Cyanobacteria are among the most diverse morphological microorganisms that inhabit a great variety of habitats. Their presence in the Azores, a volcanic archipelago of nine islands in the middle of the North Atlantic Ocean, has already been reported. However, due to the high diversity of cyanobacteria habitats, their biodiversity is still understudied, mainly in extreme environments. To address this, a total of 156 cyanobacteria strains from Azores lakes, streams, thermal and terrestrial habitats were isolated. Identification was made based on a polyphasic approach using classical taxonomy (morphological characteristics and environmental data) and phylogeny among 81 strains assessed by maximum likelihood and Bayesian analysis of 16S rDNA partial sequences. The 156 isolates showed a high genera diversity (38) belonging to the orders Chroococcales, Nostocales, Oscillatoriales, and Synechococcales. Eleven new genera for the Azores habitats are here reported, reinforcing that cyanobacteria biodiversity in these islands is still much understudied. Phylogenetic analysis showed 14 clusters associated with these cyanobacteria orders, with evidence for six new genera and valuable information towards Microchaete/Coleospermum taxonomic revision that better reflects species environmental distribution. These results emphasize the need for cyanobacteria taxonomy revisions, through polyphasic studies, mainly in Synechococcales order and in the Microchaete/Coleospermum, Nostoc, and Anabaena genera.

Eutrophication and global climate change gather advantageous conditions for cyanobacteria proliferation leading to bloom formation and cyanotoxin production. In the Azores, eutrophication is a major concern, mainly in lakes where fertilizers and organic matter discharges have increased nutrient concentration. In this study, we focused on understanding the influence of environmental factors and lake characteristics on (i) cyanobacteria diversity and biomass and (ii) the presence of toxic strains and microcystin, saxitoxin, anatoxin-a, and cylindrospermopsin cyanotoxin-producing genes. Fifteen lakes from the Azores Archipelago were sampled seasonally, environmental variables were recorded in situ, cyanobacteria were analyzed with microscopic techniques, and cyanotoxin-producing genes were targeted through conventional PCR. Statistical analysis (DistLM) showed that lake typology-associated variables (lake’s depth, area, and altitude) were the most explanatory variables of cyanobacteria biomass and cyanotoxin-producing genes presence, although trophic variables (chlorophyll a and total phosphorus) influence species distribution in each lake type. Our main results revealed higher cyanobacteria biomass/diversity, and higher toxicity risk in lakes located at lower altitudes, associated with deep anthropogenic pressures and eutrophication scenarios. These results emphasize the need for cyanobacteria blooms control measures, mainly by decreasing anthropogenic pressures surrounding these lakes, thus decreasing eutrophication. We also highlight the potential for microcystin, saxitoxin, and anatoxin-a production in these lakes, hence the necessity to implement continuous mitigation protocols to avoid environmental and public health toxicity events.

Microcystins (MCs), Saxitoxins (STXs), and Cylindrospermopsins (CYNs) are some of the more well-known cyanotoxins. Taking into consideration the impacts of cyanotoxins, many studies have focused on the identification of unknown cyanotoxin(s)-producing strains. This study aimed to screen strains from the Azorean Bank of Algae and Cyanobacteria (BACA) for MCs, STX, and CYN production. A total of 157 strains were searched for mcy, sxt, and cyr producing genes by PCR, toxin identification by ESI-LC-MS/MS, and cyanotoxin-producing strains morphological identification and confirmation by 16S rRNA phylogenetic analysis. Cyanotoxin-producing genes were amplified in 13 strains and four were confirmed as toxin producers by ESI-LC-MS/MS. As expected Aphanizomenon gracile BACA0041 was confirmed as an STX producer, with amplification of genes sxtA, sxtG, sxtH, and sxtI, and Microcystis aeruginosa BACA0148 as an MC-LR producer, with amplification of genes mcyC, mcyD, mcyE, and mcyG. Two nostocalean strains, BACA0025 and BACA0031, were positive for both cyrB and cyrC genes and ESI-LC-MS/MS confirmed CYN production. Although these strains morphologically resemble Sphaerospermopsis, the 16S rRNA phylogenetic analysis reveals that they probably belong to a new genus.

Cyanobacteria are diverse, complex and a unique group of microorganisms that inhabit a wide variety of environments. Contrarily to continental areas, studies on cyanobacteria in islands are scarce and need to be reinforced, since climate change impacts are expected to be harsher in islands, due to their geographical isolation and higher exposition to external influences. Here we present a review of the occurrence of cyanobacteria and cyanotoxins in inland and coastal ecosystems in the Atlantic Ocean islands. These microorganisms were reported from diverse habitats, including saline thermal lakes (Iceland), freshwater lakes, terrestrial habitats (Azores, Cuba), and marine coastal areas, either planktonic (Madeira, Canary Islands, Cape Verde) or associated to plants and corals (Brazil, Caribbean Sea). Most of cyanobacteria were reported from freshwaters but some species were found in different habitats. Species richness also varied between islands, with higher number in islands located in temperate regions, and the number of common taxa was low (1-3%). Several toxic species and different types of cyanotoxins were also reported in the Atlantic islands, which are expected to increase with climate change. Mitigation measures should be considered to avoid cyanotoxins risks to environmental and public health. This works shows the great potential of Atlantic islands for cyanobacteria taxonomic, ecological and biogeography research, but more studies are needed with emphasis on less studied islands and habitats and using novel approaches as molecular systematics tools. Furthermore, such studies are of paramount importance for environmental conservation and management strategies, especially facing climate changes.