Response Surfaces Method and Artificial Intelligence Approaches for Modeling the Effects of Environmental Factors on Chlorophyll a in Isochrysis galbana.

This study reported the condition optimization for chlorophyll a (Chl a) from the microalga Isochrysis galbana. The key parameters affecting the Chl a content of I. galbana were determined by a single-factor optimization experiment. Then the individual and interaction of three factors, including salinity, pH and nitrogen concentration, was optimized by using the method of Box-Benhnken Design. The highest Chl a content (0.51 mg/L) was obtained under the optimum conditions of salinity 30‱ and nitrogen concentration of 72.1 mg/L at pH 8.0. The estimation models of Chl a content based on the response surfaces method (RSM) and three different artificial intelligence models of artificial neural network (ANN), support vector machine (SVM) and radial basis function neural network (RBFNN), were established, respectively. The fitting model was evaluated by using statistical analysis parameters. The high accuracy of prediction was achieved on the ANN, SVM and RBFNN models with correlation coefficients (R2) of 0.9113, 0.9127, and 0.9185, respectively. The performance of these artificial intelligence models depicted better prediction capability than the RSM model for anticipating all the responses. Further experimental results suggested that the proposed SVM and RBFNN model are efficient techniques for accurately fitting the Chl a content of I. galbana and will be helpful in validating future experimental work on the Chl a content by computational intelligence approach.

The Growth Inhibition of Polyethylene Nanoplastics on the Bait-Microalgae Isochrysis galbana Based on the Transcriptome Analysis.

The adverse effects of microplastics on microalgae species have been extensively studied, but their impact on the bait microalgae entering the food chain has not been well understood. This study investigated the cytological and physiological response of Isochrysis galbana to polyethylene microplastics (PE-MPs, 10 µm) and nanoplastics (PE-NPs, 50 nm). The results showed that PE-MPs had no significant impact on I. galbana, while PsE-NPs obviously inhibited cell growth, reduced chlorophyll content, and caused a decline in carotenoids and soluble protein. These changes in the quality of I. galbana could negatively affect its use as aquaculture feed. To understand the molecular response mechanism of I. galbana to PE-NPs, transcriptome sequencing was performed. The result revealed that the TCA cycle, purine metabolism, and some key amino acid syntheses were down-regulated by PE-NPs, while the Calvin cycle and fatty acid metabolism were up-regulated to tolerate PE-NP pressure. Microbial analysis showed that the bacterial community structure associated with I. galbana was significantly altered at the species level by PE-NPs. In conclusion, this study provides new insights into the physiological stress response caused by microplastic pollution based on transcriptome and bacterial community analysis. The findings highlight the need to mitigate the release of microplastics into the environment to prevent their harmful effects on aquatic ecosystems and will be helpful in understanding the impact of polyethylene nanoplastics on the bait microalgae.

Efficient removal of hexavalent chromium from water by Bacillus sp. Y2-7 with production of extracellular polymeric substances.

Bioremediation is an environmentally friendly technology for the treatment of chromium-contaminated sites. Here, a hexavalent chromium [Cr(VI)]-resistant strain was isolated from oil-contaminated soil and designated as Bacillus sp. Y2-7 based on 16S rDNA sequence characterization. The effects of various factors including inoculation dose, pH value, glucose concentration, and temperature on Cr(VI) removal rates were then evaluated. Based on the response surface methodology, optimal Cr(VI) removal efficiency (above 90%) could be achieved at an initial Cr(VI) concentration of 155.0 mg·L-1, glucose concentration of 11.479 g·L-1, and pH of 7.1. The potential removal mechanisms of Cr(VI) by strain Y2-7 were also supposed. The contents of polysaccharide and protein in extracellular polymer (EPS) of strain Y2-7 decreased slowly after cultured with Cr(VI) of 15 mg·L-1 from 1 to 7 days. We thus inferred that EPS bonded with Cr(VI) and underwent morphological changes in water. Molecular operating environment (MOE) analysis suggested that macromolecular protein complexes in Bacillus sp. Y2-7 and hexavalent chromium could establish hydrogen bonds. Collectively, our findings indicate that Bacillus sp. Y2-7 is an excellent bacterial candidate for chromium bioremediation.

Bioaugmentation enhance the bioremediation of marine crude oil pollution: Microbial communities and metabolic pathways.

Bioaugmentation is an effective strategy used to speed up the bioremediation of marine oil spills. In the present study, a highly efficient petroleum degrading bacterium (Pseudomonas aeruginosa ZS1) was applied to the bioremediation of simulated crude oil pollution in different sampling sites in the South China Sea. The metabolic pathways of ZS1 to degrade crude oil, the temporal dynamics of the microbial community response to crude oil contamination, and the biofortification process were investigated. The results showed that the abundance and diversity of the microbial community decreased sharply after the occurrence of crude oil contamination. The best degradation rate of crude oil, which was achieved in the samples from the sampling site N3 after the addition of ZS1 bacteria, was 50.94% at 50 days. C13 alkanes were totally oxidized by ZS1 in the 50 days. The degradation rate of solid n-alkanes (C18-C20) was about 70%. Based on the whole genome sequencing and the metabolites analysis of ZS1, we found that ZS1 degraded n-alkanes through the terminal oxidation pathway and aromatic compounds through the catechol pathway. This study provides data support for further research on biodegradation pathways of crude oil and contributes to the subsequent development of more reasonable bioremediation strategies.

Responses and tolerance mechanisms of microalgae to heavy metal stress: A review.

Microalgae, the primary producers in water ecosystems, are the main food of fish and shrimp. Microalgae have a great capacity to absorb heavy metals, and low concentrations of heavy metals can promote the growth of them. But high concentrations have a strong influence on the physiological and biochemical processes in algae, such as growth, photosynthesis, cell ultrastructure, protein content and fatty acid composition. Heavy metals may also induce the formation of reactive oxygen species (ROS), which causes the oxidation damage of protein, lipid and thiol peptides, and activates the antioxidant system. Heavy metals can be removed or converted into another state by biosorption of cell surface, accumulation in cells, combining with antioxidant enzymes and so on. This review summarized the responses of microalgae to heavy metals and comprehensively described the removal and tolerance mechanisms by extracellular adsorption and intracellular accumulation, which are helpful to treat pollution and improve the culture of microalgae.

Impact of Petroleum Contamination on the Structure of Saline Soil Bacterial Communities.

Petroleum contamination may lead to variations in soil microbial community structure and activities. The bioremediation of petroleum-contaminated soil typically depends on the characteristics and activities of oil-degrading microorganisms, which can be introduced or be part of the native soil microbiota. Thus, analyzing the structure of the microbial community and internal relationships in the bioremediation process is critical. Our study characterized the physical and chemical properties, microbial community structure, and microbial diversity of surface soil collected near an oilfield. The total carbon (TC), total organic carbon (TOC), and microbial diversity in oil-contaminated soil was found higher than in uncontaminated samples. Proteobacteria abundance was inhibited with oil pollution, while Actinomycetes abundance was enhanced. Some indigenous hydrocarbon-degrading bactera were enriched by oil pollution, such as Bacillus, Actinomarinales norank, Balneolaceae uncultured, Marinobacter, and Pseudomonas. Furthermore, Rokubacteria, Nitrospirae, and Entotheonellaeota were significant differences in the contaminated group. There were 16 genera with significant differences in the polluted group, such as Woeseia, Pelagibius, Pontibacillus, IS_44, Aliifodinibius, while Halothiobacillus, Algoriphagus, Novosphingobium, etc. had significant differences in the uncontaminated group. Redundancy analysis demonstrated that the responses of the microorganisms to the evaluated environmental factors were different, and TC was the most important driver of microbial community variation. Moreover, TOC was the largest contributor to operational taxonomic unit (OTU) and Chao index variations. Our results provide a theoretical basis for the enhancement of microbial activity in oil-contaminated soil, which might improve bioremediation efficacy.

Petroleum spill bioremediation by an indigenous constructed bacterial consortium in marine environments.

In the process of marine oil spill remediation, adding highly efficient oil degrading microorganisms can effectively promote oil degradation. However, in practice, the effect is far less than expected due to the inadaptability of microorganisms to the environment and their disadvantage in the competition with indigenous bacteria for nutrients. In this article, four strains of oil degrading bacteria were isolated from seawater in Jiaozhou Bay, China, where a crude oil pipeline explosion occurred seven years ago. Results of high-throughput sequencing, diesel degradation tests and surface activity tests indicated that Peseudomonas aeruginosa ZS1 was a highly efficient petroleum degrading bacterium with the ability to produce surface active substances. A diesel oil-degrading bacterial consortium (named SA) was constructed by ZS1 and another oil degrading bacteria by diesel degradation test. Degradation products analysis indicated that SA has a good ability to degrade short chain alkanes, especially n-alkanes (C10-C18). Community structure analysis showed that OTUs of Alcanivorax, Peseudomona, Ruegeria, Pseudophaeobacter, Hyphomonas and Thalassospira on genus level increased after the oil spill and remained stable throughout the recovery period. Most of these enriched microorganisms were related to known alkane and hydrocarbon degraders by the previous study. However, it is the first time to report that Pseudophaeobacter was enriched by using diesel as the sole carbon source. The results also indicated that ZS1 may have a dominant position in competition with indigenous bacteria. Oil pollution has an obvious selective effect on marine microorganisms. Although the oil degradation was promoted after SA injection, the recovery of microbial community structure took a longer time.

Response and tolerance ability of Chlorella vulgaris to cadmium pollution stress.

Cadmium, which is widely used in electroplating industry, chemical industry, electronic industry and nuclear industry, is harmful to human health and ecological environment. The effects of Cd at different initial concentrations on biomass, antioxidant enzyme activity and ultrastructure of Chlorella vulgaris were analysed in the present study. The results showed that C. vulgaris maintained a slow-growth trend at 3.0 mg/L Cd, and the peroxidase (POD) enzyme activity reached the highest at this concentration, which indicated that C. vulgaris could resist the oxidative damage of cells by increasing the enzyme activity, so as to improve the tolerance of C. vulgaris to Cd. When the concentration of Cd was 5.0 mg/L, although the activity of the superoxide dismutase enzyme was still very high, POD enzyme could not remove the hydrogen peroxide produced in cells in time, leading to cell damage and even death. Therefore, when the concentration reached 5.0 mg/L, the growth of C. vulgaris began to decline after four days of stress, and the cell structure was significantly damaged after six days of stress. And the higher concentration of Cd caused more Cd accumulation in cells and a serious damage to C. vulgaris. C. vulgaris can be used as an early warning indicator of Cd pollution, and it can be used for bioremediation of Cd contaminated water through tolerant subculture.

Expression and Characterization of a Novel Cold-Adapted Chitosanase from Marine Renibacterium sp. Suitable for Chitooligosaccharides Preparation.

(1) Background: Chitooligosaccharides (COS) have numerous applications due to their excellent properties. Chitosan hydrolysis using chitosanases has been proposed as an advisable method for COS preparation. Although many chitosanases from various sources have been identified, the cold-adapted ones with high stability are still rather rare but required. (2) Methods: A novel chitosanase named CsnY from marine bacterium Renibacterium sp. Y82 was expressed in Escherichia coli, following sequence analysis. Then, the characterizations of recombinant CsnY purified through Ni-NTA affinity chromatography were conducted, including effects of pH and temperature, effects of metal ions and chemicals, and final product analysis. (3) Results: The GH46 family chitosanase CsnY possessed promising thermostability at broad temperature range (0-50 °C), and with optimal activity at 40 °C and pH 6.0, especially showing relatively high activity (over 80% of its maximum activity) at low temperatures (20-30 °C), which demonstrated the cold-adapted property. Common metal ions or chemicals had no obvious effect on CsnY except Mn2+ and Co2+. Finally, CsnY was determined to be an endo-type chitosanase generating chitodisaccharides and -trisaccharides as main products, whose total concentration reached 56.74 mM within 2 h against 2% (w/v) initial chitosan substrate. (4) Conclusions: The results suggest the cold-adapted CsnY with favorable stability has desirable potential for the industrial production of COS.

Adsorption of chromium by functionalized metal organic frameworks from aqueous solution.

Based on Cu-BTC metal-organic framework, thiol-functionalized and amino functionalized materials were prepared by the modified Stöber method. Then, the Cu3(BTC)2 and the functionalized materials were characterized by means of X-ray diffraction, SEM-EDS and FT-IR analysis. The adsorption properties of two materials for Cr(VI) were investigated. Both functionalized materials show good adsorption under acidic conditions. Through adsorption model analysis, the adsorption of Cr(VI) by the two materials were more in line with the pseudo-second-order kinetic equation. The adsorption capacities of Langmuir isothermal fitting were 15.17 mg g-1 and 7.17 mg g-1, respectively. During the adsorption process, the functionalized material does not swell and is insoluble in water. After five adsorption-desorption cycles, the adsorption capacity is basically constant and the material can be reused. The results show that the above two functionalized MOFs have good application prospects in the adsorption and removal of heavy metal Cr(VI) in aqueous solution.

Extracellular adsorption, intracellular accumulation and tolerance mechanisms of Cyclotella sp. to Cr(VI) stress.

Heavy metals have caused widespread concern due to their adverse effects on aquatic organisms. However, there are few studies on their tolerance mechanism. In this study, the tolerance mechanisms of Cyclotella sp. to Cr(VI) were explored. The increase of antioxidant enzymes activity acting as a defense mechanism could help Cyclotella sp. to reduce the oxidative damage caused by the heavy metal Cr(VI). Cr(VI) was also combined with the functional groups on the cell surface to detoxify and was transported into the cell by binding to the carrier protein. In addition, it is worth noting that the molecular docking simulation showed that Cr(VI) combined with macromolecular compounds in cells through hydrogen and ionic bonds, which can reduce the toxicity of chromium. The determination of chromium content in cells showed that chromium was accumulated in cells. Furthermore, the low concentration of Cr(VI) had a growth stimulation on Cyclotella sp., while the growth of Cyclotella sp. microalgae was obvious inhibited when Cr(VI) concentration was over 0.5 mg/L. The content of Chlorophyll a (Chl-a) and soluble protein both had a dramatic change under the stress of Cr(VI). Cell ultrastructure analysis showed that plasmolysis phenomenon and dissolution of organelle structures when Cyclotella sp. was exposed to Cr(VI). The series of changes in Cyclotella sp. allow it to be an indicator of Cr(VI) pollution in water. Meanwhile, these findings were helpful to further understand the tolerance mechanism of Cr(VI) on microalgae and provide new insights to assess Cr(VI) toxicity to the microalgae.

Physiological and morphological responses and tolerance mechanisms of Isochrysis galbana to Cr(VI) stress.

The effects of the initial concentrations of Cr(VI) on chlorophyll-a (Chl-a), soluble protein and ultrastructure were investigated. Results showed that <0.5 and >1.0 mg L-1 Cr(VI) stimulated and inhibited the growth of Isochrysis galbana, respectively. The tolerance mechanisms of I. galbana to Cr(VI) included the following: (1) increased activities of superoxide dismutase (SOD) and peroxidase (POX) for peroxidative damage resistance, (2) accumulation of Cr(VI) on the cell surface and inside the cell for detoxification and (3) conversion of intracellular Cr(VI) to less toxic Cr(III) as indicated by X-ray photoelectron spectroscopy (XPS) results. Cr(VI) enrichment by I. galbana may cause damage to marine ecology and human bodies through the food chain. The tolerance mechanisms of I. galbana to Cr(VI) may be potentially used to treat low-concentration Cr(VI) wastewater. Therefore, the responses and tolerance mechanisms of I. galbana to Cr(VI) must be further studied.

Adsorption of Cr(VI) from Aqueous Solution by Ethylenediaminetetraacetic Acid-Chitosan-Modified Metal-Organic Framework.

Cu-BTC was synthesised by hydrothermal method in this study to adsorb and remove the toxic heavy metal hexavalent chromium Cr(VI) in water. The EDTA-chitosan/Cu-BTC was prepared by the surface modification of Cu-BTC with EDTA-modified chitosan. The initial concentration effects of adsorbed chromium solution, adsorbent dosage, adsorption time, adsorption temperature and pH of chromium solution on adsorption capacity were estimated using the single-factor optimisation experiment. Results show that the adsorption capacity of the modified composite was higher than that of Cu-BTC. Cu-BTC and EDTA-chitosan/Cu-BTC exhibited significant adsorption of Cr(VI) under acidic conditions in water and basically independent of temperature. Their adsorption processes conformed with the pseudo-second-order model. The Langmuir adsorption isotherm model obtained the adsorption isotherm, which indicated that the adsorption process was single molecule adsorption. Isotherm fitting obtained the maximum adsorption amounts of Cr(VI) for Cu-BTC and EDTA-chitosan/Cu-BTC at 27.32 and 46.51 mg·g-1, respectively. Factor and principal component analyses show that the main factors affecting the adsorption of Cr(VI) in the EDTA-chitosan/Cu-BTC composites are pH, initial concentration and adsorption time. Therefore, EDTA-chitosan-modified Cu-BTC was a more feasible metal-organic framework material than Cu-BTC because of better adsorption performance, which can be used for adsorption removal of Cr(VI) in water.

Study on the degradation performance and kinetics of immobilized cells in straw-alginate beads in marine environment.

In this study, two strains Halomonas and Aneurinibacillus were mixed in equal proportions as free cells that could degrade diesel and produce biosurfactant. A new type of immobilized cells, free cells immobilized in beads combined with sodium alginate and straw, was studied. The components of straw-alginate beads were optimized by Response Surface Method, and the degradation performance of immobilized cells was determined. The result indicated that the density, strength and broken rate of straw-alginate beads were 1.04 g/cm3, 216 g and 4%, respectively. The best degradation rate of immobilized cells in straw-alginate beads could be 68.68%. Lately, by analyzing the Monod model, vmax (maximum specific degradation rate of diesel) and KS (half saturation rate constant) of immobilized cells in straw-alginate beads were 1.84 d-1 and 3.23 g/L, respectively, which explained the higher degradation performance.