Nitrate Transport and Not Photoinhibition Limits Growth of the Freshwater Cyanobacterium Synechococcus Species PCC 6301 at Low Temperature1

Abstract

The effect of low temperature on cell growth, photosynthesis, photoinhibition, and nitrate assimilation was examined in the cyanobacterium Synechococcus sp. PCC 6301 to determine the factor that limits growth. Synechococcus sp. PCC 6301 grew exponentially between 20°C and 38°C, the growth rate decreased with decreasing temperature, and growth ceased at 15°C. The rate of photosynthetic oxygen evolution decreased more slowly with temperature than the growth rate, and more than 20% of the activity at 38°C remained at 15°C. Oxygen evolution was rapidly inactivated at high light intensity (3 mE m ؊2 s ؊1 ) at 15°C. Little or no loss of oxygen evolution was observed under the normal light intensity (250 E m ؊2 s ؊1 ) for growth at 15°C. The decrease in the rate of nitrate consumption by cells as a function of temperature was similar to the decrease in the growth rate. Cells could not actively take up nitrate or nitrite at 15°C, although nitrate reductase and nitrite reductase were still active. These data demonstrate that growth at low temperature is not limited by a decrease in the rate of photosynthetic electron transport or by photoinhibition, but that inactivation of the nitrate/ nitrite transporter limits growth at low temperature.Ambient temperature is a fundamental physical parameter that can fluctuate substantially in nature, and thus cyanobacteria are expected to exhibit complex adaptive or acclimative responses to changes in temperature. Certain cyanobacteria, such as species of Anabaena, Microcystis, Trichodesmium, and Synechococcus, are capable of forming massive blooms (Waterbury et al., 1986). In the spring and summer when nutrients are abundant, cyanobacterial blooms occur as the water temperature rises, and thus temperature may be an important environmental factor that limits cyanobacterial growth in nature.In spite of the probable importance of temperature as a parameter affecting growth, studies on its effects on cyanobacterial growth and physiology are uncommon. Moreover, identification of the biochemical process responsible for the establishment of the limiting lower temperature for cell growth has not yet been reported, to our knowledge, for any cyanobacterial strain even under laboratory conditions. Until recently, many studies on the low-temperature physiology of cyanobacteria relied on assays of the damage to photosynthetic activity induced by low-temperature treatments under dark conditions (Murata et al., 1979;Murata and Nishida, 1987;Murata, 1989). However, more recent studies, including those involving genetic manipulation of acyl-lipid desaturation, have focused on the effects of excess illumination in combination with lowtemperature stress in causing damage to PSII (for recent reviews, see Murata and Wada, 1995;Nishida and Murata, 1996).As a working hypothesis to explain chilling injury to cyanobacterial cells, Murata and coworkers initially proposed that a phase separation in the plasma membrane is directly related to the irreversible damage of cells at low temperature that eventually ca...

A survey of the algal flora of anthropogenic caves of Campi Flegrei (Naples, Italy) archeological district

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Effect of nitrate and ammonium on the growth and protein concentration of Microcystis viridis Lemmermann (Cyanobacteria)

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Effects of temperature on growth rate, cell composition and nitrogen metabolism in the marine diatom Thalassiosira pseudonana (Bacillariophyceae)

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