The aim of this study was to assess the ability of selected strains of cyanobacteria and microalgae to biosynthesize silver nanoparticles (Ag-NPs) by using two procedures; (i) suspending the live and washed biomass of microalgae and cyanobacteria into the AgNO3 solution and (ii) by adding AgNO3 into a cell-free culture liquid. Ag-NPs were biosynthesized by 14 out of 16 tested strains. In most of the cases Ag-NPs were formed both in the presence of biomass as well as in the cell-free culture liquid. This indicates that the process of Ag-NPs formation involves an extracellular compound such as polysaccharide. TEM analysis showed that the nanoparticles were embedded within an organic matrix. Ag-NPs varied in shape and sizes that ranged between 13 and 31 nm, depending on the organism used. The antibacterial activity of Ag-NPs was confirmed in all but one strain of cyanobacterium (Limnothrix sp. 37-2-1) which formed the largest particles.

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The potential for exposure to aerosolized algal toxins during harmful algal blooms has not been well studied. A fundamental question about the longevity of algal toxins in the aerosol phase remains. In this study, the influence of environmental factors such as sunlight and atmospheric oxidants (e.g., ozone and OH radicals) on the lifetime of microcystin-LR (MC-LR), which is known to be the most toxic of the MCs produced by cyanobacteria, was investigated. A cyanobacterial culture aliquot (Microcystis aeruginosa and Dolichospermum sp.) spiked with MC-LR was nebulized into a large outdoor photochemical chamber and atmospherically aged in the presence and absence of sunlight or ozone. The concentrations of MC-LR in aerosol were measured using liquid chromatography/tandem mass spectrometry and the enzyme-linked immunosorbent assay (ELISA) for atmospheric aging of aerosols. With 61.5 nm3 m–3 gaseous ozone, the second-order rate constant of ELISA-based MC-LR in M. aeruginosa aerosol was approximately (3.91 ± 0.17) × 105 M–1 s–1 (54 min lifetime). Because of the involvement of OH radicals, the daytime degradation of MC-LR was significantly faster than that at night with the same amount of ozone in the chamber air. We conclude that under natural sunlight, MC-LR in cyanobacterial aerosols quickly decays through heterogeneous chemistry with atmospheric oxidants but can still impact neighboring communities.

South Florida (USA) has a subtropical to tropical climate with an extensive and diverse coastline that supports the growth of benthic cyanobacterial mats (BCMs). These BCMs are widespread and potentially house numerous bioactive compounds; however, the extent of the cyanobacterial diversity within these mats remains largely unknown. To elucidate this diversity, BCMs from select locations in South Florida were sampled and isolated into unicyanobacterial cultures for morphological and molecular studies. Phylogenetic relationships of isolated taxa were assessed using the markers 16S rRNA and 16S‐23S rRNA ITS by both maximum likelihood and Bayesian inference. We propose Affixifilum gen. nov. based on morphological characteristics and the 16S rRNA phylogeny. Two species are included: Affixifilum granulosum comb nov. (=Neolyngbya granulosa) found in Brazil and Florida (USA) and A. floridanum sp. nov. Several other features, including pair‐wise distance of 16S rRNA and 16S‐23S rRNA ITS, 16S‐23S rRNA ITS secondary structure, morphology, and ecology, provide support for Affixifilum. We also propose the transfer of Lyngbya regalis to Neolyngbya as N. regalis comb. nov. and include the description of one novel species, N. biscaynensis sp. nov.

A dense perennial bloom of Raphidiopsis raciborskii was observed in an urban lake (29°53'13"S and 51°09'29.9"W). Due to supposed toxicity, this study analyzed the morphology of the species, evaluated the main factors that influence its growth, and examined bloom toxicity. Two sites were sampled monthly from November 2009 to November 2010. The species was found in all samples and dominated in 77% of the samples. Highest density was recorded at the end of summer (March-199,550 ind.mL-1) at 26.6 ºC and pH 7.8. High densities were also found at low temperatures (72,145 ind.mL-1 at 12.6 °C and 130,475 ind.mL-1 at 14.5 °C) and at minimum (5.4) and maximum (8.7) pH, reaching 89,964 ind.mL-1 and 61,400 ind.mL-1 , respectively. Nitrogen availability was high, especially ammonium [(60-)140-660 μg.L-1 ], and phosphorus was low (orthophosphate < 10 μg.L-1). These results support that R. raciborskii has a wide tolerance to abiotic variations. Saxitoxins and gonyautoxins were found in the bloom.

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