Marine Cyanobacterium Research Articles

Reacquisition of light-harvesting genes in a marine cyanobacterium confers a broader solar niche

The evolution of phenotypic plasticity, i.e., the environmental induction of alternative phenotypes by the same genotype, can be an important mechanism of biological diversification.1,2 For example, an evolved increase in plasticity may promote ecological niche expansion as well as the innovation of novel traits;3 however, both the role of phenotypic plasticity in adaptive evolution and its underlying mechanisms are still poorly understood.4,5 Here, we report that the Chlorophyll d-producing marine cyanobacterium Acaryochloris marina strain MBIC11017 has evolved greater photosynthetic plasticity by reacquiring light-harvesting genes via horizontal gene transfer. The genes, which had been lost by the A.marina ancestor, are involved in the production and degradation of the light-harvesting phycobiliprotein phycocyanin. A.marina MBIC11017 exhibits a high degree of wavelength-dependence in phycocyanin production, and this ability enables it to grow with yellow and green light wavelengths that are inaccessible to other A.marina. Consequently, this strain has a broader solar niche than its close relatives. We discuss the role of horizontal gene transfer for regaining a lost phenotype in light of Dollo's Law6 that the loss of a complex trait is irreversible.

Dynamic Allocation of Carbon Storage and Nutrient-Dependent Exudation in a Revised Genome-Scale Model of Prochlorococcus.

Microbial life in the oceans impacts the entire marine ecosystem, global biogeochemistry and climate. The marine cyanobacterium Prochlorococcus, an abundant component of this ecosystem, releases a significant fraction of the carbon fixed through photosynthesis, but the amount, timing and molecular composition of released carbon are still poorly understood. These depend on several factors, including nutrient availability, light intensity and glycogen storage. Here we combine multiple computational approaches to provide insight into carbon storage and exudation in Prochlorococcus. First, with the aid of a new algorithm for recursive filling of metabolic gaps (ReFill), and through substantial manual curation, we extended an existing genome-scale metabolic model of Prochlorococcus MED4. In this revised model (iSO595), we decoupled glycogen biosynthesis/degradation from growth, thus enabling dynamic allocation of carbon storage. In contrast to standard implementations of flux balance modeling, we made use of forced influx of carbon and light into the cell, to recapitulate overflow metabolism due to the decoupling of photosynthesis and carbon fixation from growth during nutrient limitation. By using random sampling in the ensuing flux space, we found that storage of glycogen or exudation of organic acids are favored when the growth is nitrogen limited, while exudation of amino acids becomes more likely when phosphate is the limiting resource. We next used COMETS to simulate day-night cycles and found that the model displays dynamic glycogen allocation and exudation of organic acids. The switch from photosynthesis and glycogen storage to glycogen depletion is associated with a redistribution of fluxes from the Entner–Doudoroff to the Pentose Phosphate pathway. Finally, we show that specific gene knockouts in iSO595 exhibit dynamic anomalies compatible with experimental observations, further demonstrating the value of this model as a tool to probe the metabolic dynamic of Prochlorococcus.

Bioorganic Study of New Natural Products Isolated from Marine Cyanobacteria

Bioorganic Study of New Natural Products Isolated from Marine Cyanobacteria

Microbial production and consumption of hydrocarbons in the global ocean.

Seeps, spills and other oil pollution introduce hydrocarbons into the ocean. Marine cyanobacteria also produce hydrocarbons from fatty acids, but little is known about the size and turnover of this cyanobacterial hydrocarbon cycle. We report that cyanobacteria in an oligotrophic gyre mainly produce n-pentadecane and that microbial hydrocarbon production exhibits stratification and diel cycling in the sunlit surface ocean. Using chemical and isotopic tracing we find that pentadecane production mainly occurs in the lower euphotic zone. Using a multifaceted approach, we estimate that the global flux of cyanobacteria-produced pentadecane exceeds total oil input in the ocean by 100- to 500-fold. We show that rapid pentadecane consumption sustains a population of pentadecane-degrading bacteria, and possibly archaea. Our findings characterize a microbial hydrocarbon cycle in the open ocean that dwarfs oil input. We hypothesize that cyanobacterial hydrocarbon production selectively primes the ocean's microbiome with long-chain alkanes whereas degradation of other petroleum hydrocarbons is controlled by factors including proximity to petroleum seepage.

Komesuamide and odopenicillatamide, two linear lipopeptides from the marine cyanobacterium Caldora penicillata

The linear lipopeptides komesuamide ( 1 ) and odopenicillatamide ( 2 ) were isolated from Caldora penicillata a marine cyanobacterium collected in Okinawa. The structures of these compounds were established by spectroscopic analyses, and the absolute configurations were determined by HPLC analyses of the acid hydrolysates. Both compounds showed glucose uptake activity at 40 μM in cultured L6 myotubes.

Synthesis and Biological Activities of Cyclodepsipeptides of Aurilide Family from Marine Origin.

Aurilides are a class of depsipeptides occurring mainly in marine cyanobacteria. Members of the aurilide family have shown to exhibit strong cytotoxicity against various cancer cell lines. These compounds bear a pentapeptide, a polyketide, and an α-hydroxy ester subunit in their structure. A large number of remarkable studies on aurilides have emerged since 1996. This comprehensive account summarizes the biological activities and total syntheses of natural compounds of the aurilide family as well as their synthetic analogues.

Aplysiadione and aplysiaenal: Truncated biosynthetic intermediates of aplysiatoxins from a cyanobacterium

Aplysiatoxin and its derivatives have been isolated from marine cyanobacteria. The biosynthesis of their characteristic bicyclic skeletons from a linear polyketide intermediate has been proposed. Two polyketides, aplysiadione (1) and aplysiaenal (2), were isolated from the marine cyanobacterium Moorea producens (formerly Lyngbya majuscula) collected in the Okinawan coastal area. The polyketide chemical structures were elucidated from HR ESI-MS and NMR spectra. Aplysiadione (1) corresponds to a decarboxylated analog of the proposed biosynthetic intermediate of aplysiatoxins. Aplysiaenal (2) is a truncated analog of the linear intermediate. The isolation of aplysiadione (1) strongly supports the proposed ring formation mechanisms for the aplysiatoxins, and this compound is a rare example of a biosynthetic intermediate of polyketide secondary metabolites from marine cyanobacteria.

Cyanobacteria of the Indian Sundarbans: A Potential Source of Powerful Therapeutic Agents

Mangrove forests occupy the estuarine ecotone and harbor a wide range of microorganisms along with a rich diversity of flora and fauna. Marine and estuarine organisms are known to produce unique molecules due to the aggressive, exigent, and competitive surroundings that are unlike those produced in the terrestrial environment. Marine cyanobacteria are a vast resource for new bioactive natural products useful in the development of therapeutics. The Sundarbans mangrove ecosystem harbours various unique microorganisms having different interesting properties. Discovery of a unique alkaline serine protease enzyme tolerant to bleach, detergent, high salt concentration and solvent, isolation and identification of obligatelyhalophilic,euryhaline novel cyanobacteria from intertidal soil surface of the Sundarbans and identification of a pair of novel Streptomyces represent a few of the ongoing endeavors undertaken to explore the mostly untapped microbial diversity of the Sundarbans. This study focuses on two novel strains of cyanobacteria isolated from the intertidal soil surface biofilm of the Indian Sundarbans, which were cultivated on a large scale to yield a significant quantity of biomass for the extraction of secondary metabolites. The cyanobacterial biomass was extracted with a range of polar and non-polar solvents and the ethyl acetate fractions showed significant anti- angiogenic activity when tested against sunitinib (a protein kinase inhibitor). The extracts also showed significantly greater anti- inflammatory activity compared to dexamethasone, which has been shown to reduce the 28 day mortality rate of patients affected by COVID- 19.

Colonies of the Marine Cyanobacterium <i>Trichodesmium</i> Optimize Dust Utilization by Selective Collection and Retention of Nutrient-Rich Particles

Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple pathways for acquiring nutrients from air-borne dust, including the active collection of dust particles. Once concentrated within the colony core, dust can supply Trichodesmium with the limiting nutrients iron (Fe) and phosphorus (P). Studying particle collection by natural colonies, we recently documented a preference for Fe-rich over Fe-free particles. In this follow-up study we examined if colonies selectively collect P-rich particles. Over an entire bloom season, we incubated ~1 200 Trichodesmium colonies from the Red Sea with P-free CaCO3, P-coated CaCO 3 and dust. We utilized three discrete parameters to characterize the colony-particle interactions and integrated them to an index that describes the particle collection behavior over time. Colonies were found to preferably interact, center and retain P-coated CaCO3 in comparison to P-free CaCO3, suggesting that Trichodesmium can optimize its P-acquisition by selecting P-rich particles. In both current and former studies, colonies clearly favored dust over all other particles tested, while nutrient-free particles were barely collected or retained, indicating that Trichodesmium senses the particle composition and preferably collects nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.

Novel Integrative Elements and Genomic Plasticity in Ocean Ecosystems

Horizontal gene transfer accelerates microbial evolution, promoting diversification and adaptation. The globally abundant marine cyanobacterium Prochlorococcus has a highly streamlined genome with frequent gene exchange reflected in its extensive pangenome. The source of its genomic variability, however, remains elusive since most cells lack the common mechanisms that enable horizontal gene transfer, including conjugation, transformation, plasmids and prophages. Examining 623 genomes, we reveal a diverse system of mobile genetic elements – cargo-carrying transposons we named tycheposons – that shape Prochlorococcus’ genomic plasticity. The excision and integration of tycheposons at seven tRNA genes drive the remodeling of larger genomic islands containing most of Prochlorococcus’ flexible genes. Most tycheposons carry genes important for niche differentiation through nutrient acquisition; others appear similar to phage parasites. Tycheposons are highly enriched in extracellular vesicles and phage particles in ocean samples, suggesting efficient routes for their dispersal, transmission and propagation. Supported by evidence for similar elements in other marine microbes, our work underpins the role of vesicle- and virus-mediated transfer of mobile genetic elements in the diversification and adaptation of microbes in dilute aquatic environments – adding a significant piece to the puzzle of what governs microbial evolution in the planet’s largest habitat.

Prebiotic-Inulin as the Major Water Soluble Carbohydrates from Marine Cyanobacterium Phormidium formosum

Prebiotic-Inulin as the Major Water Soluble Carbohydrates from Marine Cyanobacterium Phormidium formosum

Uranium adsorption and oil emulsification by extracellular polysaccharide (EPS) of a halophilic unicellular marine cyanobacterium Synechococcus elongatus BDU130911

An integrated approach on uranium adsorption and emulsification of oils was evaluated using extracellular polysaccharides (EPS) of a marine unicellular cyanobacterium Synechococcus elongatus BDU130911. EPS gel of S. elongatus BDU130911 was able to adsorb uranium at the rate of 75% per gram dry weight. Uranium follows a monolayer adsorption onto EPS gel surface as revealed by Langmuir isotherm. Energy-dispersive X-ray fluorescence (EDXRF) analysis and powder X-ray diffraction analysis further confirms the uranium adsorption to the EPS gel of S. elongatus BDU130911. The culture filtrate of S. elongatus BDU130911 exhibited biosurfactant property and formed a stable emulsion with petrol (EI24 51.2%) due to the presence of uronic acid and rhamnose sugar. These findings suggest that the EPS of S. elongatus BDU130911 biomass has the potential to be used as a green adsorbing agent for the effective extraction of radionucleotide and petroleum hydrocarbons.

Isolation, Structure Determination, and Total Synthesis of Hoshinoamide C, an Antiparasitic Lipopeptide from the Marine Cyanobacterium Caldora penicillata.

Hoshinoamide C (1), an antiparasitic lipopeptide, was isolated from the marine cyanobacterium Caldora penicillata. Its planar structure was elucidated by spectral analyses, mainly 2D NMR, and the absolute configurations of the α-amino acid moieties were determined by degradation reactions followed by chiral-phase HPLC analyses. To clarify the absolute configuration of an unusual amino acid moiety, we synthesized two possible diastereomers of hoshinoamide C and determined its absolute configuration based on a comparison of their spectroscopic data with those of the natural compound. Hoshinoamide C (1) did not exhibit any cytotoxicity against HeLa or HL60 cells at 10 μM, but inhibited the growth of the parasites responsible for malaria (IC50 0.96 μM) and African sleeping sickness (IC50 2.9 μM).

Stoichiometry of Fe, Mn and Co in the marine diazotroph Crocosphaera subtropica ATCC51142 in Fe- and P-limited continuous cultures

We investigated trace element stoichiometries of the nitrogen-fixing marine cyanobacterium Crocosphaera subtropica ATCC51142 under steady-state growth conditions. We utilized exponentially fed batch cultures and varied iron (Fe) concentrations to establish nutrient limitation in C. subtropica growing at a constant growth rate (0.11 d-1). No statistical difference in cell density, chlorophyll a, particulate organic carbon (C), nitrogen (N) and phosphorus (P) were observed between consecutive days after Day 14, and cultures were assumed to be at steady state with respect to growth for the remaining 11 d of the experiment. Cultures were limited by P in the highest Fe treatment (41 nmol l-1) and by Fe in the 2 lower-concentration Fe treatments (1 and 5 nmol l-1). Cell size and in vivo fluorescence changed throughout the experiment in the 1 nmol l-1 Fe treatment, suggesting ongoing acclimation of C. subtropica to our lowest Fe supply. Nevertheless, Fe:C ratios were not significantly different between the Fe treatments, and we calculated an average (±SD) Fe:C ratio of 32 ± 14 µmol mol-1 for growth at 0.11 d-1. Steady-state P-limited cells had lower P quotas, whilst Fe-limited cells had higher manganese (Mn) and cobalt (Co) quotas. We attribute the increase in Mn and Co quotas at low Fe to a competitive effect resulting from changes in the supply ratio of trace elements. Such an effect has implications for variability in elemental stoichiometry in marine phytoplankton, and potential consequences for trace metal uptake and cycling in marine systems.

Detrimental effect of UV-B radiation on growth, photosynthetic pigments, metabolites and ultrastructure of some cyanobacteria and freshwater chlorophyta

Background Global warming directly influencing ozone layer depletion, which eventually is increasing ultraviolet radiation penetration having far-reaching impacts on living biota. This particularly influences the primary producer microalgae which are the basic unit of food webs in the aquatic habitats. Therefore, it is necessary to concentrate the research at this micro-level to understand the harmful impact of increased UV-B radiation ever before. Consequently, the present attempt aimed to focus on the influence of UV-B on growth criteria, photosynthetic pigments, some metabolites, and ultrastructure of the freshwater cyanobacteria, Planktothrix cryptovaginata (Microcoleaceae), Nostoc carneum (Nostocaceae), Microcystis aeruginosa (Microcystaceae), the Chlorophyte Scenedesmus acutus (Scenedesmaceae), and the marine Cyanobacterium Microcystis (Microcystaceae). Methods The cultures of investigated algae were subjected directly to different duration periods (1, 3, 5, and 7 h) of artificial UV-B in addition to unirradiated control culture and allowed to grow for 10 days, after which the algal samples were analyzed for growth, photosynthetic activities, primary metabolities and cellular ultrastructure. Results A remarkable inhibitory influence of UV-B was observed on growth criteria (measured as optical density and dry weight) and photosynthetic pigments of P. cryptovaginata, N. carneum, M. aeruginosa, S. acutus, and marine Microcystis. Where increasing the exposure time of UV-B was accompanied by increased inhibition. The variation in carbohydrate and protein contents under UV stress was based on the exposure periods and the algal species. The variation in algal ultrastructure by UV-B stress was noticed by an Electron Microscope. Cells damage and lysis, cell wall and cell membrane ruptured and release of intracellular substances, loss of cell inclusion, plasmolysis and necrosis, or apoptosis of the algal cells were observed by exposure to 7 h of UV-B. Conclusion Exposure to UV-B has a marked harmful impact on the growth, pigments, and metabolic activity, as well as the cellular ultrastructure of some cyanobacteria and chlorophytes.

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

Cyanobacteria are globally important primary producers and nitrogen fixers with high iron demands. Low ambient dissolved iron concentrations in many aquatic environments mean that these organisms must maintain sufficient and selective transport of iron into the cell. However, the nature of iron transport pathways through the cyanobacterial outer membrane remains obscure. Here we present multiple lines of experimental evidence that collectively support the existence of a novel class of substrate-selective iron porin, Slr1908, in the outer membrane of the cyanobacterium Synechocystis sp. PCC 6803. Elemental composition analysis and short-term iron uptake assays with mutants in Slr1908 reveal that this protein is primarily involved in inorganic iron uptake and contributes less to the accumulation of other metals. Homologues of Slr1908 are widely distributed in both freshwater and marine cyanobacteria, most notably in unicellular marine diazotrophs. Complementary experiments with a homologue of Slr1908 in Synechococcus sp. PCC 7002 restored the phenotype of Synechocystis knockdown mutants, showing that this siderophore producing species also possesses a porin with a similar function in Fe transport. The involvement of a substrate-selective porins in iron uptake may allow cyanobacteria to tightly control iron flux into the cell, particularly in environments where iron concentrations fluctuate.

Chemical and Biological Study of Novel Aplysiatoxin Derivatives from the Marine Cyanobacterium Lyngbya sp.

Since 1970s, aplysiatoxins (ATXs), a class of biologically active dermatoxins, were identified from the marine mollusk Stylocheilus longicauda, whilst further research indicated that ATXs were originally metabolized by cyanobacteria. So far, there have been 45 aplysiatoxin derivatives discovered from marine cyanobacteria with various geographies. Recently, we isolated two neo-debromoaplysiatoxins, neo-debromoaplysiatoxin G (1) and neo-debromoaplysiatoxin H (2) from the cyanobacterium Lyngbya sp. collected from the South China Sea. The freeze-dried cyanobacterium was extracted with liquid–liquid extraction of organic solvents, and then was subjected to multiple chromatographies to yield neo-debromoaplysiatoxin G (1) (3.6 mg) and neo-debromoaplysiatoxin H (2) (4.3 mg). They were elucidated with spectroscopic methods. Moreover, the brine shrimp toxicity of the aplysiatoxin derivatives representing differential structural classifications indicated that the debromoaplysiatoxin was the most toxic compound (half inhibitory concentration (IC50) value = 0.34 ± 0.036 µM). While neo-aplysiatoxins (neo-ATXs) did not exhibit apparent brine shrimp toxicity, but showed potent blocking action against potassium channel Kv1.5, likewise, compounds 1 and 2 with IC50 values of 1.79 ± 0.22 µM and 1.46 ± 0.14 µM, respectively. Therefore, much of the current knowledge suggests the ATXs with different structure modifications may modulate multiple cellular signaling processes in animal systems leading to the harmful effects on public health.

Heterologous Expression of Cryptomaldamide in a Cyanobacterial Host.

Filamentous marine cyanobacteria make a variety of bioactive molecules that are produced by polyketide synthases, nonribosomal peptide synthetases, and hybrid pathways that are encoded by large biosynthetic gene clusters. These cyanobacterial natural products represent potential drug leads; however, thorough pharmacological investigations have been impeded by the limited quantity of compound that is typically available from the native organisms. Additionally, investigations of the biosynthetic gene clusters and enzymatic pathways have been difficult due to the inability to conduct genetic manipulations in the native producers. Here we report a set of genetic tools for the heterologous expression of biosynthetic gene clusters in the cyanobacteria Synechococcus elongatus PCC 7942 and Anabaena (Nostoc) PCC 7120. To facilitate the transfer of gene clusters in both strains, we engineered a strain of Anabaena that contains S.elongatus homologous sequences for chromosomal recombination at a neutral site and devised a CRISPR-based strategy to efficiently obtain segregated double recombinant clones of Anabaena. These genetic tools were used to express the large 28.7 kb cryptomaldamide biosynthetic gene cluster from the marine cyanobacterium Moorena (Moorea) producens JHB in both model strains. S.elongatus did not produce cryptomaldamide; however, high-titer production of cryptomaldamide was obtained in Anabaena. The methods developed in this study will facilitate the heterologous expression of biosynthetic gene clusters isolated from marine cyanobacteria and complex metagenomic samples.

Photosynthetic pigment production and metabolic and lipidomic alterations in the marine cyanobacteria Synechocystis sp. PCC 7338 under various salinity conditions

Synechocystis sp. PCC 7338 (hereafter referred to as Synechocystis 7338) is a marine cyanobacterium that has the potential to produce photosynthetic pigments. In this study, we investigated the effects of various NaCl concentrations (0, 0.4, 0.8, and 1.2 M) on cell growth, photosynthetic pigments, and metabolites and intact lipid species profiles in Synechocystis 7338. The overall growth pattern of Synechocystis 7338 was similar under 0, 0.4, and 0.8 M NaCl conditions. Cell growth was retarded after reaching the exponential phase under 1.2 M NaCl; however, a similar growth pattern was observed after the exponential phase under 0.4 M NaCl (control group). The highest production of chlorophyll a (4.18 mg L−1), allophycocyanin (4.08 mg L−1), and phycoerythrin (1.70 mg L−1) were achieved under 1.2 M NaCl conditions. Altered metabolic and lipidomic profiles were observed at different NaCl conditions; significantly increased relative yields of glucosylglycerol, one diacylglyceryltrimethylhomoserine, one monogalactosyldiacylglycerol, and four phosphatidylglycerol species were observed under 1.2 M NaCl conditions using gas chromatography–mass spectrometry and direct infusion–mass spectrometry analyses. In addition, it was revealed that the photosynthetic activity recovered under 1.2 M NaCl conditions in long-term culture. Hydrogen peroxide content significantly increased under 1.2 M NaCl conditions. It is believed that glutathione content also significantly increased under high salinity conditions to retain the normal functioning of Synechocystis 7338. These results indicate that high salinity conditions for Synechocystis 7338 culture could be used for the large-scale production of chlorophyll a, allophycocyanin, phycoerythrin, and other bioactive metabolites.

Synechococcus elongatus BDU 130192, an Attractive Cyanobacterium for Feedstock Applications: Response to Culture Conditions

Marine cyanobacteria are attractive organisms as feedstock for bioethanol and biotechnological applications. Previously, a marine cyanobacterial strain Synechococcus elongatus BDU 130192 was identified which can accumulate high polyglucan levels without the need to resort to N-deprivation. In this study, among the three different temperatures (30, 34, and 38 °C) tested, the highest biomass accumulation and total carbohydrate occur at 34 °C. The biomass and total carbohydrate increased with increasing light intensities, while protein, chlorophyll, and carotenoid contents were reduced. The best growth occurred at 1.8% NaCl concentration, even though the strain could grow well until 5.8% NaCl. Among the different concentrations of CO2 tested, the best growth occurred at 5% CO2 in the air. NaNO3 gave the best growth, though the cells were able to grow well on urea and NH4Cl too. Tripling the concentration of either N or P in the medium led to a significant increase in growth rate. The strain does not require the addition of vitamin B12 for growth, and about 90% flocculation could be achieved in an hour with the addition of chitosan. High productivities of 0.5 g/L/day of biomass and 0.23 g/L/day of carbohydrates could be reached in a 3-L photobioreactor (PBR) bubbled with air. This work shows many unique properties of this strain such as high carbohydrate productivity, ability to tolerate high light intensities and high concentrations of salt and CO2, and efficient flocculation. These properties make Synechococcus elongatus BDU 130192 an attractive candidate as a feedstock for bioethanol and biotechnological applications.