Spatial and Temporal Variability of Saxitoxin-Producing Cyanobacteria in U.S. Urban Lakes

Area of Science:

• Environmental Science
• Microbiology
• Ecotoxicology

Background:

• Harmful cyanobacterial blooms (HCBs) pose significant risks to ecosystems and human health due to toxic compounds.
• Saxitoxins (STXs), a type of neurotoxic alkaloid, are produced by certain cyanobacteria and are less studied than other cyanotoxins like microcystins.
• Understanding the prevalence and sources of STX production is crucial for managing HCBs.

Purpose of the Study:

• To investigate the spatio-temporal distribution of cyanobacteria and their potential for saxitoxin (STX) production in eleven U.S. urban lakes.
• To correlate the presence and abundance of the STX-encoding gene (*sxtA*) with STX concentrations.
• To identify specific cyanobacteria genera responsible for STX production and their associated environmental factors.

Main Methods:

• Quantitative PCR (qPCR) to detect and quantify the *sxtA* gene.
• Targeted sequencing of the *sxtA* gene and 16S rRNA gene sequencing to identify cyanobacteria species.
• Correlation analysis between gene abundance, STX concentrations, and environmental parameters.

Main Results:

• The STX-encoding gene (*sxtA*) was detected in all eleven studied U.S. urban lakes during bloom conditions.
• A strong positive correlation was observed between *sxtA* gene abundance and STX concentrations, particularly in Big 11 Lake.
• Sequencing identified *Aphanizomenon* and/or *Dolichospermum* as the primary STX producers, with significant correlations to *sxtA* gene abundance and STX levels.
• *Aphanizomenon* presence was linked to conductivity, sulfate, and orthophosphate, while *Dolichospermum* correlated with temperature and pH.

Conclusions:

• This study confirms the widespread presence of STX-producing cyanobacteria in U.S. urban lakes.
• *Aphanizomenon* and *Dolichospermum* are identified as key contributors to STX production in these environments.
• The findings provide valuable insights into the ecological factors influencing STX-producing cyanobacteria, aiding in the development of HCB management strategies.