A M Romaní | PubMed Health

PubMed2003

Biofilm structure and function and possible implications for riverine DOC dynamics.

Biofilms are major sites of carbon cycling in streams and rivers. Here we elucidate the relationship between biofilm structure and function and river DOC dynamics. Metabolism (extracellular enzymatic activity) and structure (algae, bacteria, C/N content) of light-grown (in an open channel) and dark-grown (in a dark pipe) biofilms were studied over a year, and variations in dissolved organic carbon (DOC) and biodegradable DOC (BDOC) were also recorded. A laboratory experiment on 14C-glucose uptake and DOC dynamics was also performed by incubating natural biofilms in microcosms. On the basis of our field (annual DOC budget) and laboratory results, we conclude that light-grown biofilm is, on annual average, a net DOC consumer. This biofilm showed a high monthly variability in DOC uptake/release rates, but, on average, the annual uptake rate was greater than that of the dark-grown biofilm. The higher algal biomass and greater structure of the light-grown biofilm may enhance the development of the bacterial community (bacterial biomass and activity) and microbial heterotrophic activity. In addition, the light-grown biofilm may promote abiotic adsorption because of the development of a polysaccharide matrix. In contrast, the dark-grown biofilm is highly dependent on the amount and quality of organic matter that enters the system and is more efficient in the uptake of labile molecules (higher 14C-glucose uptake rate per mgC). The positive relationships between the extracellular enzymatic activity of biofilm and DOC and BDOC content in flowing water indicate that biofilm metabolism contributes to DOC dynamics in fluvial systems. Our results show that short-term fluvial DOC dynamics is mainly due to the use and recycling of the more labile molecules. At the river ecosystem level, the potential surface area for biofilm formation and the quantity and quality of available organic carbon might determine the effects of biofilm function on DOC dynamics.

Analysis of Variance↗

PubMed2000

Influence of algal biomass on extracellular enzyme activity in river biofilms.

Relationships between biofilm structural components (algal and bacterial biomass) and the activities of some extracellular enzymes that contribute to the ability to degrade organic matter) were explored for six Atlantic and three Mediterranean streams and rivers. The biofilms in these fluvial systems accounted for a wide range of bacterial and algal biomass and colonized the most common benthic habitats. Ratio of bacteria/algae biomass was lower in Atlantic than in Mediterranean streams, but enzymatic activities (β-glucosidase, β-xylosidase, phosphatase) were in general greater in the Mediterranean stream biofilms. Climatic characteristics (especially temperature) may explain the differences in enzymatic activities between biofilms of similar structure but different flow regime. The ratio β-xylosidase: β-glucosidase was similar (around 0.5) for all streams and substrata considered, showing that there is a general higher utilization of cellobiosic than xylobiosic molecules in fluvial systems. In general, highly heterotrophic biofilms showed lower extracellular enzymatic activities than more autotrophic biofilms. Maximum enzymatic activity is achieved when the algal biomass is two- to threefold higher than the bacterial biomass. The relevance of algal biomass on the heterotrophic ability of biofilms may be related to the physical proximity between the two, but also to the high proportion of polymeric carbohydrates included in algal exudates and lysis products, whose use is enzyme-mediated.

Journal Article↗