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The photosynthesis‐light curve for purple sulfur bacteria had a steeper inclination than that for green sulfur bacteria at low light intensities. Light saturation occurred at intensities of 5–7 klux in the former, in the latter at 10–30 klux. Light inhibition was observed in purple sulfur bacteria but was negligible in green sulfur bacteria. The optimal temperature for photosynthesis of these bacteria is considerably higher than that of most phytoplankton or green plants. Photosynthetic sulfur bacteria appear ordinarily in the contact layer between oxidative and reductive zones of meromictic or stagnant holomictic lakes; the light intensity in this contact layer is usually less than 10% of that at the surface. On the assumption that the photosynthetic rate of these bacteria is limited mainly by the interaction of hydrogen sulfide concentration with light intensity, their growth was analyzed with a mathematical model. The properties of the growth phase observed in lakes were similar to those calculated. The main factors determining the growth of photosynthetic sulfur bacteria in lakes are the H 2 S concentration in the upper layer and the light conditions in the deeper layer.
Takahashi et al. (Sun,) studied this question.