Study Guide Prokaryotic Growth and Nutrition
Consider the microbial characteristics used by Gram, Woese and Griffith. Is each of these enough to identify the species that is being studied? Of the 6 leveled hierarchy, which of the categories of tests mentioned in lecture do each of these fall under? Are each species specific? What other tests are similar to each of these? Which category of tests is mostly used to characterize prokaryotes?
There needs to be more than these tests to identify a species that is being studied. These test fall in the first half of the 6 leveled hierarchy. They do not do what is required to be species-specific. The last two levels are the ones used to identify the species. These tests are tests like gram and endospore staining. Also, test like nutrient and antibiotic screening. The physiological and biochemical tests are the ones that are used to characterize bacteria.
What role does pH play in the growth of different types of bacteria?
Most organisms grow in the neutral pH range of 6-8. Although most microorganisms living in soil, freshwater, or the bodies of plants and animals are neutrophiles, living within the range of pH 5.5 to 8, some can manage exposure to pH extremes. Highly acidic or alkaline habitats, such as acidic bogs and streams or alkaline soils and ponds, can provide numerous habitats for specialized microbial communities. Obligate acidophiles include Euglena mutabilis, an alga that grows in acid pools between 0 and 1.0 pH, and Thermoplasma, an archaea that lives in hot coal piles at a pH of 1 to 2 and will lyse if exposed to pH 7. A few species of algae, archaea, and bacteria can survive at a pH near that of concentrated hydrochloric acid near a pH of 0. Not only do they require such a low pH for growth, but a few species of bacteria actually help maintain the low pH by releasing strong acid. Alkalinophiles live in hot pools and soils that contain high levels of basic minerals.
Why can the nutritional requirements of bacteria be used as a tool for their identification?
Physiological and biochemical characteristics can be used to identify a bacteria by tests like nutrient and antibiotic screening. Some of these tests are glucose fermentation, lipid digestion, enterotube, and antibiotic sensitivity tests.
Describe the three different temperature regimes that are favored by different groups of bacteria. Which of these are relevant to the bacteria that cause disease?
Psychrophiles grow at a range of 0° to 20° C. Mesophiles grow at a range of 20° to 40° C. Both of these are known to have the most pathogens and are psychrotolerant bacteria. This makes them more likely to cause diseases. There are also thermophiles that grow at a range of 40° to 90° C.
Describe what is occurring during each of the 4 phases of the typical bacterial growth curve. Does this pattern of growth only apply to cells grown in the laboratory or do the same phases occur when these organisms are growing in their natural environment?
The first phase is the lag phase. The lag phase is an early "flat" period on the graph when the population is growing at less than the exponential rate. Growth lags primarily because cells in the newly inoculated culture must adapt to their new environment. The length of the lag period varies from one population to another, depending on the condition of the microbes and medium. The second phase is the exponential growth phase. The cells reach the maximum rate of cell division during the exponential growth (logarithmic or log) phase, a period during which the curve increases geometrically. This phase will continue as long as cells have adequate nutrients and the environment is favorable. During this phase, cells reach their maximum rate of growth. The next phase is the stationary phase. At the stationary growth phase, the population reaches a size limit in which some cells divide more slowly or stop dividing entirely and may even have died. The curve levels off because the number of new cells produced equals the number that have died. The number of viable cells has reached maximum and remains relatively constant during this period. The decline in the growth rate is caused by several factors. A common reason is the depletion of nutrients and oxygen. Another is that the increased cell density often causes an accumulation of organic acids and other toxic biochemicals. The last phase is the death phase. As the limiting factors intensify, the population begins to show a decline, seen as a downward slope on the curve. This stage has been called the death phase, but what is actually happening is more complex. Some cells go into dormancy and remain viable but do not grow. Some cells enter a starvation mode that helps them resist the lack of nutrients and other factors. Depending upon the species, some microbes could remain in these states for long periods. It is also apparent that many cells go through a programmed cell death and lyse during this phase, which accounts for the overall reduction in population size. Under these conditions, it is possible for persistent members of the culture to survive by using the nutrients released by the dead cells. This pattern is affected by the environmental factors these organisms
What is the mechanism used by bacteria to reproduce? How does it differ from cell division in eukaryotic cells?
The term binary means that one cell becomes two, and transverse refers to the division plane forming across the width of the cell. During the bacterial cell division cycle, the parent cell enlarges, duplicates its chromosome, and forms a central transverse septum that divides the cell into two daughter cells. This process is repeated at intervals by each new daughter cell in turn, and with each successive round of division, the population increases. Bacterial reproduction is done by a process called binary fission. Binary fission is simple and continuous cell division, where genetic variation arises almost entirely from mutations and natural selection. The cells are haploid, meaning they have a single set of unpaired chromosomes. They have a short generation time, so they reproduce rapidly, which is greatly affected by their environment.
What is generation time? How is this affected by the conditions in which the microbe is grown?
The time required for a complete fission cycle—from parent cell to two new daughter cells—is called the generation, or doubling, time. In bacteria, each new fission cycle or generation increases the population by a factor of 2 or doubles it. As long as the environment remains favorable, this doubling effect can continue at a constant rate. Environmental conditions play a big part in the effect of the growth rate.
Why are the Archaebacteria considered to be different enough to be in their own Kingdom or Domain?
There are many features that distinguish archaebacteria from eubacteria. There is no peptidoglycan. If walls are present, they are made of proteins and polysaccharides, and there are differences in cell membranes. There are rRNA sequence differences and differences in DNA sequence analysis. There are extremophiles, thermophiles, methanogens, and extreme halophiles. None are known to be pathogenic.
Contrast the 3 different strategies observed for symbiotic relationships between bacteria and their hosts. Which of these is synonymous with disease? Discuss 2 non-symbiotic relationships you might see between microbes living on or in a host.
A general term used to denote a situation in which two organisms live together in a close partnership is symbiosis, and the members are termed symbionts. Three main types of symbiosis occur. Mutualism exists when organisms live in an obligatory but mutually beneficial relationship. This association is rather common in nature because of the survival value it has for the members involved. In other symbiotic relationships, the relationship tends to be unequal, meaning it benefits one member and not the other, and it can be obligatory to one of the members but not both. In a relationship known as commensalism, the member called the commensal receives benefits, while its coinhabitant is neither harmed or benefited. The concept of parasitism, in which the host organism provides the parasitic microbe with nutrients and a habitat. Multiplication of the parasite usually harms the host to some extent. As this relationship evolves, the host may even develop a tolerance for or dependence on a parasite, at which point we call the relationship commensalism or mutualism. This is the most likely to be synonymous with disease. There are two non-symbiotic relationships. Synergism or cooperation is an interrelationship between two or more organisms that benefits all members but is not necessary for their survival. Together, the participants cooperate to produce a result that none of them could do alone. Antagonism, a type of competition, occurs when the actions of one organism affect the success or survival of others on the same community. Often, what happens is that one microbe secretes chemical substances into the substances into the surrounding environment that inhibit or destroy other microbes in the same habitat. The first microbe may gain a competitive advantage by increasing the space and nutrients available to it.
Describe the three different strategies observed among bacteria that relate to the preferred atmospheric environment in which they are able to grow.
An aerobe (aerobic organism) can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products. An organism that cannot grow without oxygen is an obligate aerobe. Most fungi and protozoa, as well as many bacteria (genera Micrococcus and Bacillus), have strict requirements for oxygen in their metabolism. A true anaerobe (anaerobic microorganism) lacks the metabolic enzyme systems for using oxygen gas in respiration. Because strict, or obligate, anaerobes also lack the enzymes for processing toxic oxygen, they cannot tolerate any free oxygen in the immediate environment and will die if exposed to it. Strict anaerobes live in highly reduced habitats, such as deep muds, lakes, oceans, and soil. A microaerophile does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it (1%-15%) in metabolism. Most organisms in this category live in a habitat such as soil, water, or the human body that provides small amounts of oxygen but is not directly exposed to the atmosphere. A facultative anaerobe is an aerobe that does not require oxygen for its metabolism and is capable of growth in its absence. This type of organism metabolizes by aerobic respiration when oxygen is present, but in its absence, it adopts an anaerobic mode of metabolism such as fermentation. Facultative anaerobes usually possess catalase and superoxide dismutase.
Why are members of the Archaebacteria sometimes referred to as extremophiles?
Any extreme habitat—whether hot, cold, salty, acidic, alkaline, high-pressure, arid, oxygen-free, or toxic—is likely to harbor microorganisms with special adaptations to these conditions. Most such inhabitants are archaea and bacteria, but certain fungi, protozoans, algae, and even viruses are also capable of living in severe habitats. Microbiologists have termed such remarkable organisms extremophiles.
What is the evidence that these organisms diverged from their common ancestry with members of the Eubacteria very early on in the history of life?
Archaebacteria have similarities with Eubacteria, but they have been around for just as long. This is why they share a common universal ancestor. They are also known to be able to survive in many different environmental conditions.
Describe how different culture media can be used to facilitate the growth and identification of particular bacterial strains? What are the advantages of growing bacteria in liquid broth cultures? Disadvantages? Same two questions for cultures grown on solid media?
Bacteria can be grown in a liquid nutrient broth. In this media, there is solid growth of bacteria. This type of growth happens quickly. Despite this being an easier approach to bacterial growth, it is harder to isolate bacteria and colonies. There are also special growth media that are used. Enriched media, for example, can be used and has extra substrate to make it. This method is used when the proper nutrients needed for growth are required. You can also test the growth in selective or differential media. Selective media gives the advantage of faster growth which helps identify the dominant type of microorganisms in the culture. Differential media allows the growth of different bacteria and makes them easier to differentiate from each other visually. Solid media give the advantage of being able to isolate colonies and bacteria. This can be used in the identification process. But can lead to the drying of bacteria or contamination of the sample.
Distinguish between classification and identification and describe the hierarchy of methods you would use to carry out either one of these activities.
Classification is the idea of sorting an object into groups or categories, while identification is being able to give the object a name. There is a hierarchy in the methods when it comes to classifying and identifying bacteria. It starts with size, shape and arrangement, and microscopic evaluation. Then it moves to colony morphology, a macroscopic evaluation of colonies in culture. Continuing on to cell morphology analysis. This analysis includes differential staining for cell wall structure and inclusions. Then you check the physiological and biochemical characteristics: nutrient and antibiotic screenings. Then you check the serology utilizing the specificity of antibody binding. Lastly is the genetic and molecular analysis, which consists of CG content, RFLP, DNA, and rRNA sequencing.
