Info

culfolobus acidocaldarum

Pressure

500-1,035 atm

Colwellia hadaliensis

Radiation

1.5 million rads

Deinococcus radiodurans

at lower temperatures (e.g., in polar regions, ice, or frozen foods). Under these conditions, the survival time of these foreign bacteria is greatly extended.

1. How can microorganisms move between different ecosystems?

2. Why might microorganisms isolated from soil or water, after being grown in the laboratory, lose the ability to survive in the environment from which they were taken?

3. What is the effect of temperature on the die-out rate of microorganisms that have been moved to a new, foreign environment?

Stress and Ecosystems

Microorganisms function in ecosystems that develop under a wide range of environmental conditions. These have varied pHs, temperatures, pressures, salinity, water availability, and ionizing radiation as summarized in table 28.7. Such stress factors have major effects on microbial populations and communities, and can create an extreme environment, as shown in figure 28.33. In these cases high salt concentrations, extreme temperature, and acidic conditions have affected the microbial communities. The microorganisms that survive in such envi ronments are described as extremophiles, and such extreme environments are usually considered to have decreased microbial diversity, as judged by the microorganisms that can be cultured. With the increased use of molecular detection techniques, however, it appears that there is surprising diversity among the microorganisms that cannot be cultured from these extreme environments. Further work to establish relationships between the microorganisms that can be observed and detected by these molecular techniques and culturable microorganisms will be required in the future. The influence of environmental factors on growth (pp. 121-31)

Many microbial genera have specific requirements for survival and functioning in such so-called extreme environments. For example, a high sodium ion concentration is required to maintain membrane integrity in many halophilic bacteria, including members of the genus Halobacterium. Halobacteria require a sodium ion concentration of at least 1.5 M, and about 3 to 4 M for optimum growth. Halophilic archaea (pp. 123; 461-63)

The bacteria found in deep-sea environments have different pressure requirements, depending on the depth from which they are recovered. These bacteria can be described as baro- or piezo-tolerant bacteria (growth from approximately 1 to 500 atm), moderately barophilic bacteria (growth optimum 5,000 meters, and still able to grow at 1 atm), and extreme barophilic bacteria, which require approximately 400 atm or higher for growth (see chapter 29).

Intriguing changes in basic physiological processes occur in microorganisms functioning under extreme acidic or alkaline conditions. These acidophilic and alkalophilic microorganisms have markedly different problems in maintaining a more neutral internal pH and chemiosmotic processes (see chapter 9). Obligately acidophilic microorganisms can grow at a pH of 3.0 or lower, and major pH differences can exist between the interior and exterior of the cell. These acidophiles include members of the genera Thiobacillus, Sulfolobus, and Thermoplasma. The higher relative internal pH is maintained by a net outward translocation of protons. This may occur as the result of unique membrane lipids, hydrogen ion removal during reduction of oxygen to water, or the pH-dependent characteristics of membrane-bound enzymes.

Recently, an archaeal iron-oxidizing acidophile, Ferro-plasma acidarmanus, capable of growth at pH 0, has been isolated from a sulfide ore body in California. This unique procary-ote, capable of massive surface growth in flowing waters in the subsurface (figure 28.34), possesses a single peripheral cytoplasmic membrane and no cell wall.

The extreme alkalophilic microorganisms grow at pH values of 10.0 and higher and must maintain a net inward translocation of protons. These obligate alkalophiles cannot grow below a pH of 8.5 and are often members of the genus Bacillus; Micrococcus and Exiguobacterium representatives have also been reported. Some photosynthetic cyanobacteria also have similar characteristics. Increased internal proton concentrations may be maintained by means of coordinated hydrogen and sodium ion fluxes.

Figure 28.33 Microorganisms Growing in Extreme Environments.

Many microorganisms are especially suited to survive in extreme environments. (a) Salterns turned red by halophilic algae and halobacteria. (b) A hot spring colored green and blue by cyanobacterial growth. (c) A source of acid drainage from a mine into a stream. The soil and water have turned red due to the presence of precipitated iron oxides caused by the activity of bacteria such as Thiobacillus.

Figure 28.34 Massive Growth of the Extreme Acidophile

Ferroplasma in a California Mine. Slime streamers of Ferroplasma acidarmanus, an archaean, which have developed within pyritic sediments at and near pH 0. This unique procaryote has a single plasma membrane and no cell wall.

Figure 28.34 Massive Growth of the Extreme Acidophile

Ferroplasma in a California Mine. Slime streamers of Ferroplasma acidarmanus, an archaean, which have developed within pyritic sediments at and near pH 0. This unique procaryote has a single plasma membrane and no cell wall.

626 Chapter 28 Microorganism Interactions and Microbial Ecology

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