Wang C L, Maratukulam P D, Lum A M, Clark D S, Keasling J D
Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USA.
Appl Environ Microbiol. 2000 Oct;66(10):4497-502. doi: 10.1128/AEM.66.10.4497-4502.2000.
The conversion of sulfate to an excess of free sulfide requires stringent reductive conditions. Dissimilatory sulfate reduction is used in nature by sulfate-reducing bacteria for respiration and results in the conversion of sulfate to sulfide. However, this dissimilatory sulfate reduction pathway is inhibited by oxygen and is thus limited to anaerobic environments. As an alternative, we have metabolically engineered a novel aerobic sulfate reduction pathway for the secretion of sulfides. The assimilatory sulfate reduction pathway was redirected to overproduce cysteine, and excess cysteine was converted to sulfide by cysteine desulfhydrase. As a potential application for this pathway, a bacterium was engineered with this pathway and was used to aerobically precipitate cadmium as cadmium sulfide, which was deposited on the cell surface. To maximize sulfide production and cadmium precipitation, the production of cysteine desulfhydrase was modulated to achieve an optimal balance between the production and degradation of cysteine.
将硫酸盐转化为过量的游离硫化物需要严格的还原条件。异化硫酸盐还原在自然界中被硫酸盐还原细菌用于呼吸作用，并导致硫酸盐转化为硫化物。然而，这种异化硫酸盐还原途径会受到氧气的抑制，因此仅限于厌氧环境。作为一种替代方法，我们通过代谢工程设计了一种新的有氧硫酸盐还原途径用于硫化物的分泌。同化硫酸盐还原途径被重新定向以过量生产半胱氨酸，过量的半胱氨酸通过半胱氨酸脱硫酶转化为硫化物。作为该途径的一种潜在应用，一种细菌被构建了该途径，并用于在有氧条件下将镉沉淀为硫化镉，硫化镉沉积在细胞表面。为了最大化硫化物的产生和镉的沉淀，对半胱氨酸脱硫酶的产生进行了调节，以实现半胱氨酸产生与降解之间的最佳平衡。
