In the filamentous cyanobacterium, Anabaena sp. PCC 7120, single heterocysts differentiate at semi-regular intervals in response to nitrogen stepdown. HetR is a principal regulator of heterocyst differentiation, and hetP and hetZ are two genes that are regulated directly by HetR. In a hetR mutant generated from the IHB (Institute of Hydrobiology) substrain of PCC 7120, heterocyst formation can be restored by moderate expression of hetZ and hetP. The resulting heterocysts are located at terminal positions. We used a tandem promoter, PrbcLPpetE, to express hetZ and hetP strongly in the hetR mutant. Co-expression of hetZ and hetP enabled the hetR mutant to form multiple contiguous heterocysts at both terminal and intercalary positions. Expression of hetZ, alone resulted in terminally located heterocysts, whereas expression of hetP, alone produced enlarged cells in strings. In the absence of HetR, formation of heterocysts was insensitive to the peptide inhibitor, RGSGR.
In the past decades, the taxonomic status of the cyanobacterial family Phormidiaceae has always been chaotic and problematic. In this study, filamentous cyanobacteria were investigated in the east of China, and twenty strains isolated from different locations of Zhejiang Province were characterized. Using the polyphasic approach combining morphological, molecular and phylogenetic features, these strains were grouped within the members of the genera Ancylothrix and Potamolinea, the newly recorded genera of cyanobacteria in China. Based on the collected taxonomic information of the family Phormidiaceae, cyanobacterial systematics at family level were further discussed. This study provided a simple and efficient example to perform the phylogenetic evaluation for the monophyly and rationality of currently used families of cyanobacteria by using the regional strains based on the polyphasic approach.
Copper (Cu2+) and zinc (Zn2+) are two kinds of heavy metals essential to living organisms. Cu2+ and Zn2+ at excessive concentrations can cause adverse effects on animals, but little is known about the thyroid-disrupting effects of these metals in fish, especially in the early developmental transition stage from embryos to larvae. Wild-type zebrafish embryos were used to expose to Cu2+ (0, 1.5, 15, and 150 μg/L) and Zn2+ (0, 20, 200, and 2000 μg/L) for 120 h. Thyroid hormone contents and transcriptional changes of the genes connected with the hypothalamic-pituitary-thyroid (HPT) axis were measured. Results showed that zebrafish embryos/larvae malformation rates were significantly increased in the Cu2+ and Zn2+ groups. Remarkably elevated thyroxine (T4) concentrations and reduced triiodothyronine (T3) concentrations were observed in Cu2+ and Zn2+ exposure fish. And the expression patterns of genes connected with the HPT axis were changed after Cu2+ and Zn2+ treatment. Based on principal component analysis (PCA) results, Zn2+ caused significant effects on the thyroid endocrine system at 200 μg/L, while Cu2+ resulted in thyroid disruption as low as 1.5 μg/L. In short, our study demonstrated that exposure to Cu2+ and Zn2+ induced developmental toxicity and thyroid disruption to zebrafish embryos/larvae.
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