Biofilm diversity, structure and matrix seasonality in a full-scale cooling tower

Biofilms commonly colonise cooling water systems, causing equipment damage and interference with the operational requirements of the systems. In this study, next-generation sequencing (NGS), catalysed reporter deposition fluorescence in situ hybridisation (CARD-FISH), lectin staining and microscopy were used to evaluate temporal dynamics in the diversity and structure of biofilms collected seasonally over one year from an open full-scale cooling tower. Water samples were analysed to evaluate the contribution of the suspended microorganisms to the biofilm composition and structure. Alphaproteobacteria dominated the biofilm communities along with Beta- and Gammaproteobacteria. The phototrophic components were mainly cyanobacteria, diatoms and green algae. Bacterial biodiversity decreased from winter to autumn, concurrently with an increase in cyanobacterial and microalgal richness. Differences in structure, spatial organisation and glycoconjugates were observed among assemblages during the year. Overall, microbial variation appeared to be mostly affected by irradiance and water temperature rather than the source of the communities. Variations in biofilms over seasons should be evaluated to develop specific control strategies.