Drought Drives Extracellular Polymeric Substances Accumulation and Functional Shifts in Streambed Biofilm Communities

Area of Science:

• Microbiology
• Ecology
• Environmental Science

Background:

• Microbial biofilms are crucial in aquatic ecosystems.
• Water scarcity poses a significant threat to stream ecosystems.
• Extracellular polymeric substances (EPS) are known to play a role in microbial survival.

Purpose of the Study:

• To investigate the adaptive response of streambed microbial biofilms to water scarcity.
• To determine the role of EPS production in biofilm adaptation to drought.
• To assess how biofilm function changes under varying hydrological conditions.

Main Methods:

• Analysis of EPS-polysaccharide content, microbial biomass, and chlorophyll-a in sediment samples from 37 streams.
• Characterization of drought conditions based on the number of dry days.
• Assessment of biofilm function using carbon substrate utilization profiles.

Main Results:

• EPS production significantly increased in intermittent streams, especially under long-term drought.
• EPS content, normalized to prokaryotic density, positively correlated with drought duration.
• Functional profiling revealed broader metabolic capabilities and increased functional diversity in intermittent streams under drier conditions.

Conclusions:

• EPS synthesis is a key microbial strategy for mitigating desiccation stress in streambed biofilms.
• Increased functional diversity in biofilms may be a mechanism for maintaining ecosystem processes under increasing aridity.
• Mediterranean microbial biofilm communities demonstrate resilience to drought, challenging assumptions from controlled experiments.