Chapter 10 bacterial reproduction and growth of microorganisms

FIG. 10-18 Cells respond to osmotic pressure. In hypotonic solutions, cells may burst.

reach a maximum. Although light intensities above this level do not result in further increases in the rates of photosynthesis, light intensities below the optimal level result in lower rates of photosynthesis.

The wavelength of light also has a marked effect on the rates of photosynthesis. Different photosynthetic microorganisms use light of different wave­lengths. For example, anaerobic photosynthetic bac­teria use light of longer wavelengths than eukaryotic algae are capable of using. Many photosynthetic mi­croorganisms have accessory pigments that enable them to use light of wavelengths other than the ab­sorption wavelength for the primary photosynthetic pigments. The distribution of photosynthetic mi­croorganisms in nature reflects the variations in the ability to use light of different wavelengths and the differential penetration of different colors of light into aquatic habitats.

The rate of photosynthesis is a function of light in­tensity and wavelength.

Exposure to visible light can also cause the death of bacteria (FIG. 10-19). Exposure to visible light can lead to the formation of singlet oxygen, which can re­sult in the death of bacterial cells. Some bacteria pro­duce pigments that protect them against the lethal ef­fects of exposure to light. For example, yellow, or­ange, or red carotenoid pigments interfere with the formation and action of singlet oxygen, preventing its lethal action. Bacteria possessing carotenoid pig­ments can tolerate much higher levels of exposure to

sunlight than nonpigmented microorganisms. Pig-1 mented bacteria often grow on surfaces that are ex­posed to direct sunlight, such as on leaves of trees. Many viable bacteria found in the air produce col­ored pigments.

FIG. 10-19 Pigmentation is important in the ability of bacteria to survive exposure to light.

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