Polyphasic Approach and Potential Cyanotoxin Production by Planktothrix from the Río Grande de Comitán and Montebello Lakes National Park, Southern Mexico.

The development of anthropic activities during recent years has led to an increase in nutrient fluxes in the Río Grande de Comitán and Montebello Lakes National Park, Mexico. In turn, this has modified the dynamics of the biotic community, specifically favoring the presence of cyanobacteria tolerant to contamination. The continual and massive presence of Planktothrix species (spp.) in the system suggests a potential detrimental impact for economic issues and human health. In this study, we identify the morphological and molecular characteristics of Planktothrix populations from seven tropical (1,380-1,740 masl, 23.0-25.5°C) and calcareous lakes and two ponds from a water treatment plant. We also assess the ecological drivers that could be related to the presence of cyanotoxins in the system. The ecological preferences, morphology, 16S rRNA structure, and 16S-23S rRNA internal transcribed spacer found evidence for three species: P. agardhii distributed in neutral to slightly basic water (pH = 7.7-8.7), and P. spiroides and Planktothrix sp. in alkaline waters (pH = 9.1). The presence of the mcyE gene and its validation by liquid chromatography confirmed the presence of two microcystin variants (MC-RR and MC-LR) in at least three populations of P. agardhii. These microcystins put the health of the ecosystem and its inhabitants at risk, a condition that should be addressed and resolved with a water management and detoxification strategy in the basin.

Description of two new species of Nostoc (Nostocales, Cyanobacteria) from central Mexico, using morphological, ecological, and molecular attributes.

The present study describes two new Nostoc species, N. montejanii and N. tlalocii, based on a polyphasic approach that combines morphological, ecological, and genetic characteristics. The five investigated populations, including those from newly collected material from central Mexico, were observed to possess morphological features characteristic of the Nostoc genus. Results showed that both new species are strictly associated with running water, and they show clear differences in their habitat preferences. The 16S rRNA gene sequences of the five strains displayed between 98% and 99% similarity to the genus Nostoc sensu stricto. The 16S rRNA gene phylogenetic analyses inferred using Bayesian inference, maximum likelihood, and parsimony methods, placed these five strains in two separate clades distinct from other Nostoc species. The secondary structures of the 16S-23S internal transcribed spacer rRNA region in the two new species showed >10.5% dissimilarities in the operons when compared with other Nostoc species. In addition, clear morphological differences were observed between the two Mexican species, including the color of the colonies (black in N. montejanii and green in N. tlalocii), the size of the cells (greater in N. montejanii), and the number of polyphosphate granules present in the cells (one in N. montejanii and up to four in N. tlalocii).