Performance of different microalgae-fungi-bacteria co-culture technologies in photosynthetic and removal performance in response to various GR24 concentrations

Screening fungal partners for enhancing the vitality of a xenic algal culture via photosynthetic efficiency

The xenic strain Chlorella sorokiniana was grown together with selected fungal strains to investigate the effect of fungi on the algal photosynthetic performance during cultivation. The introduction of well-selected fungal strains can potentially increase algal cultivation efficiency. The bacteria that inhabited the algae were identified and the coexistence of the fungi with the algae and bacteria in liquid and solid media was examined. Chlorophyll a fluorescence measurement, a commonly used method for determining the efficiency of plant photosynthesis under stressful conditions, was used to assess the condition of the algae. The algae were cultivated for eight weeks without supplementing the nutrient solution. The experiments showed that the fungal strains Clonostachys rosea, Rhodotorula mucilaginosa and Mortierella alpina formed stable interactions with the microalga C. sorokiniana and the bacteria in the microalgal culture. The time of the measurement and treatments caused changes in the fluorescence curve patterns. Differences in the profiles of the curves in different phases revealed modifications in the operation of the light-dependent photochemical reactions. Generally, the most positive changes in the chlorophyll a fluorescence induction curves (OJIP) were recorded in the double inoculation of C. sorokiniana with R. mucilaginosa + M. alpina and R. mucilaginosa + C. rosea. The results show that selected combinations of fungal strains can be a tool to improve the photosynthetic efficiency of C. sorokiniana.

Biogas slurry treatment and biogas upgrading by microalgae-based systems under the induction of different phytohormones

The low grade of biogas and the difficulty of treating biogas slurry are the two major bottlenecks limiting the sustainable development of the fermentation engineering. This study investigates the potential role of microalgae-microbial symbiosis and phytohormones in solving this challenge. Chlorella microalgae were combined with endophytic bacteria (S395-2) and Clonostachys fungus to construct symbiotic systems. Growth, photosynthetic activity, and carbon dioxide and pollutant removal out of biogas slurry and biogas were analyzed under treatment with three different phytohormones (cytokinin, synthetic strigolactones (GR24), natural strigolactones). The Chlorella-S395-2-Clonostachys symbiont achieved the highest purification efficiency under GR24 induction, with removal efficiency exceeding 86% for chemical oxygen demand, total phosphorous, and total nitrogen, as well as over 76% for CO2. Economic efficiency can be increased by about 150%. The positive correlation between treatment effectiveness and co-culture performance suggests a promising avenue for developing symbiotic systems for biogas slurry treatment and biogas upgrading.

Performance of four different microalgae-based technologies in antibiotics removal under multiple concentrations of antibiotics and strigolactone analogue GR24 administration

The formation of symbionts by using different combinations of endophytic bacteria, microalgae, and fungi to purify antibiotics-containing wastewater is an effective and promising biomaterial technology. As it enhances the mixed antibiotics removal performance of the bio-system, this technology is currently extensively studied. Using exogenous supplementation of various low concentrations of the phytohormone strigolactone analogue GR24, the removal of various antibiotics from simulated wastewater was examined. The performances of Chlorella vulgaris monoculture, activated sludge-C. vulgaris-Clonostachys rosea, Bacillus licheniformis-C. vulgaris-C. rosea, and endophytic bacteria (S395-2)-C. vulgaris-C. rosea co-culture systems were systematically compared. Their removal capacities for tetracycline, oxytetracycline, and chlortetracycline antibiotics from simulated wastewater were assessed. Chlorella vulgaris-endophytic bacteria-C. rosea co-cultures achieved the best performance under 0.25 mg L-1 antibiotics, which could be further enhanced by GR24 supplementation. This result demonstrates that the combination of endophytic bacteria with microalgae and fungi is superior to activated sludge-B. licheniformis-microalgae-fungi systems. Exogenous supplementation of GR24 is an effective strategy to improve the performance of antibiotics removal from wastewater.

Sustainable treatment of aquaculture water employing fungi-microalgae consortium: Nutrients removal enhancement, bacterial communities optimization, emerging contaminants elimination, and mechanism analysis

Fungi-microalgae consortium (FMC) has emerged as a promising system for advanced wastewater treatment due to its high biomass yield and environmental sustainability. This study aimed to investigate the nutrients removal, bacterial community shift, emerging contaminants elimination, and treatment mechanism of a FMC composed of Cordyceps militaris and Navicula seminulum for aquaculture pond water treatment. The fungi and microalgae were cultured and employed either alone or in combination to evaluate the treatment performance. The results demonstrated that the FMC could improve water quality more significantly by reducing nutrient pollutants and optimizing the bacterial community structures. Furthermore, it exhibited stronger positive correlation between the enrichment of functional bacteria for water quality improvement and pollutants removal performance than the single-species treatments. Moreover, the FMC outperformed other groups in eliminating emerging contaminants such as heavy metals, antibiotics, and pathogenic Vibrios. Superiorly, the FMC also showed excellent symbiotic interactions and cooperative mechanisms for pollutants removal. The results collectively corroborated the feasibility and sustainability of using C. militaris and N. seminulum for treating aquaculture water, and the FMC would produce more mutualistic benefits and synergistic effects than single-species treatments.

Removal of antibiotics by four microalgae-based systems for swine wastewater treatment under different phytohormone treatment

This study examined the removal of typical antibiotics from simulated swine wastewater. Microalgae-bacteria/fungi symbioses were constructed using Chlorella ellipsoidea, endophytic bacteria (S395-2), and Clonostachys rosea as biomaterials. The growth, photosynthetic performance, and removal of three types of antibiotics (tetracyclines, sulfonamides, and quinolones) induced by four phytohormones were analyzed in each system. The results showed that all four phytohormones effectively improved the tolerance of symbiotic strains against antibiotic stress; strigolactones (GR24) achieved the best performance. At 10-9 M, GR24 achieved the best removal of antibiotics by C. elliptica + S395-2 + C. rosea symbiosis. The average removals of tetracycline, sulfonamide, and quinolone by this system reached 96.2-99.4 %, 75.2-81.1 %, and 66.8-69.9 %, respectively. The results of this study help to develop appropriate bio enhancement strategies as well as design and operate algal-bacterial-fungal symbiotic processes for the treatment of antibiotics-containing wastewater.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Phytohormone gibberellins treatment enhances multiple antibiotics removal efficiency of different bacteria-microalgae-fungi symbionts

To develop and characterize novel antibiotics removal biomaterial technology, we constructed three different bacteria-microalgae-fungi consortiums containing Chlorella vulgaris (C. vulgaris), endophytic bacterium, Clonostachys rosea (C. rosea), Ganoderma lucidum, and Pleurotus pulmonarius. The results showed that under treatment with 50 mg/L of gibberellins (GAs), the three bacteria-microalgae-fungi symbionts had maximal growth rates (0.317 ± 0.030 d-1) and the highest removal efficiency for seven different antibiotics. Among them, C. vulgaris-endophytic bacterium-C. rosea symbiont had the best performance, with antibiotics removal efficiencies of 96.0 ± 1.4 %, 91.1 ± 7.9 %, 48.7 ± 5.1 %, 34.6 ± 2.9 %, 61.0 ± 5.5 %, 63.7 ± 5.6 %, and 54.3 ± 4.9 % for tetracycline hydrochloride, oxytetracycline hydrochloride, ciprofloxacin, norfloxacin, sulfadiazine, sulfamethazine, and sulfamethoxazole, respectively. Overall, the present study demonstrates that 50 mg/L GAs enhances biomass production and antibiotics removal efficiency of bacteria-microalgae-fungi symbionts, providing a framework for future antibiotics-containing wastewater treatment using three-phase symbionts.

Attenuation of antibiotics from simulated swine wastewater using different microalgae-based systems

Antibiotic misuse are potentially harmful to the environment and human health. Four algal symbionts were constructed using Chlorella vulgaris, endophytic bacterium and Clonostachys rosea (C. rosea) as the biomaterials. The growth, photosynthetic activity, and antibiotic removal efficiency of symbiont under different initial antibiotic concentrations was analyzed. The results showed that the microalgae-bacteria-fungi symbiont had a maximum growth rate of 0.307 ± 0.030 d-1 and achieved 99.35 ± 0.47%, 81.06 ± 7.83%, and 79.15 ± 7.26% removal of oxytetracycline (OTC), sulfadimethazine (SM2), and ciprofloxacin hydrochloride (CPFX), respectively, at an initial antibiotic concentration of 0.25 mg/L. C. rosea has always existed as a biocontrol fungus. In this study, it was innovatively used to construct algal symbionts and used for antibiotic wastewater treatment with a high efficiency. The results contribute to the development of appropriate bioaugmentation strategies and the design of an algal symbiont process for the treatment of antibiotic-containing wastewater.

Nutrient removal and biogas upgrade using co-cultivation of Chlorella vulgaris and three different bacteria under various GR24 concentrations by induction with 5-deoxystrigol

Algae symbiosis technology shows great potential in the synchronous treatment of biogas slurry and biogas, which has promising applications. For improving nutrients and CO₂ removal rates, the present work constructed four microalgal systems: Chlorella vulgaris (C. vulgaris) monoculture, C. vulgaris-Bacillus licheniformis (B. licheniformis), C. vulgaris-activated sludge, and C. vulgaris-endophytic bacteria (S395-2) to simultaneously treat biogas as well as biogas slurry under GR24 and 5DS induction. Our results showed that the C. vulgaris-endophytic bacteria (S395-2) showed optimal growth performance along with photosynthetic activity under the introduction of GR24 (10^-9 M). Under optimal conditions, CO₂ removal efficiency form biogas, together with chemical oxygen demand, total phosphorus and total nitrogen removal efficiencies from biogas slurry reached 67.25 ± 6.71%, 81.75 ± 7.93%, 83.19 ± 8.32%, and 85.17 ± 8.26%, respectively. The addition of symbiotic bacteria isolated from microalgae can promote the growth of C. vulgaris, and the exogenous addition of GR24 and 5DS can strengthen the purification performance of the algae symbiosis to achieve the maximum removal of conventional pollutants and CO₂.

Nutrient removal from biogas slurry and biogas upgrading by microalgae-fungi-bacteria co-cultivation under different carbon nanotubes concentration

In this study, Chlorella vulgaris, Ganoderma lucidum, and endophytic bacteria were co-cultivated with the stimulation of strigolactone analogs GR24 to prepare pellets. During the purification of biogas slurry and biogas, multi-walled carbon nanotubes (MWCNTs) were introduced to enhance the removal efficiencies of nutrients and CO₂. The results showed that both GR24 and MWCNTs affected the purification of biogas slurry and biogas. The maximum chemical oxygen demand, total nitrogen, total phosphorus, and CO₂ removal efficiencies of the Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts were 82.57 ± 7.96% (P < 0.05), 82.14 ± 7.87% (P < 0.05), 84.27 ± 7.96% (P < 0.05), and 63.93 ± 6.22% (P < 0.05), respectively, with the induction of 10^-9 M GR24 and 1 mg L^-1 MWCNTs. Moreover, the growth and photosynthetic performance of the symbionts were consistent with the removal effects. The Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts obtained high growth rates and enzyme activity with the maximum growth rate of 0.365 ± 0.03 d^-1, mean daily productivity of 0.182 ± 0.016 g L^-1 d^-1, and carbonic anhydrase activity of 31.07 ± 2.75 units, respectively. These results indicated that an appropriate concentration of GR24 and MWCNTs could promote the growth of symbionts, reinforce the purification effects of biogas slurry and biogas, and provide a new idea for the simultaneous purification of wastewater and biogas.

Effect of GR24 concentrations on tetracycline and nutrient removal from biogas slurry by different microalgae-based technologies

A biogas slurry composed of carbon, nitrogen, phosphorus, and antibiotics was generated. Investigations into the nutrient and tetracycline removal performance of four microalgae-based contaminant removal technologies, including Chlorella vulgaris, C. vulgaris co-cultured with endophytic bacteria, C. vulgaris co-cultured with Ganoderma lucidum, and C. vulgaris co-cultured with G. lucidum and endophytic bacteria, were conducted. The algal-bacterial-fungal consortium with 10^-9 M strigolactone (GR24) yielded the maximum growth rate and average daily yield for algae at 0.325 ± 0.03 d^-1 and 0.192 ± 0.02 g L^-1 d^-1, respectively. The highest nutrient/ tetracycline removal efficiencies were 83.28 ± 7.95 % for chemical oxygen demand (COD), 82.62 ± 7.97 % for total nitrogen (TN), 85.15 ± 8.26 % for total phosphorus (TP) and 83.92 ± 7.65 % for tetracycline. Adding an algal-bacterial-fungal consortium with an optimal synthetic analog GR24 concentration is seemingly an encouraging strategy for enhancing pollutant removal by algae, possibly overcoming the challenges of eutrophication and antibiotic pollution.

The effects of influent chemical oxygen demand and strigolactone analog concentration on integral biogas upgrading and pollutants removal from piggery wastewater by different microalgae-based technologies

Microalgae-based technologies are promising strategies for efficient wastewater treatment and biogas upgrading. In this study, three types of microalga-fungi/bacteria symbiotic systems stimulated with the strigolactone analog (GR24) were used to simultaneously remove nutrients from treated piggery wastewater and CO₂ from biogas. The effects of initial concentrations of chemical oxygen demand (COD) and GR24 on nutrient removal and biogas upgrading were investigated. When the initial COD concentration was 1200 mg/L, the Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria co-cultivation systems achieved the best photosynthetic performance and microalgae growth. Moreover, under the appropriate COD concentration (1200 mg/L), the highest nutrient/CO₂ removal efficiencies were obtained. In addition, 10^-9 M GR24 significantly accelerated nutrient/CO₂ removal efficiencies. These findings provide a theoretical basis for scale-up experiments using microalgae-based technologies.

Supplementation with rac-GR24 Facilitates the Accumulation of Biomass and Astaxanthin in Two Successive Stages of Haematococcus pluvialis Cultivation

The unicellular freshwater green alga Haematococcus pluvialis has attracted much research attention due to its biosynthetic ability for large amounts of astaxanthin, a blood-red ketocarotenoid that is used in cosmetics, nutraceuticals, and pharmaceuticals. Recently, numerous studies have investigated the functions of natural astaxanthin; however, the high cost of the production of astaxanthin from H. pluvialis cultures restricts its commercial viability. There is an urgent need to fulfill commercial demands by increasing astaxanthin accumulation from H. pluvialis cultures. In this study, we discovered that treatment of H. pluvialis cultures at the beginning of the macrozooid stage (day 0) with 1 μM rac-GR24, a synthetic analogue of strigolactones (a class of phytohormones), led to significant increases in biomass [up to a maximum dry cell weight (DCW) of 0.53 g/L] during the macrozooid stage and astaxanthin (from 0.63 to 5.32% of DCW) during the hematocyst stage. We elucidated that this enhancement of biomass accumulation during the macrozooid stage by rac-GR24 is due to its increasing CO₂ utilization efficiency in photosynthesis and carbohydrate biosynthesis. We also found that rac-GR24 stimulated the overproduction of nicotinamide adenine dinucleotide phosphate (NADPH) and antioxidant enzymes in H. pluvialis cultures, which alleviated the oxidative damage caused by reactive oxygen species generated during the hematocyst stage due to the exhaustion of nitrogen supplies. Moreover, rac-GR24 treatment of H. pluvialis synergistically altered the activity of the pathways of fatty acid biosynthesis and astaxanthin esterification, which resulted in larger amounts of astaxanthin being generated by rac-GR24-treated cultures than by controls. In summary, we have developed a feasible and economic rac-GR24-assisted strategy that increases the amounts of biomass and astaxanthin generated by H. pluvialis cultures, and have provided novel insights into the mechanistic roles of rac-GR24 to achieve these effects.

Enhancement of Astaxanthin and Fatty Acid Production in Haematococcus pluvialis Using Strigolactone

Improving the production rate of high-value nutraceutical compounds, such as astaxanthin and polyunsaturated fatty acids (PUFAs), is important for the commercialization of Haematococcus pluvialis biorefineries. Here, the effects of a phytohormone, strigolactone analog rac-GR24, on cell growth and astaxanthin and fatty acid biosynthesis in H. pluvialis were investigated. Four concentrations (2, 4, 6, and 8 µM) of rac-GR24 were initially added during 30 days of photoautotrophic cultivation. The addition of rac-GR24 improved cell number density and chlorophyll concentration in H. pluvialis cultures compared to the control; the optimal concentration was 8 µM. Despite a slightly reduced astaxanthin content of 30-d-old cyst cells, the astaxanthin production (26.1 ± 1.7 mg/L) improved by 21% compared to the rac-GR24-free control (21.6 ± 1.5 mg/L), owing to improved biomass production. Notably, at the highest dosage of 8 µM rac-GR24, the total fatty acid content of the treated H. pluvialis cells (899.8 pg/cell) was higher than that of the untreated cells (762.5 pg/cell), resulting in a significant increase in the total fatty acid production (361.6 ± 48.0 mg/L; 61% improvement over the control). The ratio of PUFAs, such as linoleic (C18:2) and linolenic (C18:3) acids, among total fatty acids was high (41.5–44.6% w/w) regardless of the rac-GR24 dose.