Levels of Diatom Minor Sterols Respond to Changes in Temperature and Salinity

Abstract

Diatoms are a broadly distributed and evolutionarily diversified group of microalgae that produce a diverse range of sterol compounds. Sterols are triterpenoids that play essential roles in membrane-related processes in eukaryotic cells. Some sterol compounds possess bioactivities that promote human health and are currently used as nutraceuticals. The relationship between sterol diversity in diatoms and their acclimation to different environments is not well understood. In this study, we investigated the occurrence of different sterol types across twelve diatom species, as well as the effect of temperature reduction and changes in salinity on the sterol contents of three model diatom species. In the diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum and Chaetoceros muelleri, we found that changes in the relative contents of minor sterols accompanied shifts in temperature and salinity. This may be indicative of acquired adaptive traits in diatom metabolism.Environmental conditions such as salinity [16] and the availability of nutrients including nitrogen, phosphate and silicate appear to affect sterol production in some microalgae [17,18].Since sterols are involved in cellular processes that interact with environmental conditions, such as cellular signaling and membrane fluidity [2], the regulation of sterol content by diatom species might be sensitive to changes in the environment and growth conditions. It is not known whether the wide diversity of sterols compounds in diatoms respond to changes in temperature, as in plants, or whether they are involved in complex signaling functions such as cell death [19]. The presence of 23-methyl sterols, cyclopropyl sterols and 27-norsterols is thought to provide a defence mechanism against grazers, potentially interfering with the sterol metabolism of predatory organisms [20]. Furthermore, conditions like salinity have been reported to affect important cellular processes in diatoms such as biosilicification [21].In this study, we surveyed the sterol contents of twelve diatoms representing multiple clades and environments. We then evaluated the effects of a reduction in temperature and changes in salinity on the cell growth and sterol profiles of three commonly cultured mesophilic model diatoms: the centric diatom Thalassiosira pseudonana, the pennate diatom Phaeodactylum tricornutum and the chaetocerid diatom Chaetoceros muelleri.

Overexpression of Key Sterol Pathway Enzymes in Two Model Marine Diatoms Alters Sterol Profiles in Phaeodactylum tricornutum

“…While the core reactions in sterol synthesis being conserved in T. pseudonana and P. tricornutum [ 15 ], both diatoms produce a distinctive profile of sterol compounds which variates differently upon changing environmental conditions and chemical inhibitors treatment [ 15 , 20 ]. Additionally, the sterol metabolism of the centric diatom T. pseudonana has not been explored to the same depth as the model pennate P. tricornutum.…”

“…Recent studies suggest that sterol biosynthesis is tightly regulated. Levels of intermediate compounds in sterol synthesis change in response to different environmental conditions [ 20 ] and to the addition of chemical inhibitors [ 15 ]. However, end-point sterol levels remained unchanged under the same treatments.…”

An appraisal of the variable response of microalgal lipids to culture salinity

“…Similar ST decrease under high salinity conditions has been found in the halophile Dunaliella 155 and some diatoms. 156 However, in the marine diatom Nitzschia laevis, ST increased with salinity. 121 The surprising lack of information on ST changes in salt-stressed freshwater microalgae prevents any possible discussion.…”

Microalgae as Sustainable Biofactories to Produce High-Value Lipids: Biodiversity, Exploitation, and Biotechnological Applications

“…Brassicasterol: 0.07-1.56 pg cell −1 Dinosterol: 0.20-1.30 pg cell −1 Thalassiosira pseudonana CCMP1335 Rapid cooling (18 to 4 • C) Salinity (10,17,25,30,39,47,53 and 61‰) 24-Methylenecholesta-5,24(24')-dien-3β-ol Fucosterol Isofucosterol Cholesterol [113] Phaeodactylum tricornutum CCMP632 24-Methylenechol esta-5,24(24')-dienol Fucosterol Isofucosterol Cholesterol Shifts its sterol content at a reduced temperature…”