Biofilm interactions: does temperature matter at the beginning of a relationship?

DÍAZ VILLANUEVA, VERÓNICA; YLLA, IRENE; BORREGO, CARLES; ROMANÍ, ANNA

Rostock

Simposio; 12th Symposium on Aquatic Microbial Ecology (SAME 12); 2011

Organisms in biofilms interact. They compete for space and nutrients, bacteria make use of algal exudates, ciliates feed on bacteria, and they also communicate. Communication among bacteria through the production of signal molecules (quorum sensing) is used to monitor density and induce a synchronized response. We investigated if quorum sensing is affected by algae and protozoa in biofilm accumulation at two different temperatures. Also, we experimentally tested if temperature affects biofilm formation process and how changes in the algal-bacteria interaction may determine functional diversity. The effect of temperature on the first steps of the colonization (2-28 days) was analyzed in darkness and light to separate algal-bacteria interactions. A laboratory experiment was designed considering two temperature regimes: low temperature (LT, 11-14ºC, night-day) and high temperature (HT, 14-17ºC, night-day). For each of the four treatments, three replicate microcosms were considered. Biofilm samples (1 cm2 glass substrata) were collected periodically to estimate algae, bacteria and meiofauna density. Quorum sensing was determined using two strains as exogenous signal inducers. Functional diversity was studied by Biologs. The effect of temperature on bacterial colonization depended on the light condition. On day 35, bacteria were more abundant in the low temperature treatments. Algal growth in light treatments begun after day 14, and on day 28 it was higher in high temperature regimes, when also photosynthetic efficiency was higher. Ciliates were negatively affected by temperature while rotifers were positively affected by temperature. Quorum sensing was detected on day 2, at all treatments and replicates with the A136 strain, but only in light treatments with CV026. The heterotrophic use of polysaccharides and organic phosphorus were not affected by temperature but they were higher at light conditions, as shown by the significantly higher β-glucosidase and phosphatase extracellular enzyme activity. Peptidase activity was enhanced at warming temperature at light but at dark it was lowered by temperature. Peptidase capabilities were more diverse at the beginning of the colonization. Functional diversity was affected by temperature and light and the differences among communities were stronger on day 28 than on day 7. Results suggest that increases of river water temperature up to 3ºC might determine changes in river biofilm structure and function, therefore potentially affecting whole river ecosystem functioning.