Community respiration studies in saltern crystallizer ponds

To measure community respiration by the heterotrophic Archaea (dominated by Haloquadratum) and Bacteria (Salinibacter) in the NaCl-saturated crystallizer brines of the solar salterns in Eilat, Israel, and to obtain information on the substrates preferred by the community as energy sources, we used 2 complementary approaches: monitoring of changes in oxygen concentration using planar optode sensors in short (up to 30 min) experiments, and long-term (up to 40-50 h) incubations using Winkler titration to assess changes in oxygen levels. Respiration rates measured wẽ3 fmol cell-¹ h-¹. Respiration was markedly stimulated by glycerol, dihydroxyacetone and pyruvate, but not by yeast extract, succinate, and fumarate. These findings are discussed in view of genomic information on the dominant heterotrophic organisms in the community as well as the utcome of earlier studies on the behavior of halophilic prokaryotes in situ and in laboratory cultures. Despite the low in situ respiration rate, the oxygen uptake studies added information on the activities of the heterotrophic communities in salt-saturated ecosystems and on the substrates metabolized by the microorganisms present.