Emission spectroscopy and kinetic fluorometry studies of phototrophic microbial communities along a salinity gradient in solar saltern evaporation ponds of Eilat, Israel

The planktonic and benthic microbial communities in 8 hypersaline evaporation ponds of the Israel Salt Company in Eilat, Israel, with salinities ranging from 58 to 329 g l ^-1 (total dissolved salt), were studied using fluorescence emission spectroscopy and kinetic fluorometry. With increasing salinity, the anoxygenic phototrophic bacteria (containing bacteriochlorophyll a, bchl a) formed a significant and increasing fraction of the planktonic phototrophic biomass. While the bchl a/chl a molar ratio was 0.01 at the lowest salinity, it reached almost 1 at the higher salinities. In the benthic communities, emission spectroscopy revealed depth-dependent changes in the photophysiology of benthic oxygenic phototrophs, and spatial variability in the abundance of several groups of anoxygenic photosynthetic bacteria (green bacteria containing chlorosomes and purple bacteria containing LH1). In general, the emission signal of the benthic oxygenic phototrophs (diatoms and Cyanobacteria) was dominated by photosystem I (detected in some cases down to 5 cm of sediment depth). The signal of photosystem II and phycobilisomes was several times weaker and was observed mostly in the surface layers. The spectroscopic data of microbial communities were complemented by microscopic characterization.