Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway

Abstract

Please cite this article as: Sim, M.S., Paris, G., Adkins, J.F., Orphan, V.J., Sessions, A.L., Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway, Geochimica et Cosmochimica Acta (2017), doi: http://dx.doi.org/10. 1016/j.gca.2017.02.024 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. fractionation between internal and external sulfate is up to 49‰, while at the same time that between external sulfate and sulfide is just a few permil. We interpret this pattern to indicate that enzymatic fractionations remain large but the net fractionation between sulfate and sulfide is muted by the closed-system limitation of intracellular sulfate. This 'reservoir effect' diminishes upon cessation of exponential phase growth, allowing the expression of larger net sulfur isotope fractionations. Thus, the relative rates of sulfate exchange across the membrane versus intracellular sulfate reduction should govern the overall (net) fractionation that is expressed. A strong reservoir effect due to vigorous sulfate reduction might be responsible for the well-established inverse correlation between sulfur isotope fractionation and the cell-specific rate of sulfate reduction, while at the same time intraspecies differences in sulfate uptake and/or exchange rates could account for the significant scatter in this relationship. Our approach, together with ongoing investigations of the kinetic isotope fractionation by key enzymes in the sulfate reduction pathway, should provide an empirical basis for a quantitative model relating the magnitude of microbial isotope fractionation to their environmental and physiological controls.3

Precise determination of equilibrium sulfur isotope effects during volatilization and deprotonation of dissolved H2S

“…For sulfur isotope analysis of total, gaseous, and aqueous sulfide, ZnS were washed with deionized water (DW) three times and oxidized to sulfate in 30% H 2 O 2 at 75 °C for 24 h. Sulfate as a possible minor contaminant in the sulfide stock solution, if any, should be eliminated by washing with DW, given that ZnSO 4 is extremely soluble in water (> 50g/100g H 2 O; Lide, 2006). Quantitative conversion of zinc sulfide to sulfate by H 2 O 2 was previously described in Raven et al (2016) and Sim et al (2017). After oxidation and drying, samples were dissolved in 5 mM HCl, and loaded onto AG1X8 anion exchange resin.…”

“…NaOH was then added to yield equimolar Na and SO 4 2-. Isotopic analyses were conducted on a Thermo Fischer Scientific Neptune Plus MC-ICP-MS, operated in medium resolution following the method described by Paris et al (2013) and Sim et al (2017). Samples were introduced to plasma via an ESI PFA-50 nebulizer and Cetac Aridus II desolvator.…”

A Critical Look at the Combined Use of Sulfur and Oxygen Isotopes to Study Microbial Metabolisms in Methane-Rich Environments

“…Contrarily, the measurements of ( Sim et al, 2017 ) in (fast growing) batch cultures suggest the ratio of APS to sulfite is ∼10:1 with both having relatively low concentrations resulting in a fast turnover time and therefore, less oxygen isotope exchange. A calculation of the turnover times of sulfur within a cell under conditions which produce SALP close to 0 [cell-specific sulfate reduction rate ≈50 fmol/cell/day and assumptions on cellular and intracellular parameters; cell size = 1.5 × 10 -18 m 3 , internal adenosine 5′ phosphosulfate concentration = 0.1–0.001 mM, internal sulfite concentration = 10 μM–10 mM ( Wing and Halevy, 2014 ; Sim et al, 2017 )] suggests the APS pool is turned over within a fraction of a second (<<1 s) and the sulfite pool in 0.03–30 s. In these conditions only partial oxygen isotope exchange can occur between sulfite and water. Naturally, as the cell specific sulfate reduction rates in the environment are 2–6 orders of magnitude lower than this calculation, e.g., ( Holmkvist et al, 2011 ), turnover of intracellular metabolites increases from seconds to minutes or hours and the oxygen isotope effect becomes significant.…”

“…Sulfite is the main sulfur intermediate which enables oxygen isotope exchange and does so in a matter of minutes ( Betts and Voss, 1970 ; Horner and Connick, 2003 ; Müller et al, 2013 ; Wankel et al, 2014 ). Recent theoretical work on intracellular APS and sulfite concentrations has predicted sub-micromolar and millimolar levels respectively ( Wing and Halevy, 2014 ) while measurements in pure cultures grown in batch suggest concentrations of around a hundred micromolar and ten micromolar respectively ( Sim et al, 2017 ). In the first instance, ( Wing and Halevy, 2014 ) assumed the reduction of APS and sulfite is coupled to the oxidation of menaquinone (a mildly reducing electron donor), forcing a high ratio of reduced to oxidized menaquinone to generate a favorable redox potential.…”

Experimental estimation of the bisulfite isomer quotient as a function of temperature: Implications for sulfur isotope fractionations in aqueous sulfite solutions

“…) and Archaeoglobus fulgidus ($83°C) (indicated as vertical gray lines). Although not well-known, recent determinations of the intracellular concentration of total S(IV) from Desulfovibrio alaskensis by Sim et al (2017) suggests that they may be sufficiently low such that the bisulfite dimer may be safely ignored (i.e., [S(IV)] 2 Â 10 À5 m). We note that the molecular composition of S(IV) is expected to vary considerably over these conditions, which could have implications for enzyme mediated reactions involving these compounds and their apparent overall isotope fractionations (cf.…”