Involvement of Intermediate Sulfur Species in Biological Reduction of Elemental Sulfur under Acidic, Hydrothermal Conditions

Abstract

The thermoacidophile and obligate elemental sulfur (S 8 0 )-reducing anaerobe Acidilobus sulfurireducens 18D70 does not associate with bulk solid-phase sulfur during S 8 0 -dependent batch culture growth. Cyclic voltammetry indicated the production of hydrogen sulfide (H 2 S) as well as polysulfides after 1 day of batch growth of the organism at pH 3.0 and 81°C. The production of polysulfide is likely due to the abiotic reaction between S 8 0 and the biologically produced H 2 S, as evinced by a rapid cessation of polysulfide formation when the growth temperature was decreased, inhibiting the biological production of sulfide. After an additional 5 days of growth, nanoparticulate S 8 0 was detected in the cultivation medium, a result of the hydrolysis of polysulfides in acidic medium. To examine whether soluble polysulfides and/or nanoparticulate S 8 0 can serve as terminal electron acceptors (TEA) supporting the growth of A. sulfurireducens, total sulfide concentration and cell density were monitored in batch cultures with S 8 0 provided as a solid phase in the medium or with S 8 0 sequestered in dialysis tubing. The rates of sulfide production in 7-day-old cultures with S 8 0 sequestered in dialysis tubing with pore sizes of 12 to 14 kDa and 6 to 8 kDa were 55% and 22%, respectively, of that of cultures with S 8 0 provided as a solid phase in the medium. These results indicate that the TEA existed in a range of particle sizes that affected its ability to diffuse through dialysis tubing of different pore sizes. Dynamic light scattering revealed that S 8 0 particles generated through polysulfide rapidly grew in size, a rate which was influenced by the pH of the medium and the presence of organic carbon. Thus, S 8 0 particles formed through abiological hydrolysis of polysulfide under acidic conditions appeared to serve as a growth-promoting TEA for A. sulfurireducens.

Elemental sulfur reduction in the deep‐sea vent thermophile, Thermovibrio ammonificans

“…With the nanoparticles themselves soluble and neutrally charged, we propose that these may diffuse through the cellular lipid membrane and act as a cytoplasmic terminal electron acceptor for the upregulated NSR‐like enzyme. A similar mechanism of S 0 reduction through dialysis tubing was described for Acidilobus sulfurireducens , where the authors also showed that the growth rate of sulfur nanoparticles, and thus the size distribution, was influenced by the pH of the medium as well as presence of organic carbon (Boyd and Druschel, ).…”

“…However, it has been shown that direct attachment is not necessary for growth by Pyrodictium brockii (Kelly, 1990), which still grows with bulk sulfur sequestered by dialysis tubing. Similarly, the ability to grow without direct access to sulfur was demonstrated in Acidolobus sulfurireducens (Boyd and Druschel, 2013) and in Acidianus sp. strain DS80 (Amendabar and Boyd, 2018).…”

Insight into the sulfur metabolism of Desulfurella amilsii by differential proteomics

“…Considering the conditions analyzed in this study, with polysulfide expected to be present in concentrations of circa of 0.1 mM at pH 6.5, and the presence of planktonic cells despite the dialysis membrane, it is reasonable to hypothesize that polysulfide can act as an electron acceptor for D. amilsii at pH 6.5. In the pH 3.5 culture, polysulfide is expected at very low concentration (in the order of pM), but nanosulfur particles less than 6–8 kDa could have been formed from elemental sulfur as it was shown for A. sulfurireducens (Boyd and Druschel, ). Nanosulfur particles would be able to diffuse through the dialysis membrane and become available for respiration by D. amilsii .…”

Comparative Study of Guaymas Basin Microbiomes: Cold Seeps vs. Hydrothermal Vents Sediments

“…Potential elemental sulfur disproportionation by Caldimicrobium relatives in the deepest sediment layers is also consistent with the high sulfate porewater concentrations measured in the same sediment horizons (Figure 2). Presence of these potential metabolisms only in hydrothermal sediments was therefore likely due to the hydrothermal context where substrates for these activities were generated by abiotic reactions allowed in high temperature conditions (Von Damm et al, 1985;Boyd and Druschel, 2013). These metabolisms could therefore provide additional sulfate and sustain Archaeoglobales metabolism, mainly based on sulfate or iron reduction (Brileya and Reysenbach, 2014), as well as the other potential sulfate reducing lineages identified in these sediments (e.g., GBG/HotSeep-1, SEEP-SRB, Desulfatiglans relatives, etc.…”