Expression, purification and characterization of a cysteine desulfurase, IscS, from Acidithiobacillus ferrooxidans

Complex gene response of herbicide-resistant Enterobacter strain NRS-1 under different glyphosate stresses

Knowledge of biological evolution and genetic mechanisms is gained by studying the adaptation of bacteria to survive in adverse environmental conditions. In this regard, transcriptomic profiling of a glyphosate-tolerant Enterobacter strain NRS-1 was studied under four different treatments to investigate the gene-regulatory system for glyphosate tolerance. A total of 83, 83, 60 and 74 genes were up-regulated and 108, 87, 178 and 117 genes down-regulated under 60-NPG, 110-NPG, NaCl (355 mM) and HCl (pH 4.46) stress treatments, respectively. Complex gene network was identified to be involved in regulating tolerance to glyphosate. This study revealed that NRS-1 has gained glyphosate tolerance at the cost of osmotic and acidic resistance. The 25 differentially expressed genes are reported to may have partly changed the function for providing resistance to glyphosate directly, among them genes metK, mtbK, fdnG and wzb that might detoxify/degrade the glyphosate. However, under 110-NPG condition, NRS-1 might have utilized economical and efficient ways by depressing its metabolism and activity to pass through this stress. Hence, the present study provides insights into the genes involved in glyphosate tolerance, which can be effectively utilized to engineer herbicide-resistant crop varieties after their proper validation to manage weed growth.

Expression, purification and function of cysteine desulfurase from Sulfobacillus acidophilus TPY isolated from deep-sea hydrothermal vent

The cysteine desulfurase (SufS) gene of Sulfobacillus acidophilus TPY, a Gram-positive bacterium isolated from deep-sea hydrothermal vent, was cloned and over-expressed in E. coli BL21. The recombinant SufS protein was purified by one-step affinity chromatography. The TPY SufS contained a well conserved motif RXGHHCA as found in that of other microorganisms, suggesting that it belonged to group II of cysteine desulfurase family. The recombinant TPY SufS could catalyze the conversion of l-cysteine to l-alanine and produce persulfide, and the enzyme activity was 95 μ/μL of sulfur ion per minute. The growth of E. coli BL21 was promoted by over-expressing TPY SufS in vivo or by directly adding recombinant TPY SufS in the medium (4.3-4.5 × 10⁸ cells/mL vs. 3.2-3.5 × 10⁸ cells/mL). Furthermore, the highest cell density of E. coli BL21 when the TPY SufS was over-expressed was about 3.5 times that of the control groups in the presence of sodium thiosulfate. These results indicate that the SUF system as the only assembly system of iron-sulfur clusters not only has significant roles in survival of S. acidophilus TPY, but also might be important for combating with high content of sulfide.

A simple semi-quantitative in vivo method using H₂S detection to monitor sulfide metabolizing enzymes

Here we present a simple in vivo microtiter plate assay using lead acetate [Pb(OAc)2]-soaked filter paper to detect H2S released by Escherichia coli metabolizing cysteine. The released H2S precipitates as brown lead sulfide (PbS) on Pb(OAc)2 soaked filter paper. The PbS stain quantitated by ImageJ software is proportional to the amount of H2S released from the culture. Expression of recombinant Acidithiobacillus ferrooxidans sulfide:quinone oxidoreductase (SQR) converts the H2S to sulfur, resulting in less PbS formation. The in vivo H2S oxidation activity of SQR was calculated based on the density of the PbS stain formed by E. coli expressing SQR compared with cells harboring the empty vector pLM1. The results are consistent with the in vitro activity of SQR measured by decylubiquinone (DUQ) reduction. This assay can be applied to sulfide metabolizing enzymatic studies, mutant screening and high-throughput inhibitor screens.

Characterization of iron-sulfur cluster assembly protein IscA from Acidithiobacillus ferrooxidans

IscA is a key member of the iron-sulfur cluster assembly machinery found in bacteria and eukaryotes, but the mechanism of its function in the biogenesis of iron-sulfur cluster remains elusive. In this paper, we demonstrate that Acidithiobacillus ferrooxidans IscA is a [4Fe-4S] cluster binding protein, and it can bind iron in the presence of DTT with an apparent iron association constant of 4·10(20) M(-1). The iron binding in IscA can be promoted by oxygen through oxidizing ferrous iron to ferric iron. Furthermore, we show that the iron bound form of IscA can be converted to iron-sulfur cluster bound form in the presence of IscS and L-cysteine in vitro. Substitution of the invariant cysteine residues Cys35, Cys99, or Cys101 in IscA abolishes the iron binding activity of the protein; the IscA mutants that fail to bind iron are unable to assemble the iron-sulfur clusters. Further studies indicate that the iron-loaded IscA could act as an iron donor for the assembly of iron-sulfur clusters in the scaffold protein IscU in vitro. Taken together, these findings suggest that A. ferrooxidans IscA is not only an iron-sulfur protein, but also an iron binding protein that can act as an iron donor for biogenesis of iron-sulfur clusters.

Expression, purification, and characterization of an iron chaperon protein CyaY from Acidithiobacillus ferrooxidans

CyaY is the bacterial homolog of frataxin, proposed to be involved in the assembly of iron-sulfur clusters. While, the physiological iron donor for the iron-sulfur clusters assembly remains controversial. In this study, the gene of CyaY from Acidithiobacillus ferrooxidans was cloned and expressed in Escherichia coli, the protein was purified by one-step affinity chromatography to homogeneity. The CyaY protein can bind ferric iron and serve as an iron donor for the biogenesis of iron-sulfur clusters on the scaffold protein IscU in the presence of IscS and L-cysteine in vitro.