CYANOBACTERIAL DOMINANCE OF POLAR FRESHWATER ECOSYSTEMS: ARE HIGH‐LATITUDE MAT‐FORMERS ADAPTED TO LOW TEMPERATURE?¹

Abstract

Although it is generally believed that cyanobacteria have high temperature optima for growth (> 20" C), mat-foming cyanobactm'a are dominant in many types of lakes, streams, and ponds in the Arctic and Antarctic. We studied the effect of temperature on growth (p) and relative pigment composition of 27 isolates of cyanobactm'a (matforming Oscillatoriaceae) from the Arctic, subarctic, and Antarctic to investigate whether they are a) adapted to the low temperature (i.e. psychrophilic) or b) tolerant of the low temperature of the polar regzons (i.e. psychrotrophic). We also derived a parabolic function that describes both the rise and the decline of cyanobactm'al growth rates with increasing temperature. The cyanobacteria were cultured at seuen different temperatures (5"-35" C at 5" C interuals), with continuous illumination of 225 pmol photons.m-2.s-1. The parabolic function jits the p-temperature data with 90 % conjidence for 75 % of the isolates. Among the 2 7 isolates of cyanobactm'a studied, the temperature optima (T,J for growth ranged from 15" to 35" C, with an average of 19.9" C. These results imply that most polar cyanobacteria are psychrotrophs, not psychrophiles. The cyanobactm'a grew over a wide temperature range (typically 20" C) but growth rates were low men at T& (average pmax of 0.23 2 0.069 d-I ) . extreme^ slow growth rates at low kmperature and the high temperature f i optimal growth imply that the cyanobact,ria are not adapted genetically to cold temperatures, which characterize their ambient environment. Other competitive advantages such as tolerance to desiccation, freeze-thaw cycles, and h g h t , continuous solar radiation may contribute to their dominance in polar aquatic ecosystems.

Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

“…ROS8604 eventually did not manage to cope with oxidative stress, as seen by the rising of PBS uncoupling (Figure 2b) and the cell density decrease (Figure 2a), starting from the fourth day of stress. Variability in carotenoid response to temperature has also been observed among cyanobacterial strains isolated from highlatitude freshwaters (Tang et al, 1997).…”

“…The two northern Synechococcus strains we studied cannot be considered as true psychrophilic organisms but rather as psychrotolerant ones (Tang et al, 1997). Indeed, although strains such as Synechococcus sp.…”

Strategies of thermal adaptation by high‐latitude cyanobacteria

“…zina & and Antarctic (James et al, 1995) lakes, ponds and streams. Tang et al (1997) found that, among 27 isolates of polar cyanobacteria, the temperature optimum for growth was highly variable. In the two most extreme cases, Phormidium subfuscum grew over the temperature range 5-25mC with an optimal temperature for growth of 15mC whereas for Phormidium tenue, µ increased with temperature over the range 5-35mC (Tang et al, 1997).…”

“…In the two most extreme cases, Phormidium subfuscum grew over the temperature range 5-25mC with an optimal temperature for growth of 15mC whereas for Phormidium tenue, µ increased with temperature over the range 5-35mC (Tang et al, 1997). Like all polar cyanobacteria examined to date, both isolates are tolerant rather than adapted to the cold water environment (Castenholz & Schneider, 1993 ;Tang et al, 1997 ;Roos & Vincent, 1998).…”

“…The growth rates obtained from this study were compared with published growth data on the same two isolates by Tang et al (1997) who used cultures that were not acclimated to the growth conditions. In all but three cases (P. subfuscum at 25mC and P. tenue at 5mC, 15mC), the pre-acclimated cultures had significantly higher growth rates than did the nonacclimated cultures (Table 1).…”