Adaptation to sulfide and to the underwater light field in three cyanobacterial isolates from Lake Arcas (Spain)

Abstract

Three strains of cyanobacteria isolated from karstic Lake Arcas were tested for photosynthetic adaptations to soluble sulfide. One of them, A01 1, was identified as Oscillatoriu cf. ornata, and forms dense populations in the sulfide-rich anoxic hypolimnion of this lake. This cyanobacterium was able to perform sulfide-dependent anoxygenic photosynthesis and its oxygenic photosynthesis was relatively insensitive to sulfide. The other strains studied were API and A021, identified respectively as P~eudunubuena sp. and Oscillatorin cf. tenuis. populations of which were present only in epilimnetic waters at low population densities. Pseudunubuenu sp. also carried out anoxygenic photosynthesis, but oxygenic photosynthesis was totally inhibited by 0.5 mM sulfide. Oscillatoriu cf. tenuis lost most of its oxygenic photosynthetic capacity when submitted to 0.1 mM sulfide and anoxygenic photosynthesis accounted for less than 20% of sulfide-free controls. In addition to different photosynthetic capabilities, the three cyanobacteria exhibited differences in light-harvesting photosynthetic accessory pigments. Pigment analysis of cultures grown under different light conditions showed the capacity of Oscillatoriu cf. omaru A01 I to produce phycoerythrin under low light intensity or under predominantly green light, while neither Pseudanubuerzu sp. API nor Oscillutoriu cf. fenuis A021 produced this pigment. The complementary chromatic adaptation of Oscillutoria cf. ormta correlates well with its summertime distribution under the dim light field of the hypolimnion. The distribution and abundance of specific cyanobacterial populations in Lake Arcas can thus be explained by the interplay of light regime and presence of sulfide as some of the most determinant ecological parameters.