Sulfite dehydrogenases in organotrophic bacteria: enzymes, genes and regulation

亚硫酸盐脱氢酶是将亚硫酸盐氧化为硫酸盐的酶，在泛养副球菌（paraccoccus pantotrophus）、中央星（Starkeya novella）和温绿藻（Chlorobium tepidum）等生物的化学营养和光营养生长过程中催化的硫循环的主要通量中最为人所知。较小的有机磺酸盐的有机营养通量也是硫循环的一部分，其中来自甲烷磺酸盐、二甲基亚砜、牛磺酸（及其衍生物）、磺酸盐和磺基喹啉糖的异化亚硫酸盐以及来自异种生物来源的亚硫酸盐被氧化为硫酸盐。现在的证据表明，一种新的、可诱导的亚硫酸盐脱氢酶与一种未知的天然电子受体有关。我们已经建立了Cupriavidus necator H16（以前的Ralstonia eutropha）的酶，其基因组序列是可用的，可以用铁氰化物作为电子受体进行检测，并通过柱层析分离。我们将纯化和表征酶，从而鉴定基因及其调控因子。另一个目标是天然电子受体的性质。菌株H16可能编码几种已知亚硫酸盐脱氢酶的同源物，其在有机营养代谢中的作用也将被探讨。

Sulfite dehydrogenases, which oxidize sulfite to sulfate, are best known within the major fluxes of the sulfur cycle catalyzed during chemolithotrophic and phototrophic growth of e.g. Paracoccus pantotrophus, Starkeya novella and Chlorobium tepidum. Somewhat smaller, organotrophic fluxes of organosulfonates are also part of the sulfur cycle, in which sulfite from the dissimilation of methanesulfonate, dimethylsulfoxide, taurine (and derivatives), sulfolactate and sulfoquinovose, as well as from xenobiotic sources, is oxidized to sulfate. Evidence now indicates that a novel, inducible sulfite dehydrogenase with an unknown native electron acceptor is involved in many organisms. We have established that the enzyme from Cupriavidus necator H16 (previously Ralstonia eutropha), whose genome sequence is available, can be assayed with ferricyanide as the electron acceptor and separated by column chromatography. We will purify and characterize the enzyme, and thus identify the gene and its regulator. Another target is the nature of the native electron acceptor. Strain H16 potentially encodes several orthologues of known sulfite dehydrogenases, whose role in organotrophic metabolism will also be explored.