Physiological changes of microalga Dunaliella parva under the treatment of PEG, CaCl2.

Carotenoids are antioxidants, which reduce various chronic diseases of human, and have many industrial applications. The halophilic Dunaliella parva (D. parva) is rich in carotenoids. The compounds CaCl2 and PEG are the popular metabolic enhancers. To further enhance carotenogenesis, D. parva was treated with two compounds polyethylene glycol (PEG) and CaCl2. Application of CaCl2 and PEG enhanced the carotenoids contents and the antioxidant activities of carotenoids compared to control group (no treatment of CaCl2 or PEG). The highest carotenoids contents were obtained by treating D. parva with 40 ppm CaCl2 (3.11 mg/g dry weight, DW) and 80 ppm PEG (2.78 mg/g DW) compared with control group (1.96 mg/g DW). When D. parva was treated with 40 ppm CaCl2 and 80 ppm PEG, protein contents reached the highest values (90.28 mg/g DW and 89.57 mg/g DW) compared to that of control group (73.42 mg/g DW). The antioxidant activities of carotenoids samples were determined. Generally, the antioxidant activities of carotenoids from D. parva treated with PEG and CaCl2 were superior to that of control group. The antioxidant activities of carotenoids mainly contained reducing power, hydroxyl radical scavenging activity and superoxide radical scavenging activity. The reducing powers of carotenoids extracts from 20 ppm CaCl2 group (2.07%/mg carotenoids) and 120 ppm PEG group (1.59%/mg carotenoids) were significantly higher than that of control group (<1.25%/mg carotenoids). The superoxide radical scavenging activities of carotenoids extracts from 40 ppm CaCl2 group (70.33%/mg carotenoids) and 80 ppm PEG group (65.94%/mg carotenoids) were significantly higher than that of control group (<55%/mg carotenoids). This paper laid a foundation for massive accumulation of carotenoids in microalga D. parva.

Identification of differentially expressed genes for Pseudomonas sp. Cr13 stimulated by hexavalent chromium.

Over exploitation of mineral resources has increasingly caused serious heavy metal contamination such as chromium (Cr). Cr(VI), the pathogenicity factor, is one of common environmental contaminants and widely known health hazards to living organisms. Therefore, it is urgent to control the polluted soil. Up to now, little is known about the regulatory mechanisms of Cr response in Pseudomonas sp. Cr13. In this study, transcriptome and differentially expressed genes in Pseudomonas sp. Cr13 strain was characterized by a comparison between Cr(VI)-treated sample and control sample using transcriptome sequencing approach. In total, 2974 genes were annotated, including 1245 (1154 down-regulated genes and 91 up-regulated genes) differentially expressed genes (DEGs). All DEGs could be assigned to 29 pathways, of which pathways related to amino acid metabolism, carbohydrate metabolism, energy metabolism and signal transduction mechanism were significantly enriched in Pseudomonas sp. Cr13. A possible mechanism for Cr toxicity response might be an active efflux which utilized a heavy metal translocating P-type ATPase to lower the intracellular Cr concentration. The down-regulated genes related to the antioxidant defense system had a key role in Cr reduction, such as SodA, Gst, osmC, BtuE, KatE, csdA and AhpC. The proteins that were visibly up-regulated, were likely to involve in alleviating Cr(VI) stress, and the significantly down-regulated genes such as MarR, Lrp, FhlA, GntR, HrcA, LysR family genes, were likely to reduce Cr(VI) induced oxidative stress. In addition, real-time quantitative PCR was used to analyze the expression patterns of some Cr responsive genes. This study reported the first identification of Cr responsive genes, and inferred the underlying regulatory mechanisms of response to Cr(VI) stress in Pseudomonas sp. Cr13.

Cloning and Characterization of phzR Gene from Pseudomonas aeruginosa.

A gene encoding phzR was isolated from a phenazine-producing bacterium Pseudomonas aeruginosa 2016NX1. This paper provided the full-length cDNA encoding phzR (GenBank Accession no., MW143078). The cDNA of the phzR contained an open reading frame (ORF) of 714 bp. The potential regulatory elements were predicted in the phzR promoter region. The deduced amino acid sequence of P. aeruginosa phzR showed significant homology to the known phzRs from different organisms. Gene overexpression analysis showed that the phenazine content was improved (44.39%) in comparison to wild-type 2016NX1.

Optimization of Growth Conditions of Acinetobacter sp. Cr1 for Removal of Heavy Metal Cr Using Central Composite Design.

Growth conditions can significantly affect the removal efficiency of heavy metals by microorganisms. The goal of this study was enhancing the removal efficiency of Cr(VI) and improving the application of Acinetobacter sp. Cr1 (GenBank accession number of 16S rDNA sequence, MN900681). This study focused on pH, Cr(VI) concentration and culture time, which were the major influence factors for removal efficiency of Cr(VI). A central composite design was employed to optimize the removal efficiency by optimizing three variables. The optimum growth conditions were as: pH of 9.52, Cr(VI) concentration of 128.55 mg l-1, culture time of 43.30 h, and the predicted and actual maxima were 65.13% and 67.26%, respectively. Therefore, it is suggested that the strain Acinetobacter sp. Cr1 had a promising potential to be used for bioremediation of Cr(VI).