Biofilm formation at warming temperature: acceleration of microbial colonization and microbial interactive effects

Abstract

River biofilms that grow on wet benthic surface are mainly composed of bacteria, algae, cyanobacteria and protozoa embedded in a polysaccharide matrix. The effects of increased river water temperature on biofilm formation were investigated. A laboratory experiment was designed employing two temperatures (11.1–13.2°C, night–day; 14.7–16.0°C, night–day) and two nutrient levels (0.054 mg P l⁻¹, 0.75 mg N l⁻¹; 0.54 mg P l⁻¹, 7.5 mg N l⁻¹). Biofilm formation at the higher temperature was faster, while the biomass of the mature biofilm was mainly determined by nutrient availability. The specific response of the three microbial groups that colonized the substrata (algae, bacteria and ciliates) was modulated by interactions between them. The greater bacterial growth rate and earlier bacterial colonization at the higher temperature and higher nutrient status was not translated into the accrual of higher bacterial biomass. This may result from ciliates grazing on the bacteria, as shown by an earlier increase in peritrichia at higher temperatures, and especially at high nutrient conditions. Temperature and ciliate grazing might determine the growth of a distinctive bacterial community under warming conditions. Warmer conditions also produced a thicker biofilm, while functional responses were much less evident (increases in the heterotrophic utilization of polysaccharides and peptides, but no increase in primary production and respiration). Increasing the temperature of river water might lead to faster biofilm recolonization after disturbances, with a distinct biofilm community structure that might affect the trophic web. Warming effects would be expected to be more relevant under eutrophic conditions.

Keywords:

• biofilm
• temperature
• nutrient
• algae
• bacteria
• ciliate
• extracellular enzymes

Acknowledgements

This study was funded by the project CGL2008-05618-C02-01/BOS of the Spanish Ministry of Science and Technology. A. Gaudes is acknowledged for valuable assistance with protozoan identification. J. Varela is acknowledged for her help in DGGE analysis. Thanks to M. Roldán from the Microscopic Services at the Universitat Autònoma de Barcelona for her assistance in the CLSM observations. S. Sabater is acknowledged for allowing the authors to use the ICRA facilities. V. Díaz Villanueva received a grant to participate in this project (CONICET) and is supported by FONCYT (Argentina) (Grant #PICT-2007-01747).