Dilution-Derived Growth Lag and Photosynthetic Responses in the Oleaginous Diatom Fistulifera solaris.

Highly oil-accumulative diatoms such as Fistulifera solaris JPCC DA0580 are considered promising biomass resources for biofuel production. To achieve high oil yields from diatoms, it is essential to understand their physiological status in terms of growth and photosynthesis under industrial cultivation conditions. Here, we focused on the lag phase observed in F. solaris growth after dilution during large-scale outdoor cultivation, and sought to characterize this physiological event by reproducing it under laboratory conditions with two dilution ratios and two light intensities. When the culture was inoculated into fresh medium at an initial OD₇₃₀ of 0.03, no distinct lag phase was observed under either low or high light. In contrast, dilution to an initial OD₇₃₀ of 0.003 induced a pronounced lag phase lasting approximately 1 and 2 days under low and high light, respectively. Thus, a higher dilution ratio prominently extended the lag phase in F. solaris. At the growth stage after the late logarithmic phase, photosynthetic properties were largely similar between the high- and low-dilution cultures and were mainly influenced by growth light intensity. Decreased photosynthetic activity within a day after dilution suggested that the prolonged lag phase was mainly caused by high-light induced photodamage in diluted cells. These results indicate that large-scale outdoor cultivation of F. solaris could be more efficient when initiated with higher cell densities, especially under high light.