Cyanobacteria and Eukaryotic Microalgae as Emerging Sources of Antibacterial Peptides

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.

Antimicrobial Activity of Arthrospira (Former Spirulina) and Dunaliella Related to Recognized Antimicrobial Bioactive Compounds

With the increasing rate of the antimicrobial resistance phenomenon, natural products gain our attention as potential drug candidates. Apart from being used as nutraceuticals and for biotechnological purposes, microalgae and phytoplankton have well-recognized antimicrobial compounds and proved anti-infectious potential. In this review, we comprehensively outline the antimicrobial activity of one genus of cyanobacteria (Arthrospira, formerly Spirulina) and of eukaryotic microalgae (Dunaliella). Both, especially Arthrospira, are mostly used as nutraceuticals and as a source of antioxidants for health supplements, cancer therapy and cosmetics. Their diverse bioactive compounds provide other bioactivities and potential for various medical applications. Their antibacterial and antifungal activity vary in a broad range and are strain specific. There are strains of Arthrospira platensis with very potent activity and minimum inhibitory concentrations (MICs) as low as 2-15 µg/mL against bacterial fish pathogens including Bacillus and Vibrio spp. Arthrospira sp. has demonstrated an inhibition zone (IZ) of 50 mm against Staphylococcus aureus. Remarkable is the substantial amount of in vivo studies of Arthrospira showing it to be very promising for preventing vibriosis in shrimp and Helicobacter pylori infection and for wound healing. The innovative laser irradiation of the chlorophyll it releases can cause photodynamic destruction of bacteria. Dunaliella salina has exhibited MIC values lower than 300 µg/mL and an IZ value of 25.4 mm on different bacteria, while Dunaliella tertiolecta has demonstrated MIC values of 25 and 50 μg/mL against some Staphylococcus spp. These values fulfill the criteria for significant antimicrobial activity and sometimes are comparable or exceed the activity of the control antibiotics. The bioactive compounds which are responsible for that action are fatty acids including PUFAs, polysaccharides, glycosides, peptides, neophytadiene, etc. Cyanobacteria, such as Arthrospira, also particularly have antimicrobial flavonoids, terpenes, alkaloids, saponins, quinones and some unique-to-them compounds, such as phycobiliproteins, polyhydroxybutyrate, the peptide microcystin, etc. These metabolites can be optimized by using stress factors in a two-step process of fermentation in closed photobioreactors (PBRs).

Screening of Microalgae for Bioactivity with Antiviral, Antibacterial, Anti-Inflammatory and Anti-Cancer Assays

Marine microalgae are a rich reservoir of natural compounds, including bioactives. Nonetheless, these organisms remain fairly unexplored despite their potential biotechnological applications. Culture collections with diverse taxonomic groups and lifestyles are a good source to unlock this potential and discover new molecules for multiple applications such as the treatment of human pathologies or the production of aquaculture species. In the present work extracts from thirty-three strains (including twenty dinoflagellates, four diatoms and nine strains from seven other algal classes), cultivated under identical conditions, were examined for their antiviral, antibacterial, anti-inflammatory and anti-cancer activities. Among these, antiviral and anti-inflammatory activities were detected in a few strains while the antibacterial tests showed positive results in most assays. In turn, most trials did not show any anti-cancer activity. Significant differences were observed between species within the same class, in particular dinoflagellates, which were better represented in this study. These preliminary findings pave the way for an in-depth characterization of the extracts with highest signals in each test, the identification of the compounds responsible for the biological activities found and a further screening of the CCVIEO culture collection.

Vibrio Species and Cyanobacteria: Understanding Their Association in Local Shrimp Farm Using Canonical Correspondence Analysis (CCA)

In aquatic environments, Vibrio and cyanobacteria establish varying relationships influenced by environmental factors. To investigate their association, this study spanned 5 months at a local shrimp farm, covering the shrimp larvae stocking cycle until harvesting. A total of 32 samples were collected from pond A (n = 6), pond B (n = 6), effluent (n = 10), and influent (n = 10). Vibrio species and cyanobacteria density were observed, and canonical correspondence analysis (CCA) assessed their correlation. CCA revealed a minor correlation (p = 0.847, 0.255, 0.288, and 0.304) between Vibrio and cyanobacteria in pond A, pond B, effluent, and influent water, respectively. Notably, Vibrio showed a stronger correlation with pH (6.14-7.64), while cyanobacteria correlated with pH, salinity (17.4-24 ppt), and temperature (30.8-31.5 °C), with salinity as the most influential factor. This suggests that factors beyond cyanobacteria influence Vibrio survival. Future research could explore species-specific relationships, regional dynamics, and multidimensional landscapes to better understand Vibrio-cyanobacteria connections. Managing water parameters may prove more efficient in controlling vibriosis in shrimp farms than targeting cyanobacterial populations.

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.

Current Scenario and Future Prospects of Endophytic Microbes: Promising Candidates for Abiotic and Biotic Stress Management for Agricultural and Environmental Sustainability

Globally, substantial research into endophytic microbes is being conducted to increase agricultural and environmental sustainability. Endophytic microbes such as bacteria, actinomycetes, and fungi inhabit ubiquitously within the tissues of all plant species without causing any harm or disease. Endophytes form symbiotic relationships with diverse plant species and can regulate numerous host functions, including resistance to abiotic and biotic stresses, growth and development, and stimulating immune systems. Moreover, plant endophytes play a dominant role in nutrient cycling, biodegradation, and bioremediation, and are widely used in many industries. Endophytes have a stronger predisposition for enhancing mineral and metal solubility by cells through the secretion of organic acids with low molecular weight and metal-specific ligands (such as siderophores) that alter soil pH and boost binding activity. Finally, endophytes synthesize various bioactive compounds with high competence that are promising candidates for new drugs, antibiotics, and medicines. Bioprospecting of endophytic novel secondary metabolites has given momentum to sustainable agriculture for combating environmental stresses. Biotechnological interventions with the aid of endophytes played a pivotal role in crop improvement to mitigate biotic and abiotic stress conditions like drought, salinity, xenobiotic compounds, and heavy metals. Identification of putative genes from endophytes conferring resistance and tolerance to crop diseases, apart from those involved in the accumulation and degradation of contaminants, could open new avenues in agricultural research and development. Furthermore, a detailed molecular and biochemical understanding of endophyte entry and colonization strategy in the host would better help in manipulating crop productivity under changing climatic conditions. Therefore, the present review highlights current research trends based on the SCOPUS database, potential biotechnological interventions of endophytic microorganisms in combating environmental stresses influencing crop productivity, future opportunities of endophytes in improving plant stress tolerance, and their contribution to sustainable remediation of hazardous environmental contaminants.

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.

Recent Reports on Bioactive Compounds from Marine Cyanobacteria in Relation to Human Health Applications

The ocean is a valuable natural resource that contains numerous biologically active compounds with various bioactivities. The marine environment comprises unexplored sources that can be utilized to isolate novel compounds with bioactive properties. Marine cyanobacteria are an excellent source of bioactive compounds that have applications in human health, biofuel, cosmetics, and bioremediation. These cyanobacteria exhibit bioactive properties such as anti-inflammatory, anti-cancer, anti-bacterial, anti-parasitic, anti-diabetic, anti-viral, antioxidant, anti-aging, and anti-obesity effects, making them promising candidates for drug development. In recent decades, researchers have focused on isolating novel bioactive compounds from different marine cyanobacteria species for the development of therapeutics for various diseases that affect human health. This review provides an update on recent studies that explore the bioactive properties of marine cyanobacteria, with a particular focus on their potential use in human health applications.

Antibacterial Activity against Four Fish Pathogenic Bacteria of Twelve Microalgae Species Isolated from Lagoons in Western Greece

Microalgae may produce a range of high-value bioactive substances, making them a promising resource for various applications. In this study, the antibacterial activity of twelve microalgae species isolated from lagoons in western Greece was examined against four fish pathogenic bacteria (Vibrio anguillarum, Aeromonas veronii, Vibrio alginolyticus, and Vibrio harveyi). Two experimental approaches were used to evaluate the inhibitory effect of microalgae on pathogenic bacteria. The first approach used bacteria-free microalgae cultures, whereas the second approach used filter-sterilized supernatant from centrifuged microalgae cultures. The results demonstrated that all microalgae had inhibitory effects against pathogenic bacteria in the first approach, particularly 4 days after inoculation, where Asteromonas gracilis and Tetraselmis sp. (red var., Pappas) exhibited the highest inhibitory activity, reducing bacterial growth by 1 to 3 log units. In the second approach, Tetraselmis sp. (red var., Pappas) showed significant inhibition against V. alginolyticus between 4 and 25 h after inoculation. Moreover, all tested cyanobacteria exhibited inhibitory activity against V. alginolyticus between 21 and 48 h after inoculation. Statistical analysis was performed using the independent samples t-test. These findings suggested that microalgae produce compounds with antibacterial activity, which could be useful in aquaculture.

Antimicrobial Peptides from Photosynthetic Marine Organisms with Potential Application in Aquaculture

Aquaculture production is at a record level and is estimated to increase in the coming years. However, this production can be negatively affected by infectious diseases produced by viruses, bacteria, and parasites, causing fish mortality and economic losses. Antimicrobial peptides (AMPs) are small peptides that may be promising candidates to replace antibiotics because they are the first line of defense in animals against a wide variety of pathogens and have no negative effects; they also show additional activities such as antioxidant or immunoregulatory functions, which makes them powerful alternatives for use in aquaculture. Moreover, AMPs are highly available in natural sources and have already been used in the livestock farming and food industries. Photosynthetic marine organisms can survive under all kinds of environmental conditions and under extremely competitive environments thanks to their flexible metabolism. For this reason, these organisms represent a powerful source of bioactive molecules as nutraceuticals and pharmaceuticals, including AMPs. Therefore, in this study we reviewed the present knowledge about AMPs from photosynthetic marine organism sources and analyzed whether they could be suitable for use in aquaculture.

Effect of culture conditions at lab-scale on metabolite composition and antibacterial and antibiofilm activities of Dunaliella tertiolecta

Dunaliella tertiolecta RCC6 was cultivated indoors in glass bubble column photobioreactors operated under batch and semi-continuous regimens and using two different conditions of light and temperature. Biomass was harvested by centrifugation, frozen, and then lyophilized. The soluble material was obtained by sequential extraction of the lyophilized biomass with solvents with a gradient of polarity (hexane, ethyl acetate, and methanol) and its metabolic composition was investigated through nuclear magnetic resonance (NMR) spectroscopy. The effect of light on chlorophyll biosynthesis was clearly shown through the relative intensities of the ¹ H NMR signals due to pheophytins. The highest signal intensity was observed for the biomasses obtained at lower light intensity, resulting in a lower light availability per cell. Under high temperature and light conditions, the ¹ H NMR spectra of the hexane extracts showed an incipient accumulation of triacylglycerols. In these conditions and under semi-continuous regimen, an enhancement of β-carotene and sterols production was observed. The antibacterial and antibiofilm activities of the extracts were also tested. Antibacterial activity was not detected, regardless of culture conditions. In contrast, the minimal biofilm inhibitory concentrations (MBICs) against Escherichia coli for the hexane extract obtained under semi-continuous regimen using high temperature and irradiance conditions was promising.

Antimicrobial peptides derived from microalgae for combating antibiotic resistance: Current status and prospects

Microalgae are photosynthetic cell factories that produce a spectrum of bioactive compounds extensively used for various applications. Owing to the increase in antibiotic resistance among microbial pathogens, there is a significant thrust for identifying new treatment strategies, and antimicrobial peptides (AMPs) generation is one such method. These AMPs have multiple roles and are active against bacteria, fungi, and viruses. Such peptides synthesized in microalgae have a significant role in medical application, managing aquaculture-associated diseases, and the food industry. To increase their effectiveness and novel peptides, genetically modified microalgae are used as cell factories. With the advancement of new technologies like the CRISPR-Cas system, new avenues are opened for developing novel AMPs using microalgae. This review gives us insight into the various AMPs produced by microalgae and multiple technologies involved in creating such therapeutically essential molecules.

Green Antimicrobials as Therapeutic Agents for Diabetic Foot Ulcers

Diabetic foot ulcers (DFU) are one of the most serious and devastating complications of diabetes and account for a significant decrease in quality of life and costly healthcare expenses worldwide. This condition affects around 15% of diabetic patients and is one of the leading causes of lower limb amputations. DFUs generally present poor clinical outcomes, mainly due to the impaired healing process and the elevated risk of microbial infections which leads to tissue damage. Nowadays, antimicrobial resistance poses a rising threat to global health, thus hampering DFU treatment and care. Faced with this reality, it is pivotal to find greener and less environmentally impactful alternatives for fighting these resistant microbes. Antimicrobial peptides are small molecules that play a crucial role in the innate immune system of the host and can be found in nature. Some of these molecules have shown broad-spectrum antimicrobial properties and wound-healing activity, making them good potential therapeutic compounds to treat DFUs. This review aims to describe antimicrobial peptides derived from green, eco-friendly processes that can be used as potential therapeutic compounds to treat DFUs, thereby granting a better quality of life to patients and their families while protecting our fundamental bio-resources.

Cryptic Diversity of Black Band Disease Cyanobacteria in Siderastrea siderea Corals Revealed by Chemical Ecology and Comparative Genome-Resolved Metagenomics

Black band disease is a globally distributed and easily recognizable coral disease. Despite years of study, the etiology of this coral disease, which impacts dozens of stony coral species, is not completely understood. Although black band disease mats are predominantly composed of the cyanobacterial species Roseofilum reptotaenium, other filamentous cyanobacterial strains and bacterial heterotrophs are readily detected. Through chemical ecology and metagenomic sequencing, we uncovered cryptic strains of Roseofilum species from Siderastrea siderea corals that differ from those on other corals in the Caribbean and Pacific. Isolation of metabolites from Siderastrea-derived Roseofilum revealed the prevalence of unique forms of looekeyolides, distinct from previously characterized Roseofilum reptotaenium strains. In addition, comparative genomics of Roseofilum strains showed that only Siderastrea-based Roseofilum strains have the genetic capacity to produce lasso peptides, a family of compounds with diverse biological activity. All nine Roseofilum strains examined here shared the genetic capacity to produce looekeyolides and malyngamides, suggesting these compounds support the ecology of this genus. Similar biosynthetic gene clusters are not found in other cyanobacterial genera associated with black band disease, which may suggest that looekeyolides and malyngamides contribute to disease etiology through yet unknown mechanisms.

Do photosynthetic cells communicate with each other during cell death? From cyanobacteria to vascular plants

As in metazoans, life in oxygenic photosynthetic organisms relies on the accurate regulation of cell death. During development and in response to the environment, photosynthetic cells activate and execute cell death pathways that culminate in the death of a specific group of cells, a process known as regulated cell death (RCD). RCD control is instrumental, as its misregulation can lead to growth penalties and even the death of the entire organism. Intracellular molecules released during cell demise may act as 'survival' or 'death' signals and control the propagation of cell death to surrounding cells, even in unicellular organisms. This review explores different signals involved in cell-cell communication and systemic signalling in photosynthetic organisms, in particular Ca2+, reactive oxygen species, lipid derivates, nitric oxide, and eATP. We discuss their possible mode-of-action as either 'survival' or 'death' molecules and their potential role in determining cell fate in neighbouring cells. By comparing the knowledge available across the taxonomic spectrum of this coherent phylogenetic group, from cyanobacteria to vascular plants, we aim at contributing to the identification of conserved mechanisms that control cell death propagation in oxygenic photosynthetic organisms.

Revisiting the role of cyanobacteria-derived metabolites as antimicrobial agent: A 21st century perspective

Cyanobacterial species are ancient photodiazotrophs prevalent in freshwater bodies and a natural reservoir of many metabolites (low to high molecular weight) such as non-ribosomal peptides, polyketides, ribosomal peptides, alkaloids, cyanotoxins, and isoprenoids with a well-established bioactivity potential. These metabolites enable cyanobacterial survival in extreme environments such as high salinity, heavy metals, cold, UV-B, etc. Recently, these metabolites are gaining the attention of researchers across the globe because of their tremendous applications as antimicrobial agents. Many reports claim the antimicrobial nature of these metabolites; unfortunately, the mode of action of such metabolites is not well understood and/or known limited. Henceforth, this review focuses on the properties and potential application, also critically highlighting the possible mechanism of action of these metabolites to offer further translational research. The review also aims to provide a comprehensive insight into current gaps in research on cyanobacterial biology as antimicrobials and hopes to shed light on the importance of continuing research on cyanobacteria metabolites in the search for novel antimicrobials.

Obtaining Bioproducts from the Studies of Signals and Interactions between Microalgae and Bacteria

The applications of microalgae biomass have been widely studied worldwide. The classical processes used in outdoor cultivations of microalgae, in closed or open photobioreactors, occur in the presence of bacteria. Understanding how communication between cells occurs through quorum sensing and evaluating co-cultures allows the production of microalgae and cyanobacteria to be positively impacted by bacteria, in order to guarantee safety and profitability in the production process. In addition, the definition of the effects that occur during an interaction, promotes insights to improve the production of biomolecules, and to develop innovative products. This review presents the interactions between microalgae and bacteria, including compounds exchanges and communication, and addresses the development of new pharmaceutical, cosmetic and food bioproducts from microalgae based on these evaluations, such as prebiotics, vegan skincare products, antimicrobial compounds, and culture media with animal free protein for producing vaccines and other biopharmaceutical products. The use of microalgae as raw biomass or in biotechnological platforms is in line with the fulfillment of the 2030 Agenda related to the Sustainable Development Goals (SDGs).

Potential anti-skin aging effect of a peptide AYAPE isolated from Isochrysis zhanjiangensis on UVB-induced HaCaT cells and H2O2-induced BJ cells

AYAPE (Ala-Tyr-Ala-Pro-Glu) is a pentapeptide isolated from Isochrysis zhanjiangensis, previous studies have proved that this pentapeptide has antioxidant and inflammatory activities. In this study, we determined the anti-skin aging bioactivity of AYAPE with UVB-induced human immortalized keratinocytes (HaCaT) and H₂O₂-induced human skin fibroblasts (BJ cells) as models. The results showed that AYAPE against UVB-induced photoaging on HaCaT cells via alleviating DNA damage, reducing intracellular reactive oxygen (ROS) levels, down regulating phosphorylation of proteins in MAPK/AP-1 signaling pathways. In addition, AYAPE attenuated senescence related effectors expression in H₂O₂-induced BJ cells. Furthermore, p53 showed an important role in regulation effect of AYAPE in both two cells, and AYAPE showed a directly combination with p53 by molecular docking. These results demonstrated that AYAPE is potential to against skin aging by decreasing matrix metalloproteinase-1 (MMP-1) production, inhibiting inflammation and apoptosis, and attenuating fibroblast senescence.

Two Foreign Antimicrobial Peptides Expressed in the Chloroplast of Porphyridium purpureum Possessed Antibacterial Properties

To solve the problem of antibiotic abuse in aquaculture and to utilize the application potential of antimicrobial peptides (AMPs), a chloroplast transformation system of Porphyridium purpureum was successfully constructed for effectively expressing two exogenous AMPs. The endogenous fragments of 16S rDNA/trnA-23S rDNA were used as flanking fragments for the homologous recombination in the chloroplast genome. Two AMPs encoded by the transformation vector were controlled by the native promoter psbB in a polycistron. The plasmids were transferred into P. purpureum via particle bombardment and the transformation vectors were screened using phosphinothricin (bar), a dominant selection marker under the control of the psbA promoter. Subsequently, in the positive transformed colonies, the exogenous fragments were found to be inserted in the flanking fragments directionally as expected and two foreign AMPs were successfully obtained. Finally, two exogenous peptides with antibacterial properties were obtained from the transformed strain. The two AMPs expressed by the transformed strain were shown to have similar inhibitory effects to antibiotics by inhibition tests. This suggested that AMPs can be introduced into aquaculture using baited microalgae, providing new ideas and ways to solve a series of aquaculture diseases caused by bacteria.

The Immune System of Marine Organisms as Source for Drugs against Infectious Diseases

The high proliferation of microorganisms in aquatic environments has allowed their coevolution for billions of years with other living beings that also inhabit these niches. Among the different existing types of interaction, the eternal competition for supremacy between the susceptible species and their pathogens has selected, as part of the effector division of the immune system of the former ones, a vast and varied arsenal of efficient antimicrobial molecules, which is highly amplified by the broad biodiversity radiated, above any others, at the marine habitats. At present, the great recent scientific and technological advances already allow the massive discovery and exploitation of these defense compounds for therapeutic purposes against infectious diseases of our interest. Among them, antimicrobial peptides and antimicrobial metabolites stand out because of the wide dimensions of their structural diversities, mechanisms of action, and target pathogen ranges. This revision work contextualizes the research in this field and serves as a presentation and scope identification of the Special Issue from Marine Drugs journal “The Immune System of Marine Organisms as Source for Drugs against Infectious Diseases”.

Microalgal drugs: A promising therapeutic reserve for the future

Over the decades, a variety of chemically synthesized drugs are being used to cure existing diseases but often these drugs could not be effectively employed for the treatment of serious and newly emerging diseases. Fortunately, in nature there occurs immense treasure of plants and microorganisms which are living jewels with respect to their richness of medically important metabolites of high value. Hence, amongst the existing microorganism(s), the marine world offers a plethora of biological entities that can contribute to alleviate numerous human ailments. Algae are one such photosynthetic microorganism found in both marine as well as fresh water which are rich source of metabolites known for their nutrient content and health benefits. Various algal species like Haematococcus, Diatoms, Griffithsia, Chlorella, Spirulina, Ulva, etc. have been identified and isolated to produce biologically active and pharmaceutically important high value compounds like astaxanthin, fucoxanthin, sulphur polysaccharides mainly galactose, rhamnose, xylose, fucose etc., which show antimicrobial, antifungal, anti-cancer, and antiviral activities. However, the production of either of these bio compounds is favored under conditions of stress. This review gives detailed information on various nutraceutical metabolites extracted from algae. Additionally focus has been made on the role of these bio compounds extracted from algae especially sulphur polysaccharides to treat several diseases with prospective treatment for SARS-CoV-2. Lastly it covers the knowledge gaps and future perspectives in this area of research.

Antimicrobial Compounds from Microorganisms

Antimicrobial resistance is an exigent public health concern owing to the emergence of novel strains of human resistant pathogens and the concurrent rise in multi-drug resistance. An influx of new antimicrobials is urgently required to improve the treatment outcomes of infectious diseases and save lives. Plant metabolites and bioactive compounds from chemical synthesis have found their efficacy to be dwindling, despite some of them being developed as drugs and used to treat human infections for several decades. Microorganisms are considered untapped reservoirs for promising biomolecules with varying structural and functional antimicrobial activity. The advent of cost-effective and convenient model organisms, state-of-the-art molecular biology, omics technology, and machine learning has enhanced the bioprospecting of novel antimicrobial drugs and the identification of new drug targets. This review summarizes antimicrobial compounds isolated from microorganisms and reports on the modern tools and strategies for exploiting promising antimicrobial drug candidates. The investigation identified a plethora of novel compounds from microbial sources with excellent antimicrobial activity against disease-causing human pathogens. Researchers could maximize the use of novel model systems and advanced biomolecular and computational tools in exploiting lead antimicrobials, consequently ameliorating antimicrobial resistance.

Identification and characterization of the novel bioactive compounds from microalgae and cyanobacteria for pharmaceutical and nutraceutical applications

Microalgae and cyanobacteria (blue-green algae) are used as food by humans. They have gained a lot of attention in recent years because of their potential applications in biotechnology. Microalgae and cyanobacteria are good sources of many valuable compounds, including important biologically active compounds with antiviral, antibacterial, antifungal, and anticancer activities. Under optimal growth condition and stress factors, algal biomass produce varieties of potential bioactive compounds. In the current review, bioactive compounds production and their remarkable applications such as pharmaceutical and nutraceutical applications along with processes involved in identification and characterization of the novel bioactive compounds are discussed. Comprehensive knowledge about the exploration, extraction, screening, and trading of bioactive products from microalgae and cyanobacteria and their pharmaceutical and other applications will open up new avenues for drug discovery and bioprospecting.

Microalgae and Cyanobacteria Strains as Producers of Lipids with Antibacterial and Antibiofilm Activity

Lipids are one of the primary metabolites of microalgae and cyanobacteria, which enrich their utility in the pharmaceutical, feed, cosmetic, and chemistry sectors. This work describes the isolation, structural elucidation, and the antibiotic and antibiofilm activities of diverse lipids produced by different microalgae and cyanobacteria strains from two European collections (ACOI and LEGE-CC). Three microalgae strains and one cyanobacteria strain were selected for their antibacterial and/or antibiofilm activity after the screening of about 600 strains carried out under the NoMorFilm European project. The total organic extracts were firstly fractionated using solid phase extraction methods, and the minimum inhibitory concentration and minimal biofilm inhibitory concentration against an array of human pathogens were determined. The isolation was carried out by bioassay-guided HPLC-DAD purification, and the structure of the isolated molecules responsible for the observed activities was determined by HPLC-HRESIMS and NMR methods. Sulfoquinovosyldiacylglycerol, monogalactosylmonoacylglycerol, sulfoquinovosylmonoacylglycerol, α-linolenic acid, hexadeca-4,7,10,13-tetraenoic acid (HDTA), palmitoleic acid, and lysophosphatidylcholine were found among the different active sub-fractions selected. In conclusion, cyanobacteria and microalgae produce a great variety of lipids with antibiotic and antibiofilm activity against the most important pathogens causing severe infections in humans. The use of these lipids in clinical treatments alone or in combination with antibiotics may provide an alternative to the current treatments.

Biomass pre-treatments of the N2-fixing cyanobacterium Tolypothrix for co-production of methane

Tolypothrix, a self-flocculating, fast growing, CO₂ and nitrogen-fixing cyanobacterium, can be cultivated in nutrient-poor ash dam waters of coal-fired power stations, converting CO₂ emissions into organic biomass. Therefore, the biomass of Tolypothrix sp. is a promising source for bio-fertiliser production, providing micro- and macronutrients. Energy requirements for production could potentially be offset via anaerobic digestion (AD) of the produced biomass, which may further improve the efficiency of the resulting biofertilizer. The aim of this study was to evaluate the effectiveness of pre-treatment conditions and subsequent methane (CH₄) production of Tolypothrix under out-door cultivation conditions. Pre-treatments on biogas and methane production for Tolypothrix sp. biomass investigated were: (1) thermal at 95 °C for 10 h, (2) hydrothermal by autoclave at 121 °C at 1013.25 hPa for 20 min, using a standard moisture-heat procedure, (3) microwave at an output power of 900 W and an exposure time of 3 min, (4) sonication at an output power of 10 W for 3.5 h at 10 min intervals with 20 s breaks and (5) freeze-thaw cycles at -80 °C for 24 h followed by thawing at room temperature. Thermal, hydrothermal and sonication pre-treatments supported high solubilization of organic compounds up to 24.40 g L^-1. However, higher specific CH₄ production of 0.012 and 0.01 L CH₄ g^-1 volatile solids_added. was achieved for thermal and sonic pre-treatments, respectively. High N- and low C-content of the Tolypothrix biomass affected CH₄ recovery, while pre-treatment accelerated production of volatile acids (15.90 g L^-1) and ammonia-N-accumulation (1.41 g L^-1), leading to poor CH₄ yields. Calculated theoretical CH₄ yields based on the elemental composition of the biomass were ~55% higher than actual yields. This highlights the complexity of interactions during AD which are not adequately represented by elemental composition.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Phytoplankton of the Curonian Lagoon as a New Interesting Source for Bioactive Natural Products. Special Impact on Cyanobacterial Metabolites

The bioprospecting of marine and brackish water systems has increased during the last decades. In this respect, microalgae, including cyanobacteria, and their metabolites are one of the most widely explored resources. Most of the bioactive compounds are isolated from ex situ cultures of microorganisms; however, analysis of field samples could also supply valuable information about the metabolic and biotechnological potential of microalgae communities. In this work, the activity of phytoplankton samples from the Curonian Lagoon was studied. The samples were active against antibiotic resistant clinical and environmental bacterial strains as well as against serine proteases and T47D human breast adenocarcinoma cells. No significant effect was found on Daphnia magna. In addition, using LC-MS/MS, we documented the diversity of metabolites present in field samples. A list of 117 detected cyanopeptides was presented. Cyanopeptolins constituted the largest class of cyanopeptides. As complex bloom samples were analyzed, no link between the observed activity and a specific sample component can be established. However, the results of the study showed a biotechnological potential of natural products from the Curonian Lagoon.

Anti-tumour drugs of marine origin currently at various stages of clinical trials (review)

Oncological diseases for a long time have remained one of the most significant health problems of modern society, which causes great losses in its labour and vital potential. Contemporary oncology still faces unsolved issues as insufficient efficacy of treatment of progressing and metastatic cancer, chemoresistance, and side-effects of the traditional therapy which lead to disabilities among or death of a high number of patients. Development of new anti-tumour preparations with a broad range of pharmaceutical properties and low toxicity is becoming increasingly relevant every year. The objective of the study was to provide a review of the recent data about anti-tumour preparations of marine origin currently being at various phases of clinical trials in order to present the biological value of marine organisms – producers of cytotoxic compounds, and the perspectives of their use in modern biomedical technologies. Unlike the synthetic oncological preparations, natural compounds are safer, have broader range of cytotoxic activity, can inhibit the processes of tumour development and metastasis, and at the same time have effects on several etiopathogenic links of carcinogenesis. Currently, practical oncology uses 12 anti-tumour preparations of marine origin (Fludarabine, Cytarabine, Midostaurin, Nelarabine, Eribulin mesylate, Brentuximab vedotin, Trabectedin, Plitidepsin, Enfortumab vedotin, Polatuzumab vedotin, Belantamab mafodotin, Lurbinectedin), 27 substances are at different stages of clinical trials. Contemporary approaches to the treatment of oncological diseases are based on targeted methods such as immune and genetic therapies, antibody-drug conjugates, nanoparticles of biopolymers, and metals. All those methods employ bioactive compounds of marine origin. Numerous literature data from recent years indicate heightened attention to the marine pharmacology and the high potential of marine organisms for the biomedicinal and pharmaceutic industries.

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

The review summarizes the available knowledge on toxins and their producers from rather disparate algal assemblages of aeroterrestrial, airborne and other versatile extreme environments (hot springs, deserts, ice, snow, caves, etc.) and on phycotoxins as contaminants of emergent concern in soil and plants. There is a growing body of evidence that algal toxins and their producers occur in all general types of extreme habitats, and cyanobacteria/cyanoprokaryotes dominate in most of them. Altogether, 55 toxigenic algal genera (47 cyanoprokaryotes) were enlisted, and our analysis showed that besides the “standard” toxins, routinely known from different waterbodies (microcystins, nodularins, anatoxins, saxitoxins, cylindrospermopsins, BMAA, etc.), they can produce some specific toxic compounds. Whether the toxic biomolecules are related with the harsh conditions on which algae have to thrive and what is their functional role may be answered by future studies. Therefore, we outline the gaps in knowledge and provide ideas for further research, considering, from one side, the health risk from phycotoxins on the background of the global warming and eutrophication and, from the other side, the current surge of interest which phycotoxins provoke due to their potential as novel compounds in medicine, pharmacy, cosmetics, bioremediation, agriculture and all aspects of biotechnological implications in human life.