Ling Jiang

Investigating the Influence of MoS2 Nanosheets on E. coli from Metabolomics Level

Molybdenum disulfide, a type of two-dimensional layered material with unique properties, has been widely used in many fields. However, an exact understanding of its toxicity remains elusive, let alone its effects on the environmental microbial community. In this study, we utilized metabolomics technology to explore the effects of different concentrations of molybdenum disulfide nanosheets on Escherichia coli for the first time. The results showed that with increasing concentration of molybdenum disulfide nanosheets, the survival rate of Escherichia coli was decreased and the release of lactic dehydrogenase was increased. At the same time, intracellular concentrations of reactive oxygen species were dramatically increased. In addition, metabolomics analysis showed that high concentrations of molybdenum disulfide nanosheets (100, 1000 μg/mL) could significantly affect the metabolic profile of Escherichia coli, including glycine, serine and threonine metabolism, protein biosynthesis, urea cycle and pyruvate metabolism. These results will be beneficial for molybdenum disulfide toxicity assessment and further applications.

The Role of Lipid Droplets in Mortierella alpina Aging Revealed by Integrative Subcellular and Whole-Cell Proteome Analysis

Lipid droplets (LDs) participate in many cellular processes in oleaginous microorganisms. However, the exact function of LDs in the Mortierella alpina aging process remains elusive. Herein, subcellular proteomics was employed to unveil the composition and dynamics of the LD proteome in the aging M. alpina for the first time. More than 400 proteins were detected in LDs and 62 of them changed expression significantly during aging. By combining the LD proteomic data with whole-cell data, we found that the carbohydrate metabolism and de novo lipid biosynthesis were all inhibited during aging of M. alpina mycelia. The up-regulation of fructose metabolism-related enzymes in LDs might imply that LDs facilitated the fructose metabolism, which in turn might cause pyruvate to accumulate and enter malate-pyruvate cycle, and ultimately, provide additional NADPH for the synthesis of arachidonic acid (ARA). Lysophospholipase and lecithinase were up-regulated in LDs during the aging process, suggesting that the phospholipids and lecithin were starting to be hydrolyzed, in order to release fatty acids for the cells. The impairment of the anti-oxidant system might lead to the accumulation of ROS and consequently cause the up-regulation of autophagy-related proteins in LDs, which further induces the M. alpina mycelia to activate the autophagy process.

Development of a cooperative two-factor adaptive-evolution method to enhance lipid production and prevent lipid peroxidation in Schizochytrium sp.

BackgroundSchizochytrium sp. is a marine microalga with great potential as a promising sustainable source of lipids rich in docosahexaenoic acid (DHA). This organism’s lipid accumulation machinery can be induced by various stress conditions, but this stress induction usually comes at the expense of lower biomass in industrial fermentations. Moreover, oxidative damage induced by various environmental stresses can result in the peroxidation of lipids, and especially polyunsaturated fatty acids, which causes unstable DHA production, but is often ignored in fermentation processes. Therefore, it is urgent to develop new production strains that not only have a high DHA production capacity, but also possess strong antioxidant defenses.ResultsAdaptive laboratory evolution (ALE) is an effective method for the development of beneficial phenotypes in industrial microorganisms. Here, a novel cooperative two-factor ALE strategy based on concomitant low temperature and high salinity was applied to improve the production capacity of Schizochytrium sp. Low-temperature conditions were used to improve the DHA content, and high salinity was applied to stimulate lipid accumulation and enhance the antioxidative defense systems of Schizochytrium sp. After 30 adaptation cycles, a maximal cell dry weight of 126.4xa0g/L and DHA yield of 38.12xa0g/L were obtained in the endpoint strain ALE-TF30, which was 27.42 and 57.52% higher than parental strain, respectively. Moreover, the fact that ALE-TF30 had the lowest concentrations of reactive oxygen species and malondialdehyde among all strains indicated that lipid peroxidation was greatly suppressed by the evolutionary process. Accordingly, the ALE-TF30 strain exhibited an overall increase of gene expression levels of antioxidant enzymes and polyketide synthases compared to the parental strain.ConclusionThis study provides important clues on how to overcome the negative effects of lipid peroxidation on DHA production in Schizochytrium sp. Taken together, the cooperative two-factor ALE process can not only increase the accumulation of lipids rich in DHA, but also prevent the loss of produced lipid caused by lipid peroxidation. The strategy proposed here may provide a new and alternative direction for the industrial cultivation of oil-producing microalgae.

Effects of dispersible MoS 2 nanosheets and Nano-silver coexistence on the metabolome of yeast

As a new rising star in the post-graphene two-dimensional materials (2DMs), molybdenum disulfide (MoS2) attracts increasing attentions and is widely applied. However, the chemical and toxicological interaction between MoS2 and other co-contaminants is still poorly understood. Nano-silver (N-Ag) is the most commonly used nanomaterial in commercial products and distributed widely in the environment. Herein, we investigated the effects of chitosan functionalized MoS2 (CS-MoS2) nanosheets, a water-dispersible form of MoS2, on the microbial toxicity of N-Ag. We found that the incorporation of CS-MoS2 nanosheets attenuated the oxidative stress induced by N-Ag on yeast cells, while caused more membrane stress. In addition, the inhibition of N-Ag on the metabolic activities of yeast cells could be attenuated by CS-MoS2 nanosheets as well. The coexistence of N-Ag and CS-MoS2 nanosheets mainly perturbed the amino acid-related metabolic pathways in yeast cells, and phosphoric acid was a potential nanotoxicity biomarker. We further found that CS-MoS2 nanosheets dramatically absorbed the Ag ion released from N-Ag, which might be responsible for its attenuation effect on the microbial toxicity of N-Ag. Our findings provide more new insights for the ecotoxicity evaluation of MoS2 and other 2DMs.

Effect of Bulk MoS2 on the Metabolic Profile of Yeast.

MoS2, a kind of two-dimensional material with unique performances, has been widely used in many fields. However, an in-depth understanding of its toxicity is still needed, let alone its effects on the environmental microorganism. Herein, we used different methods, including metabolomics technology, to investigate the influence of bulk MoS2 (BMS) on yeast cells. The results indicated that high concentrations (1 mg/L and more) of BMS could destroy cell membrane and induce ROS accumulation. When exposed to a low concentration of BMS (0.1 mg/L), the intracellular concentrations of many metabolites (e.g., fumaric acid, lysine) increased. However, most of their concentrations descended significantly as the yeast cells were treated with BMS of high concentrations (1 mg/L and more). Metabolomics analysis further revealed that exposure to high concentrations of BMS could significantly affect some metabolic pathways such as amino acid and citrate cycle related metabolism. These findings will be beneficial for MoS2 toxicity assessment and further applications.

How nitrogen sources influence Mortierella alpina aging: From the lipid droplet proteome to the whole-cell proteome and metabolome

Arachidonic acid (ARA) is a valuable polyunsaturated fatty acid produced by Mortierella alpina. Although some strategies such as nitrogen supplementation have shown the potential to affect the aging of M. alpina in ways which enable it to produce more ARA, the underlying mechanism remains elusive. Herein, we conducted a systematical analysis of the lipid droplet proteome, as well as the whole-cell proteome and metabolome, in order to elucidate how and why two different nitrogen sources (KNO3 and urea) affect the aging of M. alpina and the corresponding ARA concentration. We found that KNO3 promoted the ARA concentration, while urea accelerated lipid consumption and stimulated the decomposition of mycelia. Although both KNO3 and urea activated carbohydrate metabolic pathways, KNO3 exerted a stronger promoting effect on the pentose phosphate pathway and induced the lipid droplets to participate in the citrate-pyruvate cycle. The activities of malic enzyme and isocitrate dehydrogenase were also promoted more by KNO3. These pathways provided additional substrates and reducing power for ARA synthesis and ROS elimination. Accordingly, since urea showed a weaker promotion of the related pathways, it caused a depression of the antioxidant system and a consequent increase of ROS. These findings facilitate the design of nitrogen supplementation strategies to achieve higher ARA concentrations, and provide guidance for deciphering the mechanisms of similar aging phenomena in other oleaginous microorganisms.nnnSIGNIFICANCEnPolyunsaturated fatty acids such as arachidonic acid (ARA) are valuable nutrients, which play important roles in preventing numerous diseases and facilitating development. Although it has been found for years that ARA production will be increased in the aging process of Mortierella alpina (M. alpina) and nitrogen sources are involved in this process, the underlying mechanism for this phenomenon remains unknown. In this work, we used the subcellular proteomics, whole-cell proteomics and metabolomics methods to explore the mechanisms by which two different nitrogen (KNO3 and urea) affected the aging process of M. alpina. Finally, we gave some new insights for the mechanisms mentioned above. This finding will fuel the technology developments for the ARA production using microbes.

A Simple α-Ketoglutarate Electrochemical Biosensor Based on Reduced MoS2 Nanoparticle-Gold Nanoparticle Nanocomposite

Convenient and sensitive methods for the detection of α-ketoglutarate (α-KG) will be beneficial for biomedical diagnosis and microbial fermentation industry. In this work, reduced MoS2 nanoparticles (rMNs) were prepared by ultrasonication and electrochemical reduction. The rMNs were then decorated with gold nanoparticles (Aunano) to fabricate rMNs-Aunano nanocomposite. The glass carbon electrode modified with rMNs-Aunano nanocomposite (rMNs-Aunano-GCE) showed excellent electro-catalytic oxidation toward NADH with a satisfied reproducibility and exhibited linear response in the range of 38.46-214.29 μM. Moreover, the L-Glutamic dehydrogenase modified rMNs-Aunano-GCE exhibited a sensitive and fast response to α-KG, with a linear response range of 11.12-52.94 μM and a detection limit of 6.25 μM. These findings will pave ways for the α-KG detection and the application of MoS2 or other two-dimensional materials in electrochemical sensing.

An electrochemical biosensor for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles

AbstractWe present a novel simple strategy for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles. First, gold nanoparticles were chemically adsorbed onto the surface of a thiol-modified gold electrode. Subsequently, the substrate DNA1 was adsorbed onto the surfaces of the gold nanoparticles via thiol–gold bonds, so that the complementary guanine-rich DNA2 could be hybridized to the gold electrode in sequence. [Ru(NH3)6]3+ (RuHex), which can be electrostatically adsorbed onto the anionic phosphate of DNA, served as an electrochemical probe. The presence of Pb2+ can induce DNA2 to form a stable G-quadruplex and fall off the gold electrode. The amount of RuHex remaining on the electrode surface was determined by electrochemical chronocoulometry (CC). The prepared biosensor showed high sensitivity for Pb2+ with a linear range with respect to ln(cPb2+) from 0.01 to 200xa0nM and a low detection limit of 0.0042xa0nM under optimal conditions. Because of the high selectivity of the Pb2+-specific DNA2, the designed biosensor also showed low false-positive signal rates with other metal ions in real-world examples. Therefore, this strategy has the potential for practical application in environmental monitoring.n Graphical abstractᅟ