Unveiling antimicrobial activity of microalgae Chlorella sorokiniana (UKM2), Chlorella sp. (UKM8) and Scenedesmus sp. (UKM9)

Synergistic interaction between Chlorella vulgaris extract and Origanum elongatum essential oil against methicillin-resistant Staphylococcus aureus

The massive emergence of antimicrobial resistance in recent decades has rendered the use of a single-agent strategy ineffective. Consequently, the combination of different therapeutic agents has emerged as a promising new approach. The aim of the present study was to investigate the combined effect of Chlorella vulgaris methanol extract (CVME) and Origanum elongatum essential oil (OEEO) on methicillin-resistant Staphylococcus aureus (MRSA). Thus, the antibacterial activity of OEEO and CVME on Escherichia coli, Staphylococcus aureus, and MRSA was evaluated using the agar well diffusion and broth microdilution methods. The killing activity of CVME and OEEO, individually and in combination, on MRSA ATCC 43300 was tested using the time-kill assay. The synergistic effect was examined by determining the fractional inhibitory concentration index (FICI) using the checkerboard test. The results showed very significant antibacterial activity against all the bacteria tested, for both OEEO and CVME, with minimum inhibitory concentrations (MICs) ranging from 0.125 to 0.25% (v/v) for OEEO and from 3.12 to 6.25 mg mL-1 for CVME. Minimum bactericidal concentration (MBC) values for OEEO and CVME were in the range 0.125-0.5% (v/v) and 6.25-12.5 mg mL-1, respectively. The inhibition zones associated with OEEO were distinctly greater than those associated with CVME for all the bacteria examined. When used individually, the time-kill curves of OEEO and CVME revealed a dose-dependent effect on MRSA proliferation. Compared with controls, both agents were able to prolong the latent phase of growth curves and decelerate bacterial growth. The killing effect of OEEO on MRSA was considerably higher than that observed with CVME. OEEO prevented MRSA proliferation at only 1/2 of its MIC, while the CVME did so at 2 times its MIC. The combination of OEEO with CVME demonstrated a synergistic effect against MRSA, with a FIC index value of 0.49. The findings therefore suggest that the combination of C. vulgaris methanol extract and O. elongatum essential oil at very low doses may be promising anti-MRSA candidates. A search of the published literature revealed that, to our knowledge, no studies have yet been carried out on the antibacterial potential of combining essential oils and microalgae extracts in the fight against MRSA.

Valorizing Agro-Industrial By-Products for Sustainable Cultivation of Chlorella sorokiniana: Enhancing Biomass, Lipid Accumulation, Metabolites, and Antimicrobial Potential

Background/Objectives: Mixotrophic cultivation of microalgae using agro-industrial by-products as supplements offers a sustainable strategy to enhance biomass production and bioactive compound synthesis. This study aimed to evaluate the effects of different agro-industrial by-products-orange peel extract, Cladophora glomerata macroalgal hydrolysate, and solid-state fungal fermentation hydrolysate-on the growth and bioactivity of Chlorella sorokiniana. Methods: Microalgae were cultivated under mixotrophic conditions with different agro-industrial by-products as organic carbon sources. Biomass accumulation was monitored through dry weight measurements. Lipid extraction was carried out using dimethyl carbonate. The antimicrobial activity of the extracted compounds was assessed against Escherichia coli, Bacillus megaterium, and Bacillus subtilis by determining the minimal inhibitconcentrations. Results: Orange peel extract supplementation resulted in the highest biomass production. It increased dry weight by 13.86-fold compared to autotrophic conditions. Cladophora glomerata macroalgal hydrolysate followed with a 5.79-fold increase, and solid-state fungal fermentation hydrolysate showed a 4.14-fold increase. The lipophilic fraction extracted from microalgal biomass showed high yields. Orange peel extract supplementation achieved the highest extraction yield (274.36 mg/g DW). Antimicrobial activity varied based on the supplement used: biomass cultivated with orange peel extract exhibited superior activity against E. coli, whereas Cladophora glomerata macroalgal hydrolysate biomass demonstrated potent activity against B. subtilis (MIC: 5.67 g/mL). Conclusions: These findings underscore the potential of agro-industrial by-products for enhancing microalgal biomass and metabolite production. The observed antimicrobial properties highlight the application of microalgal-derived compounds in sustainable bioprocesses, supporting their use in pharmaceutical and biotechnological applications.

KEIO knockout collection reveals metabolomic crosstalk in Chlorella spp.-Escherichia coli co-cultures

The interdependence between microalgae and bacteria has sparked scientific interest over years, primarily driven by the practical applications of microalgal-bacteria consortia in wastewater treatment and algal biofuel production. Although adequate studies have focused on the broad interactions and general behavior between the two entities, there remains a scarcity of study on the metabolic role of symbiotic bacteria in promoting microalgal growth. Here, we use the KEIO Knockout Collection, an Escherichia coli gene knockout mutant library, to systematically screen for genes involved in the interdependence of Chlorella sorokiniana and E. coli. By co-cultivating C. sorokiniana and E. coli knockout mutants in 96-well microplates (200 μL medium per well) under white light at 25°C, 31 potential algal growth-promoting and 56 growth-inhibiting genes out of 3985 genes were identified that enhanced (≥1.25-fold) and diminished (≤0.8-fold) the production of algal chlorophyll-a content, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping of these growth-regulating genes suggested a metabolic symbiosis involving bacteria-derived cobalamin (cobU, cobC), biotin (bioB, bioF, bioC, bioD, fabF, fabH), riboflavin (fbp, guaB, gnd, guaA, zwf, purA), and 2,3-butanediol (fumB, adhE, mdh, frdB, pta, sdhC). The effects of these metabolites were further validated by supplementing the agents into the axenic algal cultures; Dose-dependent trends were observed for each metabolite, with a maximum four-fold increase in algal biomass productivity over the control. The specific growth rate of algae was increased by ≥1.27-fold and doubling time was shortened by ≥22.5%. The present results, obtained through genome-wide analyses of interdependence between microalgae and bacteria, reveals multiple interactions between organisms via metabolites.

Dosing Salmonella into poultryponics: Fate of Salmonella during treatment of poultry processing wastewater and irrigation of hydroponic lettuce

"Poultryponics" is a bioponics system that treats poultry processing wastewater (PPW) for hydroponic irrigation. Effective pathogen removal is an under-studied barrier to advancing bioponics technology. This study evaluated the system's capacity to manage high exogenous doses of three Salmonella serotypes commonly associated with poultry. The poultryponics treatment train, operating at ∼115 liters d-1, consisted of bioreactors (algal vs. bacterial), clarifiers, membrane filters, UV disinfection, water storage reservoir, and hydroponic grow beds. The fate of Salmonella spp. in the system was evaluated by analyzing water and lettuce samples for Salmonella contamination across three experimental stages: pre-inoculation (days 0-10), inoculation (days 11-20), and recovery (days 21-30). During the inoculation phase, bioreactors were spiked daily at levels significantly higher than those typically detected in PPW (<1 log10 CFU mL -1Salmonella). When challenged at 3 log10 CFU mL -1, the Salmonella levels observed in the algal and bacterial bioreactors were 0.6 and 1.4 log10 CFU mL -1, representing a 99.6% and 97.5% reduction, respectively (p = 0.03). UV disinfection eliminated Salmonella from water samples, with no Salmonella detection in lettuce. At the 5 log10 CFU mL -1 dosage, Salmonella counts in bioreactor effluent were reduced to approximately 3 log10 CFU mL -1 by day 15 of inoculation (99% reduction). However, as Salmonella dosage continued, removal efficiency decreased, with Salmonella detection after UV treatment but not in grow beds or lettuce. This study confirms the effectiveness of the poultryponics system in managing Salmonella under extreme contamination scenarios.

Antimicrobial peptides (AMPs) from microalgae as an alternative to conventional antibiotics in aquaculture

The excessive use of conventional antibiotics has resulted in significant aquatic pollution and a concerning surge in drug-resistant bacteria. Efforts have been consolidated to explore and develop environmentally friendly antimicrobial alternatives to mitigate the imminent threat posed by multi-resistant pathogens. Antimicrobial peptides (AMPs) have gained prominence due to their low propensity to induce bacterial resistance, attributed to their multiple mechanisms of action and synergistic effects. Microalgae, particularly cyanobacteria, have emerged as promising alternatives with antibiotic potential to address these challenges. The aim of this review is to present some AMPs extracted from microalgae, emphasizing their activity against common pathogens and elucidating their mechanisms of action, as well as their potential application in the aquaculture industry. Likewise, the biosynthesis, advantages and disadvantages of the use of AMPs are described. Currently, biotechnology tolls are used to enhance the action of these peptides, such as genetically modified microalgae and recombinant proteins. Cyanobacteria are also mentioned as major producers of peptides, among them, the genus Lyngbya is described as the most important producer of bioactive peptides with potential therapeutic use. The majority of cyanobacterial AMPs are of the cyclic type, meaning that they have cysteine and disulfide bridges, thanks to this, their greater antimicrobial activity and selectivity. Likewise, we found that large hydrophobic aromatic amino acid residues increase specificity, and improve antibacterial efficacy. However, based on the results of this review, it is possible to highlight that while microalgae show potential as a source of AMPs, further research in this field is necessary to achieve safe and competitive production. Therefore, the data presented here can aid in the selection of microalgal species, peptide structures, and target bacteria, with the goal of establishing biotechnological platforms for aquaculture applications.

Impact of Chlorella sorokiniana feed additive on poultry growth health and oxidative stress in erythrocytes

Microalgae, have emerged as a potentially promising feed additive option due to their beneficial nutritional profile rich in bioactive compounds. The present study examines the incorporation of Chlorella sorokiniana (at 0.1% and 1%) into chicken feed compared to control feed and its effect on growth and health parameters of poultry grown at pilot plant scale. Growth performance parameters (weight, feed conversion ratio (FCR), mortality, European Production Efficiency Index (EPEF)) and the immune system response are examined. In addition, it examines well-being gut health and nutrient absorption related variables via macroscopical and histological analysis. Finally, red blood cell (RBC) morphology and oxidative stress parameters (reactive oxygens species (ROS) and malondialdehyde level) in the whole blood as well as the lipid profile of the adipose tissue are determined. Addition of Chlorella sorokiniana at 0.1% resulted improved growth performance parameters whereas the ROS levels were significantly decreased indicating reduced oxidative stress. Finally, the results of histological analyses of the intestine on parameters related to nutrient absorption correlated with the results on growth performance. On the other hand, addition Chlorella sorokiniana at 1% did not affect significantly the growth performance parameters, resulted in increased footpad dermatitis, increased oxidative stress and alterations in RBC.

Discovery of antimicrobial activity in chemical extracts derived from unexplored algal-bacterial culture systems and isolates

Global health is affected by viral, bacterial, and fungal infections that cause chronic and often fatal diseases. Identifying novel antimicrobials through innovative methods that are active against human pathogens will create a new, necessary pipeline for chemical discovery and therapeutic development. Our goal was to determine whether algal production systems represent fertile ground for discovery of antibiotics and antifungals. To this end, we collected high-biomass algal-bacterial samples from outdoor mass cultivation systems, 18-L outdoor algal open cultures mesocosms, and non-axenic laboratory samples. We also cultivated 33 marine bacterial isolates for chemical extraction. Ultimately, we filtered, concentrated, extracted, and screened 77 chemically-complex mixtures using a conventional agar-based microbial growth inhibition assay against three microbes: Escherichia coli, Bacillus subtilis, and Candida albicans. We discovered that 23 of our chemical extracts (almost one-third of the chemical samples tested) exhibited some degree of growth inhibition toward B. subtilis and/or C. albicans. Our work here demonstrates the feasibility and potential of isolating bioactive natural products from high-biomass algal-bacterial samples from algal mass cultivation systems.

The potential of Chlorella spp. as antiviral source against African swine fever virus through a virtual screening pipeline

African swine fever (ASF) causes high mortality in pigs and threatens global swine production. There is still a lack of therapeutics available, with two vaccines under scrutiny and no approved small-molecule drugs. Eleven (11) viral proteins were used to identify potential antivirals in in silico screening of secondary metabolites (127) from Chlorella spp. The metabolites were screened for affinity and binding selectivity. High-scoring compounds were assessed through in silico ADMET (Absorption, Distribution, Metabolism, Excretion, Toxicity) predictions, compared to structurally similar drugs, and checked for off-target docking with prepared swine receptors. Molecular dynamics (MD) simulations determined binding stability while binding energy was measured in Molecular Mechanics - Generalized Born Surface Area (MMGBSA) or Poisson-Boltzmann Surface Area (MMPBSA). Only six (6) compounds passed until MD analyses, of which five (5) were stable after 100 ns of MD runs. Of these five compounds, only three had binding affinities that were comparable to or stronger than controls. Specifically, phytosterols 24,25-dihydrolanosterol and CID 4206521 that interact with the RNA capping enzyme (pNP868R), and ergosterol which bound to the Erv-like thioreductase (pB119L). The compounds identified in this study can be used as a theoretical basis for in vitro screening to develop potent antiviral drugs against ASFV.

Microalgae as future food: Rich nutrients, safety, production costs and environmental effects

The improvement of food security and nutrition has attracted wide attention, and microalgae as the most promising food source are being further explored. This paper comprehensively introduces basic and functional nutrients rich in microalgae by elaborated tables incorporating a wide variety of studies and summarizes factors influencing their accumulation effects. Subsequently, multiple comparisons of nutrients were conducted, indicating that microalgae have a high protein content. Moreover, controllable production costs and environmental friendliness prompt microalgae into the list that contains more promising and reliable future food. However, microalgae and -based foods approved and sold are limited strictly, showing that safety is a key factor affecting dietary consideration. Notably, sensory profiles and ingredient clarity play an important role in improving the acceptance of microalgae-based foods. Finally, based on the bottleneck in the microalgae food industry, suggestions for its future development were discussed.

A sulfated exopolysaccharide derived from Chlorella sp. exhibiting in vitro anti-α-D-Glucosidase activity

There is a great scientific curiosity to discover all environments sheltering microalgae, especially those with exceptional characteristics from coldest to hottest ones, the purpose remains to explore the potential of the native microalgae flora and the research for new bioactive compounds. This study aimed to isolate a polysaccharide-producing microalga from an extreme ecosystem and to evaluate its capacity to inhibit the α-D-glucosidase enzyme. Chlorella strain is isolated from hypersaline Lake in the Algerian desert. The exopolysaccharide extraction was performed by the concentration of free-cell supernatant in a rotary evaporator. The infrared analysis showed a characteristic footprint of carbohydrates with particular functional groups, such as sulfate. Gas chromatography-mass spectrometry has revealed a hetero-exopolysaccharide composed of galactose 35.75%, glucose 21.13%, xylose 16.81%, fructose 6.96%, arabinose 5.10%, and glucuronic acid 2.68%. The evaluation of the anti-hyperglycemic activity demonstrated a significant α-D-glucosidase inhibition of 80.94 ± 0.01% at 10 mg mL-1 with IC50 equal to 4.31 ± 0.20 mg mL-1. This study opens a vast prospect to use exopolysaccharides as natural nutraceutical or food additive.

Potential of hospital wastewater treatment using locally isolated Chlorella sp. LH2 from cocoon wastewater

Chlorella sp. is able to grow and transform inorganic and organic contaminants in wastewater to create biomass. In the present study, Chlorella sp. LH2 isolated from cocoon wastewater was able to thrive in hospital wastewater, then remove nutrients and eliminate E. coli ATCC 8739. The results indicated that optimal cultivation conditions of Chlorella sp. LH2 in hospital wastewater were pH of 8, light:dark cycle of 16:8 at 30oC. The inhibitory effect of chlorination on algae growth was accompanied with the chlorine concentration. BOD5:COD ratio of 0.77 indicated biodegradability of hospital wastewater. The untreated and treated wastewatee samples were collected to investigated the nutrient removal efficiency after 10 days. Untreated and treated results were192 ± 8.62 mg/l 23.91 ± 2.19 mg/l for BOD5; 245 ± 9.15 mg/l and 47.31 ± 5.71 mg/l for COD. The treated value met the required standards for hospital wastewater treatment. The removal efficiency total nitrogen and total phosphorus were 68.64% and 64.44% after 10 days, respectively. Elimination of E. coli ATCC 8739 after 7 days by Chlorella sp. LH2 was 88.92%. The results of this study suggest the nutrients and pathogens removal potential of Chlorella sp. LH2 in hospital wastewater for further practical applications.

Investigate Freshwater Algae Extract's Efficacy in Treating Diabetes Ulcers and Its Anti-Staphylococcal Properties

Background

Infection of diabetic foot ulcer is very common and leads in 20% of cases to amputation. Antibiotic-resistant Staphylococcus aureus is the main cause of severe infection. Antibiotic resistance is a major challenge to the global health system. This work aimed to investigate the antibacterial efficacy of some algae extracts against Staphylococcus aureus isolated from diabetic foot ulcers.

Methods

freshwater river samples were collected to isolate the algae, and PCR was used for identification. The ethanol, water, and ethyl acetate extract of these algae were prepared and analyzed using high-performance liquid chromatography-mass spectrometry to determine the key components that have antibacterial properties. The antibacterial activity of these extracts against S. aureus was determined by broth dilution and well diffusion methods.

Results

Chlorella vulgaris and Anabaena flos-aquae were isolated from freshwater river and identified by PCR. Anabaena flos-aquae has a greater antibacterial efficacy against Staphylococcus aureus in comparison to Chlorella vulgaris, and the ethanolic extract demonstrated superior outcomes compared to the aqueous and ethyl acetate extracts. The MS spectrum of both algae had a very similar pattern, but the frequency of detected peaks was different.

Conclusions

Ethanolic extract of A. flos-aquae and Chlorella vulgaris can be suggested to treat and control diabetic foot ulcer infection caused by S. aureus. Further studies are required to explore the full potential of these algae safely and extensively.

Microalgae: A potential bioagent for treatment of emerging contaminants from domestic wastewater

Water crisis around the world leads to a growing interest in emerging contaminants (ECs) that can affect human health and the environment. Research showed that thousands of compounds from domestic consumers, such as endocrine disrupting chemicals (EDCs), personal care products (PCPs), and pharmaceuticals active compounds (PhAcs), could be found in wastewater in concentration mostly from ng L-1 to μg L-1. However, generally, wastewater treatment plants (WWTPs) are not designed to remove these ECs from wastewater to their discharge levels. Scientists are looking for economically feasible biotreatment options enabling the complete removal of ECs before discharge. Microalgae cultivation in domestic wastewater is likely a feasible approach for removing emerging contaminants and simultaneously removing any residual organic nutrients. Microalgal growth rate and contaminants removal efficiency could be affected by various factors, including light intensity, CO2 addition, presence of different nutrients, etc., and these parameters could greatly help make microalgae treatment more efficient. Furthermore, the algal biomass harvests could be repurposed to produce various bulk chemicals such as sustainable aviation fuel, biofuel, bioplastic, and biochar; this could significantly enhance the economic viability. Therefore, this review summarizes the microalgae-based bioprocess and their mechanisms for removing different ECs from different wastewaters and highlights the different strategies to improve the ECs removal efficiency. Furthermore, this review shows the role of different ECs in biomass profile and the relevance of using ECs-treated microalgae biomass to produce green products, as well as highlights the challenges and future research recommendations.

Processing and characterization of antimicrobial bioplastic films based on green microalgae Scenedesmus obliquus extract-loaded polyurethane

The green microalga Scenedesmus obliquus, isolated from the Egyptian environment, was used for the synthesis of bio-based plastic materials. Polyurethane (PU) was blended with different proportions (0%, 10%, 20%, and 40%) of chloroform extract to form bioplastic films. The bioplastic films were characterized using water vapor transmission rate measurements and scanning electron microscopy (SEM). The WVTR of pure PU was 193.37 g/m2. day, while the values of algae/PU films were 129.74, 122.56, and 99.75 g/m2.day. S. obliquus reported having Palmitic, which possesses antimicrobial activity and acts as an effective antimicrobial agent in the synthesized bioplastic films. Antimicrobial activity of the algal extract and the synthesized bioplastic films were tested against two Gram-positive bacteria; Staphylococcus aureus, Enterococcus faecalis, two Gram-negative bacteria; Escherichia coli, Pseudomonas aeruginosa, and Candida albicans as a model for fungi. The results indicated that S. obliquus extract exhibited a clear antimicrobial activity against all tested microbes. The antimicrobial rate of bioplastic films containing 40% of the extract reached 100% after 2 h of contact with E. coli and E. faecalis. In conclusion, this study offers a promising future for the use of biodegradable antimicrobial bioplastic films as an affordable and environmentally friendly alternative to plastics in many applications.

Prospective Phycocompounds for Developing Therapeutics for Urinary Tract Infection

Antibiotic resistance of bacteria is causing clinical and public health concerns that are challenging to treat. Infections are becoming more common in the present era, and patients admitted to hospitals often have drug-resistant bacteria that can spread nosocomial infections. Urinary tract infections (UTIs) are among the most common infectious diseases affecting all age groups. There has been an increase in the proportion of bacteria that are resistant to multiple drugs. Herein is a comprehensive update on UTI-associated diseases: cystitis, urethritis, acute urethral syndrome, pyelonephritis, and recurrent UTIs. Further emphasis on the global statistical incidence and recent advancement of the role of natural products in treating notorious infections are described. This updated compendium will inspire the development of novel phycocompounds as the prospective antibacterial candidate.

Microalgae-Based Disinfectant Formulation for Aseptic Processing of Ethiopian Ingredient-Sourced Functional Bread and Its Molecular Docking Analysis to Reduce Hypernatremia

The global prevalence of food-borne infections has become a major concern. Food-borne pathogens like Campylobacter jejuni, Salmonella enterica, and Clostridium botulinum cause food poisoning and even mortality, necessitating the maintenance of aseptic conditions during food processing. The sterilization of food processing facilities often requires chemical and heat treatment. The formulation of many chemical-based disinfectants includes chemicals generating toxic and carcinogenic by-products. The microalgae like Chlorella spp. reportedly exhibit antimicrobial activity and therefore, can be used for formulating safer and eco-friendly natural sanitizers. This study aims to aseptically prepare functional bread using Ethiopian ingredients, highlighting the application of microalgae-based disinfectant formulation and various disinfection techniques. The functional bread was designed to be potentially effective in reducing hypernatremia condition which is indicative of high levels of sodium in serum that can cause an array of symptoms including deaths in serious cases. The physico-chemical and sensory properties of the designed functional bread were analyzed. The interaction of phytochemicals in the ingredients with the target receptor (Vasopressin V2 receptor) and their drug-likeness were determined using molecular docking and Lipinski's rule of five analyses. The results suggest that the designed functional bread incorporating Ethiopian ingredients may serve as an effective dietary strategy to prevent hypernatremia. Aseptic processing of the bread ensures longer shelf life and prevention of spoilage by food pathogens.

Study of the Antimicrobial Potential of the Arthrospira platensis, Planktothrix agardhii, Leptolyngbya cf. ectocarpi, Roholtiella mixta nov., Tetraselmis viridis, and Nanofrustulum shiloi against Gram-Positive, Gram-Negative Bacteria, and Mycobacteria

The incidence of diseases brought on by resistant strains of micro-organisms, including tuberculosis, is rising globally as a result of the rapid rise in pathogenic micro-organism resistance to antimicrobial treatments. Secondary metabolites with potential for antibacterial activity are produced by cyanobacteria and microalgae. In this study, gram-positive (S. aureus, E. faecalis) and gram-negative (K. pneumoniae, A. baumannii, P. aeruginosa) bacteria were isolated from pulmonary tuberculosis patients receiving long-term antituberculosis therapy. The antimicrobial potential of extracts from the cyanobacteria Leptolyngbya cf. ectocarpi, Planktothrix agardhii, Arthrospira platensis, Rohotiella mixta sp. nov., Nanofrustulum shiloi, and Tetraselmis (Platymonas) viridis Rouchijajnen was evaluated. On mouse splenocytes and peritoneal macrophages, extracts of cyanobacteria and microalgae had inhibitory effects. In vitro studies have shown that cyanobacteria and microalgae extracts suppress the growth of bacteria and mycobacteria. At the same time, it has been demonstrated that cyanobacterial and microalgal extracts can encourage bacterial growth in a test tube. Additionally, the enhanced fucoxanthin fraction significantly reduced the development of bacteria in vitro. In a mouse experiment to simulate tuberculosis, the mycobacterial load in internal organs was considerably decreased by fucoxanthin. According to the information gathered, cyanobacteria and microalgae are potential sources of antibacterial compounds that can be used in the manufacturing of pharmaceutical raw materials.

Scenedesmus rubescens Heterotrophic Production Strategies for Added Value Biomass

Microalgae attract interest worldwide due to their potential for several applications. Scenedesmus is one of the first in vitro cultured algae due to their rapid growth and handling easiness. Within this genus, cells exhibit a highly resistant wall and propagate both auto- and heterotrophically. The main goal of the present work is to find scalable ways to produce a highly concentrated biomass of Scenedesmus rubescens in heterotrophic conditions. Scenedesmus rubescens growth was improved at the lab-scale by 3.2-fold (from 4.1 to 13 g/L of dry weight) through medium optimization by response surface methodology. Afterwards, scale-up was evaluated in 7 L stirred-tank reactor under fed-batch operation. Then, the optimized medium resulted in an overall productivity of 8.63 g/L/day and a maximum biomass concentration of 69.5 g/L. S. rubescens protein content achieved approximately 31% of dry weight, similar to the protein content of Chlorella vulgaris in heterotrophy.

Hormone released by the microalgae Neochlorisaquatica and alkalinization influence growth of terrestrial and floating aquatic plants

The microalgae Neochloris aquatica were previously evaluated as a potential biological control agent and source of bioactive compounds against immature stages of Culex quinquefasciatus. Larvae reared on microalgae suspension showed mortality or drastic effects with morphological alterations and damage in the midgut. N. aquatica have nutritional and toxic effects, resulting in delayed life cycle and incomplete adult development. Given the possibility of its use as a biological control agent, in this work we evaluate the effect of microalgae on other organisms of the environment, such as plants. Arabidopsis thaliana, a terrestrial plant, and Lemna sp., a floating aquatic plant, were selected as examples. Interaction assays and compound evaluations showed that the microalgae release auxins causing root inhibition, smaller epidermal cells and hairy root development. In Lemna sp., a slight decrease in growth rate was observed, with no deleterious effects on the fronds. On the other hand, we detected a detrimental effect on plants when interactions were performed in a closed environment, in a medium containing soluble carbonate, in which microalgae culture rapidly modifies the pH. The experiments showed that alkalinization of the medium inhibits plant growth, causing bleaching of leaves or fronds. This negative effect in plants was not observed when plants and microalgae were cultured in carbonate-free media. In conclusion, the results showed that N. aquatica can modify plant growth without being harmful, but the rapid alkalinization produced by carbon metabolism of microalgae under CO₂-limiting conditions, could regulate the number of plants.

Microalgal bioactive metabolites as promising implements in nutraceuticals and pharmaceuticals: inspiring therapy for health benefits

The rapid increase in global population and shrinkage of agricultural land necessitates the use of cost-effective renewable sources as alternative to excessive resource-demanding agricultural crops. Microalgae seem to be a potential substitute as it rapidly produces large biomass that can serve as a good source of various functional ingredients that are not produced/synthesized inside the human body and high-value nonessential bioactive compounds. Microalgae-derived bioactive metabolites possess various bioactivities including antioxidant, anti-inflammatory, antimicrobial, anti-carcinogenic, anti-hypertensive, anti-lipidemic, and anti-diabetic activities, thereof rapidly elevating their demand as interesting option in pharmaceuticals, nutraceuticals and functional foods industries for developing new products. However, their utilization in these sectors has been limited. This demands more research to explore the functionality of microalgae derived functional ingredients. Therefore, in this review, we intended to furnish up-to-date knowledge on prospects of bioactive metabolites from microalgae, their bioactivities related to health, the process of microalgae cultivation and harvesting, extraction and purification of bioactive metabolites, role as dietary supplements or functional food, their commercial applications in nutritional and pharmaceutical industries and the challenges in this area of research.

Graphical abstract

Research Progresses on the Physiological and Pharmacological Benefits of Microalgae-Derived Biomolecules

Microalgae are a kind of photoautotrophic microorganism, which are small, fast in their growth rate, and widely distributed in seawater and freshwater. They have strong adaptability to diverse environmental conditions and contain various nutrients. Many scholars have suggested that microalgae can be considered as a new food source, which should be developed extensively. More importantly, in addition to containing nutrients, microalgae are able to produce a great number of active compounds such as long-chain unsaturated fatty acids, pigments, alkaloids, astaxanthin, fucoidan, etc. Many of these compounds have been proven to possess very important physiological functions such as anti-oxidation, anti-inflammation, anti-tumor functions, regulation of the metabolism, etc. This article aimed to review the physiological functions and benefits of the main microalgae-derived bioactive molecules with their physiological effects.

In vitro Antibiosis of Chlorella vulgaris Extract against the Phytopathogen, Stenotrophomonas maltophilia

The aim of the current study was to evaluate the antibacterial activity of Chlorella vulgaris extracts against Stenotrophomonas maltophilia CSK1 isolated from a diseased cucumber fruit. To this end, water, methanol and ethanol were used separately as solvents to extract the active compounds from the dried Chlorella vulgaris. S. maltophilia CSK1 was identified using the 16S rRNA gene sequencing at 99.93% of identity level. The identity of the bacterial strain CSK1 was confirmed by phylogenetic analyses. CSK1 was clearly clustered with the reference strain, S. maltophilia MTCC 434 (JALV01000036). The antibiosis of the extract against S. maltophilia CSK1 was estimated using agar well diffusion method. Unlike water and ethanolic extracts, the methanolic one exhibited an inhibition of CSK1 (zone of inhibition 13.4 mm), indicating the antimicrobial activity of this extract. No zone of inhibition was formed around ethanolic and water extracts, indicating that both exhibited no-observed effect against the growth of CSK1. This can be attributed to the active constituents in the extract which may varies based on various factors including the polarity of solvent used in the extraction process. The inhibitory effect of the methanolic extract against the S. maltophilia CSK1 obtained from the diseased cucumber fruit could open the door for potential application of such active ingredient within this extract against this bacteria in future.