The mechanism of carbon source utilization by microalgae when co-cultivated with photosynthetic bacteria

Employing Chlorella pyrenoidosa in eco-friendly acetylsalicylic acid degradation: Insights from physiology and transcriptomics

Emerging contaminants, often present at low concentrations, are of increasing concern due to their persistence and potential hazards. Chlorella pyrenoidosa has shown significant potential for removing these emerging contaminants from aquatic environments. In this study, C. pyrenoidosa effectively removed and degraded acetylsalicylic acid (ASA) at concentrations ranging from 2.2 to 22.1 mg/L, achieving a removal efficiency of 98.8 %, with 89.0 % of this removal attributed to biodegradation. ASA treatment also significantly promoted cellular growth, enhanced protein and soluble sugar accumulation, and improved both photosynthetic and respiratory activities. At 22.1 mg/L ASA, protein content increased by 51.9 %, and soluble sugar content rose by 34.8 %. Transcriptomic analysis revealed that ASA promoted carbon metabolism and nitrogen metabolism. These results highlight C. pyrenoidosa as a promising, eco-friendly solution for the removal of ASA, offering potential applications in sustainable wastewater treatment and resource recovery.

Construction of a microalgal-fungal spore co-culture system for the treatment of wastewater containing Zn(II) and estrone: Pollutant removal and microbial biochemical reactions

The co-culture system of Chlorella sorokiniana and Aspergillus oryzae has demonstrated exceptional tolerance and efficiency in the removal of pollutants from swine manure. This study evaluates the ability of the co-culture system to remove Zn(II) and estrone, while assessing the impact of these pollutants on the system's overall functionality. Results indicated that co-cultivation achieved higher biomass accumulation, peaking at 0.88 g/L after 96 h. Increasing estrone exposure concentration reduced photosynthetic activity and chlorophyll content, whereas Zn(II) exposure initially enhanced and later inhibited chlorophyll synthesis. Co-cultivation secreted extracellular polymeric substances, including protein-like and humus-like substances, to alleviate environmental stress and form algal-fungal community. After 96 h of cultivation, the removal efficiencies reached 86.44% for 1.5 mg/L Zn(II) and 84.55% for 20 mg/L estrone. The Quantitative Structure Activity Relationship model revealed a reduction in the ecotoxicity of estrone intermediate products to varying degrees. Metabolomics analysis showed that exposure to estrone and Zn(II) significantly boosted the production of Gibberellic acid, Indole-3-acetic acid, and Zeatin riboside in Chlorella sorokiniana, while reducing Abscisic Acid levels. Furthermore, the exposure led to an increase in various metabolites in the Tricarboxylic acid cycle of the co-cultivation system, influencing the synthesis and metabolism of key biochemical components like carbohydrates, lipids, and proteins. These findings elucidate the biochemical responses of Chlorella sorokiniana-Aspergillus oryzae co-culture system to pollutants and provide insights into its potential application in the treatment of wastewater containing endocrine disrupting chemicals and heavy metals.

Exploring microbial growth dynamics in a pilot-scale microalgae raceway fed with urban wastewater: Insights into the effect of operational variables

Microalgae-based wastewater treatment is a promising technology efficient for nutrient recycling and biomass production. Studies continuously optimize processes to reduce costs and increase productivity. However, changes in the operational conditions affect not only biomass productivity but the dynamics of the overall microbial community. This study characterizes a microalgae culture from an 80 m2 pilot-scale raceway reactor fed with untreated urban wastewater. Operational conditions such as pH, dissolved oxygen control strategies (On-off, PI, Event-based, no control), and culture height were varied to assess microbial population changes. Results demonstrate that increased culture height significantly promotes higher microalgal and bacterial diversity. pH, dissolved oxygen and culture height highly affects nitrifying bacteria activity and nitrogen accumulation. Furthermore, the system exhibited high disinfection capability with average Logarithmic Reduction Values (LRV) of 3.36 for E. coli and 2.57 for Clostridium perfringens. Finally, the fungi species detected included Chytridiomycota and Ascomycota, while purple photosynthetic bacteria were also found in significant abundance within the medium.

Stable isotope labeling and functional gene prediction elucidate the carbon metabolism in fermentative bacteria and microalgae coupling system

The application of the fermentative bacteria and microalgae coupling system in the wastewater treatment has been studied, but there remains few knowledge regarding the organic and inorganic carbon metabolism within this system. In this study, the carbon metabolism of microalgae and fermentative bacteria was elucidated by 13C stable isotope labeling and functional gene prediction, respectively. The 13C glucose and 13C NaHCO3 were used as stable isotope tracers to clarify the organic and inorganic carbon metabolism of microalgae, indicating that approximately 71.5 % of the Acetyl-CoA in microalgae was synthesized from organic carbon sources, while 26.8 % was synthesized through the utilization of inorganic carbon sources. Inorganic carbon sources can enhance the activity of photosynthetic system and facilitate the Calvin cycle. Considering the adequate organic carbon sources and insufficient inorganic carbon sources in the fermentative bacteria and microalgae coupling system, NaHCO3 was added to improve carbon utilization of microalgae. The maximum microalgal lipid yield reached 1130.37 mg/L with 1000 mg/L NaHCO3 supplementation. Functional gene prediction was used to analysis the effect of various carbon composition on the bacterial carbon metabolism. Notably, the additional inorganic carbon sources increased the abundance of bacterial functional genes associated with the fermentation and acetic acids synthesis, which was advantageous for VFAs production and further promoted microalgae growth. This study can gain a deeper understanding of microbial metabolic mechanisms during the operation of fermentative bacteria and microalgae system, and improve its sustained operational stability.

Insights into the response mechanisms of Tetradesmus obliquus to aged polylactic acid and tetracycline exposure via transcriptome analysis and physiological evaluations

Microplastics (MPs) and antibiotics, identified as emerging pollutants, are extensively prevalent in aquatic environments and display prolonged durability. Unlike conventional plastics, biodegradable plastics are more susceptible to decomposition in the environment, resulting in the generation of microplastics and posing potential risks to the aquatic ecosystems. In this study, we assessed growth inhibition, chlorophyll a content, malondialdehyde content (MDA), and antioxidant enzyme activities. These measurements were integrated with transcriptome analysis to explore the response mechanisms of virgin and aged polylactic acid (vPLA and aPLA) and tetracycline (TC) following 14-day exposure to Tetradesmus obliquus, either individually or in combination. The findings indicated that exposure to vPLA did not significantly impact the growth of T. obliquus. Conversely, aPLA demonstrated growth-promoting effects on T. obliquus, particularly in the latter incubation stages. Moreover, a 14-day exposure significantly increased the chlorophyll a content and the activities of superoxide dismutase (SOD), catalase glutathione (CAT) and glutathione S-transferase (GST) within the algal cells. Apart from 1 mg L-1, the TC concentrations of 2.5, 5.0, and 10 mg L-1 exhibited significant toxic effects on T. obliquus, including growth inhibition, decreased chlorophyll a content, elevated activities of SOD, CAT, and GST, and increased MDA levels. Exposure to a combination of 300 mg L-1 aPLA and 5.0 mg L-1 TC, compared to solely 5 mg L-1 TC, demonstrated a notable reduction in TC toxicity to T. obliquus in the presence of aPLA. This was indicated by elevated algal cell density and chlorophyll a content, as well as a decrease in MDA content. Transcriptome analysis indicated an enrichment of differentially expressed genes (DEGs) in pathways linked to porphyrin metabolism, photosynthesis, carbon fixation, and metabolism within the aPLA + TC combined exposure. The study aid in expanding our knowledge of the potential ecological risks posed by biodegradable plastics and accompanying pollutants in aquatic environments.

Unlocking synergies: Harnessing the potential of biological methane sequestration through metabolic coupling between Methylomicrobium alcaliphilum 20Z and Chlorella sp. HS2

A halotolerant consortium between microalgae and methanotrophic bacteria could effectively remediate in situ CH4 and CO2, particularly using saline wastewater sources. Herein, Methylomicrobium alcaliphilum 20Z was demonstrated to form a mutualistic association with Chlorella sp. HS2 at a salinity level above 3.0%. Co-culture significantly enhanced the growth of both microbes, independent of initial inoculum ratios. Additionally, increased methane provision in enclosed serum bottles led to saturated methane removal. Subsequent analyses suggested nearly an order of magnitude increase in the amount of carbon sequestered in biomass in methane-fed co-cultures, conditions that also maintained a suitable cultural pH suitable for methanotrophic growth. Collectively, these results suggest a robust metabolic coupling between the two microbes and the influence of the factors other than gaseous exchange on the assembled consortium. Therefore, multi-faceted investigations are needed to harness the significant methane removal potential of the identified halotolerant consortium under conditions relevant to real-world operation scenarios.

Evaluating nutrient limitation in co-culture of Chlorella pyrenoidosa and Rhodobacter sphaeroides

The influence of nitrogen deficiency on microalgae-bacteria co-culture has been studied mostly with nitrogen-fixing bacteria. Photosynthetic bacteria (PSB), which are non-nitrogen-fixing bacteria, the impact of N deficiency on its co-culture with microalgae is unknown. In this study, Chlorella pyrenoidosa and Rhodobacter sphaeroides co-culture was cultivated photoheterotrophically with acetate. The impact of N starvation and different P supply levels on oil production were examined. When phosphorus was sufficient, N starvation increased the fatty acid methyl ester (FAME) content from 21.7 % to 28.2 %, and also increased the FAME yield (g CODFAME/g CODAcetate) from 0.17 to 0.22. However, the biomass and FAME productivities decreased. Sufficient phosphorus was also essential for a high growth rate and FAME productivity. Deficiencies in either N or P led to a decrease in the proportion of unsaturated FAMEs. iTRAQ analysis indicated N starvation promoted oil accumulation by driving the carbon flow to fatty acid synthesis in microalgae from co-culture. This study improves the understanding of biomass and lipid production via microalgae-PSB co-culture in photoheterotrophic cultivation. The mechanism of interaction between microalgae and bacteria needs further study.

Degradation of polycyclic aromatic hydrocarbons in aquatic environments by a symbiotic system consisting of algae and bacteria: green and sustainable technology

Polycyclic aromatic hydrocarbons (PAHs) are genotoxic, carcinogenic, and persistent in the environment and are therefore of great concern in the environmental protection field. Due to the inherent recalcitrance, persistence and nonreactivity of PAHs, they are difficult to remediate via traditional water treatment methods. In recent years, microbial remediation has been widely used as an economical and environmentally friendly degradation technology for the treatment of PAH-contaminated water. Various bacterial and microalgal strains are capable of potentially degrading or transforming PAHs through intrinsic metabolic pathways. However, their biodegradation potential is limited by the cytotoxic effects of petroleum hydrocarbons, unfavourable environmental conditions, and biometabolic limitations. To address this limitation, microbial communities, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively investigated. The advantages of algal-bacterial cocultivation have been explored, and the limitations of PAHs degradation by monocultures of algae or bacteria have been overcome by algal-bacterial interactions. Therefore, a new model consisting of a "microalgal-bacterial consortium" is becoming a new management strategy for the effective degradation and removal of PAHs. This review first describes PAH pollution control technologies (physical remediation, chemical remediation, bioremediation, etc.) and proposes an algal-bacterial symbiotic system for the degradation of PAHs by analysing the advantages, disadvantages, and PAH degradation performance in this system to fill existing research gaps. Additionally, an algal-bacterial system is systematically developed, and the effects of environmental conditions are explored to optimize the degradation process and improve its technical feasibility. The aim of this paper is to provide readers with an effective green and sustainable remediation technology for removing PAHs from aquatic environments.

Harnessing the potential of microalgae-bacteria interaction for eco-friendly wastewater treatment: A review on new strategies involving machine learning and artificial intelligence

In the pursuit of effective wastewater treatment and biomass generation, the symbiotic relationship between microalgae and bacteria emerges as a promising avenue. This analysis delves into recent advancements concerning the utilization of microalgae-bacteria consortia for wastewater treatment and biomass production. It examines multiple facets of this symbiosis, encompassing the judicious selection of suitable strains, optimal culture conditions, appropriate media, and operational parameters. Moreover, the exploration extends to contrasting closed and open bioreactor systems for fostering microalgae-bacteria consortia, elucidating the inherent merits and constraints of each methodology. Notably, the untapped potential of co-cultivation with diverse microorganisms, including yeast, fungi, and various microalgae species, to augment biomass output. In this context, artificial intelligence (AI) and machine learning (ML) stand out as transformative catalysts. By addressing intricate challenges in wastewater treatment and microalgae-bacteria symbiosis, AI and ML foster innovative technological solutions. These cutting-edge technologies play a pivotal role in optimizing wastewater treatment processes, enhancing biomass yield, and facilitating real-time monitoring. The synergistic integration of AI and ML instills a novel dimension, propelling the fields towards sustainable solutions. As AI and ML become integral tools in wastewater treatment and symbiotic microorganism cultivation, novel strategies emerge that harness their potential to overcome intricate challenges and revolutionize the domain.