Optimisation of cyanobacterial cell productivity should consider the key factors light cycle and carbon source. We studied the influence of CO2 bubble size on carbon uptake and fixation, on basis of mRNA expression levels in Arthrospira platensis KMMCC CY-007 at 30 degrees C (light intensity: 40 mu mol m (2) s (1); 1% CO2). Growth rate, carbon fixation and lipid accumulation were examined over 7 days under fine bubble (FB) (100 mu m empty set) bulk bubble (BB) (5000 mu m empty set) and non-CO2 (NB) aeration. The low affinity CO2 uptake mRNA (NDH-I-4 complex) was stronger expressed than the high affinity NDH-I-3 complex (bicA and sbtA) under 1% CO2 and FB conditions, with no expression of bicA1 and sbtA1 after 4 days. The high affinity CO2 uptake mRNA levels corresponded to biomass, carbon content and lipid accumulation, and increase in NDH-I-3 complex (9.72-fold), bicA (5.69-fold), and sbtA (10.61-fold), compared to NB, or BB conditions. (C) 2014 Elsevier Ltd. All rights reserved.