Specific acclimations to phosphorus limitation in the marine diatom Phaeodactylum tricornutum

Physiological and transcriptomic analyses to determine the responses of the harmful algae Akashiwo sanguinea to phosphorus utilization

Phosphorus (P) is an essential nutrient driving algal growth in aquatic ecosystems. Dissolved inorganic and organic P (DIP and DOP) are the main components in the marine P pools and are closely related to harmful algal blooms. The dinoflagellate Akashiwo sanguinea is a cosmopolitan species which frequently causes dense blooms in estuaries and coasts worldwide, while the availability of P to A. sanguinea still remain unclear. Herein, the physiological and transcriptomic responses of A. sanguinea grown under P-deficient, DIP-replete and DOP-replete conditions were compared. P-deficient adversely suppressed the growth and photosynthesis of A. sanguinea, while genes associated with P transport, DOP utilization, sulfolipid synthesis, and energy production, were markedly elevated. Three forms of DOP, namely, glucose-6-phosphate (G-6-P), adenosine 5-triphosphate (ATP), and β-Glycerol phosphate (SG-P), supported A. sanguinea growth as efficiently as DIP (NaH2PO4), and no significant difference was observed in biochemical compositions and photosynthesis of A. sanguinea between the DIP and DOP treatments. While the genes related to P transporter were markedly suppressed in DOP groups compared with the DIP group. Our results indicated that A. sanguinea is a good growth strategist under P-deficient/replete conditions, and this species had evolved a comprehensive strategy to cope with P deficiency, which might be a crucial factor driving bloom formation in a low inorganic P environment.

Size-dependent effect of microplastics on toxicity and fate of diclofenac in two algae

Microplastics (MPs) are frequently detected in natural waters and usually acted as vectors for other pollutants, leading to possible threats to aquatic organisms. This study investigated the impact of polystyrene MPs (PS MPs) with different diameters on two algae Phaeodactylum tricornutum and Euglena sp., and the combined toxicity of PS MPs and diclofenac (DCF) in two algae was also studied. Significant inhibition of P. tricornutum was observed after 1 d exposure of 0.03 µm MPs at 1 mg L^-1, whereas the decreased growth rate of Euglena sp. was recovered after 2 d exposure. However, their toxicity decreased in the presence of MPs with larger diameters. The oxidative stress contributed a major for the size-dependent toxicity of PS MPs in P. tricornutum, while in Euglena sp. the toxicity was mainly caused by a combination of oxidative damage and hetero-aggregation. Also, PS MPs alleviated the toxicity of DCF in P. tricornutum and the DCF toxicity continually decreased as their diameter increased, whereas the DCF at environmentally concentration could weaken the toxicity of MPs in Euglena sp. Moreover, the Euglena sp. revealed a higher removal for DCF, especially in the presence of MPs, but the higher accumulation and bioaccumulation factors (BCFs) indicated a possible ecological risk in natural waters. The present study explored discrepancy on the size-dependent toxicity and removal of MPs associated with DCF in two algae, providing valuable data for risk assessment and pollution control of MPs associated with DCF.