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Open Access Research article

Algal production of extra and intra-cellular polysaccharides as an adaptive response to the toxin crude extract of Microcystis aeruginosa

Mostafa Mohamed El-Sheekh1*, Hanan Mohamed Khairy2 and Rania El-Shenody1

Author Affiliations

1 Botany Department, Faculty of Science, Tanta University, Tanta, Egypt

2 National Institute of Oceanography and Fisheries, Alexandria, Egypt

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Iranian Journal of Environmental Health Science & Engineering 2012, 9:10  doi:10.1186/1735-2746-9-10

The electronic version of this article is the complete one and can be found online at:

Received:29 October 2012
Accepted:18 November 2012
Published:20 November 2012

© 2012 El-Sheekh et al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This is an investigation concerned with studying the possible adaptive response of four different unicellular algae, Anabaena PCC 7120, Oscillatoria angustissima, Scendesmus obliquus and Chlorella vulgaris, to the toxin of Microcystis aeruginosa (Kützing). The effects of four different concentrations, 25, 50, 100 and 200 μg mL-1 of microcystins crude extract of M. aeruginosa, on both intra and extra-cellular polysaccharide levels, in log phase, of the four tested algae were studied. The obtained results showed differential increase in the production levels for both intra and extra-cellular polysaccharides by the tested algae, compared with the control. S. obliquus and C. vulgaris showed a resistance to crude toxin higher than Anabaena PCC 7120 and O. angustissima. The highly production of polysaccharides by green algal species under this toxic stress indicated the involvement of these polysaccharides in protecting the algal cells against toxic species and, reflect the biological behavior of particular algal species to the environmental stresses.

Allelopathy; Microcystis aeruginosa; Crude extracts; Intra and extra- cellular polysaccharides; Cyanotoxins


Microcystis aeruginosa is a common hepatotoxic cyanobacterium living in eutrophic freshwaters [1]. The inhibition of competitors by the release of compounds, a process known as allelopathy, may be important in plank tonic systems [2]. Allelopathy has been hypothesized to play a role in species succession [3], the formation of harmful algal blooms in water resources [4], and the establishment of invasive species [5]. Allelopathy is defined as any process involving secondary metabolites produced by plants and microorganisms that influence the growth and development of biological systems, including positive and negative effects [6]. These secondary metabolites are called allelochemicals and play a major role on growth and development in both natural and agro-ecosystems [7]. Most allelopathic are compounds biodegradable and at the same time natural toxins [8].

The production of biologically active substances which promotes the growth of algae and other plant organisms has been reported [9].

The algal cells can release extra-cellular polysaccharides (EPS) into the environment; these EPS are ecologically important through their influence on carbon cycle and microbial diversity [10]. They may enhance the bacterial growth and activity leading to the release of inorganic substances useful for microalgae in the same environment [11]. In addition, these polysaccharides can also make complexes with inorganic ions and thus reducing their toxicity to aquatic organisms [12].

Some green algae can develop a defense system by the production of polysaccharides to cope with oxidative stress induced by microcystin. The results of in vitro assay of antioxidant activity revealed that these polysaccharides had different activities, depending on their sulfate contents [13]. On the other hand, toxic blooms of Nodularia spumigena can provide a potential food source for the heterotrophic food chain [14]. Furthermore, bacteria can efficiently degrade microcystins in natural waters with previous cyanobacterial history, and heterotrophic nanoflagellates respond quickly to the bacterial growth [15]. However, some species of green algae e.g. Scenedesmus sp. coexist and even flourish in the presence of either toxic cyanobacteria or their toxins [16]. Mass-occurrences of cyanobacteria have been reported to increase in frequency, as well as in intensity, due to eutrophication [17]. It is therefore important to investigate how cyanobacteria influence on the structure and functioning of other surrounding organisms in the aquatic ecosystem since River water quality zoning could provide essential information for developing river water quality management policies [18].

Therefore, the aim of this study was to investigate the response of several unicellular algae to the stress of crude toxin of Microcystis aeruginosa through the production of intra and extra-cellular polysaccharides.

Materials and methods

Test organisms

Two unicellular blue green algae (Anabaena PCC. 7120 and Oscillatoria angustissima) and two green algae (Scendesmus obliquus and Chlorella vulgaris) were kindly provided from Phycology Laboratory, Faculty of Science, Tanta University.

Culture and crude extract of cyanobacterium Microcystis aeruginosa

Microcystis aeruginosa was isolated from fresh water samples from Nile river channel near Tanta city, Egypt, and spread with an inoculating needle on the surface of sterilized Petri dishes containing solidified, sterile media (Allen’s, [19]). The cultures of M. aeruginosa purified and prepared in axenic unialgal cultures by Venkataraman [20].

M. aeruginosa was cultured in 1 liter conical flasks containing 400 mL medium (Allen’s, [19]) and kept in controlled conditions of continuous light (45 μmol/ms) and temperature (25±2°C). Algal cells were harvested at the end of log growth phase, lyophilized and kept in deep freeze (−20°C).

The crude extracts were prepared by suspending 100 mg lyophilized cells in 10 mL of 75% methanol according to [21] with ultrasonication (ultrasonic probe with characteristics of ~60 W and ~20 KHZ) for 2 min followed by intermittent shaking for 1 h. Debris was removed by centrifugation for 10 min at 4000 rpm. The pellet was reextracted and the combined supernatants were evaporated to dryness at 30°C using a rotary evaporator (Perfit, India).


All experiments were carried out in 250 mL conical flasks, containing 100 mL Allen’s and Stanier medium which was adjusted to contain 0 (control), 25, 50, 100 and 200 μg/mL of lyophilized cell extract of previously mentioned cyanobacteria species. Culture conditions of the tested algae were the same as previously mentioned. The experimental cultures were harvested at 3, 6, 9, 12 and 15 days for the determination of intra and extra-cellular polysaccharides. Cultures were grown in triplicate for statistical analysis.

Measurement of intra-cellular polysaccharides (IPS)

During the growth, 100 mL of the tested algae cultures were pipette out and centrifuged at 3000 rpm for 10 min. The filtrate was used to estimate extra-cellular polysaccharides and the pellets were dried and then used to estimate intra-cellular polysaccharide as described by [22]. Intra-cellular polysaccharide (IPS) was extracted by homogenizing the derided pellet in distilled water (50 mL). The homogenates were then heated in water bath at 95°C for 6 hours. The extracts were filtrated through Whatman No.2 filter paper, then precipitated with four volumes of 95% ethanol, stirred vigorously and left overnight at 4°C. The precipitated IPS was recovered by centrifugation at 10.000 rpm for 15 min and the supernatant was discarded.

Measurement of extra-cellular polysaccharide (EPS)

The extra-cellular polysaccharides were estimated according to [23]. To precipitate proteins from the algal culture, trichloroacetic acid (TCA) was added in a final concentration of 4% and the algal filtrate was stirred for 2 h. Precipitated proteins were removed by centrifugation. The clear supernatant was collected which contains EPS. Extra-cellular polysaccharides was precipitated by ethanol and determined as described in IPS.

Statistical analysis

Results are presented as mean ±SD (standard deviation) for three replicates. Data obtained were analyzed statistically to determine the degree of significance between treatments using one, two and three way analysis of variance (ANOVA) at P ≤ 0.001. The statistical analyses were carried out using SAS program [24] version 6.12.


Data in Table 1 show the effect of various concentrations of microcystins crude extract of M. aeruginosa (25, 50, 100 and 200 μg/mL), in log phase, on both extra-cellular polysaccharides (EPS) and intra-cellular polysaccharides (IPS) of Anabaena PCC.7120. Results showed a significant increase of both EPS and IPS as compared with control. Thus, the crude microcystins extract could induce the production of polysaccharides and their amounts increased with increasing the microcystins crude extract concentration. At the end of the experiment (day15), the increase in EPS and IPS for Anabaena PCC.7120 amounted by (20%, 52.6%, 81.0% and 132.8%) and (17%, 57%, 91% and 112.6%) over control level for EPS and IPS at different concentrations, respectively. One way analysis of variance revealed a high significant increase in extra and intra-cellular polysaccharides of Anabaena PCC. 7120 as compared with control at (P ≤ 0. 001). On the other hand, in Oscillatoria angustissima, EPS and IPS increased, and amounted by 20%, 37%, 53% and 86.7% and 8.7%, 37.8%, 57.6% and 96%, respectively (Table 2). High significant increase in extra and intra-cellular polysaccharides at (P ≤ 0. 001) compared with the control at all concentrations of the microcystins crude extract except the first concentration 25 μg/mL, the increase in IPS at (all days of experiments) and EPS at 6 days were insignificant.

Table 1. Effect of different concentrations of microcystins crude extract (25, 50, 100 and 200 μg/mL) of Microcystis aeruginosa in log phase on intra (IPS) and extra-cellular polysaccharides content (EPS) in μg/mL of Anabaena PCC. 7120

Table 2. Effect of different concentrations of microcystins crude extract (25, 50, 100 and 200 μg/mL) of Microcystis aeruginosa in log phase on intra (IPS) and extra-cellular polysaccharides content (EPS) in μg/mL of Oscillatoria angustissima

The suggested model (concentrations, days and interception between them) indicated that the deviation in EPS and IPS content of Anabaena PCC.7120 were 99.88% and 98.8% for EPS and IPS, respectively (Table 3) and for O. angustissima were 99.81% and 98.8%, respectively (Table 4).

Table 3. Analysis of variance of extra and intra-cellular polysaccharides of Anabaena PCC.7120 at different concentrations (25, 50, 100 and 200 μg/mL) of microcystins crude extract of Microcystis aeruginosa

Table 4. Analysis of variance of extra and intra-cellular polysaccharides of Oscillatoria angustissima at different concentrations (25, 50, 100 and 200 μg/mL) of microcystins crude extract of Microcystis aeruginosa

Results revealed that, EPS and IPS content of Scendesmus obliquus and Chlorella vulgaris showed increasing under different concentrations (25, 50, 100 and 200 μg/mL) of microcystins crude extract of M. aeruginosa. The increasing in EPS and IPS of Sc. obliquus were (41%, 75%, 112% and 182.5%) and (33.6%, 117.8%, 212.7% and 404%) over the control value for each concentration for EPS and IPS, respectively (Table 5). On the other hand, increasing in EPS and IPS of C. vulgaris amounted by (56%, 133%, 188% and 308.6%) and (25%, 60%, 309% and 478%), respectively over than control (Table 6).

Table 5. Effect of different concentrations of microcystins crude extract (25, 50, 100 and 200 μg/mL) of Microcystis aeruginosa in log phase on intra (IPS) and extra-cellular polysaccharides content (EPS) in μg/mL of Scendesmus obliquus

Table 6. Effect of different concentrations of microcystins crude extract (25, 50, 100 and 200 μg/mL) of Microcystis aeruginosa in log phase on intra (IPS) and extra-cellular polysaccharides content (EPS) in μg/mL of Chlorella vulgaris

Analysis of variance revealed high significant increase in extra and intra-cellular polysaccharides of Sc. obliquus and Chlorella vulgaris at (P ≤ 0. 001) except at 25 μg/ml the increases in IPS of Sc. obliquus and EPS of Chlorella vulgaris (Tables 5 and 6, respectively) were insignificant at the days 6, 9 and 12, and the IPS of C.vulgaris was insignificant at days 6 and 9 as EPS of Sc. obliquus.

From the suggested statistical model (concentrations, days and interception between them), it could be observed that, the deviation for EPS and IPS content of Sc. obliquus was 98.89% and 99.68%, respectively (Table 7) and for C. vulgaris was 99.32% and 99.48%, respectively (Table 8).

Table 7. Analysis of variance of extra and intra-cellular polysaccharides of Scendesmus obliquus at different concentrations of microcystins crude extract of Microcystis aeruginosa

Table 8. Analysis of variance of extra and intra-cellular polysaccharides of Chlorella vulgaris at different concentrations of microcystins crude extract of Microcystis aeruginosa


Microcystis aeruginosa blooms are hazardous to freshwater flora and fauna due to the production of toxins [25]. M. aeruginosa produces a wide range of toxic metabolites. The physiological and ecological role of these compounds remains largely unknown. Some studies have suggested that these compounds may have allelochemical roles, such as compounds that may inhibit competing sympatric macrophytes, algae and microbes [26,27]. The adverse effects of crude microcystins (MCs) could be due to the synergistic interactions among MCs variants or to the presence of unidentified toxic other than MCs in the crude extracts [28]. Leflaive and Ten-Hage [29] reported that cellular extracts containing toxins are often more active than purified toxin, they suggests that cellular extracts contain a mix of active toxin that may act synergistically.

The possible adaptive response of four unicellular algae (Anabaena PCC. 7120 and O. angustissima as blue green algae and S. obliquus; C. vulgaris as green algae) to M. aeruginosa producing toxin were studied. The results indicated that the crude microcystins extract induces the production of extra and intra-cellular polysaccharides of the tested algae and their amounts increased with increasing the microcystins crude extract concentration. The production of polysaccharide by green algal species under toxic stress indicated the involvement of this polysaccharide in protecting the algal cells against toxic species [13].

Inhibition in the growth of Anabaena PCC 7120; Oscillatoria angustissima; Scendesmus obliquus and Chlorella vulgaris at different microcystin crude extract concentrations was previously represented by [27]. Similar results were recorded by Abdel-Rahman [30] found that growth and the physiological activities, except amino acids biosynthesis, of both Chlorococcum humicola and Chlorella vulgaris were inhibited by crude extracts of the two cyanobacteria species Microcystis and Nodularia. Singh et al. [31] reported that the crude extract of M. aeruginosa provides toxicity to green algae (Chlorella sp. and Scenedesmus sp.) and cyanobacteria (Anabaena BT1 and Nostoc muscorum). As represented by [13] pure and crude microcystins significantly decreased the growth of Scenedesmus quadricauda and Chlorella vulgaris, and these results correlated with polysaccharide contents of toxin-treated cultures. This results was in accordance with our results which indicated that S. obliquus and C. vulgaris having a resistant system to crude toxin by the production of polysaccharide more than Anabaena PCC. 7120 and O. angustissima.

The increasing in polysaccharides contents in MCs treated cultures in all experimented algae indicated that these polysaccharides may be involved in certain defense mechanisms in response to toxin stress. Some studies have reported the protective role of polysaccharides against oxidative stress and their ability in scavenging ROS in plant cells [32]. The antioxidant mechanisms may be due to the supply of hydrogen by these polysaccharides which combines with radicals and forms more stable products to terminate radical chain reaction [33].

Microcystins have been shown to induce formation of reactive oxygen species (ROS) that might cause serious cellular damage such as peroxidation of lipid membranes, genotoxicity, or modulation of apoptosis [13]. During the present study the EPS and IPS were detected in the algal medium increased with increase of MCs concentration. It has been suggested that polysaccharides are produced inside the cells during oxidative stress to scavenge the free radicals and remove them from the cells to the medium [32]. However, a variety of other mechanisms such as extra-cellular detoxification, reduced uptake, efflux, sequestration by polysaccharides have been proposed to explain algal tolerance to oxidative stress [34].

Extrusion of EPS can serve as a boundary between cells and the surrounding environment; they could fulfill a protective role against desiccation, antibacterial agents or predation by protozoan [35]. Hence, the results of present study showed that some algae can develop a defense system by the production of polysaccharides to cope with oxidative stress induced by MCs, and this may explain why some plank tonic algae present in close proximity with toxic cyanobacteria or their toxins are not affected by these toxins at environmentally relevant concentrations (1–10 μL) [36].


Here, we showed a physiological model of algal life sustainability under the stress of natural cyanobacterial toxins. The presented results showed the production of polysaccharides by tested algae as a response to the cyanobacterial toxins, microcystins. on the other hand, the release of these polysaccharides into the culture medium and most likely in the natural environment, is of ecologically importance because they may increase the polysaccharide contents of the water column and the growth of heterotrophic bacteria, and complex with heavy metals to reduce their toxicity to aquatic organisms. Therefore, in future studies involving in vitro cultures more attention should be paid to the role of algal exudates, in order to improve the significance of the results with the aim of using them as models of the real environment.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

This work is part of the Master thesis of RE where MME, supervised the thesis, suggested the problem and wrote the paper and MME participated in writing the paper and HMK helped in experiments and read the paper. All authors read and approved the final manuscript.


The authors would like to thank Prof. Hossam Easa, Microbial and Genetic Resources Research group National Institute of Advanced Industrial Science and Technology Tsukuba, Japan for critical reading of the manuscript.


  1. Beattie KA, Kaya K, Codd GA: The cyanobacterium Nodularia PCC 7804, of freshwater origin, produces [L-Har 2] nodularin.

    Phytochemistry 2000, 54(1):57-61. PubMed Abstract | Publisher Full Text OpenURL

  2. Legrand C, Rengefors K, Fistarol GO, Graneli E: Allelopathy in phytoplankton-biochemical, ecological and evolutionary aspects.

    Phycologia 2003, 42:406-419. Publisher Full Text OpenURL

  3. Keating KI: Allelopathic influence of blue-green bloom sequences in a eutrophic lake.

    Science 1977, 196:885-887. PubMed Abstract | Publisher Full Text OpenURL

  4. Smayda TJ: Harmful algal blooms: Their ecophysiology and general relevance to phytoplankton blooms in the sea.

    Limnol Oceanogr 1997, 42:1137-1153. Publisher Full Text OpenURL

  5. Figueredo CC, Giani A, Bird DF: Does allelopathy contribute to Cylindrospermopsis raciborskii (cyanobacteria) bloom occurrence and geographic expansion.

    J Phycol 2007, 43:256-265. Publisher Full Text OpenURL

  6. Torres A, Oliva RM, Castellano D, Cross P: First World Congress on Allelopathy. A Science of the Future, SAI. Spain: University of Cadiz; 1996:278. OpenURL

  7. Inderjit K, Duke SO: Ecophysiological aspects of allelopathy.

    Planta 2003, 217:529-539. PubMed Abstract | Publisher Full Text OpenURL

  8. Maćias FA, Oliva RM, Simonet AM, Galindo JCG: What are allelochemicals? In Allelopathy in Rice. Edited by Olofsdotter M. Manilla: IRRI Press; 1998. OpenURL

  9. Shanab S: Effect of fresh water cyanobacterial extracts on alkaloid production of the in vitro Solanum elaeagnifolium tissue culture.

    Arab Journal of Biotechnology 2001, 4(1):129-140. OpenURL

  10. Giroldo D, Ortolano PC, Vieira AAH: Bacteria-algae association in batch cultures of phytoplankton from a tropical reservoir: the significance of algal carbohydrates.

    Fresh Water Biology 2007, 52:1281-1289. Publisher Full Text OpenURL

  11. Azam F, Smith DC: Bacterial influence on the variability in the ocean’s biogeochemical state: a mechanistic view. In NATO ASI series, vol G27, particle analysis in oceanography. Edited by Demers S. Berlin: Springer; 1991:213-236. OpenURL

  12. De Philippis R, Paperi R, Sili C: Heavy metal sorption by released polysaccharides and whole cultures of two exopolysaccharide-producing cyanobacteria.

    Biodegradation 2007, 18:181-187. PubMed Abstract | Publisher Full Text OpenURL

  13. Mohamed ZA: Polysaccharides as a protective response against microcystin-induced oxidative stress in Chlorella vulgaris and Scenedesmus quadricauda and their possible significance in the aquatic ecosystem.

    Ecotoxicology 2008, 17(6):504-516. PubMed Abstract | Publisher Full Text OpenURL

  14. Engstrom J, Viherluto M, Vitasalo M: Effect of toxic and nontoxic cyanobacteria on grazing zooplanktivory and survival of the mysid shrimp Mysis mixta.

    J Exp Mar Biol Ecol 2001, 257:269-280. PubMed Abstract | Publisher Full Text OpenURL

  15. Christoffersen K, Lyck S, Winding A: Microbial activity and bacterial community structure during degradation of microcystins.

    Aquatic and Microbiology Ecology 2002, 27:125-136. OpenURL

  16. Mohamed ZA, Carmichael WW, Hussein AA: Estimation of microcystins in the fresh water fish Oreochromis niloticus in an Egyptian fish farm containing a Microcystis bloom.

    Environ Toxicol 2003, 18:137-141. PubMed Abstract | Publisher Full Text OpenURL

  17. O’Neil JM, Davis TW, Burford MA, Gobler CJ: The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change.

    Harmful Algae 2011, 14:313-334. OpenURL

  18. Karamouz M, Mahjouri N, Kerachian R: River Water Quality Zoning: A Case Study of Karoon and Dez River System.

    Iran J Environ Healt 2004, 1:16-27. OpenURL

  19. Allen’s MM, Stanier ST: Selective isolation of blue-green algae from water and soil.

    J Gen Microbiol 1968, 51:302. OpenURL

  20. Venkataraman GS: The cultivation of algae. New Delhi: Indian Council of Agricultural Research; 1969. OpenURL

  21. Harada KI, Suzuki M, Dahlem AM, Baesley VR, Carmichael WW, Rinehart KL: Improved methods for purification of toxic peptides produced by cyanobacteria.

    Toxicon 1988, 26:433. PubMed Abstract | Publisher Full Text OpenURL

  22. Shi Y, Sheng J, Yang F, Hu Q: Purification and identification of polysaccharide from Chlorella pyrenoidosa.

    Food Chem 2007, 103:101-105. Publisher Full Text OpenURL

  23. Berg DJC, Robijn GW, Janssen AC: Production of a novel extra cellular polysaccharide by Lactobacillus Sake01 and characterization of the polysaccharide.

    Appl Environ Microbiol 1995, 61(8):2840-2844. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  24. SAS program Cary: SAS Institute Inc; 1989–1999.

    SAS (r) Proprietary Software Release 6.12 TS020

  25. Wiegand C, Pflugmacher S: Ecotoxicological effects of selected cyanobacterial secondary metabolites: a short review.

    Toxicol Appl Pharmacol 2005, 203:201-218. PubMed Abstract | Publisher Full Text OpenURL

  26. Berry JP, Gantar M, Perez MH, Berry G, Noriega FG: Cyanobacterial toxins as allelochemicals with potential applications as algaecides, herbicides and insecticides.

    Mar Drugs 2008, 6:117-146. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  27. El-Sheekh MM, Khairy HM, El-Shenody RA: Allelopathic effects of cyanobacterium Microcystis aeruginosa Kützing on the growth and photosynthetic pigments of some algal species.

    Allelopathy Journal 2010, 26:275-290. OpenURL

  28. Palíková M, Krejeci R, Hilscherová K, Babica P, Navrátil S, Kopp R, Bláha L: Effect of different cyanobacterial biomasses and their fractions with variable microcystin content on embryonal development of carp (Cyprinus carpio L.).

    Aquat Toxicol 2007, 81:312-318. PubMed Abstract | Publisher Full Text OpenURL

  29. Leflaive J, Ten-Hage L: Algal and cyanobacterial secondary metabolites in freshwaters: a comparison of allelopathic compounds and toxins.

    Fresh Water Biology 2007, 52:199-214. Publisher Full Text OpenURL

  30. Abdel-Rahman MHM: Effect of Cyanobacteria crude extracts on growth and related physiological activities of Chlorococcum humicola and Chlorella vulgaris.

    Arab J Biotechnol 2005, 8(1):9-18. OpenURL

  31. Singh DP, Tyagi MB, Kumar A, Hu Q: Antialgal activity of hepatotoxin-producing cyanobacterium, Microcystis aeruginosa.

    World J Microbiol Biotechnol 2001, 17:15-22. Publisher Full Text OpenURL

  32. Tannin-Spitz T, Bergman M, van Moppes D, Grossman S: Antioxidant activity of the polysaccharide of the red micro alga Porphyridium sp.

    J Appl Phycol 2005, 17:215-222. Publisher Full Text OpenURL

  33. Chen Y, Xie MY, Nie SP, Li C, Wang YX: Purification, composition analysis and antioxidant activity of polysaccharide from the fruiting bodies of Ganoderma atrum.

    Food Chem 2008, 107:231-241. Publisher Full Text OpenURL

  34. Gaur JP, Rai LC: Heavy metal tolerance in algae. In Algal adaptation to environmental stresses: physiological, biochemical and molecular mechanisms. Edited by Rai LC, Gaur JP. Berlin: Springer; 2001:363-388. OpenURL

  35. De Philippis R, Vincenzini M: Exocellular polysaccharides from cyanobacteria and their possible applications.

    FEMS Microbiology Review 1998, 22:151-175. OpenURL

  36. Babic P, Hilscherova K, Bartova K, Blaha L, Marsalek B: Effects of dissolved microcystins on growth of plank tonic photoautotrophs.

    Phycologia 2007, 46:137-236. Publisher Full Text OpenURL