Culture of the marine cyanobacterium, Lyngbya majuscula (Oscillatoriaceae), for bioprocess intensified production of cyclic and linear lipopeptides

Expression of Cyanobacterial Biosynthetic Gene Clusters in Escherichia coli

Cyanobacteria represent an attractive source of natural bioactive compounds, ranging from sunscreens to cancer treatments. While many biosynthetic gene clusters (BGCs) that encode cyanobacterial natural products are known, the slow growth and lack of genetic tools in the native producers hampers their modification, characterization, and large-scale production. By engineering heterologous hosts for the expression of cyanobacterial BGCs, sufficient material can be produced for research or industry. Although several hosts have been evaluated for the expression of cyanobacterial natural products, this work details the process of expressing BGCs in Escherichia coli via promoter exchange.

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.

Peptidoglycan-Associated Cyclic Lipopeptide Disrupts Viral Infectivity

In this article, we consider a role for bacteria in shaping coronavirus infection. Taking cues from studies of enteric viruses, we initially investigated how bacterial surface components might improve CoV infection. Instead, we found that peptidoglycan-associated surfactin is a potent viricidal compound that disrupts virion integrity with broad activity against enveloped viruses. Our results indicate that interactions with commensal bacterial may improve or disrupt viral infections, highlighting the importance of understanding these microbial interactions and their implications for viral pathogenesis and treatment.

Enteric viruses exploit bacterial components, including lipopolysaccharides (LPS) and peptidoglycan (PG), to facilitate infection in humans. Because of their origin in the bat enteric system, we wondered if severe acute respiratory syndrome coronavirus (SARS-CoV) or Middle East respiratory syndrome CoV (MERS-CoV) also use bacterial components to modulate infectivity. To test this question, we incubated CoVs with LPS and PG and evaluated infectivity, finding no change following LPS treatment. However, PG from Bacillus subtilis reduced infection >10,000-fold, while PG from other bacterial species failed to recapitulate this. Treatment with an alcohol solvent transferred inhibitory activity to the wash, and mass spectrometry revealed surfactin, a cyclic lipopeptide antibiotic, as the inhibitory compound. This antibiotic had robust dose- and temperature-dependent inhibition of CoV infectivity. Mechanistic studies indicated that surfactin disrupts CoV virion integrity, and surfactin treatment of the virus inoculum ablated infection in vivo. Finally, similar cyclic lipopeptides had no effect on CoV infectivity, and the inhibitory effect of surfactin extended broadly to enveloped viruses, including influenza, Ebola, Zika, Nipah, chikungunya, Una, Mayaro, Dugbe, and Crimean-Congo hemorrhagic fever viruses. Overall, our results indicate that peptidoglycan-associated surfactin has broad viricidal activity and suggest that bacteria by-products may negatively modulate virus infection.

IMPORTANCE In this article, we consider a role for bacteria in shaping coronavirus infection. Taking cues from studies of enteric viruses, we initially investigated how bacterial surface components might improve CoV infection. Instead, we found that peptidoglycan-associated surfactin is a potent viricidal compound that disrupts virion integrity with broad activity against enveloped viruses. Our results indicate that interactions with commensal bacterial may improve or disrupt viral infections, highlighting the importance of understanding these microbial interactions and their implications for viral pathogenesis and treatment.

The Diversity of Cyanobacterial Toxins on Structural Characterization, Distribution and Identification: A Systematic Review

The widespread distribution of cyanobacteria in the aquatic environment is increasing the risk of water pollution caused by cyanotoxins, which poses a serious threat to human health. However, the structural characterization, distribution and identification techniques of cyanotoxins have not been comprehensively reviewed in previous studies. This paper aims to elaborate the existing information systematically on the diversity of cyanotoxins to identify valuable research avenues. According to the chemical structure, cyanotoxins are mainly classified into cyclic peptides, alkaloids, lipopeptides, nonprotein amino acids and lipoglycans. In terms of global distribution, the amount of cyanotoxins are unbalanced in different areas. The diversity of cyanotoxins is more obviously found in many developed countries than that in undeveloped countries. Moreover, the threat of cyanotoxins has promoted the development of identification and detection technology. Many emerging methods have been developed to detect cyanotoxins in the environment. This communication provides a comprehensive review of the diversity of cyanotoxins, and the detection and identification technology was discussed. This detailed information will be a valuable resource for identifying the various types of cyanotoxins which threaten the environment of different areas. The ability to accurately identify specific cyanotoxins is an obvious and essential aspect of cyanobacterial research.

Extending the "One Strain Many Compounds" (OSMAC) Principle to Marine Microorganisms

Genomic data often highlights an inconsistency between the number of gene clusters identified using bioinformatic approaches as potentially producing secondary metabolites and the actual number of chemically characterized secondary metabolites produced by any given microorganism. Such gene clusters are generally considered as “silent”, meaning that they are not expressed under laboratory conditions. Triggering expression of these “silent” clusters could result in unlocking the chemical diversity they control, allowing the discovery of novel molecules of both medical and biotechnological interest. Therefore, both genetic and cultivation-based techniques have been developed aimed at stimulating expression of these “silent” genes. The principles behind the cultivation based approaches have been conceptualized in the “one strain many compounds” (OSMAC) framework, which underlines how a single strain can produce different molecules when grown under different environmental conditions. Parameters such as, nutrient content, temperature, and rate of aeration can be easily changed, altering the global physiology of a microbial strain and in turn significantly affecting its secondary metabolism. As a direct extension of such approaches, co-cultivation strategies and the addition of chemical elicitors have also been used as cues to activate “silent” clusters. In this review, we aim to provide a focused and comprehensive overview of these strategies as they pertain to marine microbes. Moreover, we underline how changes in some parameters which have provided important results in terrestrial microbes, but which have rarely been considered in marine microorganisms, may represent additional strategies to awaken “silent” gene clusters in marine microbes. Unfortunately, the empirical nature of the OSMAC approach forces scientists to perform extensive laboratory experiments. Nevertheless, we believe that some computation and experimental based techniques which are used in other disciplines, and which we discuss; could be effectively employed to help streamline the OSMAC based approaches. We believe that natural products discovery in marine microorganisms would be greatly aided through the integration of basic microbiological approaches, computational methods, and technological innovations, thereby helping unearth much of the as yet untapped potential of these microorganisms.

Oxidative stress responses in the animal model, Daphnia pulex exposed to a natural bloom extract versus artificial cyanotoxin mixtures

In the natural environment, Daphnia spp. are constantly exposed to a complex matrix of biomolecules, especially during cyanobacterial bloom events. When cyanobacterial cells decay, not only are toxic secondary metabolites known as cyanotoxins released, but also multiple other secondary metabolites, some of which act as enzyme inhibitors. The present study examined the effects of such a natural toxin matrix (crude extract from a bloom) versus artificial toxin mixtures in terms of oxidative stress in Daphnia pulex. The results indicate that there is no significant effect on the survival of D. pulex. However, exposure to the bloom extract resulted in increased lipid peroxidation over a shorter exposure period and reduced antioxidative enzyme activities when compared to the artificial mixtures. The daphnids also needed a longer recovery time to reduce the increased cellular hydrogen peroxide concentration associated with the exposure to the crude extract than with the artificial mixtures. The results indicate a significant difference between the bloom crude extract and the two synthetic mixtures for all stress markers tested, indicating enhanced toxicity of the bloom extract.

A Novel, Poly(Ethyl Ethylene Ether) Inhibitor to Trypsin from Marine Cyanobacteria, Lyngbya confervoides

A novel, poly(ethyl ethylene ether) inhibitor to trypsin was purified from marine cyanobacteria, Lyngbya confervoides from the coastal areas of Thalassery, North Kerala. The kinetics and the thermodynamic parameters of its interactions with the enzyme were also studied. It was demonstrated that the substrate binding, catalytic triad of the enzyme could be blocked by the inhibitor, as expressed by molecular simulation studies. The study also showed that the cyanobacterial group could prove to be a potential source of novel enzyme inhibitors for various applications.

Cyanobacterial community composition in Arctic soil crusts at different stages of development

Cyanobacterial diversity in soil crusts has been extensively studied in arid lands of temperate regions, particularly semi-arid steppes and warm deserts. Nevertheless, Arctic soil crusts have received far less attention than their temperate counterparts. Here, we describe the cyanobacterial communities from various types of soil crusts from Svalbard, High Arctic. Four soil crusts at different development stages (ranging from poorly-developed to well-developed soil crusts) were analysed using 454 pyrosequencing of the V3-V4 variable region of the cyanobacterial 16S rRNA gene. Analyses of 95 660 cyanobacterial sequences revealed a dominance of OTUs belonging to the orders Synechococcales, Oscillatoriales and Nostocales. The most dominant OTUs in the four studied sites were related to the filamentous cyanobacteria Leptolyngbya sp. Phylotype richness estimates increased from poorly- to mid-developed soil crusts and decreased in the well-developed lichenized soil crust. Moreover, pH, ammonium and organic carbon concentrations appeared significantly correlated with the cyanobacterial community structure.

Genome mining demonstrates the widespread occurrence of gene clusters encoding bacteriocins in cyanobacteria

Cyanobacteria are a rich source of natural products with interesting biological activities. Many of these are peptides and the end products of a non-ribosomal pathway. However, several cyanobacterial peptide classes were recently shown to be produced through the proteolytic cleavage and post-translational modification of short precursor peptides. A new class of bacteriocins produced through the proteolytic cleavage and heterocyclization of precursor proteins was recently identified from marine cyanobacteria. Here we show the widespread occurrence of bacteriocin gene clusters in cyanobacteria through comparative analysis of 58 cyanobacterial genomes. A total of 145 bacteriocin gene clusters were discovered through genome mining. These clusters encoded 290 putative bacteriocin precursors. They ranged in length from 28 to 164 amino acids with very little sequence conservation of the core peptide. The gene clusters could be classified into seven groups according to their gene organization and domain composition. This classification is supported by phylogenetic analysis, which further indicated independent evolutionary trajectories of gene clusters in different groups. Our data suggests that cyanobacteria are a prolific source of low-molecular weight post-translationally modified peptides.

Natural antifoulants from the marine cyanobacterium Lyngbya majuscula

Filamentous benthic marine cyanobacteria are a prolific source of structurally unique bioactive secondary metabolites. A total of 12 secondary metabolites, belonging to the mixed polyketide-polypeptide structural class, were isolated from the marine cyanobacterium, Lyngbya majuscula, and were tested to determine if they showed activity against barnacle larval settlement. The assays revealed four compounds, dolastatin 16, hantupeptin C, majusculamide A, and isomalyngamide A, that showed moderate to potent anti-larval settlement activities, with EC(50) values ranging from 0.003 to 10.6 microg ml(-1). In addition, field testing conducted over a period of 28 days (using the modified Phytagel method) based on the cyanobacterial compound, dolastatin 16, showed significantly reduced barnacle settlement as compared to controls at all the concentrations tested. The results of this study highlight the importance of marine cyanobacteria as an underexplored source of potential environmentally friendly antifoulants.

Bioactive compounds from cyanobacteria and microalgae: an overview

Cyanobacteria (blue-green algae) are photosynthetic prokaryotes used as food by humans. They have also been recognized as an excellent source of vitamins and proteins and as such are found in health food stores throughout the world. They are also reported to be a source of fine chemicals, renewable fuel and bioactive compounds. This potential is being realized as data from research in the areas of the physiology and chemistry of these organisms are gathered and the knowledge of cyanobacterial genetics and genetic engineering increased. Their role as antiviral, anti-tumour, antibacterial, anti-HIV and a food additive have been well established. The production of cyanobacteria in artificial and natural environments has been fully exploited. In this review the use of cyanobacteria and microalgae, production processes and biosynthesis of pigments, colorants and certain bioactive compounds are discussed in detail. The genetic manipulation of cyanobacteria and microalgae to improve their quality are also described at length.

Analysis of the hupSL operon of the nonheterocystous cyanobacterium Lyngbya majuscula CCAP 1446/4: regulation of transcription and expression under a light-dark regimen

This work presents the characterization of an uptake hydrogenase from a marine filamentous nonheterocystous cyanobacterium, Lyngbya majuscula CCAP 1446/4. The structural genes encoding the uptake hydrogenase (hupSL) were isolated and characterized, and regulatory sequences were identified upstream of hupS. In silico analysis highlighted various sets of long repetitive sequences within the hupSL intergenic region and downstream of hupL. The transcriptional regulator that operates global nitrogen control in cyanobacteria (NtcA) was shown to bind to the promoter region, indicating its involvement in the transcriptional regulation of hupSL. Under N2-fixing conditions and a 12-h light/12-h dark regime, H2 uptake activity was shown to follow a daily pattern with a clear maximum towards the end of the dark period, preceded by an increase in the transcript levels initiated in the end of the light phase. Novel antibodies directed against HupL of Lyngbya majuscula CCAP 1446/4 were used to monitor the protein levels throughout the 24-h period. The results suggest that protein turnover occurs, with degradation taking place during the light phase and de novo synthesis occurring during the dark phase, coinciding with the pattern of H2 uptake. Taking into account our results and the established correlation between the uptake hydrogenase activity and N2 fixation in cyanobacteria, it seems probable that both processes are confined to the dark period in aerobically grown cells of Lyngbya majuscula CCAP 1446/4.

Screening for new metabolites from marine microorganisms

This article gives an overview of current analysis techniques for the screening and the activity analysis of metabolites from marine (micro)organisms. The sequencing of marine genomes and the techniques of functional genomics (including transcriptome, proteome, and metabolome analyses) open up new possibilities for the screening of new metabolites of biotechnological interest. Although the sequencing of microbial marine genomes has been somewhat limited to date, selected genome sequences of marine bacteria and algae have already been published. This report summarizes the application of the techniques of functional genomics, such as transcriptome analysis in combination with high-resolution two-dimensional polyacrylamide gelelectrophoresis and mass spectrometry, for the screening for bioactive compounds of marine microorganisms. Furthermore, the target analysis of antimicrobial compounds by proteome or transcriptome analysis of bacterial model systems is described. Recent high-throughput screening techniques are explained. Finally, new approaches for the screening of metabolites from marine microorganisms are discussed.

Single-cell-bioreactors as end of miniaturization approaches in biotechnology: progresses with characterised bioreactors and a glance into the future

Incidents with single cells and their genesis have not been the major focus of science up to now. This fact is supported by the difficulties one faces when wanting to monitor and cultivate small populations of cells in a defined compartment under controlled conditions, in vitro. Several approaches of up- and down-scaling have often led to poorly understood results which might be better elucidated by understanding the cellular genesis as a function of its microenvironment. This review of the approaches of scale-up and scale-down processes illustrates technical possibilities and shows up their limitations with regard to obtainable data for the characterisation of cellular genesis and impact of the cellular microenvironment. For example, stem cell research advances underline the lack of information about the impact of the microenvironment on cellular development. Finally, a proposal of future research efforts is given on how to overcome this lack of data via a novel bioreactor setup.

Utilizing the Power of Microbial Genetics to Bridge the Gap Between the Promise and the Application of Marine Natural Products

Marine organisms are a rich source of secondary metabolites. They have yielded thousands of compounds with a broad range of biomedical applications. Thus far, samples required for preclinical and clinical studies have been obtained by collection from the wild, by mariculture, and by total chemical synthesis. However, for a number of complex marine metabolites, none of these options is feasible for either economic or environmental reasons. In order to proceed with the development of many of these promising therapeutic compounds, a reliable and renewable source must be found. Over the last twenty years, the study of microbial secondary metabolites has greatly advanced our understanding of how nature utilizes simple starting materials to yield complex small molecules. Much of this work has focused on polyketides and nonribosomal peptides, two classes of molecules that are prevalent in marine micro- and macroorganisms. The lessons learned from the study of terrestrial metabolite biosynthesis are now being applied to the marine world. As techniques for cloning and heterologous expression of biosynthetic pathways continue to improve, they may provide our greatest hope for bridging the gap between the promise and application of many marine natural products.

Cryo-electron microscopy of vitreous sections of native biological cells and tissues

Cryo-electron microscopy of vitreous sections (CEMOVIS) is, in principle, the ultimate method of specimen preparation. It consists in ultra-rapid cooling of a sizable sample of biological material that is cut into thin sections. These are subsequently observed at low temperature in their fully hydrated vitreous state. Here, we show that CEMOVIS reveals the native state of cells and tissues with unprecedented quality and resolution. What is seen differs considerably from what conventional electron microscopy has shown previously and it is seen with more details. Our findings are demonstrated with images of cyanobacteria and skin.

Biosynthetic pathway and gene cluster analysis of curacin A, an antitubulin natural product from the tropical marine cyanobacterium Lyngbya majuscula

Curacin A (1) is a potent cancer cell toxin obtained from strains of the tropical marine cyanobacterium Lyngbya majuscula found in Curaçao. Its structure is unique in that it contains the sequential positioning of a thiazoline and cyclopropyl ring, and it exerts its potent cell toxicity through interaction with the colchicine drug binding site on microtubules. A series of stable isotope-labeled precursors were fed to cultures of curacin A-producing strains and, following NMR analysis, allowed determination of the metabolic origin of all atoms in the natural product (one cysteine, 10 acetate units, two S-adenosyl methionine-derived methyl groups) as well as several unique mechanistic insights. Moreover, these incorporation experiments facilitated an effective gene cloning strategy that allowed identification and sequencing of the approximately 64 kb putative curacin A gene cluster. The metabolic system is comprised of a nonribosomal peptide synthetase (NRPS) and multiple polyketide synthases (PKSs) and shows a very high level of collinearity between genes in the cluster and the predicted biochemical steps required for curacin biosynthesis. Unique features of the cluster include (1) all but one of the PKSs are monomodular multifunctional proteins, (2) a unique gene cassette that contains an HMG-CoA synthase likely responsible for formation of the cyclopropyl ring, and (3) a terminating motif that is predicted to function in both product release and terminal dehydrative decarboxylation.

Deciphering metabolic networks

All higher organisms divide major biochemical steps into different cellular compartments and often use tissue-specific division of metabolism for the same purpose. Such spatial resolution is accompanied with temporal changes of metabolite synthesis in response to environmental stimuli or developmental needs. Although analyses of primary and secondary gene products, i.e. transcripts, proteins, and metabolites, regularly do not cope with this spatial and temporal resolution, these gene products are often observed to be highly coregulated forming complex networks. Methods to study such networks are reviewed with respect to data acquisition, network statistics, and biochemical interpretation.