High cell density lipid rich cultivation of a novel microalgal isolate Chlorella sorokiniana FC6 IITG in a single-stage fed-batch mode under mixotrophic condition Vikram Kumar a , Muthusivaramapandian Muthuraj b , Basavaraj Palabhanvi b , Aloke Kumar Ghoshal a , Debasish Das a,b,⇑ a Centre for Energy, Indian Institute of Technology, Guwahati, Assam 781039, India b Department of Biotechnology, Indian Institute of Technology, Guwahati, Assam 781039, India highlights Reports a novel microalgal isolate Chlorella sorokinana FC6 IITG. Glucose & acetate was found to be growth supporting & lipid inducing, respectively. Single-stage fed-batch mixotrophic cultivation for high cell density lipid-rich FC6. Maximum productivity (mg L 1 day 1 ): biomass-1930 & lipid-550 in fed-batch. Biodiesel produced from FC6 meets international standards. article info Article history: Received 12 June 2014 Received in revised form 15 July 2014 Accepted 16 July 2014 Available online 24 July 2014 Keywords: Chlorella Photoautotrophic Mixotrophic Fed-batch Biodiesel abstract A single-stage mixotrophic cultivation strategy was developed with a novel microalgal isolate Chlorella sorokiniana FC6 IITG for high cell density lipid-rich biomass generation. The strain was evaluated for growth and lipid content under different physico-chemical parameters, nutritional conditions and trophic modes. Finally, a single-stage mixotrophic fed-batch cultivation strategy was demonstrated with intermittent feeding of key nutrients along with dynamic increase in light intensity for high cell density biomass and sodium acetate as elicitor for lipid enrichment. The key findings: (i) glucose and sodium acetate was identified as growth supporting and lipid inducing nutrients, respectively; (ii) mixotrophic batch cultivation resulted in maximum biomass and lipid productivity (mg L 1 day 1 ) of 455.5 and 111.85, respectively; (iii) single-stage mixotrophic fed-batch cultivation showed maximum biomass productivity of 1.93 g L 1 day 1 (biomass titer 15.81 g L 1 ) and lipid productivity of 550 mg L 1 day 1 ; (iv) biodiesel properties were in accordance with international standards. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Oleaginous microalgae are considered as one of the most promising feedstock for renewable and sustainable production of biodiesel. This increasing importance of microalgae may be attrib- uted to its key inherent properties such as higher photosynthetic efficiency, higher biomass and lipid productivity in comparison to other plant resources (Chisti, 2007). However, microalgae based biodiesel production technology suffer from several limitations at different stages of the upstream and downstream processes e.g. strain selection, growth of microalgal strains under outdoor condi- tions, contamination, light penetration through dense culture, har- vesting, drying, extraction and transesterification (Lam and Lee, 2012). Therefore, there is a need to design a sustainable process using hyper producing strains with improved biomass and lipid productivity. Recently, efforts have been aimed to identify robust microalgal strains with enhanced biomass productivity, and high net lipid productivity along with suitable fatty acid methyl ester (FAME) content for biodiesel production (Lam and Lee, 2012). Microalgal biomass production has mainly been achieved by photoautotrophic cultivation in open pond and photobioreactors in the presence of light and CO 2 (Brennan and Owende, 2010; Kumar et al., 2011). However, some strains have been reported http://dx.doi.org/10.1016/j.biortech.2014.07.066 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Biotechnology, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India. Tel.: +91 361 258 2221; fax: +91 361 269 0762. E-mail addresses: debasishd@iitg.ernet.in, debasis.iitb@gmail.com (D. Das). Bioresource Technology 170 (2014) 115–124 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech