The sulfur cycle in the chemocline of a meromictic salt lake

Abstract

An extremely dense layer of the purple sulfur bacterium Amoebobacter purpureus in the chemocline of meromictic Mahoney Lake (British Columbia) was investigated over a 2-yr period. Within this layer, sulfide, elemental sulfur, and polysulfides were the main species of reduced sulfur. The oxidative part of the sulfur cycle was dominated by anoxygenic photosynthesis of A. purpureus. During summer, when sulfide concentrations in the layer were limiting, intracellular sulfur became the main electron donor for photosynthesis. 634S determinations revealed that the intracellular sulfur reacts chemically with dissolved sulfide to form polysulfides. Polysulfide concentrations decreased over summer, accompanied by an increase in numbers of sulfur-reducing bacteria. Sulfate reduction was the major pathway of sulfide formation. The annual carbon requirement of sulfate-reducing bacteria in the chemocline (22.5 g C m-2 yr-I) was met by the photosynthetic C fixation of A. purpureus (33.5 g C m-2 yr-l). Carbon demand exceeded the concomitant C fixation temporarily in summer, however. The activities of biomass-degrading enzymes and the formation of volatile fatty acids were sufficient to provide the carbon substrates. Our data indicate that in Mahoney Lake, anoxygenic photosynthesis and sulfate reduction are only indirectly coupled via degradation and autolysis of photosynthetically formed biomass.

Phototropic sulfur and sulfate-reducing bacteria in the chemocline of meromictic Lake Cadagno, Switzerland

“…For sulfate-rich environments other than Lake Cadagno, higher concentrations of elemental sulfur and polysulfides are generally reported compared to sulfite and thiosulfate concentrations (van Gemerden & Mas 1995). Polysulfides are formed in an abiotic reaction of elemental sulfur with sulfide, and are in a chemical equilibrium with them (Overmann et al 1996) with an oxidation state between sulfide and elemental sulfur (Brune 1988). Polysulfides are electron-donating substrates for anoxygenic photosynthesis by Thiocapsa roseopersicina, C. vinosum and other purple sulfur bacteria (Brune 1995;Steudel et al 1990;) and can serve as electron acceptors for sulfatereducing bacteria (Overmann et al 1996;van den Ende et al 1997).…”

“…The water column of meromictic lakes is generally characterized by three distinct layers: the mixolimnion, the upper oxic layer that is usually characterized by complete circulation during the year, the monimolimnion, the anoxic lower layer that is characterized by a stagnant water body, and the chemocline, a compact transition zone between mixo-and monimolimnion usually characterized by steep, but relatively stable physico-chemical gradients (Sorokin 1970;Lindholm 1987;Pedrós-Alió & Guerrero 1993;van Gemerden & Mas 1995;Overmann et al 1996). The physico-chemical conditions in the chemocline support growth of large numbers of microorganisms with different physiological groups substituting each other at small depth intervals along the vertical gradients (Jørgensen et al 1979;Guerrero et al 1985;Overmann et al 1991).…”

Spatially resolved capture of hydrogen sulfide from the water column and sedimentary pore waters for abundance and stable isotopic analysis

“…The shallowness of the chemocline means that the top of the sulfidic waters are in the photic zone, enabling a dense layer of photosynthetic purple sulfur bacteria to colonize the chemocline (e.g., Figure 5a) (Hamilton, 2014). As a result, sulfide is removed by both phototrophic sulfide oxidation as well as abiotic oxidation with oxygen (Overmann et al, 1996). Here, films can be deployed for a rapid characterization of the position of the chemocline (e.g., Figure 5a).…”

Microbial efficiency in a meromictic reservoir

“…In meromictic lakes divided into two layers, where one is saturated with oxygen (mixolimnion) and one is anaerobic (monimolimnion), the efficiency of microbial decomposition of organic matter is an important index of metabolic transformations in the environment (Coffin et al 1993, Kroer 1993, Del Giorgio and Cole 1998, Oremland et al 2000, Humayoun et al 2003. In many meromictic lakes sulphur compounds act as electron acceptors during cellular respiration, which can cause an accumulation of hydrosulphuric acid, exerting a negative influence on biological processes (Overmann et al 1996). Lakes with a substantial concentration of sulphuric substances occur rather infrequently.…”