congresos y reuniones científicas
Biofilm formation at warming temperature
Piran, Slovenia
Congreso; 11th Symposium on Aquatic Microbial Ecology; 2009
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> River biofilms grown on any benthic wet surface (cobbles, sand, leaves) are mainly composed by bacteria, algae, cyanobacteria, fungi and protozoa embedded in a polysaccharide matrix. This structure is a highly dynamic biological layer which can change its metabolism, thickness, density and composition depending on its own evolution and/or physical-chemical conditions. In this study, the effect of warming river water temperature on biofilm formation is investigated. The main objective was to highlight the effect of increasing water temperature on the colonization process, biodiversity and metabolic changes of the different microbial groups (algae, bacteria and protozoa). The temperature effect was analyzed at distinct inorganic nutrient conditions (N and P) in order to highlight possible interactive effects of the two factors (temperature and nutrients). A laboratory experiment was designed considering two colonization temperatures: low temperature (LT, 7-11ºC, night-day), high temperature (HT, 11-15ºC, night-day); and two nutrient levels: low nutrient (LN, 0.054 mgP/L, 0.75 mgN/L), high nutrient (HN, 0.54 mgP/L, 7.5 mgN/L). For each of the four treatments, three replicate microcosms were considered. Biofilm samples (1 cm2 glass substrata) were collected from each microcosm after 1, 2, 3, 4, 7, 14, 21, 30, 44, and 58 days of colonization. Major effects of warming flowing temperature were observed at high nutrient conditions. The biofilm developing at HT-HN conditions was the thickest, showed a significantly higher algal biomass accrual (chlorophyll content being significantly highest from day 14 of colonization till the end of the experiment) and higher protozoa density. The heterotrophic use of polysaccharides and peptides was also enhanced at warming temperature and high nutrient conditions, as shown by the significantly higher β-glucosidase and peptidase extracellular enzyme activities. Although the effect of temperature was less evident at low nutrient conditions, biofilms at HT-LN conditions showed a main thickness of 193 µm (as observed by CLSM) and were mainly composed by green filamentous algae and diatoms, while biofilms at LT-LN were 88 µm thick and mainly composed by diatoms. Results suggest that increases of river water temperature up to 4ºC might determine changes in river biofilm structure and function, therefore potentially affecting whole river ecosystem functioning.