The impact of day length on cell division and efficiency of light use in a starchless mutant of Tetradesmus obliquus

Highlights

• Light is the cue for timing of cell division in T. obliquus.

• Timing of cell division is independent of the photoperiod, but it differs between the wild-type and slm1.

• T. obliquus slm1 survives dark periods to up to 12 h.

• The inability to store starch in the slm1 mutant results in less energy fixated.

Abstract

Large scale microalgal production will be primarily done under natural sunlight conditions, where microalgae will be exposed to diurnal cycles of light and dark (LD) and to differences in the length of both periods (photoperiod). Tetradesmus obliquus (formerly known as Scenedesmus obliquus), a strain with potential for biofuel production, and the starchless mutant slm1 were grown under 3 different LD periods: 16:8 h, 14:10 h and 12:12 h. Cell division started a fix number of hours after the light went on (sunrise), independently of the length of the photoperiod. For the wild-type, cell division started approximately 14 h after the beginning of the day and occurred mainly at night. For the starchless mutant slm1, timing of cell division was also independent of the photoperiod length (starting 10–12 h after sunrise). However, as opposed to the wild-type, cell division always started during the day. For both strains, growth rate increased with increased length of the light period. The slm1 mutant is capable of surviving long dark periods (up to 12 h) despite the lack of starch. In general, the slm1 mutant has a lower photosynthetic efficiency than the wild-type, with the 12:12 h LD resulting into even less efficiency than the other two LD cycles.