Evidence for the involvement of surface carbohydrates in the recognition of Haematococcus pluvialis by the parasitic blastoclad Paraphysoderma sedebokerensis Jenia GUTMAN, Aliza ZARKA, Sammy BOUSSIBA* Microalgal Biotechnology Laboratory, The Albert Katz Department of Dryland Biotechnologies, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel article info Article history: Received 2 January 2011 Received in revised form 16 May 2011 Accepted 8 June 2011 Available online 21 June 2011 Corresponding Editor: Gordon William Beakes Keywords: Blastoclad Carbohydrates Epidemic Haematococcus pluvialis Lectins Paraphysoderma sedebokerensis Parasite Recognition abstract The unicellular green alga Haematococcus pluvialis (Chlorophyta, Volvocales) is currently the best commercial source of the natural red ketocarotenoid astaxanthin. Paraphysoderma se- debokerensis (Blastocladiomycota), a parasitic blastoclad that is specific for this microalga, was recently isolated and identified in our laboratory. In this study, we investigated the recognition process between the parasite and H. pluvialis. Obligatory requirements for rec- ognition were identified as an ion concentration in the medium of 20 mM, the presence of calcium ions, and neutral to basic conditions; these requirements imply that a protein is involved in the process. In a search for potential lectinesugar interactions as a major event in the recognition process, we screened for exposed glycosidic moieties on the cell wall of the alga and on the parasite zoospore surface. Competition experiments with the appropri- ate lectins and monosugars identified Ricinus communis agglutinin (RCA 120 ) as the lectin that recognizes Gal-N-acetyl-D-glucosamine, an oligosaccharide located on the host. We pro- pose that an RCA 120 -like lectinesugar interaction mediates the highly specific interaction between the blastocladian parasite and its algal host. ª 2011 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. Introduction The freshwater alga Haematococcus pluvialis (Chlorophyta, Vol- vocales) is cultivated commercially for the large quantities of the secondary carotenoid astaxanthin it produces upon expo- sure to different stress conditions (Boussiba & Vonshak 1991; Kobayashi et al. 1991; Boussiba et al. 1999). The pigment is mainly utilized as a colourant in the farming of salmon and ornamental fish species (Goodwin 1984) and as a supplement (antioxidant properties) to the human diet (Guerin et al. 2003). One of the problems inherent in the mass cultivation of this species is that the growth conditions (Boussiba & Vonshak 1991) promote contamination of the microalgal culture by competing algal species and parasites (Margalith 1999; Aflalo & Boussiba 2005). For several decades it has been known that chytrids parasitize natural algal and cyanobacterial * Corresponding author. Tel.: þ972 8 6596795; fax: þ972 8 6596802. E-mail address: sammy@bgu.ac.il Abbreviations; BGM, blastoclad growth medium; Con A, concanavalin A; DBA, Dolichos biflorus agglutinin; FITC, fluorescein isothiocyanate; PNA, peanut agglutinin; RCA, Ricinus communis agglutinin; SBA, soybean agglutinin; UEA, Ulex europaeus agglutinin; WGA, wheat germ agglutinin journal homepage: www.elsevier.com/locate/funbio fungal biology 115 (2011) 803 e811 1878-6146/$ e see front matter ª 2011 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.funbio.2011.06.006