Analysis of the regulatory mechanism of exogenous IAA-mediated tryptophan accumulation and synthesis of endogenous IAA in Chlorococcum humicola.

The activated sludge method is widely used for the treatment of phenol-containing wastewater, which gives rise to the problem of toxic residual sludge accumulation. Indole-3-acetic acid (IAA), a typical phytohormone, facilitates the microalgal resistance to toxic inhibition while promoting biomass accumulation. In this study, Chlorococcum humicola (C. humicola) was cultured in toxic sludge extract and different concentrations of IAA were used to regulate its physiological properties and enrichment of high value-added products. Ultimately, proteomics analysis was used to reveal the response mechanism of C. humicola to exogenous IAA. The results showed that the IAA concentration of 5 × 10-6 mol/L (M) was most beneficial for C. humicola to cope with the toxic stress in the sludge extract medium, to promote the activity of rubisco enzyme, to enhance the efficiency of photosynthesis, and, finally, to accumulate protein as a percentage of specific dry weight 1.57 times more than that of the control group. Exogenous IAA altered the relative abundance of various amino acids in C. humicola cells, and proteomic analyses showed that exogenous IAA stimulated the algal cells to produce more indole-3-glycerol phosphate (IGP), indole, and serine by up-regulating the enzymes. These precursors are converted to tryptophan under the regulation of tryptophan synthase (A0A383V983), and tryptophan can be metabolized to endogenous IAA to promote the growth of C. humicola. These findings have important implications for the treatment of toxic residual sludge while enriching for high-value amino acids.

Technology transfer for green investments: exploring how technology transfer through foreign direct investments can contribute to sustainable practices and reduced environmental impact in OIC economies.

Estimating the asymmetrical influence of foreign direct investment is the primary goal of the current study. In addition, further controlled variables affect environmental degradation in OIC nations. Due to this, current research employs the asymmetric (NPARDL) approach and the data period from 1980 to 2021 to estimate about viability of the EKC (environmental Kuznets curve) theory. The study utilized greenhouse gas (GHG) including emissions of carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ecological footprint as substantial parameters of environmental quality. A nonlinear link between foreign direct investments, trade openness, economic growth, urbanization, energy consumption, and environmental pollution with CO2, N2O, CH4, and ecological footprint in the OIC nations is confirmed by the study's outcomes, which however reveals inconsistent results. Furthermore, the results also show that wrong conclusions might result from disregarding intrinsic nonlinearities. The study's conclusions provide the most important recommendations for decision-makers.

The efficient capture of polysaccharides in Tetradesmus obliquus of indole-3-acetic acid coupling sludge extraction.

Polysaccharide is an important biomass of algae. The sludge extract is rich in organic substances, which can be used by algae for biomass growth and high-value biomass synthesis, but its organic toxicity has an inhibitory effect on algae. To overcome inhibition and improve polysaccharide enrichment, Tetradesmus obliquus was cultured with sludge extract with different indole-3-acetic acid (IAA) concentrations. Within 30 days of the culture cycle, T. obliquus showed in good condition at the IAA dosage content of 10-6 M, the maximum cell density and dry weight were respectively (106.78 ± 2.20) × 106 cell/mL and 2.941 ± 0.067 g/L while the contents of chlorophyll-a, chlorophyll-b, and carotenoid were 1.79, 1.91 and 2.80 times that of the blank group, respectively. The highest polysaccharide accumulation was obtained under this culture condition, reaching 533.15 ± 21.11 mg/L on the 30th day, which was 2.49 times that in the blank group. By FT-IR and NMR analysis, it was found that the polysaccharides of T. obliquus were sulfated polysaccharide with glucose and rhamnose as the main monosaccharides. Proteomic showed that the up-regulation of A0A383WL26 and A0A383WLM8 enhanced the light trapping ability, and A0A383WMJ2 enhanced the accumulation of NADPH. The up-regulation of A0A383WHD5 and A0A383WAY6 indicated that IAA culture could repair the damage caused by sludge toxicity, thus promoting the accumulation of biomass. The above findings provided new insights into the mechanism of sludge toxicity removal of T. obliquus and the enhancement of the polysaccharide accumulation effect under different concentrations of IAA.

Proteomics reveals toxin tolerance and polysaccharide accumulation in Chlorococcum humicola under high CO2 concentration.

Algae have great application prospects in excess sludge reclamation and recovery of high-value biomass. Chlorococcum humicola was cultivated in this research, using sludge extract (mixed with SE medium) with additions of 10%, 20%, and 30% CO2 (v/v). Results showed that under 20% CO2, the dry weight and polysaccharide yield reached 1.389 ± 0.070 g/L and 313.49 ± 10.77 mg/L, respectively. 10% and 20% CO2 promoted the production of cellular antioxidant molecules to resist the toxic stress and the toxicity of 20% CO2 group decreased from 62.16 ± 3.11% to 33.02 ± 3.76%. 10% and 20% CO2 accelerated the electron transfer, enhanced carbon assimilation, and promoted the photosynthetic efficiency, while 30% CO2 led to photosystem damage and disorder of antioxidant system. Proteomic analysis showed that 20% CO2 mainly affected energy metabolism and the oxidative stress level on the early stage (10 d), while affected photosynthesis and organic substance metabolism on the stable stage (30 d). The up-regulation of PSII photosynthetic protein subunit 8 (PsbA, PsbO), A0A383W1S5 and A0A383VRI4 promoted the efficiency of PSII and chlorophyll synthesis, and the up-regulation of A0A383WH74 and A0A2Z4THB7 led to the accumulation of polysaccharides. The up-regulation of A0A383VDH1, A0A383VX37 and A0A383VA86 promoted respiration. Collectively, this work discloses the regulatory mechanism of high-concentration CO2 on Chlorococcum humicola to overcome toxicity and accumulate polysaccharides.

Excessive composite pollution carbon sources enhance the bio-fertilizer efficiency of Tetradesmus obliquus: focused on cultivation period.

Microalgae can use carbon sources in sludge extract prepared from sludge. Moreover, the high concentration of CO2 and the large number of carbon sources in the liquid phase will promote microalgae growth and metabolism. In this experiment, Tetradesmus obliquus was cultivated with sludge extract at 30% CO2. Algae liquid (the name used to describe the fertilizer made in this research) was further prepared as lettuce fertilizer. The effect of different times of microalgae culture (10, 15, 20, 25, and 30 days) on the fertilizer efficiency of the algae liquid was evaluated by lettuce hydroponic experiments. The findings indicate that lettuce cultivated in algae liquid collected on the 15th and 30th days exhibited superior performance in terms of growth, antioxidant capacity, and nutritional quality. We analyzed the experimental results in the context of microalgae metabolic mechanisms, aiming to contribute experience and data essential for the development of industrial microalgae fertilizer production.

Indole-3-acetic acid mediated removal of sludge toxicity by microalgae: Focus on the role of extracellular polymeric substances.

The use of indole-3-acid (IAA) as an additive aided in achieving the objectives of reducing sludge extract toxicity, increasing Tetradesmus obliquus biomass yield, and enhancing extracellular polysaccharide production. Proteomics analysis can unveil the microalgae's response mechanism to sludge toxicity stress. With 10-6 M IAA addition, microalgae biomass reached 3.426 ± 0.067 g/L. Sludge extract demonstrated 78.3 ± 3.2% total organic carbon removal and 72.2 ± 2.1% toxicity removal. Extracellular polysaccharides and proteins witnessed 2.08 and 1.76-fold increments, respectively. Proteomic analysis indicated that Tetradesmus obliquus directed carbon sources towards glycogen accumulation and amino acid synthesis, regulating pathways associated with carbon metabolism (glycolysis, TCA cycle, and amino acid metabolism) to adapt to the stressful environment. These findings lay the groundwork for future waste sludge treatment and offer novel insights into microalgae cultivation and extracellular polysaccharide enrichment in sludge.

Analysis of the mechanism of exogenous indole-3-acetic acid on the enrichment of d-glucose in Chlorococcum humicola cultured by sludge extracts.

Addressing problems of high organic toxicity in the wastewater treatment process, microalgae have been used to reduce the toxicity in sludge and to synthesize non-toxic and recoverable biomass of resources. Phytohormone is a core regulator of plant growth and current research has generally focused on their promotion of cell division and cell expansion. Effects of phytohormone on the enrichment mechanism of microalgae directional polysaccharides accumulation remain poorly elucidated. This study was carried out to investigate the effects of exogenous indole-3-acetic acid (IAA) on growth characteristics, biomass accumulation, and photosynthesis capacity of Chlorococcum humicola cultured in sludge extract and further find the d-glucose enrichment mechanism of it through proteomic. The results indicated that the optimal culture conditions were the 75 % sludge extract and 25 % selenite enrichment (SE) medium with 5 × 10-6 mol/L indole-3-acetic acid. Polysaccharides increased significantly from day 20 and accumulated to (326.59 ± 13.06) mg/L on day 30, in which the d-glucose proportion increased to 61.53 %. Most notably, proteomic tests were performed and found that the photosynthesis-related proteins including the differential proteins of photosystem electron transport, ATP and NADPH catalytic synthesis were significantly up-regulated. At the end of the path, three pathways of d-glucose enrichment with α-d-Glucose-1P as a precursor were summarized through indole-3-acetic acid activation on amylase, endoglucanase and Beta-glucosidase, etc. These results provide insights to explore the directed enrichment of biomass in Chlorococcum humicola by indole-3-acetic acid.

Regulatory mechanism of high-concentration CO2 on polysaccharide accumulation in Tetradesmus obliquus cultured in sludge extract.

Microalgae such as Tetradesmus obliquus have great potential in immobilizing high-concentration CO2 and removing highly toxic organic matters, which could be produced from coal chemical industry and coal chemical wastewater biological treatment process. In this study, Tetradesmus obliquus was cultured in sludge extract and high-concentration CO2 was added. The maximum cell density and dry weight were respectively (111.46 ± 4.87) × 106 cell/mL and 3.365 ± 0.168 g/L under 30% CO2. Tetradesmus obliquus accumulated the most polysaccharides (629.60 ± 31.48 mg/L) on the 30th day under 30% CO2. The results of proteomic showed that the upregulation of A0A2Z4THB7 and A0A383VAT1 promoted polysaccharide accumulation. Polysaccharide was mainly formed at the stable phase instead of the log-growth phase due to the abiotic stress caused by high TOC at the log-growth phase. Collectively, this study revealed the regulatory mechanism of high-concentration CO2 on the toxicity removal and accumulation of polysaccharides in Tetradesmus obliquus.

Analysis of photosynthetic pigments pathway produced by CO2-toxicity-induced Scenedesmus obliquus.

The coal-to-gas process produces carbon dioxide, which increases global warming, and its wastewater treatment generates sludge with high organic toxicity. Scenedesmus obliquus is a potential solution to such environmental problems, and photosynthetic pigments are the focus of this study. The optimal concentration of CO2 for the growth of Scenedesmus obliquus was found to be 30 % after increasing the concentration of CO2 (0.05 %-100 %). The accumulation of photosynthetic pigments during cultivation could reach 31.74 ± 1.33 mg/L, 11.21 ± 0.42 mg/L, and 5.59 ± 0.19 mg/L respectively, and the organic toxicity of sludge extract could be reduced by 44.97 %. Upregulation of A0A383VSL5, A0A383WMQ3, and A0A2Z4THB7 as photo systemic oxygen release proteins and propylene phosphate isomerase resulted in oxygen-evolving proteins in photosystem II, electron transport in photosystem I, and intermediates in carbon fixation. This is achieved by increasing the intracellular antennae protein and carbon fixation pathway, allowing Scenedesmus obliquus to both tolerate and fix CO2 and reduce the organic toxicity of sludge. These findings provide insights into the innovative strategy underlining the fixation of CO2, treatment and disposal of industrial residual sludge, and the enhancement of microalgal biomass production.

Voting with Your Feet: The Impact of Urban Public Health Service Accessibility on the Permanent Migration Intentions of Rural Migrants in China.

The accessibility of urban public health services is not only relevant to the health status of rural migrants but also plays an increasingly important role in their migration decisions. Most existing studies have focused on the effects of the level of public health service provision and parity on rural migrants' migration behavior, ignoring the role of public health service accessibility. This paper systematically examines the overall impact, heterogeneous impact and mechanism of action of public health service accessibility on rural migrants' intentions to migrate permanently based on data from the 2017 China Mobile Population Dynamics Monitoring Survey using probit, IVprobit, eprobit, omitted variable test model and KHB mediating effect model. It was found that: (1) public health service accessibility significantly increased rural migrants' intentions to migrate permanently, and the results remained robust after using instrumental variables to mitigate endogeneity problems and omitted variable tests. (2) Heterogeneity analysis shows that public health service accessibility has a greater effect on enhancing the intentions to migrate permanently among females and rural migrants born in 1980 and later. (3) Further mechanism testing revealed that public health service accessibility could indirectly increase rural migrants' intentions to migrate permanently by improving health habits, health status, identity, and social integration, with identity playing a greater indirect effect. The findings of this paper not only provide empirical evidence for the existence of Tiebout's "voting with your feet" mechanism in China but also contribute to the scientific understanding of the role of equalization of public health services in the process of population migration.

Self-regulation mechanism difference of Chlorella vulgaris and Scenedesmus obliquus in toxic sludge extract caused by hydroquinone biodegradation.

Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus) were compared to remove toxicity under conditions of sludge extract cultivation for 30 days. The toxicity of sludge extract, the growth characteristics, photosynthetic pigment, superoxide dismutase (SOD) enzyme and catalase (CAT) enzyme activities of the two microalgae were studied by contrast. The results showed that small molecular organic matter (<500 Da) was more easily utilized by microalgae. The toxicity in the toxic group of C. vulgaris and S. obliquus on the 30th day decreased to 56.8 ± 1.2% and 60.7 ± 2.8%, respectively. In the toxic group, the maximal SOD enzyme activity of C. vulgaris and S. obliquus were 2.02 U/mg proteins and 8.21 U/mg proteins, respectively, demonstrating that toxicity caused more oxidative damage to S. obliquus than to C. vulgaris. Proteomics analysis revealed that C. vulgaris mainly regulates energy synthesis and distribution primarily through sugar metabolism, and biomass synthesis primarily through carbon metabolism, whereas S. obliquus mainly regulates energy synthesis and distribution primarily through sugar metabolism and oxidative phosphorylation, resulting in sludge toxicity stress regulation.

[High-level production of neutral endoglucanase 1 in Pichia pastoris].

The gene (eg1) encoding for novel endoglucanase 1 was cloned previously from Chinese straw mushroom Volvariella volvacea. EG1 has high thermal stability and optimal pH at neutral and shows great potential in textile and paper industry applications. To improve the expression level of EG1 in Pichia pastoris, the increasing copy number of clone, and its high cell density fermentation in 3.2L fermenter for its high-level expression were investigated in this work. By electro-transformation of pPICZalphaB-egl into GS115EG11 integrated with single copy of eg1 gene, A resistant transformant with 3.8 times higher level expression than GS115EG11 was screened from YPDSZ plate containing 2000 microg/mL of Zeocin. The effect of initial cell density, pH and methanol on its expression and biomass accumulation was evaluated in shaking culture. Optimal EG1 production was observed when initial cell density OD600 was 5.0. EG1 production and biomass accumulation did not seem to vary when cells were induced at different pH values. Both of EG1 and cell density were found to increase with higher methanol concentrations, reaching 62.48 IU/mL and 31.7 (OD600) respectively after 120 h induction with 2.0% (V/V) methanol compared to 30.24 IU/mL and 17.79 (OD60) with 0.25% methanol induction. EG1 expression was further increased by 6.4 times higher than shaking culture after 95.5 hours induction with methanol in fed-batch fermentation, so totally 34 times higher than that for GS115EG11 was achieved by screening of high Zeocin resistant clone and high cell density fermentation. The production of EG1 with 543.36IU/mL CMC activity and 8.80mg/mL protein expression was obtained in Pichia pastoris.