Allelopathic and bloom-forming picocyanobacteria in a changing world

Picocyanobacteria are extremely important organisms in the world’s oceans and freshwater ecosystems. They play an essential role in primary production and their domination in phytoplankton biomass is common in both oligotrophic and eutrophic waters. Their role is expected to become even more relevant with the effect of climate change. However, this group of photoautotrophic organisms still remains insufficiently recognized. Only a few works have focused in detail on the occurrence of massive blooms of picocyanobacteria, their toxicity and allelopathic activity. Filling the gap in our knowledge about the mechanisms involved in the proliferation of these organisms could provide a better understanding of aquatic environments. In this review, we gathered and described recent information about allelopathic activity of picocyanobacteria and occurrence of their massive blooms in many aquatic ecosystems. We also examined the relationships between climate change and representative picocyanobacterial genera from freshwater, brackish and marine ecosystems. This work emphasizes the importance of studying the smallest picoplanktonic fractions of cyanobacteria. © 2018 MDPI. All Rights reserved.Acknowledgments: We thank Sabina Jodłowska for execution photographic documentations of Synechococcus sp. strains on electron microscope. This study was supported by BMN grants, Poland, No. 538-G245-B568-17

Physiological effects on coexisting microalgae of the allelochemicals produced by the bloom-forming cyanobacteria synechococcus sp. And nodularia spumigena

Only a few studies have documented the physiological effects of allelopathy from cyanobacteria against coexisting microalgae. We investigated the allelopathic ability of the bloom-forming cyanobacteria Synechococcus sp. and Nodularia spumigena filtrates on several aspects related to the physiology of the target species: population growth, cell morphology, and several indexes of photosynthesis rate and respiration. The target species were the following: two species of green algae (Oocystis submarina, Chlorella vulgaris) and two species of diatoms (Bacillaria paxillifer, Skeletonema marinoi). These four species coexist in the natural environment with the employed strains of Synechococcus sp. and N. spumigena employed. The tests were performed with single and repeated addition of cyanobacterial cell-free filtrate. We also tested the importance of the growth phase in the strength of the allelopathic effect. The negative effects of both cyanobacteria were the strongest with repeated exudates addition, and generally, Synechococcus sp. and N. spumigena were allelopathic only in the exponential growth phase. O. submarina was not negatively affected by Synechococcus filtrates in any of the parameters studied, while C. vulgaris, B. paxillifer, and S. marinoi were affected in several ways. N. spumigena was characterized by a stronger allelopathic activity than Synechococcus sp., showing a negative effect on all target species. The highest decline in growth, as well as the most apparent cell physical damage, was observed for the diatom S. marinoi. Our findings suggest that cyanobacterial allelochemicals are associated with the cell physical damage, as well as a reduced performance in respiration and photosynthesis system in the studied microalgae which cause the inhibition of the population growth. Moreover, our study has shown that some biotic factors that increase the intensity of allelopathic effects may also alter the ratio between bloom-forming cyanobacteria and some phytoplankton species that occur in the same aquatic ecosystem.This research were funded by BMN grant number 538-G245-B568-17 and FCT Project UID/Multi/04423/2019. The APC was funded by DS 530-G245-D717-18

Ecophysiological characteristics of red, green, and brown strains of the Baltic picocyanobacterium <i>Synechococcus</i> sp. – a laboratory study

The contribution of picocyanobacteria (PCY) to summer phytoplankton blooms, accompanied by an ecological crisis is a new phenomenon in Europe. This issue requires careful investigation. The present study examined the response of Synechococcus sp. physiology to different environmental conditions. Three strains of Synechococcus sp. (red BA-120, green BA-124, and brown BA-132) were cultivated in a laboratory under previously determined environmental conditions. These conditions were as follows: temperature (T) from 10 by 5 to 25&thinsp;°C, salinity from 3 by 5 to 18 PSU, and photosynthetically active radiation (PAR) from 10 by 90 to 280&thinsp;µmol&thinsp;photons&thinsp;m−2&thinsp;s−1, which gave 64 combinations of synthetic, though realistic, environmental scenarios. Scenarios reflecting all possible combinations were applied in the laboratory experiments. Results pointed to differences in final numbers of cells among strains. However, there was also a similar tendency for BA-124 and BA-132, which demonstrated the highest concentrations of PCY cells at elevated T and PAR. This was also the case for BA-120 but only to a certain degree as the number of cells started to decrease above 190&thinsp;µmol&thinsp;photons&thinsp;m−2&thinsp;s−1&thinsp;PAR. Pigmentation, chlorophyll a (Chl a), fluorescence, and rate of photosynthesis presented both similarities and differences among strains. In this context, more consistent features were observed between brown and red strains when compared to the green. In this paper, the ecophysiological responses of PCY are defined.</p

Allelopathic activity of the picocyanobacterium Synechococcus sp. on unicellular eukaryote planktonic microalgae

The production and release of allelopathic compounds is an important adaptation by which some species of cyanobacteria can achieve a competitive advantage over other primary producers. In the present study we tested the allelopathic activity of the picocyanobacterium Synechococcus sp. against the following coexisting unicellular eukaryote microalgae: Porphyridium purpureum, Stichococcus bacillaris, Prymnesium parvum and Nitzschia dissipata. With these species, we covered a wide range of taxonomic groups. We demonstrated that both the addition of Synechococcus sp. cell-free filtrate and coculture inhibited the growth, chlorophyll content and photosynthetic rate of P. purpureum and S. bacillaris. Conversely, P. parvum, a well-known mixotroph, was positively affected by both Synechococcus sp. treatments. In contrast, N. dissipata was not affected by either the picocyanobacterial filtrate or coculture. These results suggest that the negative allelopathic effect is related to a reduction in the photosynthetic rate, and that Synechococcus sp. allelopathy should be taken into account in the interactions between picocyanobacteria and eukaryote competitors coexisting in a planktonic system. © CSIRO.This study was supported by grants from BMN, Poland (number 538-G245-B568-17) and FCT Project UID/Multi/04423/2013