Étude préliminaire des communautés bactériennes épiphytes de Laminara digitata

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Abstract
Algal samples from different parts of the frond of Laminaria digitata (young, adult and aged tissues) and from macroscopic fragments naturally separated from the thallus were collected on the Atlantic coast of France (Brittany) during winter and spring. Bacterial communities associated with the different levels were compared, and the ATP content was determined and used as an indicator of the physiological state of the tissues. It is higher in young tissue (55 nmol/g of fresh kelp) than in fragments (9 nmol/g of fresh kelp), showing a decrease in the number of metabolically active cells. If total bacterial density values are relatively close on the different parts of the kelp (average, 2.9 × 107 bacteria/cm2), culturable microflora increased from young tissue (minimum, 15 cfu/cm2) to fragments (average, 3.6 × 107 bacteria/cm2). Characterization of strains showed an increase of metabolic activity together with a diversification in the culturable fraction with the age of algal tissues.Key words: epiphytic bacteria, kelp, Laminaria digitata.