Accelerating losses of seagrass meadows has led to efforts to restore these highly productive and beneficial ecosystems globally. Depth and light availability are critical determinants of seagrass restoration success. Eelgrass ( Zostera marina L.) is the dominant seagrass species in the temperate northern hemisphere, but its global distribution has reduced dramatically. The main aims of this study were to determine: (1) the depth limit for Z. marina survival in Ailian Bay, north China, and (2) how light availability affects the growth and recruitment of Z. marina as a basis for identifying a suitable depth range for successful restoration. To achieve these aims, Z. marina shoots were transplanted from a nearby donor site, Swan Lake, to an experimental site, Ailian Bay, and the temporal responses of Z. marina shoots to light availability at water depths ranging from 1 to 8 m were investigated using in situ suspended cultures. Four suspended shoot transplantation experiments were conducted in 4 years. The results showed that the transplanted Z. marina shoots could survive and branch during an annual growth cycle, permanently underwater, at a depth ≤3 m. Due to the local turbidity of the waters in Ailian Bay, a depth of 4 m led to sufficient light deprivation (reduced to 6.48–10.08% of surface irradiance) to negatively affect seagrass shoot density and clonal reproduction. In addition, reproductive shoot density also tended to decline with water depth and light deprivation. Our results indicated that Z. marina population recruitment, through sexual and asexual (clonal growth) reproduction, were negatively affected by increasing water depth and light deprivation. These findings may provide a suitable depth range for the successful restoration of Z. marina in local coastal waters. They may also be applied to the management and restoration of Z. marina globally.
Abstract Type III secretion system (T3SS)‐dependent translocation has been used to deliver heterologous antigens by vaccine carriers into host cells. In this research, we identified the translocation signal of Edwardsiella piscicida T3SS effector EseG and constructed an antibiotic resistance‐free balanced‐lethal system as attenuated vaccine carrier to present antigens by T3SS. Edwardsiella piscicida LSE40 asd gene deletion mutant was constructed and complemented with pYA3342 harbouring the asd (aspartate β‐semialdehyde dehydrogenase) gene from Salmonella . Fusion proteins composed of EseG N‐terminal 1–108 amino acids and the TEM1‐β‐lactamase reporter were inserted in plasmid pYA3342. The fusion protein could secrete into the cell culture, translocate into HeLa cells, and localize in the membrane fraction. Then, the double gene deletion mutant LSE40Δ asd Δ purA was constructed as an attenuated vaccine carrier, and Aeromonas hydrophila GapA (glyceraldehyde‐3‐phosphate dehydrogenase) was fused with the translocation signal, instead of the TEM1‐β‐lactamase reporter. The bivalent vaccine could protect blue gourami ( Trichogaster trichopterus ) against E . piscicida and A . hydrophila , with the relative per cent survival of 80.77% and 63.83%, respectively. These results indicated that EseG N‐terminal 1–108 amino acid peptide was the translocation signal of E. piscicida T3SS, which could be used to construct bivalent vaccines based on an attenuated E. piscicida carrier.
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