Biphasic effects of typical chlorinated organophosphorus flame retardants on Microcystis aeruginosa.

The potential accumulation of chlorinated organophosphorus flame retardants (Cl-OPFRs) in aquatic environments sparked interest in studying the effects of Cl-OPFRs on cyanobacterial blooms. In this work, two common Cl-OPFRs, tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tris(2-chloroethyl) phosphate (TCEP), induced dose-dependent biphasic effect on bloom-forming M. aeruginosa. The hormetic response to low-dose Cl-OPFRs was associated with the upregulation of the type I NADH dehydrogenase (NDH-1) complex and its mediated cyclic electron transfer (CET) pathway, as reflected by a transient post-illumination increase in chlorophyll fluorescence, the dark reduction of P700+ and the change of NDH-1-related gene expression. The increased CET activity and carotenoid content jointly reduced the intracellular ROS production, facilitating cyanobacterial growth. Conversely, a higher concentration of both Cl-OPFRs induced severe inhibition of growth and photosynthetic oxygen-evolving activity through an imbalance between PSII and PSI. Toxic-dose Cl-OPFRs inhibited state transition and fixed cells into the State I with a higher PSII/PSI ratio, as indicated by chlorophyll fluorescence induction, 77 K fluorescence emission spectra and photosystem stoichiometry. The elevated PSII/PSI ratio created an imbalance between the two photosystems and eventually lead to ROS overproduction, which generate adverse effects on cell growth. This work provides important insights into the hormetic mechanism of Cl-OPFRs on Microcystis aeruginosa and their potential roles in harmful cyanobacteria blooms.

The effective astaxanthin productivities of immobilized Haematococcus pluvialis with bacterial cellulose.

Haematococcus pluvialis is traditionally cultivated in a suspension for astaxanthin production. This study presents the novel cultivation approach by immobilized H. pluvialis in bacterial cellulose (BC) produced from the symbiosis of Gluconacetobacter xylinus and H. pluvialis. It was observed that the immobilization itself was a regulator to increase the astaxanthin content. The key genes associated to astaxanthin synthesis, such as psy, lcy, bkt, chy, were significantly up-regulated after immobilization. BC immobilized gel can be utilized concurrently with different technologies to improve astaxanthin accumulation (e.g., amount of induction medium, area of biogel, et al). A small-scale screen panel photobioreactor was design to explore the application of the cultivation approach. Compared to suspended culture, the induction time was shortened from 7 days to 3 days. Astaxanthin productivity of red stage reached 343.2 mg·m-2·d-1. This was greater than that of many other cultivation systems.