongation and termination. The initiation stage starts with the ordered assembly of "initiator" proteins at the origin region of the chromosome, called oriC. These assembly stages are regulated to ensure that chromosome replication occurs only once in each cell cycle. During the elongation phase of replication, the enzymes that were assembled at oriC during initiation proceed along each arm ("replichore") of the chromosome, in opposite directions away from the oriC, replicating the DNA to create two identical copies. This process is known as bidirectional replication. The entire assembly of molecules involved in DNA replication on each arm is called a "replisome." At the forefront of the replisome is a DNA helicase that unwinds the two strands of DNA, creating a moving "replication fork". The two unwound single strands of DNA serve as templates for DNA polymerase, which moves with the helicase (together with other proteins) to synthesise a complementary copy of each strand. In this way, two identical copies of the original DNA are created. Eventually, the two replication forks moving around the circular chromosome meet in a specific zone of the chromosome, approximately opposite oriC, called the terminus region. The elongation enzymes then disassemble, and the two "daughter" chromosomes are resolved before cell division is completed.Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.[1] This takes place through a pilus.[2]

It is a mechanism of horizontal gene transfer as are transformation and transduction although these two other mechanisms do not involve cell-to-cell contact.[3]

transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to take place, the recipient bacterium must be in a state of competence, which might occur in nature as a time-limited response to environmental conditions such as starvation and cell density, and may also be induced in a laboratory.[1]Transduction is the process by which foreign DNA is introduced into a cell by a virus or viral vector.[1] An example is the viral transfer of DNA from one bacterium to another and hence an example of horizontal gene transfer.[2] Transduction does not require physical contact between the cell donating the DNA and the cell receiving the DNA (which occurs in conjugation), and it is DNase resistant (transformation is susceptible to DNase). Transduction is a common tool used by molecular biologists to stably introduce a foreign gene into a host cell's genome (both bacterial and mammalian cells).Mutations come from errors made during the replication of DNA or from exposure to mutagens. Mutation rates vary widely among different species of bacteria and even among different clones of a single species of bacteria.[116] Genetic changes in bacterial genomes come from either random mutation during replication or "stress-directed mutation", where genes involved in a particular growth-limiting process have an increased mutation rate.[117]