Rapid and continuous degradation of toxic organic pollutants and conversion to microalgae biomass are attracting enormous interest for resource recovery and wastewater treatment. Aiming toward this goal, we develop and demonstrate a novel photocatalytic-biological system in which photocatalytic optical hollow fibers coated with the N-doped TiO2 photocatalyst and a Scenedesmus obliquus biofilm cooperatively convert phenol to microalgae biomass. The photocatalytic optical hollow fibers exhibit high UV–visible photocatalytic activity to rapidly degrade phenol and emit visible light for biofilm growth, lipid synthesis, and O2 production. O2 produced as an electron acceptor is transferred to the surface of the photocatalytic optical hollow fibers, limiting electron–hole recombination and generating reactive oxygen species such as •OH and •O2–. Upregulation of nicotinamide adenine dinucleotide + hydrogen and adenosine triphosphate and enrichment of Rhodococcus and Pseudomonas in the biofilm enhance the resistance to phenol toxicity, maintain rapid and stable biofilm growth, and increase lipid content. This photocatalytic-biological system rapidly and sustainably converts phenol to microalgae biomass.
Cottonseed meal has been one of the predominant protein feedstuffs used in aqua feed, which contains gossypol . It is well known that gossypol, a natural polyphenolic compound found in seeds, can be toxic to fish. The toxicity of gossypol persists even after a recovery period; however, the underlying mechanism remains largely unknown. To investigate the toxic mechanism of gossypol after the recovery period, Cyprinus carpio were administered a continuous oral dose of 20 mg/kg·d gossypol (gossypol acetate dose/fish weight·d) for one week, followed by a two-week recovery period. The spleen index, spleen morphology, lysozyme (LZM) activity, acid phosphatase (ACP) activity and nitric oxide (NO) concentration were obviously changed in the spleens of C. carpio after two weeks of recovery. Then, miRNA sequencing identified 22 differentially expressed miRNAs in the spleens of C. carpio two weeks after the gossypol treatment. The mRNA expression levels of immune-associated genes were significantly increased in the spleens after recovery. MiR-194 was chosen for future study through a search of existing literature and an analysis of miRNA and mRNA expression levels. To further characterize the potential target of miR-194, we identified putative miR-194 binding sites in the 3′UTR of myeloid differentiation factor 88a (MyD88a). Dual-luciferase reporter assays revealed that miR-194 downregulated the expression level of MyD88a through binding to seed-matching sequence in the 3′ UTR of MyD88a. Moreover, C. carpio were intraperitoneally administered with miR-194 antagomir. Furthermore, down-regulation of miR-194 increased the expression levels of MyD88a and some pro-inflammatory cytokines and anti-inflammatory cytokines. Altogether, the results demonstrate miR-194 can target MyD88a to regulate the immune response of C. carpio after a two-week recovery period following gossypol administration.
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