Major Questions in Microbiology - Essay Example

? Microbiology Exam How do viruses, viroids, prions, and bacteria differ in terms of their biological identity and method of infection? Viruses are small microorganisms as compared to bacteria as their size ranges from (0.1-0.4) µM. They are composed of either ribonucleic acid (RNA), which is single stranded or deoxyribonucleic acid (DNA) that is double stranded. Either nucleic acid is enclosed in a proteinaceous coat referred to as a capsid. The core structural units of the capsid are known as capsomeres. Some viruses (animal viruses and bacteriophages) have the capsid encased in an envelope. In addition they are non-membraneous and cannot yield energy. They are also devoid of metabolic enzymes and ribosomes that form the sites for protein biosynthesis.Moreover, they need host cells to replicate. Viruses are transmitted via salivary drops, respiratory fluids, sexual contact, fecal-oral especially in case of contaminated food, animal vectors and via blood. Viroids- Comprise of single-stranded and circular RNA which is noncoding and infect plants. As compared to viruses their genome is much smaller, are protein non-coding, and unlike viruses some possess ribozyme activity. They initiate infection in plants via chloroplast or nuclear replication and they are conveyed in cells via plasmodesmata. Prions- Infectious agents that solely comprise of a protein whose form is misfolded. This is a distinguishing feature as they lack nucleic acids i.e. RNA/DNA. These potent agents means of propagation is via inducing folded proteins in healthy organisms to change (misfold) and assume the form of the prion; these have the ability to cause disease. The resultant stable structure causes cell death and tissue damage (Tortora, Funke & Case, 2010). 2. How can viruses lead to cancer? Be sure to use specific examples (e.g. virus name and the cancer it causes) to illustrate your points. Viral transformation mediated via viral genes results to uncontrolled cell growth with contact inhibition loss, tumor formation as well as chromosomal aberrations. In addition viral oncogenes that transform normal cells into malignant cells are transmitted by viruses. Viruses also inactivate the tumor suppressor proteins. The human papilloma virus (HPV) is the causative agent for cervical cancer and it integrates in the host’s genome and suppresses the expression E2 viral gene which represses the expression of viral oncoproteins E7 and E6. E6 has a high binding affinity for p53(tumor suppressor gene) and triggers its degradation and E7 binds to retinoblastoma(Rb). Rb and p53 are tumor suppressor proteins. This results to apoptosis inhibition and dysregulation of cell growth. E6 possesses the ability to trigger telomerase activity as well as immortalizing cells. E7 also triggers abnormal centriole biosynthesis as well as aneuploidy during the initial oncogenic process. Hence, E7 and E6 are synergistic in transforming normal cells to a state of malignancy. However, there is a genetic predisposition to the progression of cervical cancer. Moreover, acute immunosuppression heightens the propensity of cervical dysplasia and subsequent cancer progression (Damania, 2006). 3. You are growing Bacillus subtilis in nine 16,000-liter fermenters to produce enzymes for industrial use. The Bacillus cultures had been growing for 2 days when the cells in one of the fermenters lysed. Explain what happened in this fermenter. This is likely to be a case of bacteriophage contamination. Bacteriophages are a class of viruses that infect bacteria. Upon infecting bacterial cultures, they cause serious problems and this entails complete loss of bioproducts; in this respect enzymes and their subsequent proliferation in the plant (to other fermentors). This results to culture lysis and unless it is contained, the problem is bound to reoccur even after stringent sterilization of equipment. Decontamination is much difficult in such a large scale fermentor. It is has been proven that phage propagation in such a bioreactor can easily spread in the plant and survive in untreated areas for long durations. Such phage contamination infects non-lysogenic cells. Lytic development of these phages causes destruction of the culture. The phage problem can also reappear several months later following one infection. In this respect bacteriophage contamination inhibited Bacillus subtilis growth and cell lysis. Technical measures should be taken to contain virulent phage contamination. This includes: maintaining top-notch sterility of the fermentor, using alternative cultures, Using mutants that are phage resistant, use of bacteriophage inhibitors and use of bacterial cells that have been immobilized (Tortora, Funke & Case, 2010). 4. What are the defining characteristics of protozoa in general, and, specifically, how can you differentiate the following phyla of protozoa: Archaezoa, Microspora, Amoebozoa, Apicomplexa, Ciliophora, and Euglenozoa? Be sure to use specific examples (e.g. specific species of protozoan) to illustrate your points. The defining characteristics of protozoa include: 1. Cell wall absence but some possess a pellicle, flexible layer, or rigid shell made of inorganic substances that enclose the cell membrane. 2. Locomotion ability during life cycle via means of locomotor organelles or gliding mechanism. 3. Heterotrophic nutrition by free living protozoa forms whereas parasititc protozoa obtain nutrition via host’s body fluids. 4. Reproduction is primarily asexual but sexual reproduction occurs in some groups (Tortora, Funke & Case, 2010). Archaezoa- They lack chloroplasts/plastids and mitochondria (anaerobic). They possess simple cytoskeletons, chemoheterotrophs, mainly parasitic. Their rRNA resemble prokaryotes as compared to eukaryotes. Giardia lamblia is an example. Amoebazoa-Possess pseudopodia for locomotion, jhave an ectoplasm i.e outer cytoplasm layer whose appearance is clear. The endoplasm i.e. inner cytoplasm region has a granular appearance. Have one nucleus, food vacuoles and a contractile vacuole. An example is Amoeba proteus. Ciliophora - Possess cilia for locaomotion, have pellicle (flexible outermost layer), food vacuoles and a contractile vacuole. They also have an oral groove (the indentation leads to the gullet and mouth. Possess a macronucleus (it is large and controls cell activities) and a micronucleus (functions in conjugation). Euglenozoa- Includes heterotrophic and autotrophic flagellates. Characterized by anterior pocket where flagella emerge. They also possess a glucose polymer referred to as paramylum. Euglena is an example. Microspora-They lack mitochondria, are non motile and are largely intracellular parasites. Common microsporidians belong to the genus Nosema. Apicomplexa- Lack locomotor organelles but immature forms exhibit movement. All members are parasites. The most common members belong to the Plasmodium genus. 5. What are the distinguishing characteristics of lichens with regard to their nutritional needs, and what are the roles of the fungus and the alga that make up lichens? Lichens are a group of fungi that exist in a symbiotic relationship with an autotrophic photobiont which could be a cyanobacterium or green alga. Most lichens are epiphytes which grow on plants. They are highly susceptible topollution and are utilized in pollution assessment. They are poikilohydric i.e can survive in extreme low water levels. The mycobiont i.e fungal partner is mainly an ascomycete. However zygomycetes comprise of only 2% of mycobionts. The fungi enclose algal cells to form complex tissues. These fungi penetrate algal cell walls and in the process form haustoria like pathogenic fungi. The fungus protects the alga via production of a thallus(vegetative body). In addition, the fungus conserves water and mineral salts for both the alga and itself. Conversely, the alga is photosynthetic and produces carbohydrates for both the fungus and itself. Algal species and fungal species do not always associate to form lichens. Thallus produced with differing algal partners is similar with identical secondary metabolites. The alga can also form symbiotic relationships with differing fungi. Lichens are formed when one fungus associates with 2/3 algal species but the reverse rarely occurs. Hence, they are named on the basis of the fungus e.g. ascolichens normally comprise of ascomycete fungi (Tortora, Funke & Case, 2010). 6. Describe the physiological characteristics that differentiate the eleven major phyla present in the Domain Bacteria and discuss the importance to humans or the environment of representative member genera from each of these phyla. 1. Purple Bacteria- Produce energy via photosynthesis. This aided by various pigments such as bacteriochlorophyll b or a and a variety of carotenoids that impart colors ranging from red, purple, orange and brown. Importance Members of Thiobacillus genera are rod shaped,colorless, Gram-ve bacteria that bear polar flagella. They have iron oxidase, and this enables metabolism of metal ions especially ferrous iron as well as inorganic sulphur compounds. This oxidation helps in the recovery of iron, uranium and copper. 2. Gram Positive Eubacteria Their walls possess additional peptidoglycan, both chemoheterotrophic and photosynthetic, but are mainly chemoheterotrophic, form endospores to survive in harsh conditions. Importance Actinobacteria decompose organic material e.g. cellulose and chitin and this enables the turnover of organic matter, a vital aspect of the carbon cycle. This also enhances humus formation. 3. Cyanobacteria/Blue green bacteria They utilize photosynthesis to obtain energy and are color blue. Importance Anabaena- Cyanobacteria that can fix nitrogen are used in rice plantations as paddy fertilizer. 4. Spirochetes They are gram-ve bacteria, chemoheterotrophic and have unique flagella in form of axial filaments that cause a twisted motion during locomotion. They have the shape of helical coils.Most are anaerobic and free living and undergo asexual binary fission during reproduction. However there are parasitic forms (Tortora, Funke & Case, 2010). Importance Treponema Pallidum which belongs to the genera Treponema is the causative agent of syphilis. 5. Green sulphur bacteria- They are anaerobic obligate phototrophes, are non-motile and shapes include spirals, rods and spheres. Photosynthesis is mediated by bacteriochlorophyll e,d, a or c. Importance Chlorobium ferrooxidans, a member of the genera Chlorobium is utilized in the oxidation of ferrous iron. 6. Bacteroides- Do not form endospores, are anaerobes, either motile/non-motile. They are largely commensals that proliferate in the host’s gastrointestinal tract. Some species are pathogenic. Importance Bacteroides fragilis causes intra-abdominal peritonitis, infections and abscesses. 7. Planctomyces- These free living bacteria are devoid of peptidoglycan. Stabilization is mediated by sacculus protein which has disulphide bonds. Reproduction is via budding. Importance They are generally a source of contamination in the course of invertebrate tissue culture. 8. Chlamydiae- They are intracellular obligate pathogens and hosts provide a reservoir for most members. Importance Chlamydia trachomatis causes Chlamydia, a sexually transmitted disease. 9. Thermotogae- Hyperthermophilic bacteria enclosed in a toga( sheath-like membrane), are gram –ve, and possess a peptidoglycan which is thin. They are anaerobes. Importance Members and can reduce sulphur to H2S. 10. Green non-sulfur bacteria-They are anoxygenic phototrophs, form chlorosomes, lack gas vesicles, are filamentous, and possess gliding mobility. Photosynthesis occurs in carotenoids and bacteriochlorophyll. Importance Chloroflexus spp. carry out photosynthesis hence contributing to the carbon cycle. 11. Radioresistant micrococci These bacteria are radio-resistant and can survive harsh conditions such as acid, vacuum, dehydration and cold and are therefore referred to as polyextremophiles. Importance Deinococcus has undergone genetic modification for bioremediation use to degrade heavy metals and solvents in radioactive sites (Tortora, Funke & Case, 2010). 7. What is the Bergey's Manual, and how is it used as a tool in the classification or identification of bacteria? Bergey’s Manual is invaluable as a source of information on a broad spectrum of bacteria. It was formulated to aid in the identification of prokaryotes. In addition, it assists in assessing relatedness in prokaryote groups. The first edition was published in 1923 and was authored by David Hendricks Bergey. Bacteria were classified on the basis of functional and structural features and were arranged into familial orders. The latest Bergey’s manual classifies bacteria and finds relatedness according to 16S rRNA phylogeny. For the systematic bacteriology manual, locate the bacteria on the ‘contents’ after constructing the Phylogenetic tree and locate the class, order, family and genus. The genus gives different species. Alternatively, locate the genus in the manual’s index and species will be found under the genus. Page numbers are highlighted in bold and this give articles on the organism. Non-bold texts refer to articles that have cited the bacteria. The manual has165 genera and 413 species of bacteria. The phyla represented comprise of Euryarchaeota, Chloroflexi, Crenarchaeota, Deinococcus, Thermatogae, Nitrospira, Cyanobacteria, Thermodesulfobacteria, Deferribacteres, Chlorobi, Chrysiogenetes and Aquificae (Tortora, Funke & Case, 2010). References Damania, B.(2006). DNA tumor viruses and human cancer. TRENDS in Microbiology, 15 (1), 1-7. Tortora, Gerard J., Funke, Berdell R., & Case, Christine L. (2010). Microbiology: An Introduction. San Francisco: Pearson Education. Read More