Bioactive compounds produced by cyanobacteria

Cyanobacteria produce a large number of compounds with varying bioactivities. Prominent among these are toxins: hepatotoxins such as microcystins and nodularins and neurotoxins such as anatoxins and saxitoxins. Cytotoxicity to tumor cells has been demonstrated for other cyanobacterial products, including 9-deazaadenosine, dolastatin 13 and analogs. A number of compounds in cyanobacteria are inhibitors of proteases — micropeptins, cyanopeptolins, oscillapeptin, microviridin, aeruginosins- and other enzymes, while still other compounds have no recognized biological activities. In general cyclic peptides and depsipeptides are the most common structural types, but a wide variety of other types are also found: linear peptides, guanidines, phosphonates, purines and macrolides. The close similarity or identity in structures between cyanobacterial products and compounds isolated from sponges, tunicates and other marine invertebrates suggests the latter compounds may be derived from dietary or symbiotic blue-green algae.     

Stimulation of aquatic bacterial activity by cyanobacteria

The time-course response of natural bacterial populations and isolates from lake water to various densities of the filamentous cyanobacteriaAphanizomenon flos-aquae andLyngbya birgei collected from the same lake is reported. The cyanobacteria were separated from the bacteria by dialysis membranes that allowed only dissolved cyanobacterial products to pass. Bacterial³H-thymidine incorporation and cell number were significantly (p<0.05) correlated with cyanobacterial density for both species. Estimated dissolved organic carbon (DOC) utilization, based on bacterial biomass changes over time, were usually significantly (p<0.01) correlated with cyanobacterial density and the decrease in bulk pool DOC for both species. Bacterial volume per cell increased significantly (p<0.05) in response to cyanobacterial density on day 5 of the experiments; cell volume remained unchanged on day 1. Bacterial cell numbers on outer surfaces of the tubular membrane containing the cyanobacteria (on the side exposed to the test bacteria) were significantly (p<0.01) correlated with cyanobacterial density. Statistical analysis inferred that bacteria closely associated with cyanobacteria (i.e. attached) responded more strongly to cyanobacterial products than free-living bacteria. Overall, our results indicate that cyanobacterial products have a potentially important role in regulating bacterioplankton productivity in aquatic systems.     

Strategies of thermal adaptation by high-latitude cyanobacteria

Although mat-forming cyanobacteria dominate many freshwater ecosystems in the Arctic and Antarctic, their optimal temperature for growth (T_opt) is usually much higher than the temperature range of their native habitat. The present study compared the temperature dependence of growth, pigment composition and absorbance, photosynthesis and photosynthate partitioning for two strains of cyanobacteria with contrasting T_opt values; Phormidium subfuscum , isolated from McMurdo Ice Shelf, Antarctica, and Phormidium tenue , collected from the Kuparuk River in the tundra region of northern Alaska. Phormidium subfuscum grew between 5 and 20°C with a T_opt of 15°C whereas P. tenue showed detectable growth from 10 to 40°C and a T_opt of 30°C. Light utilization efficiency, photosynthetic capacity and the irradiance at the onset of light saturation increased with increasing temperature up to T_opt in both strains. The cellular concentrations of chlorophyll a (Chl a) and carotenoid (CAR) and the in vivo absorbance maxima for Chl a, CAR, C-phycocyanin and allophycocyanin changed little for P. subfuscum but all these variables increased across the temperature range up to T_opt for P. tenue . Neither P. subfuscum nor P. tenue showed changes in relative carbon allocation with varying temperature, suggesting that gross biochemical alterations are not a characteristic of temperature acclimation in these cyanobacteria. We conclude that the eurythermal cyanobacterium P. tenue optimizes growth over a wide range of temperatures by adjusting its light-capturing as well as carbon fixation characteristics, whereas stenothermal P. subfuscum relies on changes in carbon fixation without concomitant shifts in pigment content.     

Surfactant-Induced hydrogen production in cyanobacteria

Addition of Tween 85 to aqueous suspensions of Anabaena variabilis induced photosynthetic evolution of hydrogen over a time span of several weeks: As much as 148 nmol H(2)/h . mg dry weight was produced in the first week by a suspension containing 4.2 mg dry weight of cells and 77 mM Tween 85. The chemical structure of Tween 85 was a necessary prerequisite for inducing hydrogen production, as compounds such as Tween 20, 60, and 80 had a quite different effect. There was a coupling between photosynthetic oxygen evolution and hydrogen evolution: Hydrogen evolution started to be effective only when oxygen evolution subdued. The presence of heterocysts in A. variabilis was also required for the Tween-induced hydrogen production. Based on these observations, possible mechanisms for the photosynthetic effect of Tween 85 are advanced and discussed. (c) 1993 John Wiley & Sons, Inc.     

Accumulation of zirconium by microalgae and cyanobacteria

The accumulation of zirconium (Zr) as [Zr₄-(OH)₈(H₂O)₁₆]⁸⁺ by cyanobacteria and microalgae has been characterized. In all the cyanobacterial and microalgal species examined, accumulation consisted of a single rapid energy-independent phase (biosorption) and no energy-dependent accumulation was observed. Biosorption of Zr was concentration-dependent, followed a Freundlich adsorption isotherm, and was dependent on pH, showing decreased accumulation with decreased pH. Prior treatment with Na⁺, K⁺, Cs⁺, Ca²⁺, Mg⁺ and Sr²⁺ (added as chlorides) also decreased Zr accumulation by cyanobacteria and microalgae, probably a result of competition between Zr ions and other cations, including H⁺, for available binding sites on the cell walls. Zr desorption from microalgae and cyanobacteria was increased by increasing external cation concentrations or by decreasing the pH of the desorption agent. Correspondence to: G. M. Gadd     

灰树花漆酶酶学性质的初步研究

漆酶是一种具有广泛应用前景的多功能酶,但能否大规模工业化生产成了制约其应用开发的主要瓶颈之一。担子菌类真菌是分泌漆酶的主要来源之一,灰树花隶属于担子菌,但有关其分泌漆酶的研究鲜有报道。本文初步探讨了pH值、温度及不同阴、阳离子等因素对灰树花孢外漆酶酶学特性的影响,结果表明灰树花孢外漆酶最适反应pH值为2.2,最适反应温度65℃,且反应体系中缓冲液的组成也会影响灰树花漆酶的活性。灰树花漆酶具有较强的热稳定性,但反应体系中若存在卤族离子则会强烈抑制灰树花漆酶的活性。本研究为今后开发利用灰树花漆酶提供了借鉴。     

Rapid small-scale plasmid isolation by several methods from filamentous cyanobacteria

Fifteen strains of cyanobacteria, mainly Nostoc and Anabaena species, were screened for plasmids using five rapid procedures. Two of these methods, based on alkaline extraction and phenol extraction of cleared lysates respectively, were successful with a total of ten species, the latter method proving more sensitive. Plasmids ranging from less than 2.6 to at least 30 mD were isolated; most of the strains examined possessed one or two plasmids, while five lacked detectable plasmid DNA.     

Photoautotrophic synthesis of butyrate by metabolically engineered cyanobacteria

Direct conversion of carbon dioxide into chemicals using engineered autotrophic microorganisms offers a potential solution for both sustainability and carbon mitigation. Butyrate is an important chemical used in various industries, including fragrance, food, and plastics. A model cyanobacterium Synechococcus elongatus PCC 7942 was engineered for the direct photosynthetic conversion of CO ₂ to butyrate. An engineered Clostridium Coenzyme A (CoA)-dependent pathway leading to the synthesis of butyryl-CoA, the precursor to butyrate, was introduced into S. elongatus PCC 7942. Two CoA removal strategies were then individually coupled to the modified CoA-dependent pathway to yield butyrate production. Similar results were observed between the two CoA removal strategies. The best butyrate producing strain of S. elongatus resulted in an observed butyrate titer of 750 mg/L and a cumulative titer of 1.1 g/L. These results demonstrated the feasibility of photosynthetic butyrate production and expanded the chemical repertoire accessible for production by photoautotrophs.     

Cell composition and metal tolerance in cyanobacteria

This review examines interactions between cyanobacteria and metals with an emphasis on metal tolerance in these organisms. Aspects of metal toxicity and accumulation in various cyanobacteria species as related to cell composition will also be reviewed.     

Enhancement of phycobiliprotein production in nitrogen-fixing cyanobacteria

The influence of several environmental factors on the phycobiliprotein content of two phycoerythrin-rich nitrogen-fixing cyanobacteria has been studied in order to maximize pigment production. Total phycobiliprotein content was enhanced when either temperature within the optimum range for growth or cell density of the culture was increased. The phycobiliprotein level increased also in response to a decrease in irradiance. In all cases the effect was more marked for C-phycoerythrin than for C-phycocyanin and allophycocyanin. The cellular content in C-phycoerythrin was also preferentially enhanced when cultures were irradiated with green light. On the other hand, red light induced an increase in the C-phycocyanin content, but the C-phycoerythrin level decreased considerably.     

Iron deprivation in cyanobacteria

Iron is an essential component of electron transport in almost all living organisms. It is particularly important to phototrophs like cyanobacteria because 22–23 irons are required for a complete functional photosynthetic apparatus. Since the low solubility of Fe⁺⁺⁺ above neutral pH in oxic ecosystems severely limits the biological availability of iron to aquatic microorganisms, cyanobacteria and other microbes have developed a number of responses to cope with iron deficiency. Cyanobacterial responses to iron stress include the synthesis of an efficient, siderophore-based system to scavenge iron and the substitution of ferredoxin with flavodoxin. An additional response in cyanobacteria involves the alteration of the light-harvesting apparatus that includes the appearance of a new, iron-stress-induced, photosystem II, chlorophyll-binding protein. Although cytochromec-553 has a potential non-iron-containing replacement in plastocyanin, a copper-containing protein, iron stress appears to favor the utilization of cytochromec-553 because siderophores also bind copper and form a complex that is excluded from the cell.This paper is intended primarily as a review of molecular and physiological responses of actively growing cyanobacterial cultures to conditions of iron stress, where iron is present but essentially insoluble, and to differentiate these responses from iron starvation, where the amount of iron in the system is not sufficient for cell growth.     

Applications of cyanobacteria in biotechnology

Cyanobacteria have gained a lot of attention in recent years because of their potential applications in biotechnology. We present an overview of the literature describing the uses of cyanobacteria in industry and services sectors and provide an outlook on the challenges and future prospects of the field of cyanobacterial biotechnology. Cyanobacteria have been identified as a rich source of biologically active compounds with antiviral, antibacterial, antifungal and anticancer activities. Several strains of cyanobacteria were found to accumulate polyhydroxyalkanoates, which can be used as a substitute for nonbiodegradable petrochemical-based plastics. Recent studies showed that oil-polluted sites are rich in cyanobacterial consortia capable of degrading oil components. Cyanobacteria within these consortia facilitated the degradation processes by providing the associated oil-degrading bacteria with the necessary oxygen, organics and fixed nitrogen. Cyanobacterial hydrogen has been considered as a very promising source of alternative energy, and has now been made commercially available. In addition to these applications, cyanobacteria are also used in aquaculture, wastewater treatment, food, fertilizers, production of secondary metabolites including exopolysaccharides, vitamins, toxins, enzymes and pharmaceuticals. Future research should focus on isolating new cyanobacterial strains producing high value products and genetically modifying existing strains to ensure maximum production of the desired products. Metagenomic libraries should be constructed to discover new functional genes that are involved in the biosynthesis of biotechnological relevant compounds. Large-scale industrial production of the cyanobacterial products requires optimization of incubation conditions and fermenter designs in order to increase productivity.     

Vertical thin-layer photoreactor for controlled cultivation of cyanobacteria

Nostoc sp. was cultivated in an air-lift reactor with continuous recirculation of the head gas phase that aerated and agitated the cyanobacterial suspension at regulated flow rates. The supply of inorganic carbon for growth was coupled with pH control, in the range of 7.7 to 8.1, by intermittent sparging of CO₂-head gas mixtures. The formation of irregular bubbles with swirling motion at the photostage of the reactor promoted efficient CO₂ transference in dense populations of Nostoc sp. (1.1 g/l) when bubbling at flow rates of 10 l/min. Biomass productivity was almost six-fold higher in the photoreactor (16.4 mg/l.h) than in a conventional system (2.8 mg/l.h). The exponential growth phase of cultures in the photoreactor amounted to 60% of the total growth period.The authors are with the Laboratorio de Alimentos, Area Microbiologia, Facultad de Quimica Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis, Argentina     

Bacillus volatiles antagonize cyanobacteria

Abstract Vegetative cells of Dictyostelium discoideum were synchronized by a size selection method which gave good synchrony without indication of any respiratory perturbation or abnormal cellular appearance. During synchronous growth, fluctuations in respiratory activity and in total cellular protein content were consistently observed (14 experiments). Control cultures in which the entire exponential population was selected for under identical centrifugation conditions employed to produce the synchronous cultures did not show this pattern; neither did cells subjected to anaerobiosis, cold shock or centrifugation, which were performed to induce perturbation. It appears that extensive turnover of cellular proteins accompanied by respiratory fluctuations occur in the absence of perturbation during vegetative growth of Dictyostelium discoideum . This picture may represent the changes occurring in single cells which would not be evident in time-averaged observations of exponential cultures.     

Heavy metal sorption by released polysaccharides and whole cultures of two exopolysaccharide-producing cyanobacteria

The metal removal capacity of cultures of two capsulated, exopolysaccharide-producing cyanobacteria, Cyanospira capsulata and Nostoc PCC7936, were tested using copper (II) as the model metal. C. capsulata cultures removed the greatest amount of copper, with a maximum per unit of biomass (q _max) of 115.0±5.1 mg copper g⁻¹ of protein, compared with 85.0±3.2 removed with Nostoc PCC7936 cultures. Water solutions of pure polysaccharides (RPSs) released into the culture medium by C. capsulata and Nostoc PCC7936 achieved q _max values of 20.2±0.8 mg g⁻¹ copper per polysaccharide dry weight with C. capsulata RPS and 11.0±1.5 mg g⁻¹ with Nostoc PCC7936 RPS. Cultures of the two cyanobacteria also removed Zn (II) and Ni (II), in both single-metal systems and in multimetal systems with Cu; in the various single-metal systems more copper was removed than Zn or Ni, while in the multimetal systems a smaller amount of each individual metal was removed but the overall amount of all metal ions sorbed or the amount of copper sorbed in the copper-only system was almost the same with C. capsulata, and slightly higher with Nostoc PCC7936.     

Oxidative stress in cyanobacteria

Reactive oxygen species (ROS) are byproducts of aerobic metabolism and potent agents that cause oxidative damage. In oxygenic photosynthetic organisms such as cyanobacteria, ROS are inevitably generated by photosynthetic electron transport, especially when the intensity of light-driven electron transport outpaces the rate of electron consumption during CO₂ fixation. Because cyanobacteria in their natural habitat are often exposed to changing external conditions, such as drastic fluctuations of light intensities, their ability to perceive ROS and to rapidly initiate antioxidant defences is crucial for their survival. This review summarizes recent findings and outlines important perspectives in this field.     

Alkali-labile precursors of dimethyl sulfide in marine benthic cyanobacteria

By the method of cold alkali hydrolysis, 29 marine benthic cyanobacteria were screened for production of alkali-labile precursors of dimethyl sulfide (DMS) including dimethylsulfoniopropionate (DMSP), a compound of significant importance in marine environments. Concentrations of DMS precursors ranged from undetectable to 0.8 mmol (g Chl a)^–1. The data correspond to some previous investigations concerning DMSP content of marine cyanobacteria and suggest that marine benthic cyanobacteria are only minor producers of DMSP. Received: 3 July 1997 / Accepted: 21 October 1997     

蓝细菌对汞耐受机制的研究进展

蓝细菌对不同形态的汞具有很强的耐受和富集能力，能够改变环境中的汞浓度，影响汞的生物地球化学循环。同时，蓝细菌是生态系统中重要的初级生产者，经过蓝细菌富集的汞更容易进入食物链，影响人类健康。本文系统总结了蓝细菌对汞的耐受机制，主要包括：(1)在细胞壁外合成胶质鞘隔离汞；(2)通过与自身化合物结合钝化汞的毒性；(3)利用自身抗氧化机制修复汞对细胞的损伤；(4)利用自身酶转化汞的形态降低毒性；(5)与抗汞细菌共生抵御汞。基于此，本文展望了蓝细菌汞耐受机制的进一步研究方向，以及利用蓝细菌进行汞解毒和污染修复的前景。