Indian Journal of Biotechnology Vol I, July 2002, pp 255-262 Cultivation of Spirulina in Gas Induced Photobioreactor and Isolation of Phycobiliproteins Harshal H Kshirsagar, Madhavi S Revankar, Madhusudan Y Kamat and Smita S Lele* Food and Fermentation Technology Department, University Institute of Chemical Technology, University of Mumbai, Matunga, Mumbai 400019, India Received 26 September 200 I .. accepted 4 April 2002 A novel design of Gas Induced Mechanically Agitated Photobioreactor (GIMAP) using the principle of hollow shaft impeller to sparge air is tested with Spirulina as model system. Gas induced impeller is a lesser-explored type of mechanically agitated contactor. It possesses unique characteristics like no separate power requirement for the sparging of the gas, moderate values of mass transfer coefficient and relatively low values of shear stress. These characteristics make it suitable as a photobioreactor although it may not be the best choice for the classical fermentations. GIMAP exhibited good performance giving biomass concentration and high specific growth rate of 4.44 gil and 1.33 d- I , respectively. Hydrodynamic stress developed in GIMAP was found to have favourable effect that resulted in production of biomass with more permeable cell walls. As a result it was possible to extract phycobiliproteins without cell rupture by simply changing the pH of the buffer. Further it was possible to recover 23% of phycobiliproteins (92% yield) from the GIMAP culture along with a by-product namely exhaust cell mass with 25 % proteins. Simpler downstream processing, additional byproduct coupled and higher growth rates of Spirulina than the conventional cultivation methods indicate the commercial potential of the proposed GIMAP design as photobioreactor. Keywords: Spirulina, phycobiliproteins, microalgae, photobioreactor, gas-inducing impellers Introduction Spiruiina, one of the important and the oldest known microalgal species, has gained attention as a food source because of the high protein and vitamin content and due to its ability to produce large quantities of high value products like phycobiliproteins (Sarada et ai, 1999). Traditionally, micro-algae are cultivated in open ponds. This mode of cultivation has a number of drawbacks including low cell densities, potential to contamination by other microorganisms and the inability to control environmental factors such as light, irradiation and temperature (Weismann et ai, 1988; Chen & Zhang, 1997). Though these systems are being improved with respect to temperature control, supply of appropriate nutrients, optimization of pond depth, carbon dioxide injection, etc. still productivity remains fairly low (-100 g dry algal biomass/m 2 /day), hence are not commercially viable due to cost implications. Several alternatives, proposed to the open pond culture technique, recommend the use of photobioreactors *Author for correspondence: Tel: +91-022-4145616; Fax: +91-022-4145614 E-ma il: sslele @foodbio.udct.ernet.in (tubular, column type with circulation, with recycle, etc.). The growth rate increases by 100% in indoor systems with internal illumination arrangements (Pulz & Scheibenbogen, 1998). Sophisticated photo- bioreactors such as photobioreactor with efficient light emitting diodes (Lee & Palsson, 1994), fibre optic based photobioreactor (Javanmardian & Palsson, 1991), tubular photobioreactor for outdoor cultivation (Torzillo et ai, 1993), etc. tried at laboratory scale are not cost-effective. Hence, there is a need to explore newer designs which are compact, have lower power consumption and can achieve high growth rates without much initial investments. In the present work, authors report a novel design of photobioreactor for cultivation of Spiruiina and recovery of phycobiliproteins, called Gas Induced Mechanically Agitated Photobioreactor (GIMAP). GIMAP is a less explored design for fermentation in general, and as a photobioreactor in particular. It offers several advantages over conventional stilTed vessel in terms of lower power consumption and lower shear levels. However, it may not be a good choice for biological systems having fast growth kinetics and oxygen mass transfer limitations. GIMAP as a photobioreactor was thought to be worth