CHARACTERIZATION OF PSYCHROPHILIC OSCILLATORIANS (CYANOBACTERIA) FROM ANTARCTIC MELTWATER PONDS

• Published in: Journal of Phycology
• Main Authors: Nadeau, Tracie‐Lynn, Castenholz, Richard W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2000
• Subjects: Antarc*; Antarctic; Ice Shelf; McMurdo Ice Shelf
• Online Access: http://dx.doi.org/10.1046/j.1529-8817.2000.99201.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1529-8817.2000.99201.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1529-8817.2000.99201.x

Oscillatorian cyanobacteria dominate benthic microbial mat communities in many polar freshwater ecosystems. Capable of growth at low temperatures, all benthic polar oscillatorians characterized to date are psychrotolerant (growth optima > 15° C) as opposed to psychrophilic (growth optima ≤ 15° C). Here, psychrophilic oscillatorians isolated from meltwater ponds on Antarctica's McMurdo Ice Shelf are described. Growth and photosynthetic rates were investigated at multiple temperatures, and compared with those of a psychrotolerant isolate from the same region. Two isolates showed a growth maximum at 8° C, with rates of 0.12 and 0.08 doublings·d − 1 , respectively. Neither displayed detectable growth at 24° C. The psychrotolerant isolate showed almost imperceptible growth at 4° C and a rate of 0.9 doublings·d − 1 at its optimal temperature of ∼23° C. In both photosynthesis versus irradiance and photosynthesis versus temperature experiments, exponentially growing cultures were acclimated for 14 days at 3, 8, 12, 20, and 24° C under saturating light intensity, and [ 14 C] photoincorporation rates were measured. Psychrophilic isolates acclimated at 8° C showed greatest photosynthetic rates; those acclimated at 3° C were capable of active photosynthesis, but photoincorporation was not detected in cells acclimated at 20 and 24° C, because these isolates were not viable after 14 days at those temperatures. The psychrotolerant isolate, conversely, displayed maximum photosynthetic rates at 24° C, though photoincorporation was actively occurring at 3° C. Within acclimation temperature treatments, short‐term photosynthetic rates increased with increasing incubation temperature for both psychrophilic and psychrotolerant isolates. These results indicate the importance of temperature acclimation before assays when determining optimal physiological temperatures. All isolates displayed photosynthetic saturation at low light levels (<128 μmol·m − 2 ·s − 1 ) but were not photoinhibited at the highest light treatment (233 ...