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Abstract
In the present study, biomass development and changes in community composition of phototrophic biofilms grown under different controlled ambient conditions (light, temperature and flow) were examined. Source communities were taken from a wastewater treatment plant and used to inoculate growth surfaces in a semi-continuous-flow microcosm. We recorded biofilm growth curves in cultures over a period of 30 days across 12 experiments. Biovolume of phototrophs and community composition for taxonomic shifts were also obtained using light and electron microscopy. Species richness in the cultured biofilms was greatly reduced with respect to the natural samples, and diversity decreased even further during biofilm development. Diadesmis confervacea, Phormidium spp., Scenedesmus spp. and Synechocystis spp. were identified as key taxa in the microcosm. While a significant positive effect of irradiance on biofilm growth could be identified, impacts of temperature and flow rate on biofilm development and diversity were less evident. We discuss the hypothesis that biofilm development could have been subject to multistability, i.e. the existence of several possible stable biofilm configurations for the same set of environmental parameters; small variations in the species composition might have been sufficient to switch between these different configurations and thus have contributed to overwriting the original effects of temperature and flow velocity.
Acknowledgements
This work is dedicated to the memory of Patrizia Albertano who led the research performed at the LBA in the frame of the EU Quality of Life Project, PHOBIA (PHOtotrophic BIofilms and their potential Applications: towards the development of a unifying concept), contract no. QLK3-CT2002-01938. AB acknowledges support by Fundação para a Ciência e a Tecnologia, Portugal, through grants PTDC/BIA-MIC/72512/2006, PEst-OE/EQB/LA0004/2011 and program Ciência 2007, funded by the Programa Operacional Potencial Humano (Quadro de Referência Estratégica Nacional).