ENVIRONMENTAL MICROBIOLOGY Isolation and Characterization of Exopolysaccharide Secreted by a Toxic Dinoflagellate, Amphidinium carterae Hulburt 1957 and Its Probable Role in Harmful Algal Blooms (HABs) Subir Kumar Mandal & Ravindra Pal Singh & Vipul Patel Received: 31 December 2010 / Accepted: 21 March 2011 # Springer Science+Business Media, LLC 2011 Abstract Extracellular polymeric substances (EPS) pro- duced by a toxic dinoflagellate Amphidinium carterae Hulburt 1957 was isolated and characterized. Molecular masses of the EPS were about 233 and 1,354 kDa. Spectral analyses by 1 H nuclear magnetic resonance and Fourier Transformed–Infrared Spectroscopy revealed the character- istic of the functional groups viz. primary amine, carboxyl, halide, and sulfate groups present in the EPS. However, five elements (C, O, Na, S, and Ca) were detected by scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDX) analysis. X-ray diffraction and differential scanning calorimetric analysis confirmed the amorphous nature of EPS, which was comprised of an average particle size of 13.969 μm(d 0.5) with 181 nm average roughness. Two monosaccharide constituents, galactose (73.13%) and glucose (26.87%) were detected by gas chromatography–mass spectroscopy analysis. Ther- mal gravimetric analysis revealed that degradation of EPS obtained from A. carterae takes place in three steps. The EPS produced by A. carterae was found to be beneficial for the growth of both A. carterae and Bacillus pumilus. The potential heterogeneous properties of EPS may play an important role in harmful algal bloom. Introduction The dynamics of rapid (massive) increase or almost equally decrease of phytoplankton populations is a common feature in marine plankton ecology and is known as bloom. This phenomenon generally occurs within a matter of days and also disappears just as rapidly. Harmful algal blooms (HABs) occur due to the interaction of many microorganisms like bacteria, cya- nobacteria, phytoplankton (diatoms and dinoflagellates), and zooplanktons. It starts from chaotic form and reaches organized form. Later on, it is dominated by a very few microorganisms that may or may not be toxic [7]. Exopolysaccharides also play key roles in communities’ succession and nutrient recycling in marine environment [34]. Many biotic and abiotic factors (temperature, pH, salinity, and nutrients like nitrate, phosphate, and silicate) trigger the harmful algal bloom formation. In this micro- environment, live cells of phytoplankton and bacteria stick to each other due to the presence of extracellular polymeric substances (EPS) that serve as biological glue and provide required stickiness for cell–cell attachment [12, 38]. The importance of microbial EPS production by bacteria [13], cyanobacteria [9], yeast [11], and basidio- mycetes [8, 21] are already reported as well. However, phytoplankton cells including desmids [19], diatoms [36], and cyanobacteria [28] are also known to produce EPS into their external medium. The organic exudates become highest during the stationary growth phase of marine microorganism [18, 29]. Amphidinium carterae Hulburt 1957 is a known toxic marine dinoflagellate known to cause red tide and also reported as the causative organism for mass mortality of fish [26]. It is also listed as harmful toxic microalgae by Electronic supplementary material The online version of this article (doi:10.1007/s00248-011-9852-5) contains supplementary material, which is available to authorized users. S. K. Mandal (*) : R. P. Singh : V. Patel Discipline of Marine Biotechnology and Ecology (MBE), Central Salt and Marine Chemicals Research Institute (CSMCRI), Council of Scientific and Industrial Research (CSIR), G. B. Marg, Bhavnagar 364021, India e-mail: skmandal@csmcri.org Microb Ecol DOI 10.1007/s00248-011-9852-5