ORIGINAL PAPER A new tool to detect high viscous exopolymers from microalgae S. Badel • F. Callet • C. Laroche • C. Gardarin • E. Petit • H. El Alaoui • T. Bernardi • P. Michaud Received: 17 April 2010 / Accepted: 1 July 2010 Ó Society for Industrial Microbiology 2010 Abstract Microalgae are microorganisms often sur- rounded by a slime layer made of secreted polymeric substances sometimes including polysaccharides. These polysaccharides, weakly described in the literature, can constitute value-added molecules in several industrial areas. The aim of this article is to show that a new tool, the BioFilm Ring Test Ò , can be used to detect viscous micro- algal exopolymers. Two red microalgal strains (Rhodella violacea and Porphyridium purpureum), one cyanobacte- rium (Arthrospira platensis) and their excreted polymeric fractions were studied. R. violacea and P. purpureum induced a positive response with the BioFilm Ring Test Ò contrary to A. platensis. Finally, the understanding of the fractions viscosity involvement in the BRT response was performed by a rheological study. Keywords Exopolymer  Polysaccharide  Microalgae  BioFilm Ring Test Ò Introduction Microalgal biofilms represent a general term to depict an assembly of species living wherever the surface gets in contact with water [28]. In these photosynthetic structures, whose average thickness is several micrometers, the microalgae are arranged into parallel layers surrounded by extracellular polymeric substances [21]. This matrix plays a part in the protection against external attacks. It also contributes to biofilm structure, keeping water and capture of nutrients or microorganisms by their adhesive properties [32]. Often described as exopolysac- charides, these exopolymeric substances are more complex and diversified as they include proteins and nucleic acids [2]. Moreover, some biofilms can be structured without secretion of exopolysaccharides. Their morphology is different but their strength is not altered [10, 33]. Only a few studies have investigated the structures of exopolymers or cell-bound polymers from microalgae, implied or not in biofilms, such as those produced by Cyanospira capsulata [17], Porphyridium sp. [19], Chlo- rella vulgaris [24], Arthrospira platensis [29], Dixioniella grisea [1], Botryococcus braunii [15] or Rhodella violacea [5]. In all cases, polysaccharides or proteoglycans have been identified and some of them found industrial appli- cations as those produced by Porphyridium species [13, 34]. So, in a context where microalgae are increasingly used in industrial applications, it is important to find a new tool able to detect the ability of microalgae to excrete biopolymers such as exopolysaccharides. This new device is the BioFilm Ring Test Ò whose principle is based on S. Badel  F. Callet  C. Laroche  C. Gardarin  P. Michaud (&) Laboratoire de Ge ´nie Chimique et Biochimique, Clermont Universite ´, Universite ´ Blaise Pascal, Polytech’ Clermont Ferrand, 24 avenue des Landais, BP 206, 63174 Aubie `re Cedex, France e-mail: philippe.michaud@univ-bpclermont.fr S. Badel  F. Callet  T. Bernardi BioFilm Control, Biopo ˆle Clermont Limagne, 63360 Saint Beauzire, France E. Petit Laboratoire des Polysaccharides Microbiens et Ve ´ge ´taux, IUT d’Amiens, Avenue des Faculte ´s Le Bailly, 80025 Amiens Cedex, France H. El Alaoui Laboratoire Microorganismes Ge ´nome et Environnement, UFR Sciences et Technologies, Clermont Universite ´, Universite ´ Blaise Pascal, 24 avenue des Landais, BP 80026, 63171 Aubie `re Cedex, France 123 J Ind Microbiol Biotechnol DOI 10.1007/s10295-010-0775-9