3D Impedimetric Biosensor for Cyanobacteria Detection in Natural Water Sources

The excessive growth of cyanobacteria in freshwater sources produces the development of toxic blooms mainly due to the production of cyanotoxins. Here, a novel impedimetric biosensor based on a three-dimensional interdigitated electrode array (3D-IDEA) for detection of cyanobacteria cells is reported. The 3D-IDEA sensor surface biofunctionalization was performed by means of the layer-by-layer method using polyethyleneimine (PEI) as the anchoring layer and concanavalin A (Con A) as the bioreceptor to lipopolysaccharides of cyanobacteria cells. The developed PEI-Con A 3D-IDEA sensors show a linear response (R2 = 0.992) of the impedance changes (RS) versus the logarithm of cyanobacteria concentrations in the range of 102–105 cells·mL−1 with the detection limit of 100 cells·mL−1. Moreover, to prevent the interference from components that may be present in real water samples and minimize a possible sample matrix effect, a filtration methodology to recover cyanobacterial cells was developed. The proposed methodology allows 91.2% bacteria recovery, permitting to obtain results similar to controlled assays. The developed system can be used in aquatic environments to detect cyanobacteria and consequently to prevent the formation of blooms and the production of cyanotoxins. Con A can bind to most polysaccharides and so react with other types of bacteria. However, currently, on the market, it is not possible to find specific biorecognition elements for cyanobacteria. Taking into consideration the specificity of samples to be analyzed (natural water resources), it is difficult to expect high concentration of other bacteria. In this sense, the developed methodology may be used as an alarm system to select samples for more thorough and precise laboratory analysis.

Long-Term Variations in Species Composition of Bloom-Forming Toxic Pseudo-nitzschia Diatoms in the North-Western Sea of Japan during 1992–2015

This review aimed to summarize original and published data on the bloom events caused by toxic diatoms of the genus Pseudo-nitzschia and to assess long-term variations in the composition of bloom-forming species in the northwestern Sea of Japan during 1992−2015. This information is crucial to understanding the potential threat of toxic blooms and their effects. A change in species composition was observed within the genus Pseudo-nitzschia: it was dominated by Pseudo-nitzschia multiseries during 1992–1993, 2002, and a shift towards the dominance of Pseudo-nitzschia multistriata and Pseudo-nitzschia calliantha occurred in 2005–2015. We assume that the increased sea surface temperature recorded from Amursky Bay in the period of 1998–2009 compared to the data of 1980–1989 might be one of the causative factors for the shift observed. The absence of highly toxic Pseudo-nitzschia multiseries among the bloom-forming species is considered as one of the possible explanations for the lack of damage from the blooms of Pseudo-nitzschia over the past 15 years in the study area.

Cyanobacterial blooms in freshwaters bodies in a semiarid region, northeastern Brazil: A review

Harmful cyanobacterial blooms have caused several problems in freshwater environments due to their prolific growth and the harmful cyanotoxins produced by some species. The occurrence of these organisms has increased in recent decades due to climate change and eutrophication, although most studies are from temperate regions in the Northern hemisphere. This review presents data about cyanobacteria occurrence, dominance, and toxicity events in freshwater bodies in a semiarid region of Northeast Brazil, in the tropical Southern hemisphere. We performed a literature survey of cyanobacteria publications from 1930 to 2016. We made a list of all the dominant species registered in each state, noted their distribution and occurrence of dominance events involving one or more species, and the registered records of toxic blooms, including information about the toxins involved and the range of values. We selected 102 publications that described cyanobacteria occurrence from states in Northeast Brazil; these publications included relevant contributions regarding cyanobacteria distribution, richness, density, and biomass. Forty-nine dominant species were recorded, with the most representation found in the state of Pernambuco (30 spp.). The genera with the highest occurrences were Microcystis, Cylindrospermopsis, Planktothrix, Dolichospermum (=Anabaena), and Geitlerinema, especially the species Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Planktothrix agardhii. Episodes of toxic blooms were observed in four states. Microcystins, cylindrospermopsin, saxitoxins, and anatoxin-a(S) were found to be associated with these blooms. In Northeast Brazil, harmful cyanobacterial blooms are common in urban and public reservoirs. However, in recent years, cyanobacterial blooms in this region have been more intense and perennial, with high biomass occurring throughout the year.

The effect of algal blooms on fish in their inshore nursery grounds in the Gulf of Gdańsk

Studies of cyanobacterial bloom dynamics show that the highest biomass accumulation of Nodularia spumigena is observed in the shallowest area of the Gulf of Gdańsk in summer. In the same region and time, the highest fish abundance is observed. Mostly young individuals of gobies, small sandeel, flounder, three-spine stickleback and young herring occur. In this work we compare how toxic blooms of cyanobacteria influence the number and structure of fish communities in a coastal zone. The results obtained in our study were rather unexpected. More fish species were caught and the biomass of fish was higher during a bloom than in a month following the sampling (no bloom).

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria)

Although Planktothrix agardhii often produces toxic blooms in eutrophic water bodies around the world, little is known about the fate of the organic matter released by these abundant Cyanobacteria. Thus, this study focused in estimating the bacterial consumption of the DOC and DON (dissolved organic carbon and dissolved organic nitrogen, respectively) produced by axenic P. agardhii cultures and identifying some of the bacterial OTUs (operational taxonomic units) involved in the process. Both P. agardhii and bacterial inocula were sampled from the eutrophic Barra Bonita Reservoir (SP, Brazil). Two distinct carbon degradation phases were observed: during the first three days, higher degradation coefficients were calculated, which were followed by a slower degradation phase. The maximum value observed for particulate bacterial carbon (POC) was 11.9 mg L-1, which consisted of 62.5% of the total available DOC, and its mineralization coefficient was 0.477 day-1 (t½ = 1.45 days). A similar pattern of degradation was observed for DON, although the coefficients were slightly different. Changes in the OTUs patterns were observed during the different steps of the degradation. The main OTUs were related to the classes Alphaproteobacteria (8 OTUs), Betaproteobacteria (2 OTUs) and Gammaproteobacteria (3 OTUs). The genus Acinetobacter was the only identified organism that occurred during the whole process. Bacterial richness was higher at the slower degradation phase, which could be related to the small amounts of DOM (dissolved organic matter) available, particularly carbon. The kinetics of the bacterial degradation of P. agardhii-originated DOM suggests minimal loss of DOM from the Barra Bonita reservoir.