Chapter 6 Micobiology

The conversion of nitrogen gas to ammonia is called nitrogen __________.

Fixation

Organisms that require organic sources of carbon and energy are called __________.

Chemoheterotrophs

The __________ radical is formed during the incomplete reduction of O2 during electron transport in aerobes.

Superoxide

The __________ growth temperature is the temperature at which an organism exhibits the highest growth rate.

Optimum

Bacteria that thrive at human body temperatures are classified as __________.

Mesophiles

Alkalinophiles can survive in water up to pH __________. (Be sure your answer is a numeral.)

11.5

Cells that are exposed to hypertonic environments will exhibit __________.

Crenation

A(n) __________ is a sample of microorganisms introduced into a growth medium.

Inculum

A pure culture is composed of cells that arise from a single __________.

Colony

A gelling agent derived from algae that is useful for creating solid growth media is called __________.

Agar

A sample placed into fresh medium is typically initially in the __________ phase of microbial growth.

Lag

A growth curve plots the __________ of organisms in a growing population over time.

Number

Flow __________ is a method of counting cells that have been stained or tagged with fluorescent dyes.

Cytometry

A film of cells at the surface of a solid medin is called a(n) __________.

Pellicle

A(n) __________ can measure changes in the turbidity of a bacterial culture.

Spectrophotometer

Explain how aerobic organisms tolerate the presence of oxygen in their metabolic pathways despite its toxic properties.

Oxygen is toxic to organisms only because of the highly reactive alternative forms of the molecule. These forms of oxygen can accumulate in cells and damage them by oxidizing key cellular molecules and structures. to tolerate the presence of oxygen (to allow aerobic cellular respiration to take place), cells must have ways of converting these toxic forms of oxygen to less harmful molecules. Cells use a variety of enzymes to accomplish this. These enzymes are superoxide dismutase (for elimination of the superoxide radical) and catalase and peroxidase (for the removal of hydrogen peroxide from cells). By continuous use of these enzymes, aerobic cells can use oxygen in their metabolism without suffering too many of the adverse effects of oxygen. Likewise, one major reason obligate anaerobes cannot tolerate any oxygen in their environment is the absence or reduced activity of such enzymes in those cells.

Explain how temperature and pH levels can influence microbial infections in the human body.

ll microbes have particular ranges of temperature and pH within which they exist. When the temperature or pH of their environment falls outside this range, their growth is inhibited, and they may even die as a result of the adverse conditions. Therefore, only those microbes whose pH and temperature requirements match those conditions found in the human body will be able to grow and reproduce there. For example, because the temperature of the human body is 37�C, only mesophiles can reproduce there. In addition, the pH of most tissues and fluids in the body is 6.5-7.5, which matches the pH requirements of neutrophiles. Therefore, it is not surprising that most human pathogens are mesophiles and neutrophiles. However, this is not always the case. Some microbes have adapted to environments that would otherwise be extremely hostile to most microbes. A good example is the bacterium Helicobacter pylori, which is able to live in the extremely acidic conditions of the stomach by secreting substances that help to neutralize the acid. The result is an infection that can lead to stomach ulcers.

Genetic methods of detecting microorganisms reveal that the number of bacterial species in nature exceeds previous estimates by several orders of magnitude. In the human mouth, for example, it is estimated that 500-700 microbial species are normally prese

Previous estimates of microbial diversity were largely based on the ability to detect microbes in samples handled in a typical laboratory setting. In most cases, laboratory conditions represent a narrow range of growth parameters, including temperature range, oxygen and other gas levels, and spectrum of nutrients. Even in cases where attempts are made to simulate the normal conditions for microbes (e.g., providing a high-pressure environment for organisms collected from hyperbaric environment), microorganisms must frequently tolerate fluctuations in the growth environment or even exposure to extremely adverse conditions for short periods of time. Organisms that are intolerant of significant fluctuation in their environmental requirements do not survive transport to the lab to be measured or cultured. As a consequence, only the relatively few microbes that are versatile in their nutrient requirements and can tolerate fluctuations in their growth environment have been observed or isolated in the laboratory. This, in turn, resulted in misleadingly low estimates of microbial diversity.