Removal of parabens from wastewater by Chlorella vulgaris-bacteria co-cultures

Qualitative Assessment of Microalgae-Bacteria Biofilm Development on K5 Carriers: Photoheterotrophic Growth in Wastewater

Wastewater (WW) treatment using biofilms harboring bacteria and microalgae is considered a promising polishing solution to improve current treatment technologies present in wastewater treatment plants (WWTPs), but their interaction in a sessile community remains to be understood. In this work, multi-species biofilms of Chlorella vulgaris, Chlorella sorokiniana, or Scenedesmus obliquus were selected as representative microalgae species of interest for WW bioremediation, and Rhodococcus fascians, Acinetobacter calcoaceticus, or Leucobacter sp. were selected as the bacteria for co-cultivation in a synthetic WW since they are normally found in WW treatment processes. The attached consortia were developed in specific carriers (K5 carriers) for 168 h, and their biofilm formation ability was evaluated in a profilometer and via scanning electron microscopy (SEM) imaging. From the selected microorganisms, C. sorokiniana was the microalga that adapted best to co-cultivation with R. fascians and A. calcoaceticus, developing a thicker biofilm in these two consortia (3.44 ± 0.5 and 4.51 ± 0.8 µm, respectively) in comparison to the respective axenic cultures (2.55 ± 0.7 µm). In contrast, Leucobacter sp. did not promote biofilm growth in association with C. vulgaris and C. sorokiniana, while S. obliquus was not disturbed by the presence of this bacterium. Some bacterial clusters were observed through SEM, especially in A. calcoaceticus cultures in the presence of microalgae. In some combinations (especially when C. vulgaris was co-cultivated with bacteria), the presence of bacteria was able to increase the number of microalga cells adhered to the K5 carrier. This study shows that biofilm development was distinctly dependent on the co-cultivated species, where synergy in biofilm formation was highly dependent on the microalgae and bacteria species. Moreover, profilometry appears to be a promising method for biofilm analyses.

The influence of photoperiod and organic carbon levels in parabens removal from wastewater by Chlorella vulgaris

Parabens are emerging contaminants due to their abundant use as preservatives and inefficient treatment in wastewater (WW) treatment plants. To overcome the limitations of WW treatment plants in removing parabens, microalgae-based bioremediation has aroused great interest as an effective and sustainable process. Nevertheless, several factors affect the WW bioremediation capacity, which must be studied to achieve an effective biological treatment. The main objective of the present work was to evaluate the effects of photoperiod and WW composition, specifically organic carbon concentration (sourced as glucose), on the ability of the microalga Chlorella vulgaris to remove methylparaben (MetP). For that, two photoperiods (12/12 h light/dark and 24 h light) were studied and the composition of synthetic WW (SWW) was manipulated to have a glucose concentration of 0, 3, 30, or 300 mg/L. It was observed that the photoperiod significantly affects the bioremediation process. For a 12/12 h photoperiod, MetP was not removed. Removal was effective for a 24 h photoperiod, with percentages of MetP removal over 88% for glucose concentrations lower than 30 mg/L, decreasing for higher glucose levels. MetP photodegradation was negligible. For the 24 h photoperiod, it was possible to verify that higher glucose concentrations decreased microalga growth, with a decrease in the specific growth rate and the production of photosynthetic pigments. Furthermore, with the increase of the glucose concentration, the MetP constant rate of degradation decreased and its half-life time increased, taking longer to degrade the contaminant (through diauxic growth). Also, C. vulgaris exhibited strong growth ability and removed over 80% of nitrogen and phosphorous, unaffected by the presence of MetP and proportional to glucose levels, underscoring its potential for treating WW contaminated with high concentrations of parabens.

Comprehensive analysis of biotransformation pathways and products of chloramphenicol by Raoultella Ornithinolytica CT3: Pathway elucidation and toxicity assessment

Microbial degradation of chloramphenicol (CAP) has become important for reducing the adverse impact of environmental pollution with antibiotics. Although several pathways for CAP degradation have been identified in various bacteria, multiple metabolic pathways and their respective intermediate metabolites within a single strain are rarely reported. Here, Raoultella ornithinolytica CT3 was first isolated from silkworm excrement using CAP as the sole carbon source, and 100 mg/L CAP was almost completely degraded within 48 h. The biodegradation type of CAP followed first-order kinetics. Twenty-two CAP biotransformation products were identified using high-performance liquid chromatography and ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. The CAP biotransformation pathways were predicted mainly in the acetylation and auxiliary pathways of propionylation and butyrylation. The toxicity of CAP biotransformation products was evaluated using the ecological structure-activity relationship (ECOSAR) model and biological indicators. The results showed that the toxicity of the intermediate metabolites changed slightly, but the final metabolite was harmless to the environment. Genomic analysis predicted that genes encoding acetyltransferase, amido-linkage hydrolase, nitroreductase, haloacetate dehalogenase, and protocatechuate 3,4-dioxygenase were associated with CAP biodegradation. This study provides new insights into the microbial degradation pathway of CAP and constitutes an ecological safety assessment for CAP-contaminated environments.

Review of the Integrated Approaches for Monitoring and Treating Parabens in Water Matrices

Due to their antibacterial and antifungal properties, parabens are commonly used as biocides and preservatives in food, cosmetics, and pharmaceuticals. Parabens have been reported to exist in various water matrices at low concentrations, which renders the need for sample preparation before their quantification using analytical techniques. Thus, sample preparation methods such as solid-phase extraction (SPE), rotating-disk sorptive extraction (RDSE), and vortex-assisted dispersive liquid-liquid extraction (VA-DLLE) that are commonly used for parabens extraction and preconcentration have been discussed. As a result of sample preparation methods, analytical techniques now detect parabens at trace levels ranging from µg/L to ng/L. These compounds have been detected in water, air, soil, and human tissues. While the full impact of parabens on human health and ecosystems is still being debated in the scientific community, it is widely recognized that parabens can act as endocrine disruptors. Furthermore, some studies have suggested that parabens may have carcinogenic effects. The presence of parabens in the environment is primarily due to wastewater discharges, which result in widespread contamination and their concentrations increased during the COVID-19 pandemic waves. Neglecting the presence of parabens in water exposes humans to these compounds through contaminated food and drinking water. Although there are reviews that focus on the occurrence, fate, and behavior of parabens in the environment, they frequently overlook critical aspects such as removal methods, policy development, and regulatory frameworks. Addressing this gap, the effective treatment of parabens in water relies on combined approaches that address both cost and operational challenges. Membrane filtration methods, such as nanofiltration (NF) and reverse osmosis (RO), demonstrate high efficacy but are hindered by maintenance and energy costs due to extensive fouling. Innovations in anti-fouling and energy efficiency, coupled with pre-treatment methods like adsorption, help mitigate these costs and enhance scalability. Furthermore, combining adsorption with advanced oxidation processes (AOPs) or biological treatments significantly improves economic and energy efficiency. Integrating systems like O₃/UV with activated carbon, along with byproduct recovery strategies, further advances circular economy goals by minimizing waste and resource use. This review provides a thorough overview of paraben monitoring in wastewater, current treatment techniques, and the regulatory policies that govern their presence. Furthermore, it provides perspectives that are critical for future scientific investigations and shaping policies aimed at mitigating the risks of parabens in drinking water.

Enhancing treatment performance of Chlorella pyrenoidosa on levofloxacin wastewater through microalgae-bacteria consortia: Mechanistic insights using the transcriptome

Microalgae-bacteria consortia (MBC) system has been shown to enhance the efficiency of microalgae in wastewater treatment, yet its effectiveness in treating levofloxacin (LEV) wastewater remains unexplored. This study compared the treatment of LEV wastewater using pure Chlorella pyrenoidosa (PA) and its MBC constructed with activated sludge bacteria. The results showed that MBC improved the removal efficiency of LEV from 3.50-5.41 % to 33.62-57.20 % by enhancing the growth metabolism of microalgae. The MBC increased microalgae biomass and extracellular polymeric substance (EPS) secretion, yet reduced photosynthetic pigment content compared to the PA. At the phylum level, Proteobacteria and Actinobacteriota are the major bacteria in MBC. Furthermore, the transcriptome reveals that the growth-promoting effects of MBC are associated with the up-regulation of genes encoding the glycolysis, the citrate cycle (TCA cycle), and the pentose phosphate pathway. Enhanced carbon fixation, coupled with down-regulation of photosynthetic electron transfer processes, suggests an energy allocation mechanism within MBC. The up-regulation of porphyrin and arachidonic acid metabolism, along with the expression of genes encoding LEV-degrading enzymes, provides evidence of MBC's superior tolerance to and degradation of LEV. Overall, these findings lead to a better understanding of the underlying mechanisms through which MBC outperforms PA in treating LEV wastewater.

Microalgal-bacterial interactions: Research trend and updated review

Microalgae are being recognized as the key contributor to sustainability in many sectors, starting from energy up to food industries. The microorganism has also been utilized as environmental remediator, capable of converting organic compounds into economically valuable biomass. To optimize the use of microalgae in these sectors, researchers have explored various approaches, of which is the use of bacteria. The interaction between bacteria and microalgae can potentially be harnessed, but its complexity requires extensive research. Herein, we present the bibliometric analysis on microalgal-bacterial interactions. The metadata of published literature was collected through Scopus database on August 4, 2023. The downloaded.csv file was uploaded to VOSViewer and biblioshiny for network visualization. We found that the research has gained a lot of attention from researchers since 2012 with an exponential increase of the publication number. The United States and China are leading the research with a strong collaboration. Based on the research sub-topic clusters, the interaction is mostly studied for wastewater treatment, biomass production, and algal bloom control. Updated reviews on this topic reveal that researchers are now focus on optimizing the efficacy of microalgae-bacteria system, investigating the modes of actions, and identifying challenges in its real-world implementation. The microalgal-bacterial interaction is a promising approach for microalgae utilization in wastewater treatment, biomass production, and algal bloom control.

Potential applications of microalgae-bacteria consortia in wastewater treatment and biorefinery

The use of microalgae-bacteria consortia (MBC) for wastewater treatment has garnered attention as their interactions impart greater environmental adaptability and stability compared with that obtained by only microalgae or bacteria use, thereby improving the efficiency of pollutant removal and bio-product productivity. Additionally, the value-added bio-products produced via biorefineries can improve economic competitiveness and environmental sustainability. Therefore, this review focuses on the interaction between microalgae and bacteria that leads to nutrient exchange, gene transfer and signal transduction to comprehensively understand the interaction mechanisms underlying their strong adaptability. In addition, it includes recent research in which MBC has been efficiently used to treat various wastewater. Moreover, the review summarizes the use of MBC-produced biomass in a biorefining context to produce biofuel, biomaterial, high-value bio-products and bio-fertilizer. Overall, more effort is needed to identify the symbiotic mechanism in MBC to provide a foundation for circular bio-economy and environmentally friendly development programmes.

Bacteria and microalgae associations in periphyton-mechanisms and biotechnological opportunities

Phototrophic and heterotrophic microorganisms coexist in complex and dynamic structures called periphyton. These structures shape the biogeochemistry and biodiversity of aquatic ecosystems. In particular, microalgae-bacteria interactions are a prominent focus of study by microbial ecologists and can provide biotechnological opportunities for numerous applications (i.e. microalgal bloom control, aquaculture, biorefinery, and wastewater bioremediation). In this review, we analyze the species dynamics (i.e. periphyton formation and factors determining the prevalence of one species over another), coexisting communities, exchange of resources, and communication mechanisms of periphytic microalgae and bacteria. We extend periphyton mathematical modelling as a tool to comprehend complex interactions. This review is expected to boost the applicability of microalgae-bacteria consortia, by drawing out knowledge from natural periphyton.