Growth and photosynthesis in an extreme thermophile, Synechococcus lividus (Cyanophyta)
- Cite this article as:
- Meeks, J.C. & Castenholz, R.W. Archiv. Mikrobiol. (1971) 78: 25. doi:10.1007/BF00409086
- 469 Downloads
A high temperature strain of the blue-green alga, Synechococcus lividus has been cultured and cloned in defined medium.
S. lividus (Culture OH-68-s, Clone H-Xf) is an obligate thermophile with a temperature range of growth from 54 to 72°C. The optimal conditions for growth were at 63 to 67°C and a light intensity greater than 700 ft-c, resulting in a reproducible minimum generation time of 11 hours. Growth was depressed in the supra-optimal range from 68 to 72°C. The temperature characteristic or coefficient (μ) of growth was calculated as 13,750 cal mole-1. This value would not distinguish this organism from mesophilic and psychrophilic yeasts and bacteria.
Clone H-Xf photosynthesized from as low as 33 to 75°C during short exposure times (20 min) without prior acclimation to the incubation temperatures. Longer exposures to the higher temperatures indicated that the “stable” upper limit for photosynthesis was 73°C when cells were grown above 60°C, but was only 70°C for cultures grown at 55 and 57°C.
Abrupt shifts of exponential cultures between optimal (65°C) and near minimal (55°C) growth temperatures showed that lag periods occurred before normal growth commenced at the new temperatures. However, these lag periods on downward temperature shifts followed only after a period of residual growth. Similar shifts from optimal to subminimal (45°C) temperatures indicated that growth continued for a period of time before entering an extended stationary phase prior to senescence. Both of the latter types of experiments may indicate that products synthesized at 65°C are consumed by residual growth after the shifts to lower temperatures, but that these are replaced after a long delay (acclimation) at 55°C and not at all at 45°C.
Photoincorporation of 14C−NaHCO3 was highly sensitive to subminimal temperatures after the first hour of exposure. The data suggest that the photosynthetic system could be involved in determining both the upper and lower limits of growth in this organism.