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.

使用稳定同位素追踪生物地球化学硫的循环依赖于对代谢网络如何施加同位素分级的理解。我们研究了异化硫酸盐还原（DSR）网络中前两个酶促步骤（硫酸盐通透酶和硫酸腺苷酸转移酶（Sat））对残留硫酸盐中硫和氧同位素组成的影响。的突变株寻常脱硫弧菌海峡 这些酶表达受到干扰的希尔登伯勒（DvH）在分批培养中生长，其中一部分在连续培养中生长，以检查这些酶促步骤与野生型相比对生长速率，细胞特异性硫酸盐还原速率和同位素分馏的影响应变。几个渗透酶基因的缺失仅导致硫同位素分级的微小变化（约1‰），这一差异接近测量的不确定性。扰乱Sat表达的突变体显示出比野生型菌株更高的分离率。这种增加可能与硫酸盐和APS之间的物料通量增加有关，从而允许限速APS还原酶的表达级分增加。