115 Annales Universitatis Paedagogicae Cracoviensis Studia Naturae, 1: 115–126, 2016, ISSN 2543-8832 Sylwia Śliwińska-Wilczewska*, Kinga Gergella, Adam Latała Institute of Oceanography, University of Gdańsk, Av. Piłsudskiego 46, 81-378 Gdynia, Poland, *ocessl@ug.edu.pl Allelopathic activity of the Synechococcus sp. (Cyanobacteria, Chroococcales) on selected cyanobacteria species Introduction Allelopathy may be one of the factors contributing to the formation and maintenance of cyanobacterial blooms, which strongly a�ect coastal marine ecosystems and cause economic problems for commercial aquaculture (Gross, 2003). Furthermore, some species of cyanobacteria are able to produce and release secondary metabolites that may be harmful to microorganisms, phyto- and zooplankton, crustaceans, �sh and even humans (Stal et al., 2003; Mazur-Marzec et al., 2015). Cyanobacteria are known to produce a wide range of secondary metabolites with various biological actions. Some of them, termed allelopathic compounds, have been shown to play a role in allelopathy (Le�aive, Ten-Hage, 2007). �e precise mode of action of allelopathic compounds remains relatively poor- ly known due to methodological di�culties. It is believed that the allelopathic com- pounds may be responsible for the natural selection of organisms, competition and ecological succession (Legrand et al., 2003). Moreover, it was indicated that some cyanobacteria are able to produce and release allelopathic compounds that a�ect the growth and development of other organisms (Gross, 2003; Żak, Kosakowska, 2015). �is can be important for many areas of science and industry. Secondary metabolites isolated from cyanobacteria can be used in medicine, agriculture, as herbicides or insecticides, and maybe even in the creation of drugs (Berry et al., 2008; Hernández-Carlos, Gamboa-Angulo, 2011). Generally, the blooms of cyanobac- teria that develop each summer in the freshwater and brackish ecosystems are com- posed of two di�erent groups: the large, colony-forming, filamentous cyanobacteria and small-sized picocyanobacteria from the genus Synechococcus and Synechocystis. Picocyanobacteria fraction may comprise as much as 80% of the total cyanobacterial biomass and contribute as much as 50% of the total primary production of a cyano- 116 S yl w ia Ś liw iń sk a- W ilc ze w sk a, K in ga G er ge lla , A da m L at ał a bacterial bloom (Stal et al., 2003). Picocyanobacteria strain of the genus Synechococcus are very important organisms in the world’s oceans, however, the information about allelopathic interactions between pico- and �lamentous cyanobacteria in aquatic eco- systems are scarce. �e main aim of this work was to estimate the allelopathic interac- tion of picocyanobacterium Synechococcus sp. on selected cyanobacteria. In this study, the in�uence of allelopathic compounds on the growth, cell-morphology, photosyn- thetic pigments, chlorophyll �uorescence and performance of photosynthesis in the analysed species was investigated by single and multiple addition of cell-free �ltrate obtained from picocyanobacterium Synechococcus sp. In this experiment we inves- tigated the e�ect of single and multiple addition of cell-free �ltrate obtained from Synechococcus sp. on selected pico- and �lamentous cyanobacteria: Synechocystis sp., Geitlerinema amphibium, Nodularia spumigena and Nostoc sp. Future studies should examine the allelopathic activity of di�erent strains of picocyanobacteria, including Synechocystis and Aphanocapsa. Material and methods �e experiments were conducted on the picocyanobacterium Synechococcus sp. (BA- 124) and the cyanobacteria Geitlerinema amphibium (BA-13), Nodularia spumigena (BA-15), Nostoc sp. (BA-81) and Synechocystis sp. (BA-153). �e strains were isolated from the coastal zone of the Gulf of Gdańsk (southern Baltic Sea) and are maintained as unialgal cultures in the Culture Collection of Baltic Algae (CCBA) at the Institute of Oceanography, University of Gdańsk, Poland (Latała et al., 2006). �e tests on batch cultures were carried out in 25 mL glass Erlenmeyer �asks containing sterilized f/2 medium (Guillard, 1975). �e media were prepared from Baltic water with a salin- ity of about 8 psu, which was �ltered through Whatman GF/C glass �ber �lters, and autoclaved. Analyzed cyanobacteria were grown 7 days in constant conditions of 20°C and 8 psu, under a 16:8h light : dark cycle at 10 μmol m-2·s-1 and this were the control treatment conditions. Fluorescent lamps (Cool White 40W, Sylvania, USA) were used as source of irradiance. �e intensity of PAR was measured using a LI-COR quantum-meter with a cosine collector. �e donor and target cyanobacteria were ac- climated to these culture conditions for 7 days; a�erwards, actively growing cultures were used for the establishment of the allelopathic experiment. Allelopathic interactions were determined by using the method proposed by Śliwińska-Wilczewska et al. (2016a). Allelopathic interaction was studied by add- ing the single and multiple cell-free �ltrate obtained from picocyanobacterial cul- ture to tested cyanobacteria. �e culture of Synechococcus sp. was �ltered through 0.45 µm pore size Macherey-Nagel MN GF-5 �lters. �e cell-free �ltrate (V = 2 mL) was added to 25 mL Erlenmeyer �asks containing the tested cyanobacteria (V = 20 117 mL). In all experiments, the ratio of picocyanobacterium to target species in Erlen- meyer �asks was adjusted to 1:1 based on the chlorophyll a content (�nal chlorophyll a concentration in the experimental cultures was 0.8 µg chl a mL-1). Control samples were prepared by adding mineral medium f/2 with a volume equal to the added cell-free �ltrate. To simulate the e�ects of continuously released picocyanobacterial allelochemicals on target species, picocyanobacterial �ltrates were added daily to the target cultures for one week. �e �rst addition was made as described above. Subse- quent additions were made by removing 2 mL of test volume, used for cell counts each day and replacing it with an equal volume of fresh �ltrate or control medium. Tests were conducted in triplicate and all analysed species were obtained from early expo- nential growth phase. �e identi�cation of allelopathic compounds is a di�cult and time-consuming task and will need further investigation. Culture density was determined by the number of cells and optical density (OD). �e number of cells was counted using Bürker chamber and OD was measured spectrophotometrically at 750 nm with a Multiskan GO �ermo Scienti�c UV-VIS spectrophotometer. �e results of cell counts and respective OD measurements were then used to determine the linear correlation between them for each spe- cies. Determined relationships were then used to estimate the number of cells in the experimental cultures a�er 1st, 3rd and 7th day of the cyanobacteria exposure to the picocyanobacterial �ltrate. In addition, the morphological changes of target cyanobacteria were documented using a Nikon Eclipse 80i microscope with a cam- era Nikon DSU2. In this work the concentration of photosynthetic pigments of target organisms was measured by spectrophotometric method a�er one week of exposure to the picocy- anobacteria cell-free �ltrate. Chlorophyll a, carotenoids and phycobilins were deter- mined with a �ermo Scienti�c spectrophotometer UV-VIS Multiscan GO using 1 cm glass cuvette. �e concentration of pigments was calculated according to equations provided by Je�rey and Humphrey (1975), Strickland and Parsons (1972) and Bennett and Bogorad (1973). Chlorophyll a �uorescence was measured with a Pulse Amplitude Modulation (PAM) �uorometer (FMS1, Hansatech), using 594 nm amber modulating beam with 4 step frequency control as a measuring light. Analysed species were taken for chlo- rophyll �uorescence analysis a�er 7th day of exposure to the �ltrate. Before measure- ments, each sample taken from the culture was �ltered through 13 mm glass �b- er �lters (Whatman GF/C). Before starting the experiment, the �lter sample was adapted in the dark for about 15 minutes. Fluorescence parameters such as maxi- mum PSII quantum e�ciency (Fv/Fm) and e�ective PSII quantum e�ciency (ΦPSII) were calculated (Campbell et al., 1998). A llelopathic activity of the Synechococcus sp. (C yanobacteria, C hroococcales) on selected cyanobacteria species 118 S yl w ia Ś liw iń sk a- W ilc ze w sk a, K in ga G er ge lla , A da m L at ał a �e measurements of oxygen evolution were carried out on the 7th day of the experiment by using Clark-type oxygen electrode (Chlorolab 2, Hansatech). Tem- perature was controlled at 20°C with a cooling system LAUDA (E100, Germany). Il- lumination was provided by a high intensity probe-type light array with 11 red LED’s centered on 650 nm. Irradiance was measured with a quantum sensor (Quantitherm, Hansatech). Dark respiration was estimated from O2 uptake by cells incubated in the dark. Experimental data were �tted to the photosynthesis-irradiance curve using equation (Jassby, Platt, 1976). Analysis of variance (ANOVA) was used to test for di�erences in analysed pa- rameters between the target cyanobacteria cultures treated with picocyanobacterial cell-free �ltrates and the control over the experimental period. a post hoc test (Tuk- ey’s HSD) was used to show which experiments of picocyanobacterial �ltrate a�ected the growth of target cyanobacteria di�erently. Data is reported as mean ± standard deviation (SD). Levels of signi�cance were: * p < 0.05. �e statistical analyses were performed using the Statistica® 12 so�ware. Results �e e�ect of the cell-free �ltrate addition obtained from Synechococcus sp. cultures on the growth of Geitlerinema amphibium, Nodularia spumigena, Nostoc sp. and Syn- echocystis sp. a�er 1, 3 and 7 days of exposition to the �ltrates are shown in �gure 1. �e results showed that addition of cell-free �ltrate from Synechococcus sp. decreased the number of cells of G. amphibium, N. spumigena and Nostoc sp. compared to their control. On the basis of the results it was found that the �ltrate obtained from pico- cyanobacterium had the strongest e�ect on G. amphibium. A�er the 7th for a single and multiple �ltrate addition obtained from Synechococcus sp. growth inhibition of G. amphibium expressed as a percent of culture density (% of control) constituted 48% and 56% respectively (p < 0.05). It was also observed, that the single addition of cell-free �ltrate obtained from Synechococcus sp. signi�cantly decreased the number of cells of N. spumigena and Nostoc sp. (p < 0.05). On the 1st, 3rd and the 7th day of the experiment, the minimum cell response of N. spumigena constituted 94%, 81% and 79% (p < 0.05) respectively, and for Nostoc sp. the percent of culture density constitut- ed 87%, 81% and 82% (p < 0.05) respectively, in comparison to the control treatment. Moreover, on the 3rd and the 7th day of the experiment, the minimum cell response of N. spumigena a�er multiple addition of the cell-free �ltrate, constituted 55% and 63%, respectively (p < 0.05). In addition, it was observed that the cell-free �ltrate obtained from Synechococcus sp. did not a�ect the number of cells of Synechocystis sp. (p > 0.05). �e morphological changes of the target cyanobacteria a�er the picocyanobacte- rial cell-free �ltrate addition was shown in �gure 2. It was shown that the addition 119 Fig. 1. �e e�ect of the a) single and b) multiple additions of cell-free �ltrate from Synechococcus sp. cultures on the growth of Geitlerinema amphibium (BA-13), Nodularia spumigena (BA-15), Nostoc sp. (BA-81) and Synechocystis sp. (BA-153) a�er 1, 3 and 7 days of exposition to the �ltrates, expressed as a percent of culture density (% of control). �e values refer to means (n = 3, mean ± SD). Asterisk indi- cates signi�cant di�erence compared with control Fig. 2. �e cells morphology of a) Geitlerinema amphibium, b) Nodularia spumigena, c) Nostoc sp. and d) Synechocystis sp. for A) control sample and B) in the experiments with the addition of cyanobacte- rial cell-free �ltrate a�er 7 days of exposure of cell-free �ltrate caused a decline of pigmentation and cell lysis of G. amphibium, N. spumigena and Nostoc sp. compared to the control culture. In contrast, it was observed that the cell-free �ltrate obtained from Synechococcus sp. had no e�ect on the picocyanobacterium Synechocystis sp. �e e�ect of the single and multiple additions of cell-free �ltrate from Synechococ- cus sp. cultures on the pigment contents of G. amphibium a�er one week of exposition is shown in �gure 3. �e results showed that allelochemicals released by picocyanobacterium Syne- chococcus sp. signi�cantly decreased the chlorophyll a and phycobilins of G. amphi- bium compared to their control (p < 0.05). A�er one week of exposition, it was noted that the single addition of the �ltrate resulted in decrease of chlorophyll a and phy- cobilins in the cells of analysed cyanobacterium, which was lower by 28% and 50%, respectively, compared to a control (p < 0.05). Based on the results, it was found that the multiple addition of cell-free �ltrate obtained from Synechococcus sp. also caused A llelopathic activity of the Synechococcus sp. (C yanobacteria, C hroococcales) on selected cyanobacteria species 120 S yl w ia Ś liw iń sk a- W ilc ze w sk a, K in ga G er ge lla , A da m L at ał a a signi�cant change in the pigment contents of G. amphibium cells. A�er one week of the experiment, chlorophyll a of this cyanobacterium was lower by 44% compared to control (p < 0.05). In addition, in this study it was observed that the cell-free �ltrate obtained from Synechococcus sp. did not a�ect the carotenoids content of analysed cyanobacterium (p > 0.05). �e e�ects of picocyanobacterial cell-free �ltrate on chlorophyll a �uorescence af- ter 7 days of incubation are shown in �gure 4. It was observed, that the single addition of cell-free �ltrate from Synechococcus sp. signi�cantly stimulated the values of ΦPSII (p < 0.05). Moreover, the multiple additions of cell-free �ltrate from Synechococcus sp. Fig. 3. �e e�ect of the a) single and b) multiple additions of cell-free �ltrate from Synechococcus sp. cultures on the pigment contents: chlorophyll a (chl a), carotenoids (car) and phycobilins (phyco) for Geitlerinema amphibium (BA-13) a�er 7 days of exposure. �e values refer to means (n = 3, mean ± SD). Asterisk indicates signi�cant di�erence compared with control Fig. 4. �e e�ect of the single and multiple additions of cell-free �ltrate from Synechococcus sp. cultures on the �uorescence parameter Fv/Fm and ΦPSII for Geitlerinema amphibium (BA-13) a�er 7 days of ex- posure. �e values refer to means (n = 3, mean ± SD). Asterisk indicates signi�cant di�erence compared with control inhibited the values of the analysed parameters Fv/Fm and ΦPSII which amounted to 94% (p > 0.05) and 57% (p < 0.05) in comparison to the control, respectively. P-E curves for analysed G. amphibium treated with single and multiple cell-free �ltrate obtained from Synechococcus sp. are presented in �gure 5. It was demonstrated that the investigated cyanobacterium was sensitive to the picocyanobacterial cell-free 121 �ltrate. In this study the in�uence of picocyanobacterial allelochemicals on the max- imum photosynthesis (Pm) of the tested cyanobacterium was noted and its value con- stituted 31% and 27% (p < 0.05), respectively, in comparison to the control treatment. Discussion Allelopathic interaction may play a signi�cant role in an aquatic ecosystem (Gross, 2003). Allelopathy is considered one of the factors promoting and maintaining cyano- bacterial blooms in freshwater, brackish and marine ecosystems around the world. Although the allelopathy phenomenon is common in aquatic ecosystems, the mode of action of allelopathic compounds produced by picocyanobacteria on cyano- bacteria remains poorly investigated. Inhibition of growth of the target organism by production of allelopathic com- pounds is relatively widespread and the most frequently reported mode of action of cyanobacteria (Issa, 1999; Schagerl et al., 2002). In this study it was demonstrated that the addition of cell-free �ltrate from Synechococcus sp. decreased the number of cells of �lamentous cyanobacteria Geitlerinema amphibium, Nodularia spumigena and Nostoc sp. compared to their control. �e results also showed that the allelochemicals produced by the picocyanobacterium had the strongest e�ect on G. amphibium. It was also observed, that for G. amphibium, the e�ect of single cyanobacterial �ltrate additions was stronger than the e�ect of multiple additions. Surprisingly, it was ob- served that the cell-free �ltrate obtained from Synechococcus sp. did not a�ect the number of cells of picocyanobacterium Synechocystis sp. Picocyanobacteria of the genus Synechococcus plays an important role in aquatic ecosystems but not much is known about its allelopathic activity. Information about the ability of allelop- athic interactions of picocyanobacterium Synechococcus sp. was described by Śli- Fig. 5. P-E curves for Geitlerinema amphibium (BA-13) for control and a) single and b) multiple additions of cell-free �ltrates obtained from Synechococcus sp. cultures a�er 7 days of exposure. �e values refer to mean ± SD (n = 3) A llelopathic activity of the Synechococcus sp. (C yanobacteria, C hroococcales) on selected cyanobacteria species 122 S yl w ia Ś liw iń sk a- W ilc ze w sk a, K in ga G er ge lla , A da m L at ał a wińska-Wilczewska et al. (2016a). In this work the authors showed that addition of the cell-free �ltrate obtained from the picocyanobacterium Synechococcus sp. had a sig- ni�cant inhibitory e�ect on N. spumigena. Authors described that the longer the ex- posure time, the slower the growth of the analysed �lamentous cyanobacterium, and on the 7th day of experiment the minimum cells response constituted about 60% in comparison to control treatment. In another work Schagerl et al. (2002) also demon- strated growth in inhibition of cyanobacteria Anabaena cylindrica and Microcystis �os-aquae a�er adding the �ltrate from the cyanobacterium Anabaena torulosa. Also Issa (1999) investigated the e�ect of allelopathic compounds produced by Oscillato- ria angustissima and Calothrix parietina on Microcystis aeruginosa, Synechococcus sp., Scytonema hofmonni, Anabaena spiroides, Phormidium mölle, Nostoc muscorum, Os- cillatoria angustissima and Calothrix parietina. Author noted that cyanobacteria of the genus Oscillatoria, Calothrix, Nostoc and Anabena were resistant to allelopathic compounds released by analysed cyanobacteria. Moreover, the recovery of G. am- phibium growth a�er a multiple �ltrate additions may have been due to, e.g., its ability to metabolise allelochemicals, as suggested by Suikkanen et al. (2004). It is believed that selective inhibition of growth of the target organism may a�ect the succession of selected cyanobacteria in aquatic ecosystem (Legrand et al., 2003). �ere are only several reports indicating that the chemical compounds can cause structural and morphological changes in target cells (Gantar et al., 2008). In the pres- ent study it was shown that the tested allelopathic compounds obtained from Syn- echococcus sp. caused restriction of pigmentation and cell lysis of all analysed �la- mentous cyanobacteria. Gantar et al. (2008) also noted that a�er being exposed to the crude extract from Fischerella sp., cells of Chlamydomonas sp. showed distinctive morphological and structural changes. �e electron microscopy revealed degenera- tion of thylakoids and disappearance of other cell structures including the nucleus. �e results may in part explain the reasons for achieving competitive advantage of picocyanobacterium Synechococcus sp. over other �lamentous cyanobacteria in many aquatic ecosystems. �e precise mode of action of allelopathic compounds remains relatively poorly known due to methodological di�culties. �erefore, there are only a few reports that allelopathic compounds may a�ect the pigments content, chlorophyll �uorescence and photosynthesis of target organisms (Gross et al., 1991; Śliwińska-Wilczewska et al., 2016b). In the present study it was shown that the tested allelopathic compounds obtained from Synechococcus sp. caused restriction of pigmentation and inhibition of photosynthetic activity of analysed G. amphibium compared to the control culture. Literature data indicates that allelopathic compounds produced by cyanobacteria can a�ect the photosynthesis, and detailed studies have shown that they act mainly on the photosystem II (PSII). Gross et al. (1991) showed that �scherellin a produced by cy- 123 anobacterium Fischerella muscicola, and the compounds released by Trichormus dolio- lum and Oscillatoria late-virens inhibited activity of PSII in selected cyanobacteria and microalgae. In addition, Śliwińska-Wilczewska et al. (2016b) showed that the addition of cell-free �ltrate from Synechococcus sp. cultures grown under varied light, temper- ature and salinity signi�cantly inhibited the values of Fv/Fm of the diatom Navicula perminuta. Moreover, authors noted that the lowest values of Pm in N. perminuta were observed a�er addition of cell-free �ltrate obtained from Synechococcus sp. grown at 25°C, and was 49% lower than for the control group. Inhibition of photosynthesis, the major physiological process of competing phytoplankton species, can be a defensive strategy of co-occurring cyanobacteria (Gross, 2003). �erefore, allelopathic inter- action may result in inhibition of pigments content, photosynthesis and growth of target organisms which in part explain the domination of picocyanobacteria in many aquatic ecosystems. Many studies indicated that cyanobacteria produced a wide spectrum of second- ary metabolites, a source of a new bioactive and natural compounds, which can be used in medicine and pharmaceutical industry as antibacterial, antiviral and antifun- gal compounds and even against tumor cells (Berry et al., 2008; Hernández-Carlos, Gamboa-Angulo, 2011). �e compounds produced by cyanobacteria can also be used in agriculture as herbicides, or insecticides, and may also have potential applications in biotechnology (Le�aive, Ten-Hage, 2007). It is also believed that allelopathy may be one of the important factors a�ecting the formation of massive cyanobacterial blooms in the aquatic environment (Gross, 2003; Legrand et al., 2003). Species forming harm- ful blooms in many places in the world are a serious problem, both ecologically and economically. 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DOI: 10.1016/j.csr.2003.06.001 Strickland, I.D.H., Parsons, T.R. (1972). a practical handbook of seawater analysis. Journal of the Fisheries Research Board of Canada, 167, 1–310. 125 Suikkanen, S., Fistarol, G.O., Granéli, E. (2004). Allelopathic e�ects of the Baltic cyanobacteria Nodularia spumigena, Aphanizomenon �os-aquae and Anabaena lemmermannii on algal monocultures. Journal of Experimental Marine Biology and Ecology, 308, 85–101. DOI: 10.1016/j.jembe.2004.02.012 Śliwińska-Wilczewska, S., Pniewski, F., Latała, A. (2016a). Allelopathic interactions between Synechococ- cus sp. and Nodularia spumigena under di�erent light conditions. Allelopathy Journal, 37(2), 241–252. Śliwińska-Wilczewska, S., Pniewski, F., Latała, A. (2016b). Allelopathic activity of the picocyanobac- terium Synechococcus sp. under varied light, temperature and salinity conditions. International Review of Hydrobiology, 101, 1–9. DOI: 10.1002/iroh.201501819 Żak, A., Kosakowska, A. (2015). �e in�uence of extracellular compounds produced by selected Baltic cyanobacteria, diatoms and dino�agellates on growth of green algae Chlorella vulgaris. Estuarine, Coastal and Shelf Science, 167, 113–118. DOI: 10.1016/j.ecss.2015.07.038 Abstract Picocyanobacterium Synechococcus sp. is very important but still poorly understood component of ma- rine and freshwater ecosystems. In this study, the e�ect of single and multiple addition of cell-free �ltrate obtained from Synechococcus sp. on selected cyanobacteria Synechocystis sp., Geitlerinema amphibium, Nodularia spumigena and Nostoc sp. was investigated. �e species present in this work are groups of aquatic phototrophs known to co-occur in the Baltic Sea. �e study showed that the picocyanobacterial cell-free �ltrate inhibits the growth and changes the cell morphology of �lamentous cyanobacteria G. am- phibium, N. spumigena and Nostoc sp. It was shown that the addition of cell-free �ltrate caused a decline of pigmentation and cell lysis of G. amphibium, N. spumigena and Nostoc sp. compared to the control culture. In addition, it was observed that the �ltrate obtained from Synechococcus sp. did not a�ect the Synechocystis sp. It was found that the �ltrate obtained from picocyanobacterium had the strongest e�ect on growth of G. amphibium, therefore for this cyanobacteria additional experiments were performed to show whether the �ltrate a�ected also photosynthetic pigments, chlorophyll �uorescence and photo- synthesis. �e study proved that the picocyanobacterial allelopathic compounds reduce the e�ciency of photosynthesis, which results in the inhibition of growth of target organisms. �is way of interaction may explain the formation of almost monospeci�c cyanobacterial blooms in many aquatic ecosystems, including the Baltic Sea. Key words: allelopathy, cyanobacteria, �uorescence, growth, photosynthesis, photosynthetic pigments Received: [2016.06.08] Accepted: [2016.09.06] Zjawisko oddziaływania allelopatycznego sinicy Synechococcus sp. (Cyanobacteria, Chroococcales) na wybrane gatunki sinic Streszczenie Pikoplanktonowa sinica Synechococcus sp. jest bardzo ważnym, lecz nadal słabo poznanym składnikiem wodnych ekosystemów. W przeprowadzonych badaniach określono wpływ pojedynczo i wielokrotnie dodawanego przesączu uzyskanego z Synechococcus sp. na wybrane gatunki pikoplanktonowych i nit- kowatych sinic: Synechocystis sp., Geitlerinema amphibium, Nodularia spumigena oraz Nostoc sp. Badane gatunki sinic występują w tych samych ekosystemach i znane są z odgrywania istotnej roli w Morzu Bał- tyckim. W pracy wykazano, że przesącz wpływał hamująco na wzrost nitkowatych sinic G. amphibium, N. spumigena oraz Nostoc sp. Nie zanotowano natomiast istotnych zmian liczebności u pikoplanktonowej sinicy Synechocystis sp. Dla wszystkich gatunków badanych sinic zostały wykonane analizy zmian morfo- logicznych, które zaszły w ich komórkach pod wpływem dodania przesączu uzyskanego z kultur Synecho- coccus sp. Na podstawie uzyskanych wyników wykazano, że przesącz powodował utratę pigmentacji i lizę komórek nitkowatych sinic. Ponadto dla sinicy G. amphibium zostały wykonane dodatkowe ekspery- menty, na podstawie których stwierdzono, że dodany przesącz hamował �uorescencję chloro�lu a, tempo A llelopathic activity of the Synechococcus sp. (C yanobacteria, C hroococcales) on selected cyanobacteria species 126 S yl w ia Ś liw iń sk a- W ilc ze w sk a, K in ga G er ge lla , A da m L at ał a fotosyntezy, a także wpływał znacząco na zawartość barwników fotosyntetycznych. W pracy wykazano, że związki allelopatyczne produkowane i uwalniane przez Synechococcus sp. ograniczały sprawność foto- syntezy, co skutkowało zahamowaniem wzrostu organizmów targetowych. Tego rodzaju oddziaływanie może wyjaśniać tworzenie się prawie monogatunkowych zakwitów sinic w wielu zbiornikach wodnych, w tym również w Morzu Bałtyckim. Słowa kluczowe: allelopatia, sinice, �uorescencja, wzrost, fotosynteza, barwniki fotosyntetyczne Information on the authors Sylwia Śliwińska-Wilczewska Currently she is researching the allelopathic activity of picocyanobacteria. Recently she has examined that the Synechococcus sp. reveals allelopathic activity on the photosynthesis and chlorophyll �uorescen- ce, which results in the inhibition of growth of analyzed target species. She has also discovered that pi- cocyanobacterium Synechococcus sp. produces and releases allelopathic compounds which have negative in�uence on di�erent green algae, diatoms and �lamentous cyanobacteria. Kinga Gergella �e �eld of her interest is allelopathic interactions of phytoplankton, in particular of Baltic microalgae and cyanobacteria. She is investigating what in�uence allelopathic compounds have on those organisms. In her studies she uses innovative methods: analyzing chlorophyll a �uorescence and measuring rate of photosynthesis to determine what impact allelochemicals have on algae. Adam Latała He has wide experience in ecophysiology and ecotoxicology of marine benthic and planktonic algae. He is interested in in�uence of the main environmental factors, such as salinity, temperature and light, on the photosynthesis, photoacclimation, �uorescence, respiration and growth of algae from natural communi- ties and cultured under laboratory conditions. He uses �uorescence techniques to determine algal and cyanobacterial ecophysiology and ecotoxicology.