# Electrophysiological monitoring of nutrient stress in Oscillatoria sp. cohorts: Toward an early-warning tool for harmful algal blooms

## TL;DR

Researchers used electrical signals to detect nutrient stress in Oscillatoria, a cyanobacterium linked to harmful algal blooms, suggesting a new early warning tool for water management.

## Contribution

This study introduces electrophysiological monitoring as a novel, real-time method to detect nitrogen stress in Oscillatoria, potentially enabling early warning of harmful algal blooms.

## Key findings

- Electrical signaling in Oscillatoria increased under nitrogen deprivation, with spike rates and amplitudes rising over time.
- Nitrogen repletion rapidly reduced electrical activity within 24 hours, indicating recovery of nutrient balance.
- The method shows promise as a non-invasive, real-time tool for monitoring harmful algal bloom initiation.

## Abstract

Cyanobacterial harmful algal blooms (HABs) are a growing challenge for freshwater management, traditionally addressed through phosphorus (P) limitation strategies. However, increasing evidence highlights nitrogen (N) availability as a key driver of bloom initiation and persistence. Here, we report extracellular voltage recordings from Oscillatoria cohorts exposed to four days of N starvation followed by ammonium (NH₄⁺) repletion using 5 mg L−1. Under N deprivation, electrical signalling developed progressively with a median of 1–2 events min−1 and amplitudes between 3-4 µV on day 1 and 2, following a marked increase in activity by days 3 and 4, with median spike rates of 5 events min−1 and amplitudes up to 17 µV. Following NH4+ repletion, signalling activity declined within 24 h, indicating rapid restoration of N balance. These results suggest that electrophysiological monitoring can serve as a real-time, non-invasive indicator of nutrient stress in Oscillatoria and provides a potential early warning tool for HAB onset and associated taste and odour (T&O) outbreaks in freshwater systems.

The online version contains supplementary material available at 10.1557/s43580-025-01486-3.