Analysis of UV irradiation-induced cell settling of an oleaginous diatom, Fistulifera solaris, for efficient biomass recovery

This study investigates UV irradiation-induced cell settling, followed by cell aggregation, of the oleaginous diatom Fistulifera solaris. Cell settling was observed after 24 h of cultivation following UV irradiation. The highest cell settling rate was obtained at a light intensity of 10 mJ/cm2. The cell settling was induced by irradiating with UV (254 nm), but was ineffective with light of other wavelengths (474 or 620 nm). The settling response was not observed in other microalgae, such as Chlamydomonas reinhardtii and Phaeodactylum tricornutum, with the same treatment, suggesting that this response was specific to F. solaris. The optical and SEM images revealed the occurrence of cell aggregation with the UV treatment, resulting in the subsequent cell settling. Although there was no significant change in the lipid, protein, and sugar content, secreted acidic polysaccharide was found in the F. solaris cell culture following UV irradiation. Therefore, this polysaccharide was considered likely to be the cell aggregation-inducing factor. The energy consumption of this UV-induced cell settling for cell recovery method was estimated to be approximately 0.77 × 10−1 kWh/m3, which is lower than the energy consumption of existing methods. Therefore, this method could be applied for harvesting F. solaris cells from large-scale cultures. •A new algal cell response to UV light irradiation was observed.•Irradiation with a weak UV light intensity induces cell aggregation.•UV irradiation can be used as a cost effective cell recovery technique.