Ecophysiology of the Cyanobacterium Dactylococcopsis salina: Effect of Light Intensity, Sulphide and Temperature

Abstract

~~~Dactylococcopsis salina is a planktonic gas-vacuolated cyanobacterium that forms a distinct bacterial plate at the metalimnion of Solar Lake, Sinai. Temperature, light intensity and sulphide concentration were examined as possible limiting factors determining the distribution of D. salina during the annual limnological cycle of Solar Lake. Both laboratory cultures and in situ samples were examined for their photosynthetic activity at a wide range of temperature, light intensity and sulphide concentrations. The cyanobacterium showed a considerable light adaptation and a capacity for photosynthetic activity at high light intensities. It also showed anoxygenic photosynthesis using H2S as an alternative electron donor, but this activity was only 4% of oxygenic photosynthesis. Furthermore, H2S was highly toxic to D. salina and no C 0 2 photoassimilation could be detected at pH 7 and 1 mM-sulphide. Temperature is the primary environmental factor governing the distribution of D. salina in Solar Lake.

Halophilic Microorganisms and their Environments

“…At the border between the aerobic epilimnion and the hot, anaerobic hypolimnion a population of Dactylococcopsis salina is found. This species has yellow to orange cells that contain gas vesicles and grow in culture between salt (optimum 75-150 g It tolerates temperatures up to 45 °C (Potts, 1980;van Rijn and Cohen, 1983;Walsby et al, 1983).…”

Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

“…The general morphology conforms to descriptions of the genus as established by Komárek (26,27) and elaborated on by Waterbury and Rippka (56) and Komárek and Cepak (28). This morphology of the cytoplasm does, however, bear a striking resemblance to the internal organization of Dactylococcopsis salina as shown by Van Rijn and Cohen (53), and although our phylogenetic analysis certainly suggests some relatedness between the two, the overall morphology is quite distinct, since Dactylococcopsis is a sickle-or spindle-shaped cell, where the organism here preserves the spherical or ovate-ellipsoid form FIG. 7.…”

“…The only similar reports are from work with Dactylococcopsis salina recovered from Solar Lake, Sinai, which undergoes seasonal population expansions and becomes spatially concentrated in the lake, forming a dense narrow band constrained by its intolerance of H 2 S in deeper water and high insolation and zooplankton predation in the upper layers (49,53,54). We believe that ours is the first recorded bloom of the genus Cyanothece.…”

“…4A and 5). The content of the vacuoles is unknown, but in other cyanobacteria, similar vacuoles have been shown to contain lipids, glycogen, or gas (53,56). The stellate vacuolar structure may be specific to this strain of Cyanothece: it has not been de- scribed for C. aeruginosa, the type species of the genus (26), nor for strains BH63 and BH68 (43), C. halobia (10), or C. minervae/cedrorum (28), three strains described by Porta et al (42), nor for any others we have considered from the literature, such as the study reported by Garcia-Pichel et al (22).…”

Nitrogen uptake dynamics of a persistent cyanobacterium Cyanothece sp. bloom in Lake St Lucia, South Africa

“…Also, many cyanobacteria exhibit optimum growth at temperatures >25 °C (Sellner 1997;Coles and Jones 2000). Van Rijn and Cohen (1983) reported an optimum temperature range of 40-45 °C for photosynthesis by the hypersaline-tolerant Dactylococcopsis salina. Consequently, elevated temperatures may favour cyanobacterial bloom formation (Sellner 1997), given that most eukaryotic primary producers, such as diatoms, chlorophytes, cryptophytes and dinoflagellates, have thermal tolerances far below 30 °C, which limits their productivity (Jöhnk et al 2008).…”