ABSTRACT

Rivers and streams make up less than 1 % of the total surface freshwater available on earth, but are of enormous ecological and societal significance. Recently, biofilm forming toxic cyanobacteria, commonly known as benthic harmful cyanobacterial blooms, have become widespread in many rivers and streams. These cyanobacteria produce toxins as secondary metabolites which are harmful to humans and other animals when consumed. Species from the benthic cyanobacterial genus Microcoleus (formerly Phormidium) can form thick mats in flowing freshwaters which produce cyanotoxins in spatial and temporal patterns that are challenging to predict. Microcoleus benthic mats have become widespread and exhibit intriguing emergent behavior. Toxic strains of Microcoleus co-exist with its non-toxic counterparts and other cyanobacteria. Many metabolic pathways of toxic Microcoleus species operate differently from conventional pathways of other cyanobacteria. Through a combination of laboratory and field scale testing using a suite of genomic and modeling tools, this project seeks to understand the spatial and temporal dynamics of Microcoleus and the rule of life controlling the dynamics and emergent behavior of Microcoleus genera leading to toxic benthic mats. The results are expected to open new opportunities in the ecological science of benthic toxic mats in freshwater streams and to be applicable to cyanobacterial bloom mitigation. This project will broaden participation and promote student training in environmental biology, data science, ecological engineering, chemistry, mathematical modeling and computer science with an emphasis on training students from underrepresented groups.

Despite recent findings that toxic and non-toxic strains of Microcoleus synergize their metabolic efforts to facilitate each other during colonization, how nutrient concentrations, riverbed type, and other environmental factors play a role in the Emergent Rule of Life governing the colonization and toxin production in Microcoleus are not well understood. Therefore, the rule of life this project aims to investigate is how mat formation and toxin production by Microcoleus emerge from its interactions with its non-toxic counterparts and other coexisting bacteria in the benthic mats. The project will study (1) how within-mat species interactions and biogeochemical conditions facilitate Microcoleus growth and toxin production in low-nutrient streams, (2) the molecular mechanisms (e.g., gene expression level) by which toxic non-heterocytous (e.g., Microcoleus) and heterocytous cyanobacteria (diazotrophs able to fix atmospheric nitrogen gas, e.g., Anabaena) flourish in nitrogen and/or phosphorus deficient flowing waters and, (3) develop models to predict the occurrence and dynamics of toxic Microcoleus at river scales and quantify how cyanobacterial community dynamics and abiotic environmental conditions drive benthic cyanobacteria and toxin production over the growing season.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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