Improved fermentative l-cysteine overproduction by enhancing a newly identified thiosulfate assimilation pathway in Escherichia coli

Abstract

Sulfate (SO) is an often-utilized and well-understood inorganic sulfur source in microorganism culture. Recently, another inorganic sulfur source, thiosulfate (SO), was proposed to be more advantageous in microbial growth and biotechnological applications. Although its assimilation pathway is known to depend on O-acetyl-L-serine sulfhydrylase B (CysM in Escherichia coli), its metabolism has not been extensively investigated. Therefore, we aimed to explore another yet-unidentified CysM-independent thiosulfate assimilation pathway in E. coli. ΔcysM cells could accumulate essential L-cysteine from thiosulfate as the sole sulfur source and could grow, albeit slowly, demonstrating that a CysM-independent thiosulfate assimilation pathway is present in E. coli. This pathway is expected to consist of the initial part of the thiosulfate to sulfite (SO) conversion, and the latter part might be shared with the final part of the known sulfate assimilation pathway [sulfite → sulfide (S) → L-cysteine]. This is because thiosulfate-grown ΔcysM cells could accumulate a level of sulfite and sulfide equivalent to that of wild-type cells. The catalysis of thiosulfate to sulfite is at least partly mediated by thiosulfate sulfurtransferase (GlpE), because its overexpression could enhance cellular thiosulfate sulfurtransferase activity in vitro and complement the slow-growth phenotype of thiosulfate-grown ΔcysM cells in vivo. GlpE is therefore concluded to function in the novel CysM-independent thiosulfate assimilation pathway by catalyzing thiosulfate to sulfite. We applied this insight to L-cysteine overproduction in E. coli and succeeded in enhancing it by GlpE overexpression in media containing glucose or glycerol as the main carbon source, by up to ~1.7-fold (1207 mg/l) or ~1.5-fold (1529 mg/l), respectively.

Crystal structure of a YeeE/YedE family protein engaged in thiosulfate uptake

“…The energy efficiency of Cys synthesis from thiosulfate is better than that from sulfate because of the lower number of synthesis steps in the cytoplasm (2,4). Therefore, thiosulfate is considered a better sulfur source than sulfate in E. coli (7)(8)(9), and in the yeast Saccharomyces cerevisiae (10). Here, by performing growth tests of an E. coli strain lacking an unknown functional gene, yeeE, we have demonstrated that bacterial YeeE imports thiosulfate as a sulfur source.…”

Differences among patients with and without nonalcoholic fatty liver disease having elevated alanine aminotransferase levels at various stages of metabolic syndrome

“…Sulfur metabolomics was performed by the Sulfur Index service in Japan (http://www.euglena.jp/sulfurindex/; Euglena Co. Ltd., Tokyo, Japan). The sulfur index uses a technology where metabolites are detected as S-bimanyl derivatives by LC-MS/MS (Shimadzu (Nexera UHPLC system with on-line LC-MS 8040, Shimadzu, Corporation, Kyoto, Japan) as described previously [15,16]. Briefly, the sulfur-containing compounds in the samples were extracted by adding methanol and converting to fluorescent derivatives with monobromobimane.…”

The Complete Pathway for Thiosulfate Utilization in Saccharomyces cerevisiae

“…S7). The physiological level of rhodanese activities is also not sufficient to support thiosulfate utilization in an E. coli cysM mutant that resumed growth with the overexpression of the E. coli rhodanese GlpE (30). Thus, any organisms with the sulfate assimilation system may use thiosulfate as a sulfur source with the help of a rhodanese.…”