Metagenomic mapping of cyanobacteria and potential cyanotoxin producing taxa in large rivers of the United States

Cyanobacterial Harmful Algal Mats (CyanoHAMs) in tropical rivers of central Mexico and their potential risks through toxin production

Cyanobacteria inhabiting lotic environments have been poorly studied and characterized in Mexico, despite their potential risks from cyanotoxin production. This article aims to fill this knowledge gap by assessing the importance of benthic cyanobacteria as potential cyanotoxin producers in central Mexican rivers through: (i) the taxonomic identification of cyanobacteria found in these rivers, (ii) the environmental characterization of their habitats, and (iii) testing for the presence of toxin producing genes in the encountered taxa. Additionally, we introduce and discuss the use of the term "CyanoHAMs" for lotic water environments. Populations of cyanobacteria were collected from ten mountain rivers and identified using molecular techniques. Subsequently, these taxa were evaluated for genes producing anatoxins and microcystins via PCR. Through RDA analyses, the collected cyanobacteria were grouped into one of three categories based on their environmental preferences for the following: (1) waters with high ionic concentrations, (2) cold-temperate waters, or (3) waters with high nutrient enrichment. Populations from six locations were identified to genus level: Ancylothrix sp., Cyanoplacoma sp., and Oxynema sp. The latter was found to contain the gene that produces anatoxins and microcystins in siliceous rivers, while Oxynema tested positive for the gene that produces microcystins in calcareous rivers. Our results suggest that eutrophic environments are not necessarily required for toxin-producing cyanobacteria. Our records of Compactonostoc, Oxynema, and Ancylothrix represent the first for Mexico. Four taxa were identified to species level: Wilmottia aff. murrayi, Nostoc tlalocii, Nostoc montejanii, and Dichothrix aff. willei, with only the first testing positive using PCR for anatoxin and microcystin-producing genes in siliceous rivers. Due to the differences between benthic growths with respect to planktonic ones, we propose the adoption of the term Cyanobacterial Harmful Algal Mats (CyanoHAMs) as a more precise descriptor for future studies.

Geospatial analysis of cyanobacterial exposure and liver cancer in the contiguous United States

BACKGROUND AND AIMS

Cyanobacteria are commonly found in water bodies and their production of hepatotoxins can contribute to liver damage. However, the population health effects of cyanobacteria exposure (CE) are unknown. Our objectives were to determine the effect of chronic exposure to cyanobacteria through proximity to water bodies with high cyanobacteria counts on the incidence and mortality of liver cancers, as well as to identify location-based risk factors.

APPROACH AND RESULTS

Across the contiguous United States, regions with high cyanobacteria counts in water bodies were identified using satellite remote sensing data. The data were geospatially mapped to county boundaries, and disease mortality and incidence rates were analyzed. Distinctive spatial clusters of CE and mortality related to liver diseases or cancer were identified. There was a highly significant spatial association between CE, liver disease, and liver cancer but not between CE and all cancers. Hot spots of CE and mortality were identified along the Gulf of Mexico, eastern Texas, Louisiana, and Florida, and cold spots across the Appalachians. The social vulnerability index was identified as a major location-based determinant by logistic regression, with counties in the fourth or fifth quintiles having the highest prevalence of hot spots of CE and mortality from liver cancer.

CONCLUSIONS

These findings emphasize the importance of environmental exposure to cyanobacteria as a location-based determinant of mortality from liver cancer. Public health initiatives addressing CE may be considered to reduce mortality, particularly in areas of high social vulnerability.