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Nutritional quality of biofilms.

Examination of the nutritional quality of a biofilm involves analysis of an entire community of microbenthic-organisms including algae, bacteria, protozoa, fungi, microbenthic invertebrates, and small organic particulates (an important part of the food web). Community composition and nutritional quality is an interaction between biological, chemical and physical mechanisms, and factors influencing nutritional components have not been well researched. The exopolysaccharide component of a biofilm is considered a very important food source for grazers, and is contributed to predominantly by extracellular carbohydrate and algae. Differences in composition and properties of the EPS mean biofilm varies in food quality and digestibility for consumers such as invertebrates.

Nutritional value has often been assessed by using the C:N ratio . This ratio is a relative comparison which compares the amount of carbon content present to nitrogen content present. Biofilms with low C:N ratio is dominated by bacteria and biofilms while biofilms with high C:N ratio is dominated by algae. Low C:N ratio is an indication of higher nitrogen, amino acids, and protein and these are normally limiting factors for organisms to grow. Carbon has lower nutritional value than nitrogen, hence food with a low C:N ratio is considered as being “nutritious” and advantageous for organisms that feed upon it. High C:N ratio is found in biofilms with relatively higher carbohydrate than protein. Quinn et al (2000) investigated the degradation of leaves in streams in New Zealand , and concluded that microbial colonisation is necessary (of very high C:N ratio) in order to improve the nutritional quality. Microbial biofilms can store organic compounds as extracellular enzymes which are produced by the microbes and this allows biofilms to decompose non-labile compounds such as lignin which would otherwise be unavailable as a food source for free swimming bacteria (Storey, Fulthorpe, & Williams, 1999) .

Many factors can affect the biofilm structure and community composition within a stream, within this particular part of the research team the temporal and spatial effects on biofilms nutrition has already been looked at; currently the effects of light on various nutritional components are being investigated, which include total Carbohydrate; total Protein; total Organic Carbon; total Inorganic Carbon; total Chlorophyll a,b,c; total phosphorous; total nitrogen of the biofilms. As nutrition infers the food web structure of the biofilms, this part of the research will be crucial for the buildup of a comprehensive picture of stream biofilms.

 

 

 

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