Harnessing the potential of microalgae-based systems for mitigating pesticide pollution and its impact on their metabolism.

Due to increased pesticide usage in agriculture, a significant concentration of pesticides is reported in the environment that can directly impact humans, aquatic flora, and fauna. Utilizing microalgae-based systems for pesticide removal is becoming more popular because of their environmentally friendly nature, ability to degrade pesticide molecules into simpler, nontoxic molecules, and cost-effectiveness of the technology. Thus, this review focused on the efficiency, mechanisms, and factors governing pesticide removal using microalgae-based systems and their effect on microalgal metabolism. A wide range of pesticides, like atrazine, cypermethrin, malathion, trichlorfon, thiacloprid, etc., can be effectively removed by different microalgal strains. Some species of Chlorella, Chlamydomonas, Scenedesmus, Nostoc, etc., are documented for >90% removal of different pesticides, mainly through the biodegradation mechanism. The antioxidant enzymes such as ascorbate peroxidase, superoxide dismutase, and catalase, as well as the complex structure of microalgae cell walls, are mainly involved in eliminating pesticides and are also crucial for the defense mechanism of microalgae against reactive oxygen species. However, higher pesticide concentrations may alter the biochemical composition and gene expression associated with microalgal growth and metabolism, which may vary depending on the type of strain, the pesticide type, and the concentration. The final section of this review discussed the challenges and prospects of how microalgae can become a successful tool to remediate pesticides.

Comprehensive Analysis of Lutein and Loroxanthin in Scenedesmus obliquus: From Quantification to Isolation.

Carotenoids are hydrophobic pigments produced exclusively by plants, fungi, and specific microbes. Microalgae are well suited for the production of valuable carotenoids due to their rapid growth, efficient isoprenoid production pathway, and ability to store these compounds within their cells. The possible markets for bio-products range from feed additives in aquaculture and agriculture to pharmaceutical uses. The production of carotenoids in microalgae is affected by several environmental conditions, which can be utilized to enhance productivity. The current study focused on optimizing the extraction parameters (time, temperature, and extraction number) to maximize the yield of carotenoids. Additionally, the impact of various nitrogen sources (ammonia, nitrate, nitrite, and urea) on the production of lutein and loroxanthin in Scenedesmus obliquus was examined. To isolate the carotenoids, 0.20 g of biomass was added to 0.20 g of CaCO3 and 10.0 mL of ethanol solution containing 0.01% (w/v) pyrogallol. Subsequently, the extraction was performed using an ultrasonic bath for a duration of 10 min at a temperature of 30 °C. This was followed by a four-hour saponification process using a 10% methanolic KOH solution. The concentration of lutein and loroxanthin was measured using HPLC-DAD at 446 nm, with a flow rate of 1.0 mL/min using a Waters YMC C30 Carotenoid column (4.6 × 250 mm, 5 µm). The confirmation of carotenoids after their isolation using preparative chromatography was achieved using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with an atmospheric pressure chemical ionization (APCI) probe and UV-vis spectroscopy. In summary, S. obliquus shows significant promise for the large-scale extraction of lutein and loroxanthin. The findings of this study provide strong support for the application of this technology to other species.

Mitigating salinity stress through interactions between microalgae and different forms (free-living & alginate gel-encapsulated) of bacteria isolated from estuarine environments.

Salinity stress in estuarine environments poses a significant challenge for microalgal survival and proliferation. The interaction between microalgae and bacteria shows promise in alleviating the detrimental impacts of salinity stress on microalgae. Our study investigates this interaction by co-cultivating Chlorella sorokiniana, a freshwater microalga, with a marine growth-promoting bacterium Pseudomonas gessardii, both of which were isolated from estuary. In this study, bacteria were encapsulated using sodium alginate microspheres to establish an isolated co-culture system, preventing direct exposure between microalgae and bacteria. We evaluated microalgal responses to different salinities (5 PSU, 15 PSU) and interaction modes (free-living, gel-encapsulated), focusing on growth, photosynthesis, cellular metabolism, and extracellular polymeric substances (EPS) properties. High salinity inhibited microalgal proliferation, while gel-fixed interaction boosted Chlorella growth rate by 50.7 %. Both attached and free-living bacteria restored Chlorella's NPQ to normal levels under salt stress. Microalgae in the free-living interaction group exhibited a significantly lower respiratory rate compared to the pure algae group (-17.2 %). Increased salinity led to enhanced EPS polysaccharide secretion by microalgae, particularly in interaction groups (19.7 %). Both salt stress and interaction increased the proportion of aromatic proteins in microalgae's EPS, enhancing its stability by modulating EPS glycosidic bond C-O-C and protein vibrations. This alteration caused microalgal cells to aggregate, free-living bacteria co-culture group, and fixed co-culture group increasing by 427.5 %, 567.1 %, and 704.1 %, respectively. In gel-fixed bacteria groups, reduced neutral lipids don't accumulate starch instead, carbon redirects to cellular growth, aiding salt stress mitigation. These synergistic activities between salinity and bacterial interactions are vital in mitigating salinity stress, improving the resilience and growth of microalgae in saline conditions. Our research sheds light on the mechanisms of microalgal-bacterial interactions in coping with salt stress, offering insights into the response of estuarine microorganisms to global environmental changes and their ecological stability.

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review.

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Productivity, amino acid profile, and protein bioaccessibility in heterotrophic batch cultivation of Galdieria sulphuraria.

The polyextremophilic Galdieria sulphuraria is emerging as a promising microalgal species for food applications. This work explores the potential of heterotrophically cultivated G. sulphuraria as a protein producer for human consumption. To this end, the performances of four G. sulphuraria strains grown under the same conditions were compared. Amino acid profiles varied among strains and growth phases, but all samples met FAO dietary requirements for adults. The specific growth rates were between 1.01 and 1.48 day-1. After glucose depletion, all strains showed an increase of 38-49 % in nitrogen content within 48 h, reaching 7.8-12.0 % w/w. An opposite trend was observed in protein bioaccessibility, which decreased on average from 69 % during the exponential phase to a minimum of 32 % 48 h after stationary phase, with significant differences among the strains. Therefore, selecting the appropriate strain and harvesting time is crucial for successful single-cell protein production.

Bioprospecting of Chlamydomonas reinhardtii for boosting biofuel-related products production based on novel aggregation-induced emission active extracellular polymeric substances nanoprobes.

Biofuel production from microalgae has been greatly restricted by low biomass productivity and long-term photosynthetic efficacy. Here, a novel strategy for selecting high-growing, stress-resistant algal strains with high photosynthetic capacity was proposed based on biocompatible extracellular polymeric substances (EPS) probes with aggregation-induced emission (AIE) properties. Specifically, AIE active EPS probes were synthesized for in-situ long-term monitoring of the EPS productivity at different algal growth stages. By coupling the AIE-based fluorescent techniques, algal cells were classified into four diverse populations based on their chlorophyll and EPS signals. Mechanistic studies on the sorted algal cells revealed their remarkable stress resistance and high expression of cell division, biopolymer production and photosynthesis-related genes. The sorted and subcultured algal cells consistently exhibited relatively higher growth rates and photosynthetic capacities, resulting in an increased (1.2 to 1.8-fold) algal biomass production, chlorophyll, and lipids. This study can potentially open new strategies to boost microalgal-based biofuel production.

Effects of chemical oxygen demand and chloramphenicol on attached microalgae growth: Physicochemical properties and microscopic mass transfer in biofilm.

During the wastewater treatment and resource recovery process by attached microalgae, the chemical oxygen demand (COD) can cause biotic contamination in algal culture systems, which can be mitigated by adding an appropriate dosage of antibiotics. The transport of COD and additive antibiotic (chloramphenicol, CAP) in algal biofilms and their influence on algal physiology were studied. The results showed that COD (60 mg/L) affected key metabolic pathways, such as photosystem II and oxidative phosphorylation, improved biofilm autotrophic and heterotrophic metabolic intensities, increased nutrient demand, and promoted biomass accumulation by 55.9 %, which was the most suitable COD concentration for attached microalgae. CAP (5-10 mg/L) effectively stimulated photosynthetic pigment accumulation and nutrient utilization in pelagic microalgal cells. In conclusion, controlling the COD concentration (approximately 60 mg/L) in the medium and adding the appropriate CAP concentration (5-10 mg/L) are conducive to improving attached microalgal biomass production and resource recovery potential from wastewater.

Simultaneous production of algal biomass and lipid by heterotrophic cultivation of linoleic acid-rich oleaginous microalga Chlorella sorokiniana using high acetate dosage.

The low-cost carbon source, acetate, was utilized to feed a linoleic acid-rich Chlorella sorokiniana for microalgal biomass and lipid accumulation. Remarkably high tolerance capability to high acetate dosage up to 30 g/L was observed, with heterotrophy being the preferred trophic mode for algal growth and lipogenesis when supplemented 20 g/L acetate. Transcriptome analysis revealed a marked activation of pathways involved in acetate bioconversion and lipogenesis upon exposure to high-level of acetate. However, the enhancement of photorespiration inhibited photosynthesis, which ultimately led to a decrease in biomass and lipid under mixotrophy. Heterotrophic acetate-feeding generated more superior amino acid profiling of algal biomass and a predominant linoleic acid content (50 %). Heterotrophic repeat fed-batch strategy in 5 L fermenter significantly increased the growth performance and lipid titer, with the highest levels achieved being 23.4 g/L and 7.0 g/L, respectively. This work provides a viable approach for bio-products production through acetate-based heterotrophic algal cultivation.

Recent advances and fundamentals of microalgae cultivation technology.

Microalgae are considered to be a promising group of organisms for fuel production, waste processing, pharmaceutical applications, and as a source of food components. Unicellular algae are worth being considered because of their capacity to produce comparatively large amounts of lipids, proteins, and vitamins while requiring little room for growth. They can also grow on waste and fix CO2 and nitrogen compounds. However, production costs limit the industrial use of microalgae to the most profitable applications including micronutrient production and fish farming. Therefore, novel microalgae based technologies require an increase of the production efficiencies or values. Here we review the recent studies focused on getting strains with novel characteristics or cultivating techniques that improve production's robustness or efficiency and categorize these findings according to the fundamental factors that determine microalgae growth. Improvements of light and nutrient delivery, as well as other aspects of photobioreactor design, have shown the highest average increase in productivity. Other methods, such as an improvement of phosphorus or CO2 fixation and temperature adaptation have been found to be less effective. Furthermore, interactions with particular bacteria may promote the growth of microalgae, although bacterial and grazer contaminations must be managed to avoid culture failure. The competitiveness of the algal products will increase if these discoveries are applied to industrial settings.

Phosphorus-supplemented seawater-wastewater cyclic system for microalgal cultivation: Production of high-lipid and high-protein algae.

The reuse of wastewater after seawater cultivation is critically important. In this study, a phosphorus-supplemented seawater-wastewater cyclic system (PSSWCS) based on Chlorella pyrenoidosa SDEC-35 was developed. With the addition of phosphorus, the algal biomass and the ability to assimilate nitrogen and carbon were improved. At the nitrogen to phosphorus ratio of 20:1, the biomass productivity per mass of nitrogen reached 3.6 g g-1 (N) day-1 in the second cycle. After the third cycle the protein content reached 35.7% of dry mass, and the major metabolic substances in PSSWCS reached the highest content level of 89.5% (35.7% protein, 38.3% lipid, and 15.5% carbohydrate). After the fourth cycle the lipid content maintained at 40.1%. Furthermore, 100.0% recovery of wastewater in PSSWCS increased the nitrogen and carbon absorption to 15.0 and 396.8 g per tonne of seawater. This study achieved seawater-wastewater recycle and produced high-lipid and high-protein algae by phosphorus addition.

Comparative dynamic optimization study of batch hydrothermal liquefaction of two microalgal strains for economic bio-oil production.

This work presents dynamic optimization strategies of batch hydrothermal liquefaction of two microalgal species, Aurantiochytrium sp. KRS101 and Nannochloropsis sp. to optimize the reactor temperature profiles. Three dynamic optimization problems are solved to maximize the endpoint biocrude yield, minimize the final time, and minimize the reactor thermal energy. The biocrude maximization and time minimization problems demonstrated 11% and 6.18% increment in the optimal biocrude yields and reduction of 78.2% and 61.66% in batch times compared to the base cases for the microalgae with higher lipid and protein fractions, respectively. The energy minimization problem revealed a significant reduction in the reactor thermal energies to generate the targeted biocrude yields compared to the biocrude maximization. Therefore, the identified optimal temperature trajectories outperformed the conventional fixed temperature profiles and could improve the overall economics of the batch bio-oil production from the algal-based biorefineries by significantly enhancing the reactor performance.

Protein extraction from chlorella pyrenoidosa microalgae: Green methodologies, functional assessment, and waste stream valorization for bioenergy production.

C. pyrenoidosa, a species of microalgae, has been recognized as a viable protein source for human consumption. The primary challenges in this context are the development of an efficient extraction process and the valorization of the resultant waste streams. This study, situated within the paradigm of circular economy, presents an innovative extraction approach that achieved a protein extraction efficiency of 62 %. The extracted protein exhibited remarkable oil-water emulsifying performances, such as uniform morphology with high creaming stability, suggesting a sustainable alternative to conventional emulsifiers. Additionally, hydrothermal liquefaction technique was employed for converting the residual biomass and waste solution from the extraction process into biocrude. A biocrude yield exceeding 40 wt%, characterized by a carbon content of 73 % and a higher heating value of 36 MJ/kg, were obtained. These findings demonstrate the promising potential of microalgae biorefinery, which is significant for paving toward circular economy and zero-waste society.

Dietary microalgal-fabricated selenium nanoparticles improve Nile tilapia biochemical indices, immune-related gene expression, and intestinal immunity.

BACKGROUND: Feed supplements, including essential trace elements are believed to play an important role in augmenting fish immune response. In this context, selenium nanoparticles (SeNPs) in fish diets via a green biosynthesis strategy have attracted considerable interest. In this investigation, selenium nanoparticles (SeNPs, 79.26 nm) synthesized from the green microalga Pediastrum boryanum were incorporated into Nile tilapia diets to explore its beneficial effects on the immune defense and intestinal integrity, in comparison with control basal diets containing inorganic Se source. Nile tilapia (No. 180, 54-57 g) were fed on three formulated diets at concentrations of 0, 0.75, and 1.5 mg/kg of SeNPs for 8 weeks. After the trial completion, tissue bioaccumulation, biochemical indices, antioxidant and pro-inflammatory cytokine-related genes, and intestinal histological examination were analyzed. RESULTS: Our finding revealed that dietary SeNPs significantly decreased (P < 0.05) serum alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and cholesterol, while increasing (P < 0.05) high-density lipoproteins (HDL). The Se concentration in the muscle tissues showed a dose-dependent increase. SeNPs at a dose of 1.5 mg/kg significantly upregulated intestinal interleukin 8 (IL-8) and interleukin 1 beta (IL-1ß) gene transcription compared with the control diet. Glutathione reductase (GSR) and glutathione synthetase (GSS) genes were significantly upregulated in both SeNPs-supplemented groups compared with the control. No apoptotic changes or cell damages were observed as indicated by proliferating cell nuclear antigen (PCNA) and caspase-3 gene expression and evidenced histopathologically. SeNPs supplementation positively affects mucin-producing goblet cells (GCs), particularly at dose of 1.5 mg/kg. CONCLUSION: Therefore, these results suggest that Green synthesized SeNPs supplementation has promising effects on enhancing Nile tilapia immunity and maintaining their intestinal health.

Photoheterotroph improved the growth and nutrient levels of Chlorella vulgaris and the related molecular mechanism.

Microalgae are rich in fatty acids, proteins, and other nutrients, which have gained the general attention of researchers all over the world. For the development of Chlorella vulgaris in food and feed industry, this study was conducted to investigate the differences in C. vulgaris' growth and nutritional components under different culture conditions (autotrophic, heterotrophic, photoheterotrophic) and the internal factors through cell counting in combination with transcriptome and nutrient analyses. The results showed that, under the photoheterotrophic condition, Chlorella's growth and the contents of lipid and protein were significantly higher than that under the heterotrophic condition, and the moisture content was lower than that under the heterotrophic condition. The saturated fatty acid content under the photoheterotrophic condition was the lowest, while the polyunsaturated fatty acid content was significantly higher than those under the other two conditions. There were 46,583 differentially expressed genes (DEGs), including 33,039 up-regulated DEGs (70.93%) and 13,544 down-regulated DEGs (29.07%), under the photoheterotrophic condition in comparison with the autotrophic condition. The fold change between the two conditions of samples of up-regulated genes was higher than that of the down-regulated genes. The KEGG enrichment showed that the up-regulated DEGs in the photoheterotrophic condition were significantly enriched in 5 pathways, including protein processing in endoplasmic reticulum pathway, photosynthesis pathway, photosynthesis-antenna protein pathway, endocytosis pathway, and phosphonate and phosphinate metabolism pathway. DEGs related to fatty acid metabolic pathways were significantly enriched in the fatty acid biosynthesis pathway and the biosynthesis of unsaturated fatty acid pathway. The qPCR analysis showed that the expression pattern of the selected genes was consistent with that of transcriptome analysis. The results of this study lay a theoretical foundation for the large-scale production of Chlorella and its application in food, feed, and biodiesel. KEY POINTS: • Nutrient levels under photoheterotrophic condition were higher than other conditions. • Six important pathways were discovered that affect changes in nutritional composition. • Explored genes encode important enzymes in the differential metabolic pathways.

Exogenous GABA supplementation to facilitate Cr (III) tolerance and lipid biosynthesis in Chlorella sorokiniana.

Microalgae possess the prospective to be efficiently involved in bioremediation and biodiesel generation. However, conditions of stress often restrict their growth and diminish different metabolic processes. The current study evaluates the potential of GABA to improve the growth of the microalga Chlorella sorokiniana under Cr (III) stress through the exogenous administration of GABA. The research also investigates the concurrent impact of GABA and Cr (III) stress on various metabolic and biochemical pathways of the microalgae. In addition to the control, cultures treated with Cr (III), GABA, and both Cr (III) and GABA treated were assessed for accurately analysing the influence of GABA. The outcomes illustrated that GABA significantly promoted growth of the microalgae, resulting in higher biomass productivity (19.14 mg/L/day), lipid productivity (3.445 mg/L/day) and lipid content (18%) when compared with the cultures under Cr (III) treatment only. GABA also enhanced Chl a content (5.992 µg/ml) and percentage of protein (23.75%). FAMEs analysis by GC-MS and total lipid profile revealed that GABA treatment can boost the production of SFA and lower the level of PUFA, a distribution ideal for improving biodiesel quality. ICP-MS analysis revealed that GABA supplementation could extend Cr (III) mitigation level up to 97.7%, suggesting a potential strategy for bioremediation. This novel study demonstrates the merits of incorporating GABA in C. sorokiniana cultures under Cr (III) stress, in terms of its potential in bioremediation and biodiesel production without disrupting the pathways of photosynthesis and protein production.

Lipids productivity of cyanobacterium Anabaena vaginicola in an internally illuminated photobioreactor using LED bar lights.

Concerns over environmental issues exists and desire to decrease of their extent, have directed efforts toward green energy production. Growth behavior of Anabaena vaginicola was determined in a photobioreator which illuminated internally (IIPBR) using LED bar light. Excessive heat generated in the IIPBR was taken care of by applying a novel air-cooled system. Further note in experimentation was to find favorable cultivation conditions in the IIPBR for A. vaginicola growth and its lipids production capacity. The following results are expressed: 80 µmol photons m-2 s-1 as light intensity, 0.5 g/l as NaNO3, and 120 ml/min as CO2 amount being expressed in terms of aeration rate. The findings were interpreted in terms of a two-component system where the genes encoded to the relevant proteins are present in cyanobacteria and their expressiveness depends on environmental stress. By determining growth rate constant as 0.11 d-1, the productivity in terms of biomass formation was calculated as 202.6 mg L-1 d-1. While rate of lipids production by the test cyanobacterium is 15.65 mg L-1 d-1. Based on total energy used for IIPBR performance, biomass productivity per unit power input equals to 0.74 g W-1 d-1 and this is in favorable position compared with other photobioreactors.

Roles of pH and phosphate in rare earth element biosorption with living acidophilic microalgae.

The increasing demand for rare earth elements (REEs) has spurred interest in the development of recovery methods from aqueous waste streams. Acidophilic microalgae have gained attention for REE biosorption as they can withstand high concentrations of transition metals and do not require added organic carbon to grow, potentially allowing simultaneous sorption and self-replication of the sorbent. Here, we assessed the potential of Galdieria sulphuraria for REE biosorption under acidic, nutrient-replete conditions from solutions containing ≤ 15 ppm REEs. Sorption at pH 1.5-2.5 (the growth optimum of G. sulphuraria) was poor but improved up to 24-fold at pH 5.0 in phosphate-free conditions. Metabolic activity had a negative impact on REE sorption, additionally challenging the feasibility of REE biosorption under ideal growth conditions for acidophiles. We further examined the possibility of REE biosorption in the presence of phosphate for biomass growth at elevated pH (pH ≥ 2.5) by assessing aqueous La concentrations in various culture media. Three days after adding La into the media, dissolved La concentrations were up to three orders of magnitude higher than solubility predictions due to supersaturation, though LaPO4 precipitation occurred under all conditions when seed was added. We concluded that biosorption should occur separately from biomass growth to avoid REE phosphate precipitation. Furthermore, we demonstrated the importance of proper control experiments in biosorption studies to assess potential interactions between REEs and matrix ions such as phosphates. KEY POINTS: • REE biosorption with G. sulphuraria increases significantly when raising pH to 5 • Phosphate for biosorbent growth has to be supplied separately from biosorption • Biosorption studies have to assess potential matrix effects on REE behavior.

Unveiling the role of ferrous ion in driving microalgae granulation from salt-tolerant strains for mariculture wastewater treatment.

Development of microalgal-bacterial granular sludge (MBGS) from saline-adapted microalgae is a promising approach for efficient mariculture wastewater treatment, whereas the elusive mechanisms governing granulation have impeded its widespread adoption. In this study, spherical and regular MBGS were successfully developed from mixed culture of pure Spirulina platensis and Chlorella sp. GY-H4 at 10 mg/L Fe2+ concentration. The addition of Fe2+ was proven to induce the formation of Fe-precipitates which served as nucleation sites for microbial attachment and granulation initiation. Additionally, Fe2+ increased the prevalence of exopolysaccharide-producing cyanobacteria, i.e. Synechocystis and Leptolyngbya, facilitating microbial cell adhesion. Furthermore, it stimulated the secretion of extracellular proteins (particularly tryptophan and aromatic proteins), which acted as structural backbone for the development of spherical granule form microalgal flocs. Lastly, it fostered the accumulation of exogenous heterotrophic functional genera, resulting in the efficient removal of DOC (98 %), PO43--P (98 %) and NH4+-N (87 %). Nevertheless, inadequate Fe2+ hindered microalgal floc transformation into granules, excessive Fe2+ expanded the anaerobic zone within the granules, almost halved protein content in the TB-EPS, and inhibited the functional genes expression, ultimately leading to an irregular granular morphology and diminished nutrient removal. This research provides valuable insights into the mechanisms by which Fe2+ promotes the granulation of salt-tolerant microalgae, offering guidance for the establishment and stable operation of MBGS systems in mariculture wastewater treatment.

Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater.

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

One-step bioremediation of hypersaline and nutrient-rich food industry process water with a domestic microbial community containing diatom Halamphora coffeaeformis.

Proper treatment of hypersaline and nutrient-rich food industry process water (FIPW) is challenging in conventional wastewater plants. Insufficient treatment leads to serious environmental hazards. However, bioremediation of FIPW with an indigenous microbial community can not only recover nutrients but generate biomass of diverse applications. In this study, monoculture of Halamphora coffeaeformis, together with synthetic bacteria isolated from a local wastewater plant, successfully recovered 91% of NH4+-N, 78% of total nitrogen, 95% of total phosphorus as well as 82% of total organic carbon from medium enriched with 10% FIPW. All identified organic acids and amino acids, except oxalic acid, were completely removed after 14 days treatment. A significantly higher biomass concentration (1.74 g L-1) was achieved after 14 days treatment in the medium with 10% FIPW than that in a nutrient-replete lab medium as control. The harvested biomass could be a potential feedstock for high-value biochemicals and fertilizer production, due to fucoxanthin accumulation (3 mg g-1) and a fantastic performance in P assimilation. Metagenomic analysis revealed that bacteria community in the algal system, dominated by Psychrobacter and Halomonas, also contributed to the biomass accumulation and uptake of nutrients. Transcriptomic analysis further disclosed that multiple pathways, involved in translation, folding, sorting and degradation as well as transport and catabolism, were depressed in H. coffeaeformis grown in FIPW-enriched medium, as compared to the control. Collectively, the proposed one-step strategy in this work offers an opportunity to achieve sustainable wastewater management and a way towards circular economy.