# Responses of Biofilm-Forming Halophilic Calothrix and Coelastrella Strains to Environmental Stressors Associated with Climate Change

## TL;DR

This study examines how two types of microorganisms respond to climate change stressors like higher temperatures and UV radiation, revealing strain-specific effects that complicate predictions about ecosystem changes.

## Contribution

The study provides new insights into how biofilm-forming halophilic cyanobacteria and microalgae respond to climate change stressors.

## Key findings

- Elevated UV radiation caused Calothrix sp. to produce screening compounds and coil trichomes for self-shading.
- Increased CO2 boosted Calothrix sp. growth, biomass, and pigment production.
- Higher temperatures reduced growth in both strains but triggered EPS and lipid production.

## Abstract

Research into the effects of environmental stressors associated with global climate change (GCC) on cyanobacteria and microalgae is scarce, with bloom-forming planktonic cyanobacteria being the exception. This study aimed to address the issue by assessing morphological and biochemical changes in cyanobacterial and microalgal cells exposed to an increased temperature (T), ultraviolet radiation (UVR) and carbon dioxide (CO2) concentration. The strains selected were Calothrix sp. SLM0211 and Coelastrella sp. SLM0503, which were isolated from a coastal environment in the central Mediterranean island of Malta. Elevated UVR had a pronounced effect on Calothrix sp. filaments, which produced screening compounds and resorted to trichome coiling to enhance self-shading. Enhanced growth was observed in cultures of Calothrix sp. grown at an increased CO2 concentration, which produced significantly high amounts of biomass, chlorophylls and carotenoids. An increased T resulted in stunted growth and low biomass accumulation in both strains. Each strain exhibited a unique response to T and UVR stressors, which stimulated the production of exopolymeric substances (EPS) and mycosporine-like amino acids (MAAs) in cultures of Calothrix sp. and lipid production in Coelastrella sp. cells. Our findings indicate that the effects of stressors related to GCC on cyanobacterial and microalgal cells are strain-specific, making changes at community and ecosystem levels difficult to predict.