Microbially mediated sulphide production in a thermal, acidic algal mat community in Yellowstone National Park

Abstract

Summary Our objective in this study was to characterize prokaryotic sulphide production within the oxygenic, predominantly eukaryotic algal mat in an acidic stream, Nymph Creek, in Yellowstone National Park (YNP). We used microsensors to examine fluctuations in H 2 S and O 2 concentrations over time through the vertical aspect of the ∼3 mm mat in a 46–48°C region of the creek. We also used analyses of PCR‐amplified 16S rRNA gene sequences obtained from denaturing gradient gels, and PCR‐amplified sequences of a functional gene associated with microbial sulphate respiration ( dsrA ) to characterize the bacterial community in the same region of the mat. During midday, photosynthesis rates were high within the first 500 µm interval of the mat and high oxygen concentrations (600% air saturation) penetrated deeply (>1800 µm) into the mat. During early evening and night, oxygen concentrations within the first 1100 µm of the mat decreased over time from 60% air saturation (a.s) to 12% a.s. A precipitous decline in oxygen concentration occurred at a depth of 1100 µm in all night measurements and anoxic conditions were present below 1200 µm. Within this anoxic region, sulphide concentrations increased from nearly 0 µM at 1200 µm depth to 100 µM at 2400 µm depth. Enrichment cultures inoculated with Nymph Creek mat organisms also produced H 2 S. Sequence analyses of 16S rRNA and dsrA genes indicated the presence of at least five bacterial genera including species involved in dissimilative sulphate or sulphur reduction.

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