Researchers have identified specific types of bacteria whose presence can signal that a blue-green algae bloom is toxic, a discovery that could lead to a cost-effective early warning system for water safety. A team from McGill University found that shifts in the populations of these bacteria happen at the same time that algal blooms begin producing dangerous toxins, offering a new method for monitoring water quality.
This development comes as cyanobacterial blooms, commonly known as blue-green algae, are becoming more frequent and intense, a trend linked to climate change. These blooms can release a variety of contaminants called cyanotoxins, which pose serious health risks to people, pets, and wildlife, and can contaminate drinking water sources. The new technique, based on analyzing bacterial DNA in the water, could provide a more affordable and timely way for authorities to determine if a bloom requires further, more expensive testing for specific toxins.
The Rising Danger in Waterways
Blue-green algae are not true algae but a type of bacteria called cyanobacteria that are a natural part of most aquatic ecosystems. Under certain conditions—typically warm, calm, and nutrient-rich water—these bacteria can multiply rapidly, creating dense mats on the water surface often described as looking like spilled green paint or pea soup. While many of these blooms are harmless, certain species of cyanobacteria can produce potent toxins, such as microcystin, the most common type found in the lakes studied by the McGill researchers.
Exposure to these toxins can cause a range of health effects in humans, from skin irritation and hayfever-like symptoms to more severe issues like vomiting, diarrhea, fever, and headaches if ingested. The toxins can also impact the liver and nervous system. A significant challenge for public health officials is that it is impossible to know if a bloom is toxic simply by its appearance. This uncertainty often leads to broad “when in doubt, stay out” advisories, highlighting the need for more precise monitoring tools. The increasing prevalence of these harmful algal blooms (HABs) threatens not only recreational waters but also the headwaters of major drinking water supplies.
A New Strategy for Detection
The new method focuses on the broader bacterial community, known as bacterioplankton, that coexists with cyanobacteria in the water. The study, published in the journal Harmful Algae, was led by Lara Jansen, a Ph.D. student, in the lab of Professor Jesse Shapiro in McGill University’s Department of Microbiology and Immunology. The core finding is that the composition of the bacterioplankton community changes in predictable ways during a toxic cyanobacterial bloom.
Harnessing the Power of DNA
To identify these changes, the research team collected water samples and performed DNA sequencing on the entire aquatic bacterial community. By comparing the DNA sequences to a large database, they could identify the specific types of bacteria present and their relative abundance. Jansen noted that this approach has become increasingly practical as the cost of DNA sequencing has dropped significantly. This affordability makes it a viable tool for monitoring remote lakes and water bodies that are often far from major research centers.
Identifying the Bacterial Indicators
The analysis revealed that certain bacterioplankton were consistently more abundant during toxic blooms. Some of these indicator bacteria are related to microbes known to be capable of breaking down cyanotoxins. Their increased presence suggests a direct ecological response to the production of toxins by the blue-green algae. The researchers confirmed this link by testing for microcystin, finding that the spike in the indicator bacteria population occurred in the same timeframe as the appearance of the toxin. This confirmed that the shift in the bacterial community serves as a reliable proxy for the presence of toxins.
Validating the Method Across Ecosystems
To ensure the findings were not unique to a specific environment, the study was conducted in two ecologically distinct lakes located in the Cascade Mountains. These lakes had different nutrient levels and other environmental characteristics, yet the results were consistent across both ecosystems. The bacterial communities in both lakes reflected the toxicity of the blooms in the same way, suggesting that this detection method could be broadly applicable to a wide range of freshwater systems. The chosen study sites are important as they are popular for recreation and are located at the headwaters of significant drinking water sources, where toxins pose a risk of downstream migration.
Implications for Water Safety Management
This research offers a significant advancement in the management of public health risks associated with harmful algal blooms. By sampling and sequencing the DNA of bacteria in the water, water resource managers can gain a quick and cost-effective assessment of the potential for toxicity. This allows for a more targeted approach, where a positive signal from the bacterial community would trigger more intensive and specific testing for cyanotoxins.
This proactive strategy could allow for more timely public health warnings and interventions, preventing exposure before it occurs. It enhances the ability to monitor water quality more frequently and in more locations than is currently feasible with expensive toxin-specific tests. By better understanding the microbial community dynamics, scientists and officials can more effectively safeguard recreational waters and drinking water supplies from the growing threat of toxic blue-green algae.