Colonization characteristics of bacterial communities on microplastics compared with ambient environments (water and sediment) in Haihe Estuary.

The bacterial communities on microplastics in marine and freshwater environments have been described by many studies. However, the migration and transportation processes of bacterial communities on microplastics in estuarine areas remain unclear. In this study, the bacterial communities on three substrates (microplastics, surface water and sediment) in estuarine areas (the Haihe Estuary (HHE) in Bohai Bay, China) were investigated based on 16S rRNA sequencing. The mean OTUs of the three substrates - water, microplastics and sediments - were 1091, 2213 and 3419, respectively. The partitioning of the OTUs among the three substrates indicated that the microplastics could be messengers facilitating the bacterial transportation between water and sediment. According to nMDS and relative abundance analyses, it was found that the microplastics enriched the particular bacteria (e.g., Halobacteriaceae and Pseudoalteromonadaceae) and weakened the influence of environmental variation. In addition, taxonomic and metabolic-pathway analyses indicated that the abundance of potentially pathogenic bacteria (e.g., Pseudomonas and Bacillus) on microplastics was significantly higher than that in the ambient environment. Meanwhile, the microplastic polymer types had little effect on the abundance and structure of the bacterial communities. Compared with surface water and sediments, microplastics could be a good habitat for bacterial communities and could lead to potential ecological risks because of the high stability, pathogenicity and stress tolerance of the bacterial communities on microplastics.

How long-term exposure of environmentally relevant antibiotics may stimulate the growth of Prorocentrum lima: A probable positive factor for red tides.

Antibiotics have been widely detected in the ocean and have various impacts on the environment, while knowledge of their chronic influence on phytoplankton, especially red tide algae, is still limited. Dinoflagellates and green algae are common phytoplankton in marine ecosystems. The former is the main red tide algae, and the latter is an important primary producer. We investigated the long-term responses of two representative algae, Prorocentrum lima and Chlorella sp., to two common antibiotics (sulfamethoxazole (SMX) and norfloxacin (NFX)) at environmentally relevant levels (10 and 100 ng/L) during simulated natural conditions. The cell density and activities of three antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) were analyzed. The results showed that the influence of each antibiotic on Chlorella sp. was not significant (p > 0.05) during the first 10 days, but the influence of the antibiotics later began to show significant inhibition (p < 0.05) compared with the control group, especially during mixed exposure. P. lima was not inhibited, but its cell density increased. SMX had a superior stimulation effect on P. lima. The three enzymes activities of P. lima increased, and the antioxidant mechanism was not seriously impacted. However, for Chlorella sp., the activity of SOD increased while the activities of CAT and POD decreased, suggesting that this algae's antioxidant system was unbalanced due to oxidative stress. Based on our results, the growth of P. lima was different from green algae Chlorella sp. as well as other inhibited marine algae (such as diatom, golden algae) studied in previous studies. Therefore, as a typical pollutant in the ocean, antibiotics may play a positive role in the bloom of dinoflagellate red tides.

Colonization Characteristics of Bacterial Communities on Plastic Debris Influenced by Environmental Factors and Polymer Types in the Haihe Estuary of Bohai Bay, China.

The colonization characteristics of bacterial communities on microplastics or plastic debris (PD) have generated great concern in recent years. However, the influence of environmental factors and polymer types on the formation of bacterial communities on PD in estuarine areas is less studied. To gain additional insights, five types of PD (polyvinyl chloride, polypropylene, polyethylene, polystyrene, and polyurethane) were exposed for three-time periods (two weeks, four weeks, and six weeks) in the Haihe Estuary. 16S rRNA gene sequencing was used to identify the bacterial communities on PD, in seawater, and in sediment samples. The results indicate that the average growth rate of a biofilm is affected by nutrients (total nitrogen and total phosphorus) and salinity. Furthermore, salinity is the primary factor affecting bacterial diversity of the colonies on PD. In addition, genera of bacteria show selectivity toward the PD polymer type and tend to colonize their preferred substrate. Compared with seawater and sediment, PD could be carriers for enrichment of Vibrio in the estuarine environment with salinity ≥26 (± 2‰), which might increase the ecological risk of PD in marine environments.

The effect of environmentally relevant emerging per- and polyfluoroalkyl substances on the growth and antioxidant response in marine Chlorella sp.

The 6:2 chlorinated polyfluoroalkyl ether sulfonic acids (6:2 Cl-PFAES), 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-propanoic acid (HFPO-DA) and perfluoroethylcyclohexane sulfonate (PFECHS) are emerging per- and polyfluoroalkyl substances (PFASs) that are being applied to replace phased-out PFASs, which have high persistency, high bioaccumulation potential and high toxicity. Recently, these emerging PFASs were observed in estuary and marine areas with a pollution level of ng/L. In this study, three levels (10 ng L-1, 100 ng L-1 and 1000 ng L-1) for these PFASs were selected to investigate the response of marine Chlorella sp. to 14 days of exposure. The growth of Chlorella sp. was significantly inhibited by each PFAS over time. Treatments with 1000 ng/L exposure caused the most severe reduction in growth for each PFAS treatment. For the first half of the experimental period (from Day 0 to Day 6), the influence of each PFAS was not significant (p > 0.05). However, treatments with all concentrations of 6:2 Cl-PFAES, HFPO-DA and 1000 ng L-1 PFECHS significantly reduced the growth of Chlorella sp. from Day 8. The superoxide dismutase (SOD) activities in Chlorella sp. were significantly increased (p < 0.05) when exposed to 6:2 Cl-PFAES, HFPO-DA and PFECHS. The catalase (CAT) and peroxidase (POD) activities in Chlorella sp. were significantly inhibited (p < 0.05) by each PFAS. The glutathione (GSH) contents in Chlorella sp. were significantly increased by each PFAS. However, the increases in GSH concentration in Chlorella sp. were low. The inhibition of algal growth was primarily due to the reduction of the activities of CAT and POD. PFECHS had the lowest toxicity among the three PFASs, and it induced less oxidized damage to Chlorella sp. In conclusion, as alternatives to phased-out PFASs, the emerging PFASs are not safe in aquatic environment, and attention should be paid to the management and restriction of these emerging PFASs.

The protective effects of osmolytes on yeast alcohol dehydrogenase conformational stability and aggregation.

The protective effects of four osmolytes (trehalose, dimethysulfoxide, glycine and proline) on the conformational stability and aggregation of guanidine-denatured yeast alcohol dehydrogenase (YADH) have been investigated in this paper. The results show that the four osmolytes protect YADH against unfolding and inactivation by reducing ki (inactivation rate constants), increasing DeltaDeltaGi (transition free energy changes at 25 degrees C), increasing Cm (value for the midpoint of denaturation) and decreasing its ANS-binding fluorescence intensity. Furthermore, these osmolytes can prevent YADH aggregation in a concentration-dependent manner during YADH refolding.

Effect of Cl- on tyrosinase: complex inhibition kinetics and biochemical implication.

Tyrosinase plays a core role in melanogenesis of the various organisms. Therefore, the regulation of the tyrosinase activity is directly related with melanin synthesis. In this study, we investigated the Cl(-)-induced inhibition of human tyrosinase and the potent role of Cl(-) as a negative regulator in melanogenesis. For the inhibition kinetic studies, human tyrosinase was differently prepared from the TXM13 melanotic cells as well as from cells that had undergone gene transfection. We found that Cl(-) inhibited tyrosinase in a slope-parabolic competitive manner and tyrosinase gene transfection into HEK293 cell significantly down-regulated the expression levels of solute carrier family 12, member 4 (potassium/chloride transporters, SLC12A7) and solute carrier family 12, member 7 (potassium/chloride transporters, SLC12A7), which are known to be Cl(-) transporters. From the results of the inhibition kinetic studies and the Cl(-) transporter expression level, we suggested that Cl(-) might act as a potent regulatory factor in melanogenesis. It is worth notice that a high content of Cl(-) exists physiologically and tyrosinase reacts sensitively to Cl- in a complex interaction manner.

The inhibition kinetics and thermodynamic changes of tyrosinase via the zinc ion.

We found that Zn(2+) conspicuously inactivated tyrosinase in a mixed-type inhibition manner: the final level of residual activity was abolished at the equilibrium state with concentration of 0.25 mM Zn(2+). Changes of both K(m) and V(max) by various concentrations of Zn(2+) in Lineweaver-Burk plot were observed. To see whether Zn(2+) also induced conformational change of tyrosinase and how thermodynamical changes by ligand binding were occurred, the intrinsic fluorescence studies as well as calorimetric measurements were conducted. The results showed that the Zn(2+) binding to tyrosinase directly induced conformational change of tyrosinase, and the changes of thermodynamic parameters such as enthalpy (DeltaH), Gibbs free-energy (DeltaG), and entropy (DeltaS) were obtained as 60+/-7.0 kJ/mol, -14.54 kJ/mol and 248.53 J/(K mol), respectively. The inactivating effect of Zn(2+) on tyrosinase was completely prevented by incubation with bovine serum albumin, which has a Zn(2+) binding motif in its structure. We suggested that Zn(2+) ligand-binding affected the substrate's accessibility due to the conformational changes and thus, the complex type of inhibition has occurred with the calorimetric changes.