Bacterial functional responses to environmental variability: a case study in three distinct mountain lakes within a single watershed

The utilization of carbon substrates (CSs) is crucial for the functioning of heterotrophic bacterial communities and aquatic ecosystems. This study used the Biolog EcoplateTM technique to explore spatial and temporal community-level physiological profiles (CLPPs) of bacteria in three eutrophic-dystrophic mountain lakes in Bulgaria. Bacterial metabolic activity varied among the lakes, being highest in the lake dominated by phytoplankton and lowest in the lake dominated by macrophyte primary producers. CLPP highlighted specific bacterial metabolic preferences to certain carbon guilds (CGs), showing a higher affinity for carbohydrates and polymers and lower preferences for amino acids and amines. The overall metabolic dissimilarity among the lakes was approximately 32%, primarily driven by the CGs of amino acids and amines. The most preferred CSs included the carbohydrates D-Mannitol and N-Acetyl-D-glucosamine, and the carboxylic acid D-Galacturonic acid. Bacterial functional diversity was high (H′: 3.18 − 3.33) due to the high evenness of CS utilization. Multidimensional analyses revealed significant influences of lake-specific characteristics, sampling month, and the interaction between these factors on CLPP patterns. Nutrients and water temperature were identified as the most influential environmental factors affecting bacterial communities. This study enhances our understanding of bacterial functional responses to changing environments, demonstrating the effectiveness of the Biolog EcoplateTM technique in providing insights into these changes.