Antioxidant Systematic Alteration Was Responsible for Injuries Inflicted on the Marine Blue Mussel Mytilus edulis Following Strontium Exposure.

The ionic properties of strontium (Sr), a significant artificial radionuclide in the marine environment, were estimated using a stable nuclide-substituting experimental system under controlled laboratory conditions. The bio-accumulation of Sr and its impacts, as well as any possible hidden mechanisms, were evaluated based on the physiological alterations of the sentinel blue mussel Mytilus edulis. The mussels were exposed to a series of stress-inducing concentrations, with the highest solubility being 0.2 g/L. No acute lethality was observed during the experiment, but sublethal damage was evident. Sr accumulated in a tissue-specific way, and hemolymph was the target, with the highest accumulating concentration being 64.46 µg/g wet weight (ww). At the molecular level, increases in the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and changes in ROS components (H2O2, O2-, and -OH) and antioxidant system activity indicated that the redox equilibrium state in hemocytes was disturbed. Furthermore, the rise in the hemocyte micronucleus (MN) rate (4‱ in the high-concentration group) implied DNA damage. At the cellular level, the structures of hemocytes were damaged, especially with respect to lysosomes, which play a crucial role in phagocytosis. Lysosomal membrane stability (LMS) was also affected, and both acid phosphatase (ACP) and alkaline phosphatase (AKP) activities were reduced, resulting in a significant decline in phagocytosis. The hemolymph population structure at the organ level was disturbed, with large changes in hemocyte number and mortality rate, along with changes in component ratios. These toxic effects were evaluated by employing the adverse outcome pathway (AOP) framework. The results suggested that the disruption of intracellular redox homeostasis is a possible explanation for Sr-induced toxicity in M. edulis.

Developmental toxicity in marine medaka (Oryzias melastigma) embryos and larvae exposed to nickel.

As an important trace metal, nickel (Ni) has been reported extensively in the studies on freshwater animals. However, the toxic effects of Ni on marine organisms are not clearly understood. Therefore, in order to investigate the toxic effects of Ni on the early development of marine fish, the marine medaka (Oryzias melastigma) embryos and larvae were immersed in 0.13-65.80 mg/L Ni solution. The results showed that Ni exposure changed the egg size and heart rate of the embryos, lowered the hatchability, increased the deformity rate, and shortened the total body length of newly hatched larvae. Besides, it was found that before organogenesis and post-hatching periods were the sensitive periods of embryos to Ni. The 25 d LC50 value of embryos was 49.28 mg/L, and the 5 d LC50 of larvae was 55.92 mg/L, indicating that the embryos were more sensitive to Ni than the larvae. Furthermore, the expressions of the metallothionein (MT) gene, the skeletal development-related gene (Cyp26b1) and the cardiac development-related genes (ATPase, smyd1, cox2 and bmp4) were determined, and the results showed that the expressions of ATPase and smyd1 were up-regulated, while MT, Cyp26b1 and cox2 were significantly down-regulated at 9 days post-fertilization (dpf). Overall, Ni exposure caused a significant toxic effect on the early development of the O. melastigma embryos and larvae. Our findings could provide an important supplement to the toxicity data of tropical Ni and provide a reference for the exploration of the molecular mechanisms of Ni toxicity.

Complete Genome Sequence of an N-Acyl Homoserine Lactone Producer, Breoghania sp. Strain L-A4, Isolated from Rhizosphere of Phragmites australis in a Coastal Wetland.

The Breoghania sp. strain L-A4 was isolated from the rhizosphere of Phragmites australis in the Qinhaungdao coastal wetland in China. Here, we present the complete genome sequence of strain L-A4, which consists of a chromosome of 5,029,620 bp with a G+C content of 64.53% and 4,964 coding DNA sequences. This strain was the first detected to produce N-acyl homoserine lactone (AHL) signals in a member of this genus.

Quorum sensing of microalgae associated marine Ponticoccus sp. PD-2 and its algicidal function regulation.

Quorum sensing (QS) systems play important roles in regulating many physiological functions of microorganisms, such as biofilm formation, bioluminescence, and antibiotic production. One marine algicidal bacterium, Ponticoccus sp. PD-2, was isolated from the microalga Prorocentrum donghaiense, and its N-acyl-homoserine lactone (AHL)-mediated QS system was verified. In this study, we analyzed the AHLs profile of strain PD-2. Two AHLs, 3-oxo-C8-HSL and 3-oxo-C10-HSL, were detected using a biosensor overlay assay and GC-MS methods. Two complete AHL-QS systems (designated zlaI/R and zlbI/R) were identified in the genome of strain PD-2. When expressed in Escherichia coli, both zlaI and zlbI genes could each produce 3-oxo-C8-HSL and 3-oxo-C10-HSL. Algicidal activity was investigated by evaluating the inhibitory rate (IR) of microalgae growth by measuring the fluorescence of viable cells. We found that the metabolites of strain PD-2 had algicidal activity against its host P. donghaiense (IR 84.81%) and two other red tide microalgae, Phaeocystis globosa (IR 78.91%) and Alexandrium tamarense (IR 67.14%). ß-cyclodextrin which binds to AHLs and inhibits the QS system reduced the algicidal activity more than 50%. This indicates that inhibiting the QS system may affect the algicidal metabolites production of strain PD-2. Our study indicated that a QS-regulated algicidal system may play a potential role in the process of red tides disintegration. QS might be a potential way to control red tides.