Data_Sheet_2_Isotopic Fractionation Associated With Sulfate Import and Activation by Desulfovibrio vulgaris str. Hildenborough.CSV

The use of stable isotopes to trace biogeochemical sulfur cycling relies on an understanding of how isotopic fractionation is imposed by metabolic networks. We investigated the effects of the first two enzymatic steps in the dissimilatory sulfate reduction (DSR) network – sulfate permease and sulfate adenylyl transferase (Sat) – on the sulfur and oxygen isotopic composition of residual sulfate. Mutant strains of Desulfovibrio vulgaris str. Hildenborough (DvH) with perturbed expression of these enzymes were grown in batch culture, with a subset grown in continuous culture, to examine the impact of these enzymatic steps on growth rate, cell specific sulfate reduction rate and isotopic fractionations in comparison to the wild type strain. Deletion of several permease genes resulted in only small (∼1‰) changes in sulfur isotope fractionation, a difference that approaches the uncertainties of the measurement. Mutants that perturb Sat expression show higher fractionations than the wild type strain. This increase probably relates to an increased material flux between sulfate and APS, allowing an increase in the expressed fractionation of rate-limiting APS reductase. This work illustrates that flux through the initial steps of the DSR pathway can affect the fractionation imposed by the overall pathway, even though these steps are themselves likely to impose only small fractionations.

利用稳定同位素追踪生物地球化学硫循环的过程，依赖于对代谢网络如何施加同位素分馏机制的理解。本研究调查了在异化硫酸盐还原（DSR）网络中前两个酶促步骤——硫酸盐透酶和硫酸腺苷转移酶（Sat）——对残留硫酸中硫和氧同位素组成的影响。通过批量培养，对Desulfovibrio vulgaris Hildenborough菌株（DvH）的突变菌株进行培养，其中一部分在连续培养中进行，以比较这些酶促步骤对生长速率、细胞特异性硫酸盐还原速率以及与野生型菌株相比的同位素分馏的影响。透酶基因的删除仅导致硫同位素分馏的小幅变化（∼1‰），这一变化接近测量不确定性。Sat表达受到扰动的突变体显示出比野生型菌株更高的分馏。这种增加可能与硫酸盐和APS之间物质通量的增加有关，从而允许限制性APS还原酶表达的分馏率增加。本工作表明，DSR途径初始步骤的通量可以影响整个途径施加的分馏，尽管这些步骤自身可能只会产生较小的分馏。