Sulfate reduction dynamics and enumeration of sulfate-reducing bacteria inhypersaline sediments of the Great Salt Lake (Utah, USA)

Bacterial sulfate reduction activity (SRA) was measured in surface sediment s and slurries from three sites in the Great Salt Lake (Utah, USA) using ra diolabeled S-35-sulfate. High rates of sulfate reduction (363 +/- 103 and 6 ,131 +/- 835 nmol cm(-3) d(-1)) were measured at two sites in the moderatel y hypersaline southern arm of the lake, whereas significantly lower rates ( 32 +/- 9 nmol cm(-3) d(-1)) were measured in the extremely hypersaline nort hern arm. Bacterial sulfate reduction was strongly affected by salinity and showed an optimum around 5-6% NaCl in the southern arm and an optimum of a round 12% NaCl in the more hypersaline northern arm of the lake. High densi ties of sulfate-reducing bacteria (SRB) ranging from 2.2 x 10(7) to 6.7 x 1 0(8) cells cm(-3) were determined by a newly developed tracer MPN-technique (T-MPN) employing sediment media and S-35-sulfate. Calculation of specific sulfate reduction rates yielded values comparable to those obtained in pur e cultures of SRB. However, when using a conventional MPN technique with sy nthetic media containing high amounts of Fe(II), the numbers of SRB were un derestimated by 1-4 orders of magnitude as compared to the T-MPN method. Ou r results suggest that high densities of slightly to moderately halophilic and extremely halotolerant SRB are responsible for the high rates of sulfat e reduction measured in Great Salt Lake sediments.