Cold Shock Syndrome in Anacystis nidulans

The phenomenon of cold shock in Anacystis nidulans has been explored further in terms of loss of viability and immediate and subsequent metabolic effects. Cold shock was observed also in two closely related strains in which unsaturated fatty acid contents are also known to be low and temperature-dependent. Loss of viability was maximum for cells grown at temperatures above 40 C (<10⁻⁴ survivors after 5 min at 0 C) but became negligibly small for cells grown below 34 C. Development of the cold-sensitive condition after transfer 25 → 39 C was slow and comparable to rate of growth; development of the insensitive condition after transfer 39 → 25 C was rapid, implying rapid in situ alteration. An immediate metabolic effect, observed as a decrease in rate of photosynthetic O₂ evolution measured at growth temperature, was less severe than loss of viability. Continued light incubation under growth conditions led to slow decay in rate of O₂ evolution accompanied by loss of membrane chlorophyll. The multiple effects which comprise the cold shock syndrome appear to be membrane-related phenomena and thereby provide an experimental probe of normal membrane function.