Microbial genetics
Microbial genetics is a subject area within microbiology and genetic engineering. Microbial genetics studies microorganisms for different purposes. The microorganisms that are observed are bacteria and archaea. Some fungi and protozoa are also subjects used to study in this field. The studies of microorganisms involve studies of genotype and expression system. Genotypes are the inherited compositions of an organism. Genetic Engineering is a field of work and study within microbial genetics. The usage of recombinant DNA technology is a process of this work. The process involves creating recombinant DNA molecules through manipulating a DNA sequence. That DNA created is then in contact with a host organism. Cloning is also an example of genetic engineering.
Role in understanding evolution
Microbial genetics can focus on Charles Darwin's work and scientists have continued to study his work and theories by the use of microbes. Specifically, Darwin's theory of natural selection is a source used. Studying evolution by using microbial genetics involves scientists looking at evolutionary balance. An example of how they may accomplish this is studying natural selection or drift of microbes. Application of this knowledge comes from looking for the presence or absence in a variety of different ways. The ways include identifying certain pathways, genes, and functions. Once the subject is observed, scientist may compare it to a sequence of a conserved gene. The process of studying microbial evolution in this way lacks the ability to give a time scale of when the evolution took place. However, by testing evolution in this way, scientist can learn the rates and outcomes of evolution. Studying the relationship between microbes and the environment is a key component to microbial genetics evolution.Microorganisms whose study is encompassed by microbial genetics
Bacteria
have been on this planet for approximately 3.5 billion years, and are classified by their shape. Bacterial genetics studies the mechanisms of their heritable information, their chromosomes, plasmids, transposons, and phages.Gene transfer systems that have been extensively studied in bacteria include genetic transformation, conjugation and transduction. Natural transformation is a bacterial adaptation for DNA transfer between two cells through the intervening medium. The uptake of donor DNA and its recombinational incorporation into the recipient chromosome depends on the expression of numerous bacterial genes whose products direct this process. In general, transformation is a complex, energy-requiring developmental process that appears to be an adaptation for repairing DNA damage.
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. Bacterial conjugation has been extensively studied in Escherichia coli, but also occurs in other bacteria such as Mycobacterium smegmatis. Conjugation requires stable and extended contact between a donor and a recipient strain, is DNase resistant, and the transferred DNA is incorporated into the recipient chromosome by homologous recombination. E. coli conjugation is mediated by expression of plasmid genes, whereas mycobacterial conjugation is mediated by genes on the bacterial chromosome.
Transduction is the process by which foreign DNA is introduced into a cell by a virus or viral vector. Transduction is a common tool used by molecular biologists to stably introduce a foreign gene into a host cell's genome.
Archaea
is a domain of organisms that are prokaryotic, single-celled, and are thought to have developed 4 billion years ago. "They have no cell nucleus or any other organelles inside their cells."Archaea replicate asexually in a process known as binary fission. The cell division cycle includes when chromosomes of daughter cells replicate. Because archea have a singular structure chromosome, the two daughter cells separate and cell divides. Archaea have motility include with flagella, which is a tail like structure. Archaeal chromosomes replicate from different origins of replication, producing two haploid daughter cells. " They share a common ancestor with bacteria, but are more closely related to eukaryotes in comparison to bacteria. Some Archaea are able to survive extreme environments, which leads to many applications in the field of genetics. One of such applications is the use of archaeal enzymes, which would be better able to survive harsh conditions in vitro.Gene transfer and genetic exchange have been studied in the halophilic archaeon Halobacterium volcanii and the hyperthermophilic archaeons Sulfolobus solfataricus and Sulfolobus acidocaldarius. H. volcani forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another in either direction. When S. solfataricus and S. acidocaldarius are exposed to DNA damaging agents, species-specific cellular aggregation is induced. Cellular aggregation mediates chromosomal marker exchange and genetic recombination with high frequency. Cellular aggregation is thought to enhance species specific DNA transfer between Sulfolobus cells in order to provide increased repair of damaged DNA by means of homologous recombination. Archaea are divided into 3 subgroups which are halophiles, methanogens, and thermoacidophiles. The first group, methanogens, are archaeabacteria that live in swamps and marshes as well as in the gut of humans. They also play a major role in decay and decomposition with dead organisms. Methanogens are anaerobic organisms, which are killed when they are exposed to oxygen. The second subgroup of archaeabacteria, halophiles are organisms that are present in areas with high salt concentration like the Great Salt Lake and the Dead Sea. The third subgroup thermoacidophiles also called thermophiles, are organisms that live in acidic areas. They are present in area with low pH levels like hot springs and geyers. Most thermophiles are found in the Yellowstone National Park.
Archaeal Genetics is the study of genes that consist of single nucleus-free cells. Archaea have a single, circular chromosomes that contain multiple origins of replication for initiation of DNA synthesis. DNA replication of Archaea involves similar processes including initiation, elongation, and termination. The primase used to synthesize a RNA primer varies than in eukaryotes. The primase by archaea is highly derived version of RNA recognition motif. Archaea come from Gram positive bacteria, which both have a single lipid bilayer, which are resistant to antibiotics. Archaea are similar to mitochondria in eukaryotes in that they release energy as adenosine triphosphate through the chemical reaction called metabolism. Some archaea known as phototrophic archaea use the sun's energy to produce ATP. ATP synthase is used as photophosphorylation to convert chemicals into ATP.
Archaea and bacteria are structurally similar even though they are not closely related in the tree of life. The shapes of both bacteria and archaea cells vary from a spherical shape known as coccus or a rod-shape known as bacillus. They are also related with no internal membrane and a cell wall that assists the cell maintaining its shape. Even though archaeal cells have cells walls, they do not contain peptidoglycan, which means archaea do not produce cellulose or chitin. Archaea are most closely related to eukaryotes due to tRNA present in archaea, but not in bacteria. Archaea have the same ribosomes as eukaryotes that synthesize into proteins. Aside from the morphology of archaea and bacteria, there are other differences between these domains. Archaea that live in extreme and harsh environments with low pH levels such as salt lakes, oceans, and in the gut of ruminants and humans are also known as extremophiles. In contrast, bacteria are found in various areas such as plants, animals, soil, and rocks.
Fungi
can be both multicellular and unicellular organisms, and are distinguished from other microbes by the way they obtain nutrients. Fungi secrete enzymes into their surroundings, to break down organic matter. Fungal genetics uses yeast, and filamentous fungi as model organisms for eukaryotic genetic research, including cell cycle regulation, chromatin structure and gene regulation.Studies of the fungus Neurospora crassa have contributed substantially to understanding how genes work. N. crassa is a type of red bread mold of the phylum Ascomycota. It is used as a model organism because it is easy to grow and has a haploid life cycle that makes genetic analysis simple since recessive traits will show up in the offspring. Analysis of genetic recombination is facilitated by the ordered arrangement of the products of meiosis in ascospores. In its natural environment, N. crassa lives mainly in tropical and sub-tropical regions. It often can be found growing on dead plant matter after fires.
Neurospora was used by Edward Tatum and George Beadle in their experiments for which they won the Nobel Prize in Physiology or Medicine in 1958. The results of these experiments led directly to the one gene-one enzyme hypothesis that specific genes code for specific proteins. This concept proved to be the opening gun in what became molecular genetics and all the developments that have followed from that.
Saccharomyces cerevisiae is a yeast of the phylum Ascomycota. During vegetative growth that ordinarily occurs when nutrients are abundant, S. cerevisiae reproduces by mitosis as diploid cells. However, when starved, these cells undergo meiosis to form haploid spores. Mating occurs when haploid cells of opposite mating types MATa and MATα come into contact. Ruderfer et al. pointed out that, in nature, such contacts are frequent between closely related yeast cells for two reasons. The first is that cells of opposite mating type are present together in the same acus, the sac that contains the cells directly produced by a single meiosis, and these cells can mate with each other. The second reason is that haploid cells of one mating type, upon cell division, often produce cells of the opposite mating type. An analysis of the ancestry of natural S. cerevisiae strains concluded that outcrossing occurs very infrequently. The relative rarity in nature of meiotic events that result from outcrossing suggests that the possible long-term benefits of outcrossing are unlikely to be sufficient for generally maintaining sex from one generation to the next. Rather, a short-term benefit, such as meiotic recombinational repair of DNA damages caused by stressful conditions may be the key to the maintenance of sex in S. cerevisiae.
Candida albicans is a diploid fungus that grows both as a yeast and as a filament. C. albicans is the most common fungal pathogen in humans. It causes both debilitating mucosal infections and potentially life-threatening systemic infections. C. albicans has maintained an elaborate, but largely hidden, mating apparatus. Johnson suggested that mating strategies may allow C. albicans to survive in the hostile environment of a mammalian host.
Among the 250 known species of aspergilli, about 33% have an identified sexual state. Among those Aspergillus species that exhibit a sexual cycle the overwhelming majority in nature are homothallic. Selfing in the homothallic fungus Aspergillus nidulans involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self-fertilization does not bypass required pathways for outcrossing sex but instead requires activation of these pathways within a single individual. Fusion of haploid nuclei occurs within reproductive structures termed cleistothecia, in which the diploid zygote undergoes meiotic divisions to yield haploid ascospores.