ORIGINAL ARTICLE Effect of organic carbon sources and environmental factors on cell growth and lipid content of Pavlova lutheri Khawaja Muhammad Imran Bashir 1,2 & Sana Mansoor 3 & Na-Ri Kim 1 & Florian Rolando Grohmann 4 & Abid Ali Shah 1 & Man-Gi Cho 1 Received: 17 June 2018 /Accepted: 13 December 2018 /Published online: 4 January 2019 # Università degli studi di Milano 2019 Abstract The present study aimed to investigate the effects of organic carbon sources, cultivation methods, and environmental factors on growth and lipid content of Pavlova lutheri for biodiesel production. In the 250-mL flask bioreactors, P. lutheri was cultivated in the modified artificial seawater (ASW) medium containing glucose, glycerol, sodium acetate, or sucrose as an organic carbon substrate. The effects of different growth conditions (phototrophic, mixotrophic, and heterotrophic) and environmental factors such as photoperiod, light intensity, and salinity were evaluated. Growth of P. lutheri was inhibited under heterotrophy but was enhanced in mixotrophy as compared to phototrophy. Biomass and lipid content of P. lutheri were significantly (p < 0.05) affected by changing photoperiod, light intensity, and salinity. Higher biomass concentration and lipid content were observed at a light intensity of 100 ± 2 μmol photons m -2 s -1 , 18 h photoperiod, and 30% salinity, in a modified ASW medium supple- mented with 10 mmol sucrose. An increase in biomass concentration from 320 ± 25.53 to 1106 ± 18.52 mg L -1 and high lipid content of 31.11 ± 1.65% (w/w) were observed with the optimized culture conditions, demonstrating a significant (p < 0.05) enhancement in biomass and lipid content due to the improved culture conditions. The present study emphasizes the possible use of sucrose for biomass and lipid production with P. lutheri under the optimized culture conditions. Using low-cost and relatively easy accessible feedstock such as sucrose would be a valuable alternative for growing microalgae with enhanced lipid content. Keywords Biomass . Growth optimization . Growth kinetics . Haptophyte . Lipid content . Pavlova lutheri Introduction Microalgae are recognized as photosynthetic microorgan- isms that produce biomass and energy. Microalgae species have also been successfully grown under mixotrophic and heterotrophic conditions. The choice of cultivation method depends on the purpose of culturing. Mixo- and heterotro- phic culture conditions have been reported to overcome the growth inhibition challenges in light and aeration-dependent microalgal growth (Lee 2001). In phototrophy, microalgae grow under light; however, in heterotrophy, cells grow under complete dark using external carbon in the medium. In mixotrophy, cells obtain energy from both light and organic car- bon in the medium (Perez-Garcia and Bashan 2015); thus, it is suitable for microalgal species that cannot grow in dark condi- tions but require low light or agitation for optimum growth. The growth of microalgae under mixotrophy or heterotro- phy could be several times higher than under phototrophy alone (Wen and Chen 2000; Heredia-Arroyo et al. 2010, 2011). Heterotrophic cultivation is suitable for culturing microalgae for wastewater treatment (Perez-Garcia and Bashan 2015), where microalgae are grown in complete dark with a supply of external carbon source. Higher protein levels are observed in phototrophy compared to heterotrophy, whereas, the biomass and lipid productivities of mixotrophic Khawaja Muhammad Imran Bashir and Sana Mansoor contributed equally to this work. * Man-Gi Cho mgcho@gdsu.dongseo.ac.kr 1 Department of Biotechnology, Division of Energy and Bioengineering, Dongseo University, Busan, Republic of Korea 2 Research Center for Extremophiles and Microbiology, College of Medical and Life Sciences, Silla University, Busan, Republic of Korea 3 Department of Environmental Engineering, College of Engineering, Dong-A University, Busan, Republic of Korea 4 Institute of Biotechnology, Technische Universität Berlin, Berlin, Germany Annals of Microbiology (2019) 69:353–368 https://doi.org/10.1007/s13213-018-1423-2