Functional analysis of a chromosomal arsenic resistance operon in Pseudomonas fluorescens strain MSP3

The Effects of Paddy Cultivation and Microbiota Members on Arsenic Accumulation in Rice Grain

Access to safe food is one of the most important issues. In this context, rice plays a prominent role. Because high levels of arsenic in rice grain are a potential concern for human health, in this study, we determined the amounts of arsenic in water and soil used in the rice development stage, changes in the arsC and mcrA genes using qRT-PCR, and the abundance and diversity (with metabarcoding) of the dominant microbiota. When the rice grain and husk samples were evaluated in terms of arsenic accumulation, the highest values (1.62 ppm) were obtained from areas where groundwater was used as irrigation water, whereas the lowest values (0.21 ppm) occurred in samples from the stream. It was observed that the abundance of the Comamonadaceae family and Limnohabitans genus members was at the highest level in groundwater during grain formation. As rice development progressed, arsenic accumulated in the roots, shoots, and rice grain. Although the highest arsC values were reached in the field where groundwater was used, methane production increased in areas where surface water sources were used. In order to provide arsenic-free rice consumption, the preferred soil, water source, microbiota members, rice type, and anthropogenic inputs for use on agricultural land should be evaluated rigorously.

The potential of Pseudomonas for bioremediation of oxyanions

Non-metal, metal and metalloid oxyanions occur naturally in minerals and rocks of the Earth's crust and are mostly found in low concentrations or confined in specific regions of the planet. However, anthropogenic activities including urban development, mining, agriculture, industrial activities and new technologies have increased the release of oxyanions to the environment, which threatens the sustainability of natural ecosystems, in turn affecting human development. For these reasons, the implementation of new methods that could allow not only the remediation of oxyanion contaminants but also the recovery of valuable elements from oxyanions of the environment is imperative. From this perspective, the use of microorganisms emerges as a strategy complementary to physical, mechanical and chemical methods. In this review, we discuss the opportunities that the Pseudomonas genus offers for the bioremediation of oxyanions, which is derived from its specialized central metabolism and the high number of oxidoreductases present in the genomes of these bacteria. Finally, we review the current knowledge on the transport and metabolism of specific oxyanions in Pseudomonas species. We consider that the Pseudomonas genus is an excellent starting point for the development of biotechnological approaches for the upcycling of oxyanions into added-value metal and metalloid byproducts.

Characterization, real-time quantification and in silico modeling of arsenate reductase (arsC) genes in arsenic-resistant Herbaspirillum sp. GW103

This study investigated the mechanism of arsenic resistance in the diazotrophic bacterium Herbaspirillum sp. GW103 isolated from rhizosphere soil of Phragmites austrails. The isolate Herbaspirillum sp. GW103 exhibited maximum tolerance to arsenic (550 mg/L). Four different arsenate reductase (arsC) genes (arsC1, arsC2, arsC3 and arsC4) were located in the genome of the isolate Herbaspirillum sp. GW103. The expression pattern of the arsC1 differed from other genes. All four types of arsC genes had different protein secondary structures and stereochemical properties. Molecular modeling and structural analysis of arsC genes revealed close structural homology with arsC family proteins from Escherichia coli (PDB ID: 1I9D) and Pseudomonas aeruginosa (PDB ID: 1RW1).

A novel Escherichia coli solubility enhancer protein for fusion expression of aggregation-prone heterologous proteins

Through the proteome analysis of Escherichia coli BL21(DE3), we previously identified the stress-responsive protein, arsenate reductase (ArsC), that showed a high cytoplasmic solubility and a folding capacity even in the presence of stress-inducing reagents. In this study, we used ArsC as an N-terminal fusion partner to synthesize nine aggregation-prone proteins as water-soluble forms. As a result, solubility of the aggregation-prone proteins increased dramatically by the fusion of ArsC, due presumably to its tendency to facilitate the folding of target proteins. Also, we evaluated and confirmed the efficacy of ArsC-fusion expression in making the fusion-expressed target proteins have their own native function or structure. That is, the self-assembly function of human ferritin light chain, l-arginine-degrading function of arginine deiminase, and the correct secondary structure of human granulocyte colony stimulating factor were clearly observed through transmission electron microscope analysis, colorimetric enzyme activity assay, and circular dichroism, respectively. It is strongly suggested that ArsC can be in general an efficient fusion expression partner for the production of soluble and active heterologous proteins in E. coli.

Molecular cloning of cecropin B responsive endonucleases in Yersinia ruckeri

We have previously demonstrated that Yersinia ruckeri resists cecropin B in an inducible manner. In this study, we sought to identify the molecular changes responsible for the inducible cecropin B resistance of Y. ruckeri. Differences in gene expression associated with the inducible resistance were investigated. Cultures of Y. ruckeri were exposed to a sublethal concentration of cecropin B and resultant changes in the messenger RNA population of the bacteria were assayed using the differential display reverse transcription polymerase chain reaction (DD-RT-PCR). A single band was consistently increased in intensity in all repeats of the experiment. The band was excised, cloned, sequenced, and used to screen a Y. ruckeri genomic DNA library. The DD-RT-PCR fragment shared 100% identity to the cDNA sequence of an ATP-dependent endonuclease of the overcome lysogenization defect (OLD) family of Y. ruckeri 29473. The genomic clone that was recovered was not identical to the DD-RT-PCR clone, but harbored a gene for a secreted endonuclease 1 (nucM) homologue. It was determined that transcription of the gene was upregulated following exposure to cecropin B via RT-PCR. Furthermore, an increase in the nuclease activity of culture supernatants of Y. ruckeri following exposure to cecropin B was demonstrated. These findings demonstrate that cecropin B exposure increases the expression of at least two endonucleases in Y. ruckeri. The production and secretion of an endonuclease by Y. ruckeri in response to an antimicrobial peptide indicates the involvement of both intracellular and extracellular DNA in the toxic effects of cecropin B.

Construction of WCB-11: a novel phiYFP arsenic-resistant whole-cell biosensor

The prediction and assessment of environmental pollution by arsenic are important preconditions of advocating environmental protection and human health risk assessment. A yellow fluorescent protein-based whole-cell biosensor for the detection of arsenite and arsenate was constructed and tested. An arsenic-resistant promoter and the regulatory gene arsR were obtained by PCR from the genome of Escherichia coli DH5alpha, and phiYFP was introduced into E. coli DH5alpha as a reporter gene to construct an arsenic-resistant whole-cell biosensor (WCB-11) in which phiYFP was expressed well for the first time. Experimental results demonstrated that the biosensor has a good response to arsenic and the expression of phiYFP. When strain WCB-11 was exposed to As3+ and As5+, the expression of yellow fluorescence was time-dependent and dose-dependent. This engineered construct is expected to become established as an inexpensive and convenient method for the detection of arsenic in the field.

Pentavalent arsenate reductase activity in cytosolic fractions of Pseudomonas sp., isolated from arsenic-contaminated sites of Tezpur, Assam

Pentavalent arsenate reductase activity was localized and characterized in vitro in the cytosolic fraction of a newly isolated bacterial strain from arsenic-contaminated sites. The bacterium was gram negative, rod-shaped, nonmotile, non-spore-forming, and noncapsulated, and the strain was identified as Pseudomonas sp. DRBS1 following biochemical and molecular approaches. The strain Pseudomonas sp. DRBS1 exhibited enzymatic machinery for reduction of arsenate(V) to arsenite(III). The suspended culture of the bacterium reduced more than 97% of As(V) (40-100 mM) to As(III) in 48 h. The growth rate and total cellular yield decreased in the presence of higher concentration of arsenate. The suspended culture repeatedly reduced 10 mM As(V) within 5 h up to five consecutive inputs. The cell-free extracts reduced 86% of 100 microM As(V) in 40 min. The specific activity of arsenate reductase enzyme in the presence of 100 microM arsenate is 6.68 micromol/min per milligram protein. The arsenate reductase activity is maximum at 30 degrees C and at pH 5.2. The arsenate reductase activity increased in the presence of electron donors like citrate, glucose, and galactose and metal ions like Cd(+2), Cu(+2), Ca(+2), and Fe(+2). Selenate as an electron donor also supports the growth of strain DRBS1 and significantly increased the arsenate reduction.