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.

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.

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.

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.

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.

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.

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.