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Radiosumins are a structurally diverse family of low molecular weight natural products that are produced by cyanobacteria and exhibit potent serine protease inhibition. Members of this family are dipeptides characterized by the presence of two similar non-proteinogenic amino acids. Here we used a comparative bioinformatic analysis to identify radiosumin biosynthetic gene clusters from the genomes of 13 filamentous cyanobacteria. We used direct pathway cloning to capture and express the entire 16.8 kb radiosumin biosynthetic gene cluster from Dolichospermum planctonicum UHCC 0167 in Escherichia coli. Bioinformatic analysis demonstrates that radiosumins represent a new group of chorismate-derived non-aromatic secondary metabolites. High-resolution liquid chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy and chemical degradation analysis revealed that cyanobacteria produce a cocktail of novel radiosumins. We report the chemical structure of radiosumin D, an N-methyl dipeptide, containing a special Aayp (2-amino-3-(4-amino-2-cyclohexen-1-ylidene) propionic acid) with R configuration that differs from radiosumin A-C, an N-Me derivative of Aayp (Amyp) and two acetyl groups. Radiosumin C inhibits all three human trypsin isoforms at micromolar concentrations with preference for trypsin-1 and -3 (IC50 values from 1.7 mu M to >7.2 mu M). These results provide a biosynthetic logic to explore the genetic and chemical diversity of the radiosumin family and suggest that these natural products may be a source of drug leads for selective human serine proteases inhibitors.

Harmful cyanobacterial blooms (cyanoHABs) cause recurrent toxic events in global watersheds. Although public health agencies monitor the causal toxins of most cyanoHABs and scientists in the field continue developing precise detection and prediction tools, the potent anticholinesterase neurotoxin, guanitoxin, is not presently environmentally monitored. This is largely due to its incompatibility with widely employed analytical methods and instability in the environment, despite guanitoxin being among the most lethal cyanotoxins. Here, we describe the guanitoxin biosynthesis gene cluster and its rigorously characterized nine-step metabolic pathway from l-arginine in the cyanobacterium Sphaerospermopsis torques-reginae ITEP-024. Through environmental sequencing data sets, guanitoxin (gnt) biosynthetic genes are repeatedly detected and expressed in municipal freshwater bodies that have undergone past toxic events. Knowledge of the genetic basis of guanitoxin biosynthesis now allows for environmental, biosynthetic gene monitoring to establish the global scope of this neurotoxic organophosphate.

Soda lakes environment is known to be variable and can have distinct differences according to geographical location. In this study, we investigated the effect of different environmental conditions of six adjacent soda lakes on bacterial communities and their functioning using a metagenomic approach combined with flow cytometry and chemical analyses. Ordination analysis using flow cytometry and water chemistry data from two sampling periods (wet and dry) clustered soda lakes in three different profiles: eutrophic turbid (ET), oligotrophic turbid (OT), and clear vegetated oligotrophic (CVO). Analysis of bacterial community composition and functioning corroborated this ordination; the exception was one ET lake, that was similar to one OT lake during the wet season, indicating drastic shifts between seasons. Microbial abundance and diversity increased during the dry period, along with a considerable number of limnological variables, all indicative of a strong effect of the precipitation-evaporation balance in these systems. Cyanobacteria were linked to high electric conductivity, pH, and nutrient availability, whereas Actinobacteria, Alphaproteobacteria, and Betaproteobacteria were correlated with landscape morphology variability (surface water, surface perimeter, and lake volume) and less stressed lake conditions. Stress response metabolism was overrepresented in ET and OT lakes and underrepresented in CVO lakes. Altogether, this study illustrated the sensitivity of tropical soda lakes to climate change, as slight changes in hydrological regimes might produce drastic shifts in community diversity.

Soda lake environments are known to be variable and can have distinct differences according to geographical location. In this study, we investigated the effects of different environmental conditions of six adjacent soda lakes in the Pantanal biome (Mato Grosso do Sul state, Brazil) on bacterial communities and their functioning using a metagenomic approach combined with flow cytometry and chemical analyses. Ordination analysis using flow cytometry and water chemistry data from two sampling periods (wet and dry) clustered soda lakes into three different profiles: eutrophic turbid (ET), oligotrophic turbid (OT), and clear vegetated oligotrophic (CVO). Analysis of bacterial community composition and functioning corroborated this ordination; the exception was one ET lake, which was similar to one OT lake during the wet season, indicating drastic shifts between seasons. Microbial abundance and diversity increased during the dry period, along with a considerable number of limnological variables, all indicative of a strong effect of the precipitation-evaporation balance in these systems. Cyanobacteria were associated with high electric conductivity, pH, and nutrient availability, whereas Actinobacteria, Alphaproteobacteria, and Betaproteobacteria were correlated with landscape morphology variability (surface water, surface perimeter, and lake volume) and with lower salinity and pH levels. Stress response metabolism was enhanced in OT and ET lakes and underrepresented in CVO lakes. The microbiome dataset of this study can serve as a baseline for restoring impacted soda lakes. Altogether, the results of this study demonstrate the sensitivity of tropical soda lakes to climate change, as slight changes in hydrological regimes might produce drastic shifts in community diversity.

The cyanobacterial genus Nostoc is an important contributor to carbon and nitrogen bioavailability in terrestrial ecosystems and a frequent partner in symbiotic relationships with non-diazotrophic organisms. However, since this currently is a polyphyletic genus, the diversity of Nostoc -like cyanobacteria is considerably underestimated at this moment. While reviewing the phylogenetic placement of previously isolated Nostoc -like cyanobacteria originating from Brazilian Amazon, Caatinga and Atlantic forest samples, we detected 17 strains isolated from soil, freshwater, rock and tree surfaces presenting patterns that diverged significantly from related strains when ecological, morphological, molecular and genomic traits were also considered. These observations led to the identification of the evaluated strains as representative of three novel nostocacean genera and species: Amazonocrinis nigriterrae gen. nov., sp. nov.; Atlanticothrix silvestris gen. nov., sp. nov.; and Dendronalium phyllosphericum gen. nov., sp. nov., which are herein described according to the rules of the International Code of Nomenclature for algae, fungi and plants. This finding highlights the great importance of tropical and equatorial South American ecosystems for harbouring an unknown microbial diversity in the face of the anthropogenic threats with which they increasingly struggle.

The saline-alkaline lakes (soda lakes) are the habitat of the haloalkaliphilic cyanobacterium Anabaenopsis elenkinii, the type species of this genus. To obtain robust phylogeny of this type species, we have generated whole-genome sequencing of the bloom-forming Anabaenopsis elenkinii strain CCIBt3563 isolated from a Brazilian soda lake. This strain presents the typical morphology of A. elenkinii with short and curved trichomes with apical heterocytes established after separation of paired intercalary heterocytes and also regarding to cell dimensions. Its genome size is 4 495 068 bp, with a G+C content of 41.98 %, a total of 3932 potential protein coding genes and four 16S rRNA genes. Phylogenomic tree inferred by RAxML based on the alignment of 120 conserved proteins using GTDB-Tk grouped A. elenkinii CCIBt3563 together with other genera of the family Aphanizomenonaceae. However, the only previous available genome of Anabaenopsis circularis NIES-21 was distantly positioned within a clade of Desikacharya strains, a genus from the family Nostocaceae. Furthermore, average nucleotide identity values from 86–98 % were obtained among NIES-21 and Desikacharya genomes, while this value was 76.04 % between NIES-21 and the CCIBt3563 genome. These findings were also corroborated by the phylogenetic tree of 16S rRNA gene sequences, which also showed a strongly supported subcluster of A. elenkinii strains from Brazilian, Mexican and Kenyan soda lakes. This study presents the phylogenomics and genome-scale analyses of an Anabaenopsis elenkinii strain, improving molecular basis for demarcation of this species and framework for the classification of cyanobacteria based on the polyphasic approach.

The saline-alkaline lakes (soda lakes) are the habitat of the haloalkaliphilic cyanobacterium

Interactions between climate change and ultraviolet radiation (UVR) have a substantial impact on aquatic ecosystems, especially on photosynthetic organisms. To counteract the damaging effects of UVR, cyanobacteria developed adaptive strategies such as the biosynthesis of secondary metabolites. This study aimed to evaluate the effects of UVR on the metabolomic profiles of potentially toxic cyanobacteria. Twelve strains were irradiated with ultraviolet A and ultraviolet B radiation and parabolic aluminized reflector lamps for 3 days, followed by liquid chromatography–tandem mass spectometry (LC-MS/MS) analysis to assess changes in metabolomic profiles. Matrices were used to generate principal component analysis biplots, and molecular networks were obtained using the Global Natural Products platform. Most strains showed significant changes in their metabolomic profiles after UVR exposure. On average, 7% of MS features were shown to be exclusive to metabolomic profiles before UVR exposure, while 9% were unique to metabolomic profiles after UVR exposure. The identified compounds included aeruginosins, spumigins, cyanopeptolins, microginins, namalides, pseudospumigins, anabaenopeptins, mycosporine-like amino acids, nodularins and microcystins. Data showed that cyanobacteria display broad metabolic plasticity upon UVR exposure, including the synthesis and differential expression of a variety of secondary metabolites. This could result in a competitive advantage, supporting cyanobacterial blooms under various UVR light exposures.

The bloom-forming cyanobacterium Nodularia spumigena CENA596 encodes the biosynthetic gene clusters (BGCs) of the known natural products nodularins, spumigins, anabaenopeptins/namalides, aeruginosins, mycosporin-like amino acids, and scytonemin, along with the terpenoid geosmin. Targeted metabolomics confirmed the production of these metabolic compounds, except for the alkaloid scytonemin. Genome mining of N. spumigena CENA596 and its three closely related Nodularia strains&mdash, two planktonic strains from the Baltic Sea and one benthic strain from Japanese marine sediment&mdash, revealed that the number of BGCs in planktonic strains was higher than in benthic one. Geosmin&mdash, a volatile compound with unpleasant taste and odor&mdash, was unique to the Brazilian strain CENA596. Automatic annotation of the genomes using subsystems technology revealed a related number of coding sequences and functional roles. Orthologs from the Nodularia genomes are involved in the primary and secondary metabolisms. Phylogenomic analysis of N. spumigena CENA596 based on 120 conserved protein sequences positioned this strain close to the Baltic Nodularia. Phylogeny of the 16S rRNA genes separated the Brazilian CENA596 strain from those of the Baltic Sea, despite their high sequence identities (99% identity, 100% coverage). The comparative analysis among planktic Nodularia strains showed that their genomes were considerably similar despite their geographically distant origin.

É crescente o reconhecimento da importância de micro-organismos diazotróficos assimbióticos em florestas tropicais. Nos últimos anos, tem sido demostrado que suas contribuições para o ganho de nitrogênio em ecossistemas naturais podem ser até maiores do que as contribuições dos sistemas simbióticos. No entanto, a diversidade e os mecanismos que determinam a estruturação das comunidades de diazotróficos assimbióticos são pouco conhecidos. Para compreender melhor a diversidade e a estruturação de suas comunidades na Floresta Amazônica, os diazotróficos assimbióticos da filosfera, serapilheira e rizosfera de nove espécies arbóreas em três épocas distintas foram avaliados utilizando-se sequenciamento em larga escala dos genes rRNA 16S e nifH. Os resultados mostraram que cada micro-habitat seleciona comunidades diazotróficas distintas, as quais variam também com a época do ano. As comunidades de diazotróficos também mostraram ser dependentes dos táxons das árvores, com o maior efeito seletivo na filosfera. Para todas as condições estudadas, as comunidades diazotróficas apresentaram altos índices de diversidade e riqueza, com os maiores índices de Shannon e Chao1 na Serapilheira (9,57 e 5222, respectivamente), em relação a filosfera (7,4 e 3145, respectivamente) e a rizosfera (8,65 e 2868, respectivamente). A maior proporção de bactérias diazotróficas em relação a comunidade total de bactérias, com base na abundância de sequências do gene rRNA 16S, foi observada na filosfera (23%), em relação a serapilheira (20%) e rizosfera (18%). De uma maneira geral, essa proporção relativa não foi afetada pela época de amostragem, muito embora as estruturas das comunidades tenham variado, sugerindo existência de redundância funcional para FBN. Os três micro-habitats mostraram dominância do filo Proteobacteria, com frequências aproximadas a 81% na filosfera, 93% na rizosfera de 82% na serapilheira. O filo Cyanobacteria apresentou frequências relevantes na filosfera e serapilheira, com aproximadamente 17% e 5%, respectivamente. Firmicutes mostrou frequências, na serapilheira e rizosfera, de aproximadamente 12% e 5%, respectivamente. Estes resultados mostram que os micro-organismos diazotróficos assimbóticos associados com as árvores podem ter um importante papel na entrada do nitrogênio em florestas tropicais e que a estrutura de tais comunidades é determinada pelo seu micro-habitat, hospedeiro e época do ano. There is increasing recognition of the importance of assimbiotic diazotrophic microorganisms in tropical forests. In recent years, it has been shown that their contributions to the nitrogen inputs can be even higher than the contributions of symbiotic systems in natural ecosystems. However, the diversity and the mechanisms driving the assembling of the communities of assimbiotic diazotrophs in tropical forests are poorly understood. To better understand the diversity and assembling of the diazothrophs communities in the Amazon forest, the assimbiotic diazotrophs in the phyllosphere, litter and rhizosphere from nine tree species in three distinct times of year were evaluated using large-scale sequencing of 16S rRNA and nifH genes. The results showed that each microhabitat selected distinct diazotrophic communities, which were also affected by the time of year. The structure of the communities of putative diazotrophs were also dependent on the tree taxa, with greater selection effect on the phyllosphere. For all conditions studied, the communities of putiative diazothrophs showed high diversity indexes and OTU richness, with the highest Shannon and Chao1 indexes detected for the litter (9.57 and 5222, respectively), as compared to phyllosphere (7.4 and 3145, respectively) and rhizosphere (8.65 and 2868, respectively). The highest proportion of diazotrophic bacteria in relation to the total bacteria, based on the abundance of sequences of 16S rRNA genes, was observed in the phyllosphere (23%), as compared to litter (20%) and rhizosphere (18%). Overall, the relative abundance of dizothrophic bacteria in the bacterial community was not affected by the sampling time, even though the community structures varied, suggesting the occurrence of functional redundancy for BNF. In the three microhabitats, dominance of the phylum Proteobacteria, with frequencies of approximately 81% in the phyllosphere, 93% in the rhizosphere and 82% in the litter, was observed. Cyanobacteria showed significantly higher frequencies in the phyllosphere and litter, approximately 17% and 5%, respectively, as compared to rhizosphere. Firmicutes also showed high frequencies in the litter and rhizosphere, approximately 12 % and 5%, respectively. These results showed that the assimbiotic putative diazotrophic microorganisms associated with trees may play an important role in the input of nitrogen in tropical forests and that the structure of their communities is determined by the microhabitat, host taxon and time of year.