SULFATE-REDUCING BACTERIA AND THEIR ACTIVITIES IN CYANOBACTERIAL MATSOF SOLAR LAKE (SINAI, EGYPT)

The sulfate-reducing bacteria within the surface layer of the hypersal ine cyanobacterial mat of Solar Lake (Sinai, Egypt) were investigated with combined microbiological, molecular, and biogeochemical approache s. The diurnally oxic surface layer contained between 10(6) and 10(7) cultivable sulfate-reducing bacteria ml(-1) and showed sulfate reducti on rates between 1,000 and 2,200 nmol ml-l day(-1), both in the same r ange as and sometimes higher than those in anaerobic deeper mat layers . In the oxic surface layer and in the mat layers below, filamentous s ulfate-reducing Desulfonema bacteria were found in variable densities of 10(4) to 106 cells ml(-1). A Desulfonema-related, diurnally migrati ng bacterium was detected with PCR and denaturing gradient gel electro phoresis within and below the oxic surface layer. Facultative aerobic respiration, filamentous morphology, motility, diurnal migration, and aggregate formation were the most conspicuous adaptations of Solar Lak e sulfate-reducing bacteria to the mat matrix and to diurnal oxygen st ress. A comparison of sulfate reduction rates within the mat and previ ously published photosynthesis rates showed that CO2 from sulfate redu ction in the upper 5 mm accounted for 7 to 8% of the total photosynthe tic CO2 demand of the mat.