[Analysis of Mechanism and Start-up Thresholds of Seasonal Algal Blooms in a Northern Eutrophic Stratified Reservoir].

Seasonal algal blooms produce a high risk for water supply safety. To explore the mechanism of seasonal algal blooms in northern eutrophic stratified reservoirs, the combination of taxonomic and functional classifications, local weighted regression (LOWESS), and Boundary line analysis (BLA) were employed to obtain the succession features and environmental thresholds of seasonal (e.g., spring and summer) algal blooms, based on the long-term and high-frequency monitoring from 2017 to 2020 in Lijiahe Reservoir. The results showed that:① the succession and response mechanisms of algal blooms were different in spring and summer. In detail, Chlorophyta, Bacillariophyta, and Dinoflagellates (e.g., low-temperature, small, high surface-to-volume genera) dominated in spring, whereas Chlorophyta, Bacillariophyta, and Cyanobacteria (e.g., high-temperature, large or colonial, low surface-to-volume genera) dominated in summer. The differences in physiological and morphological characteristics of algae were the internal cause triggering seasonal algal blooms. ② The main drivers of algal blooms were different in spring and summer. Spring blooms were controlled by water temperature (WT), mixing depth (i.e., Zmix), and light availability (i.e., Zeu/Zmix), whereas summer blooms were jointly influenced by WT, Zmix, Zeu/Zmix, and total phosphorus (TP). The differences in the changes of the major drivers were external causes triggering seasonal algal blooms. ③ The water environment thresholds starting seasonal algal blooms were different in spring and summer. The thresholds of WT, Zmix, and Zeu/Zmix in spring were>9.4℃, <10.9 m, and>0.24, respectively, whereas the thresholds of WT, Zmix, Zeu/Zmix, and TP in summer were>16.0℃, <11.6 m, >0.16, and>0.011 mg·L-1, respectively. Based on the research on the mechanism of seasonal algal blooms and related thresholds, this work will provide a reference for the control of subsequent algal blooms.

Boron Contents of German Mineral and Medicinal Waters and Their Bioavailability in Drosophila melanogaster and Humans.

SCOPE: Boron is a trace element that naturally occurs in soil, making mineral and medicinal water important contributors to overall intake. Thus, in a systematic screening, the mean boron concentrations of 381 German mineral and medicinal waters are determined. METHODS AND RESULTS: Boron concentrations in mineral and medicinal waters are analyzed by inductively coupled mass spectrometry (ICP-MS). Highest boron values find in waters from the southwest of Germany. The boron content of the waters is positively correlated with the concentration of most other analyzed bulk elements, including calcium, potassium, magnesium, and sodium. Mineral waters with either low (7.9 µg L-1 ), medium (113.9 µg L-1 ), or high (2193.3 µg L-1 ) boron content are chosen for boron exposure experiments in fruit flies (Drosophila melanogaster) and humans. In flies, boron-rich mineral water significantly increases boron accumulation, with the accumulation predominantly occurring in the exoskeleton. In humans, serum boron and 24-h urinary boron excretion significantly increase only in response to the intake of boron-rich mineral water. CONCLUSION: Overall, the current data demonstrate that mineral and medicinal waters vary substantially in the content of boron and that boron-rich mineral water can be used to elevate the boron status, both in flies and humans.

Application of uniform design to evaluate the different conditions on the growth of algae Prymnesium parvum.

Prymnesium parvum is an environmentally harmful algae and well known for its toxic effects to the fish culture. However, there is a dearth of studies on the growth behavior of P. parvum and information on how the availability of nutrients and environmental factors affect their growth rate. To address this knowledge gap, we used a uniform design approach to quantify the effects of major nutrients (N, P, Si and Fe) and environmental factors (water temperature, pH and salinity) on the biomass density of P. parvum. We also generated the growth model for P. parvum as affected by each of these nutrients and environmental factors to estimate optimum conditions of growth. Results showed that P. parvum can reach its maximum growth rate of 0.789, when the water temperature, pH and salinity is 18.11 °C, 8.39, and 1.23‰, respectively. Moreover, maximum growth rate (0.895-0.896) of P. parvum reached when the concentration of nitrogen, phosphorous, silicon and iron reach 3.41, 1.05, 0.69 and 0.53 mg/l, respectively. The order of the effects of the environmental factors impacting the biomass density of P. parvum was pH > salinity > water temperature, while the order of the effects of nutrients impacting the biomass density of P. parvum was nitrogen > phosphorous > iron > silicon. These findings may assist to implement control measures of the population of P. parvum where this harmful alga threatens aquaculture industry in the waterbodies such as Ningxia region in China.

Creatine improves the flesh quality of Pacific white shrimp (Litopenaeus vannamei) reared in freshwater.

Creatine improves flesh quality on mammalian but studies on crustaceans are scarce. In the present study, diets with six levels of creatine (1.23, 2.58, 5.12, 8.28, 14.12, 24.49 g kg-1 diet) were hand-fed to juvenile Litopenaeus vannamei (IBW: 1.50 ± 0.02 g) reared in freshwater for 46 days. Results showed creatine supplementation did not affect the growth performance (FBW: 17.04 ± 1.28 g) or the content of guanidinoacetic acid in muscle and hepatopancreas whereas significantly increased muscular creatine content. Diet with 8.28 g kg-1 creatine significantly increased muscular hardness and chewiness by decreasing myofiber diameter and increasing myofiber density. Additionally, creatine downregulated the mRNA expression of fast sMyHC1, sMyHC2, sMyHC6a and upregulated slow sMyHC5 and sMyHC15 mRNA expression. Muscular protein, collagen, total amino acid and flavor amino acid contents increased with creatine supplementation. In conclusion, the diet with 8.28 g kg-1 creatine improved the flesh quality of L. vannamei.

Effects of Environmentally Relevant Residual Levels of Diluted Bitumen on Wild Fathead Minnows (Pimephales promelas).

Transportation of crude oil across North America's boreal ecozone creates the potential for spills in freshwater where less is known about the sensitivity of resident fish than for marine systems. The sensitivity of wild fathead minnows (FHM) to residual concentrations (ppb range) of the water accommodated fraction (WAF) of diluted bitumen (dilbit) was assessed by exposing them for 21 days followed by a 14 days depuration. Target concentrations were well below detection limits for GC-MS, but were estimated by dilution factor (1:100,000 and 1:1,000,000 WAF:water) to contain less than 0.0003 µg/L of polycyclic aromatic compounds. Confinement and handling stress caused by transfer of wild fish into tanks much smaller than their natural range resulted in mortality and lower body condition among all groups, but interactive effects of oil exposures still resulted in females with smaller cortical alveolar oocytes, and males with larger testicular lobe lumen sizes. Additional studies examining the compounded effects of stress and environmentally relevant oil exposures in wild fishes are needed.

Applying Al2O3@Ag@trithiocyanuric acid as an efficient metal ion scavenger for the selective extraction of iron (III) and lead (II) from environmental waters.

In the present study, silver (Ag) atoms were chemically deposited on γ-alumina (Al2O3) nanospheres to be further functionalized with trithiocyanuric acid (TTC). The result was Al2O3@Ag@TTC composites, which were used for the selective extraction and preconcentration of Fe (III) and Pb (II) ions in seawater and river water samples. TTC is a potent scavenger of heavy metal ions with multiple nitrogen- and sulfur-containing functional groups. The concentrations of analytes were determined by flame atomic absorption spectrometry, and the structure of the synthetic adsorbent was characterized by spectral and microscopic techniques. Furthermore, the fundamental parameters influencing the extraction and desorption of the target ions were evaluated. Under optimized conditions, the calibration curve was linear in the range of 10-100 ng mL-1 for both analytes. The detection limits of the proposed method for Fe (III) and Pb (II) ions were 1.5 ng mL-1 and 0.8 ng mL-1, respectively, with a relative standard deviation of less than 6.1% (n = 7). Moreover, the proposed method tolerated salinities of up to 50.0 g L-1 without exhibiting any decrease in selectivity or recovery. The developed method was successfully applied to extract Fe (III) and Pb (II) ions from seawater and river water samples. The extraction recovery rates of the spiked ions were at least 93% for Fe (III) and 97 % for Pb (II).

Quality and management status of the drinking water supplies in a semiarid region of Northeastern Brazil.

Surface and groundwater resources in the Seridó Region (Brazilian semiarid) were investigated to evaluate their current quality conditions and suitability for domestic use. The water was characterized in terms of physical, chemical, and radiological parameters; including those required by the Brazilian Drinking Water Quality Standard (DWQS). Information about major and trace elements and radiological aspects of the water are reported for the first time. Salinization was confirmed as a key problem in the region, driven natural and anthropogenic. Overall, water has poor organoleptic characteristics. The concentration of most trace elements was below the recommended level, except for uranium and selenium in groundwater. Gross alpha and beta activities higher than the recommended levels were also recorded in several water samples, mostly from the investigated aquifers. In these samples, a detailed radionuclide analysis is required to estimate the effective dose received by the local population. Overall, the results show that water from the investigated region is not suitable for human consumption unless proper treatment is applied. Water requires proper treatment to decrease the content of dissolved salts, toxic elements, and radionuclides responsible for the high gross alpha and beta activities.

Proteome changes in muscles, ganglia, and gills in Corbicula fluminea clams exposed to crude oil: Relationship with behavioural disturbances.

The use of online remote control for 24/7 behavioural monitoring can play a key role in estimating the environmental status of aquatic ecosystems. Recording the valve activity of bivalve molluscs is a relevant approach in this context. However, a clear understanding of the underlying disturbances associated with behaviour is a key step. In this work, we studied freshwater Asian clams after exposure to crude oil (measured concentration, 167 ± 28 µg·L-1) for three days in a semi-natural environment using outdoor artificial streams. Three complementary approaches to assess and explore disturbances were used: behaviour by high frequency non-invasive (HFNI) valvometry, tissue contamination with polycyclic aromatic hydrocarbons (PAH), and proteomic analysis. Two tissues were targeted: the pool adductor muscles - retractor pedal muscle - cerebral and visceral ganglia, which is the effector of any valve movement and the gills, which are on the frontline during contamination. The behavioural response was marked by an increase in valve closure-duration, a decrease in valve opening-amplitude and an increase in valve agitation index during opening periods. There was no significant PAH accumulation in the muscle plus nervous ganglia pool, contrary to the situation in the gills, although the latter remained in the low range of data available in literature. Major proteomic changes included (i) a slowdown in metabolic and/or cellular processes in muscles plus ganglia pool associated with minor toxicological effect and (ii) an increase of metabolic and/or cellular processes in gills associated with a greater toxicological effect. The nature of the proteomic changes is discussed in terms of unequal PAH distribution and allows to propose a set of explanatory mechanisms to associate behaviour to underlying physiological changes following oil exposure. First, the first tissues facing contaminated water are the inhalant siphon, the mantle edge and the gills. The routine nervous activity in the visceral ganglia should be modified by nervous information originating from these tissues. Second, the nervous activity in the visceral ganglia could be modified by its own specific contamination. Third, a decrease in nervous activity of the cerebral ganglia close to the mouth, including some kind of narcosis, could contribute to a decrease in visceral ganglia activity via a decrease or blockage of the downward neuromodulation by the cerebro-visceral connective. This whole set of events can explain the decrease of metabolic activity in the adductor muscles, contribute to initiate the catch mechanism and then deeply modify the valve behaviour.

Aqueous inorganic uranium speciation in European stream waters from the FOREGS dataset using geochemical modelling and determination of a U bioavailability baseline.

The concentration of the bioavailable uranium fraction (Ubio) at the European scale was deduced by geochemical modelling considering several definitions found in the literature and the FOREGS European stream waters geochemical atlas dataset to produce a Ubio baseline. A sensitivity analysis was performed using three thermodynamic databases. We also investigated the link between total dissolved uranium (Uaq) concentrations, speciation and global stream water chemistry on the one hand, and the lithology and ages of the surrounding rocks on the other. The more U-enriched the stream sediments or rock type contexts are, which tends to be the case with rocks containing silicates (4.1 mg/kg), the less U-concentrated the stream waters are (0.15 µg/L). Sedimentary rocks lead to slightly higher Uaq concentrations (0.34 µg/L) even if the concentration in sediment (Used) is relatively low (1.6 mg/kg). This trend is reversed for Ubio, with higher concentrations in a crystalline context. The mean estimated Ubio value ranges from 1.5.10-3 to 65.3 ng/L and can fluctuate by 3 orders of magnitude depending on the considered definition as opposed to by 2 orders of magnitude accountable to differences between thermodynamic databases. The classification of the water in relation to the two surrounding rock lithologies makes it possible to reduce the mean variability for the Ubio concentrations. Irrespective of the definition of Ubio considered, in 59% of cases the Ubio fraction represents less than 1% of Uaq. Several threshold values relating to Ubio were proposed, assuming knowledge only of the aqueous concentrations of the major elements and Uaq.

Effects of diluted bitumen exposure and recovery on the seawater acclimation response of Atlantic salmon smolts.

Petrogenic chemicals are common and widespread contaminants in the aquatic environment. In Canada, increased extraction of bitumen from the oil sands and transport of the major crude oil export product, diluted bitumen (dilbit), amplifies the risk of a spill and contamination of Canadian waterways. Fish exposed to sublethal concentrations of crude oil can experience a variety of adverse physiological effects including osmoregulatory dysfunction. As regulation of water and ion balance is crucial during the seawater transition of anadromous fish, the hypothesis that dilbit impairs seawater acclimation in Atlantic salmon smolts (a fish at risk of exposure in Canada) was tested. Smolts were exposed for 24 d to the water-soluble fraction of dilbit in freshwater, and then transferred directly to seawater or allowed a 1 wk depuration period in uncontaminated freshwater prior to seawater transfer. The seawater acclimation response was quantified at 1 and 7 d post-transfer using established hematological, tissue, and molecular endpoints including gill Na+/K+-ATPase gene expression (nka). All smolts, irrespective of dilbit exposure, increased serum Na+ concentrations and osmolality within 1 d of seawater transfer. The recovery of these parameters to freshwater values by 7 d post-transfer was likely driven by the increased expression and activity of Na+/K+-ATPase in the gill. Histopathological changes in the gill were not observed; however, CYP1A-like immunoreactivity was detected in the pillar cells of gill lamellae of fish exposed to 67.9 µg/L PAC. Concentration-specific changes in kidney expression of a transmembrane water channel, aquaporin 3, occurred during seawater acclimation, but were resolved with 1 wk of depuration and were not associated with histopathological changes. In conclusion, apart from a robust CYP response in the gill, dilbit exposure did not greatly impact common measures of seawater acclimation, suggesting that significant osmoregulatory dysfunction is unlikely to occur if Atlantic salmon smolts are exposed sub-chronically to dilbit.

The shift of phosphorus transfers in global fisheries and aquaculture.

Global fish production (capture and aquaculture) has increased quickly, which has altered global flows of phosphorus (P). Here we show that in 2016, [Formula: see text] Tg P yr-1 (mean and interquartile range) was applied in aquaculture to increase fish production; while [Formula: see text] Tg P yr-1 was removed from aquatic systems by fish harvesting. Between 1950 and 1986, P from fish production went from aquatic towards the land-human systems. This landward P peaked at 0.54 Tg P yr-1, representing a large but overlooked P flux that might benefit land activities under P scarcity. After 1986, the landward P flux decreased significantly, and became negative around 2004, meaning that humans spend more P to produce fish than harvest P in fish capture. An idealized pathway to return to the balanced anthropogenic P flow would require the mean phosphorus use efficiency (the ratio of harvested to input P) of aquaculture to be increased from a current value of 20% to at least 48% by 2050 - a big challenge.

Hysteretic response of Microbial Eukaryotic Communities to Gradually Decreased Nutrient Concentrations in Eutrophic Water.

External environments to microbial eukaryotic communities often change gradually with time. However, whether the responses of microbial eukaryotic communities to these gradually changed environments are continuous or hysteretic and the mechanisms underlying these responses are largely unknown. Here, we used a microcosm to investigate the temporal variation of microbial eukaryotic communities with the gradually decreased nutrient concentrations (nitrogen and phosphorus). We found the differences of microbial eukaryotic community composition and species richness between the control and treatment groups were low during the days 0 to 12, although the nutrient concentrations decreased rapidly during this period in treatment group. However, these differences were clear during the days 14 to 18, although the nutrient concentrations decreased slowly during this period in treatment group. The mechanisms for these results are that the strong homogenous selection (perhaps due to the biotic factors) during the days 8 to 10 in treatment group might enhance the stability of microbial eukaryotic communities. However, the continuously decreased nutrient concentrations weakened the homogenous selection and promoted the strength of environmental filtering, and therefore resulted in the distinct change of microbial eukaryotic communities during the days 14 to 18 in treatment group. Fungi, Chlorophyta and Chrysophyta which associated with the nutrient removal played important roles in this hysteretic change of microbial eukaryotic communities. Overall, our findings suggest that disentangling the non-linear response of communities to gradual environmental changes is essential for understanding ecosystem restoration and degradation in future.

Green Synthesized Zinc Oxide Nanoparticles as Feed Additives to Improve Growth, Biochemical, and Hematological Parameters in Freshwater Fish Labeo rohita.

Zinc deficiency in aquatic animals affects the biological processes and physiological functions. Thus, the supplement of ZnONPs can be used as an alternative method to overcome zinc deficiency. Nanoparticles have the potential to enhance the growth and health of the fish. The main aim of this study is to evaluate the growth efficacy of ZnONP-supplemented diet with fingerlings of Labeo rohita. The green synthesized ZnONPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transformer infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Different concentrations of ZnONPs (5, 7.5, and 10 mg/kg) were administered in the basal diet of freshwater fish Labeo rohita for 45 days to observe the growth and metabolic functions of the body. However, the fish fed with 10 mg/kg ZnONP-supplemented diet shows that the growth performance was highly increased followed by 7.5 mg/kg and 5 mg/kg ZnONPs when compared with the control. The biochemical, hematological, and digestive enzyme activities were also significantly increased with different concentrations of ZnONPs. The effects of zinc oxide nanoparticles show the higher improvement of growth and metabolic functions in Labeo rohita. These results suggest that the nanotechnology could apply for feed formulation technology and pave the way for the dietary supplementation of zinc oxide nanoparticles as safe ingredients for aquatic animals to overcome the zinc deficiency.

Asiatic clam Corbicula fluminea exhibits distinguishable behavioural responses to crude oil under semi-natural multiple stress conditions.

Aquatic ecosystems are subject to many anthropogenic disturbances, and understanding their possible impacts is a real challenge. Developing approaches based on the behaviour of bivalve mollusks, an integrating marker of the state of the organisms, and therefore of their environment, is relevant, whether within a natural ecosystem or an ecosystem subject to industrial activities. The main objective of this study was to identify by HFNI Valvometry a reliable and reproducible clam behavioural response in the presence of crude oil in a multistress context. To closely replicate actual field conditions, Corbicula fluminea was exposed in outdoor artificial streams that were subject to natural variations and were continuously fed by fresh water from the Gave de Pau (S.W. France). After a period of 26 days in these artificial streams, the clams (n = 14-16 per condition) were separately exposed for 10 days to crude oil alone, crude oil and barium, crude oil and noise pollution, crude oil and turbidity pulses, barium alone, noise pollution alone, turbidity pulses alone or natural changes alone. The secondary objective was to characterize the accumulation of polycyclic aromatic hydrocarbons (PAH) in 3 tissues (gills, adductor muscles and foot) in clams exposed for 10 days to crude oil alone or under multistress conditions (n = 5 clams per condition) and then to compare the accumulation and behaviour of clams under these conditions. The response of clams to crude oil alone or under multistress conditions was visually and statistically significant and not confounded by the other disturbances tested, despite large variations in water temperature. In the presence of crude oil, the behaviour of clams was characterized by an increase in valve-closure duration, a decrease in valve-opening amplitude and an increase in valve agitation index. In the presence of crude oil, the clam behaviour showed no direct relationship with PAH accumulation in the gills, adductor muscles or foot, although hypothetical mechanisms are discussed. This work supports the growing interest in studying the behaviour of bivalve mollusks in the context of biomonitoring of the aquatic environment surrounding oil facilities.

Nutrient enrichment induces a shift in dissolved organic carbon (DOC) metabolism in oligotrophic freshwater sediments.

Dissolved organic carbon (DOC) turnover in aquatic environments is modulated by the presence of other key macronutrients, including nitrogen (N) and phosphorus (P). The ratio of these nutrients directly affects the rates of microbial growth and nutrient processing in the natural environment. The aim of this study was to investigate how labile DOC metabolism responds to changes in nutrient stoichiometry using 14C tracers in conjunction with untargeted analysis of the primary metabolome in upland peat river sediments. N addition led to an increase in 14C-glucose uptake, indicating that the sediments were likely to be primarily N limited. The mineralisation of glucose to 14CO2 reduced following N addition, indicating that nutrient addition induced shifts in internal carbon (C) partitioning and microbial C use efficiency (CUE). This is directly supported by the metabolomic profile data which identified significant differences in 22 known metabolites (34% of the total) and 30 unknown metabolites (16% of the total) upon the addition of either N or P. 14C-glucose addition increased the production of organic acids known to be involved in mineral P dissolution (e.g. gluconic acid, malic acid). Conversely, when N was not added, the addition of glucose led to the production of the sugar alcohols, mannitol and sorbitol, which are well known microbial C storage compounds. P addition resulted in increased levels of several amino acids (e.g. alanine, glycine) which may reflect greater rates of microbial growth or the P requirement for coenzymes required for amino acid synthesis. We conclude that inorganic nutrient enrichment in addition to labile C inputs has the potential to substantially alter in-stream biogeochemical cycling in oligotrophic freshwaters.

The role of the freshwater oligochaete Limnodrilus hoffmeisteri in the distribution of Se in a water/sediment microcosm.

Selenite(IV) and selenate(VI) are the major species of Se in the seleniferous aquatic ecosystem. The redistribution of Se in the water/sediment microcosm by bioturbation remains largely unknown. In this study, the redistribution of Se in the water/sediment microcosm by the benthic oligochaete Limnodrilus hoffmeisteri was assessed. The worms were exposed to 2-40 µg/g dry weight of Se(IV) or Se(VI) in the sediment (diet) for 2 months. The changes in the Se levels in different compartments of the microcosm (sediment, overlying water, and worms) were quantified after 2 weeks and 2 months. The subcellular distribution of Se in the worms were also evaluated. Finally, the volatilization of Se from the two Se sources was estimated. The results showed that Se concentration in the overlying water and Se bioaccumulation in the worms were increased with Se levels in the sediments. Approximately 1.6-9.8% of Se was volatilized in the absence of the worms and was intensified in the presence of the worms (2.1-25.7%). The subcellular distribution witnessed high levels of Se in the cell debris (>60%). Se(IV) and Se(VI) differ in their bioaccumulation, redistribution and the effects on the growth of the worms. Our results suggest that the bioturbation by benthos play an essential role in the redistribution of Se in the water/sediment microcosm.

Single and Combined Effects of Zinc and Manganese on the Bivalve Anodontites trapesialis: Complementary Endpoints to Support the Hypothesis of Manganese Promoting Metabolic Suppression in Gills.

Manganese (Mn) might stimulate the valve closure reflex in the freshwater bivalve Anodontites trapesialis, leading to metabolic suppression, whereas zinc (Zn) is not able to modify this behavior. To investigate this particular response, we exposed A. trapesialis specimens to Mn (0.5 mg L-1 ) and Zn (1.0 mg L-1 ) alone, and to their mixture, to measure further endpoints in different clam tissues: glycogen level in gills, and calcium (Ca2+ ), sodium (Na+ ), and chloride (Cl- ) concentrations in the hemolymph. Furthermore, we used cutting-edge technology, proteomics, to evaluate modifications in protein patterns under the 3 exposure tests. The main results highlighted that only Mn caused a clear drop in glycogen levels in gills, an increase in Ca2+ and Na+ , and a simultaneous decrease in Cl- concentration in the hemolymph. The proteomic analysis confirmed that Mn promoted more effects in A. trapesialis than the other tested conditions, because the number of proteins modulated was higher than the results obtained after exposure to Zn and the mixture. Moreover, 11 of the 12 modulated proteins were down-expressed. These results consolidate the hypothesis that Mn might suppress gill metabolic rate in A. trapesialis. Environ Toxicol Chem 2019;38:2480-2485. © 2019 SETAC.

Differential gene content and gene expression for bacterial evolution and speciation of Shewanella in terms of biosynthesis of heme and heme-requiring proteins.

BACKGROUND: Most species of Shewanella harbor two ferrochelatase paralogues for the biosynthesis of c-type cytochromes, which are crucial for their respiratory versatility. In our previous study of the Shewanella loihica PV-4 strain, we found that the disruption of hemH1 but not hemH2 resulted in a significant accumulation of extracellular protoporphyrin IX (PPIX), but it is different in Shewanella oneidensis MR-1. Hence, the function and transcriptional regulation of two ferrochelatase genes, hemH1 and hemH2, are investigated in S. oneidensis MR-1. RESULT: In the present study, deletion of either hemH1 or hemH2 in S. oneidensis MR-1 did not lead to overproduction of extracellular protoporphyrin IX (PPIX) as previously described in the hemH1 mutants of S. loihica PV-4. Moreover, supplement of exogenous hemins made it possible to generate the hemH1 and hemH2 double mutant in MR-1, but not in PV-4. Under aerobic condition, exogenous hemins were required for the growth of MR-1ΔhemH1ΔhemH2, which also overproduced extracellular PPIX. These results suggest that heme is essential for aerobic growth of Shewanella species and MR-1 could also uptake hemin for biosynthesis of essential cytochrome(s) and respiration. Besides, the exogenous hemin mediated CymA cytochrome maturation and the cellular KatB catalase activity. Both hemH paralogues were transcribed in wild-type MR-1, and the hemH2 transcription was remarkably up-regulated in MR-1ΔhemH1 mutant to compensate for the loss of hemH1. The periplasmic glutathione peroxidase gene pgpD, located in the same operon with hemH2, and a large gene cluster coding for iron, heme (hemin) uptake systems are absent in the PV-4 genome. CONCLUSION: Our results indicate that the genetic divergence in gene content and gene expression between these Shewanella species, accounting for the phenotypic difference described here, might be due to their speciation and adaptation to the specific habitats (iron-rich deep-sea vent versus iron-poor freshwater) in which they evolved and the generated mutants could potentially be utilized for commercial production of PPIX.

Long-term changes in nutrient regimes and their ecological effects in the Bohai Sea, China.

The nutrient regime has changed significantly in the Bohai Sea (BS) during the past six decades because of anthropogenic perturbations. Specifically, the concentration of DIN increased by about 7-fold from the end of the 1950s to the mid-2010s, while DIP and DSi concentrations decreased from the end of the 1950s to the beginning of the 1990s, and have since increased again. Unsynchronized changes in nutrient levels have led to changes in the nutrients structure, which has caused a series of ecological effects. Phytoplankton biomass increased by 6-fold from the 1960s to the mid-2010s. Additionally, phytoplankton composition shifted from a diatom-dominated to a dinoflagellate-dominated system, and the dominant species of macrozoobenthos changed. Red tides rarely occurred before the 1980s, but have occurred periodically and frequently since the 1990s. Finally, the BS ecosystem has shifted from an N-limited oligotrophic state before the 1990s to a potentially P-limited eutrophic state.

Modeling nitrogen and phosphorus export with InVEST model in Bosten Lake basin of Northwest China.

Bosten Lake is an important region of Northwest China that has transformed from a freshwater lake to a saltwater lake since the 1970s. The water quality in the Bosten Lake basin is important for social and economic development, and nitrogen (N) and phosphorus (P) are the key indicators of water quality. The land use data, precipitation data and Digital Elevation Model (DEM) data with the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model were used to simulate the N and P exports of the Bosten Lake basin. The spatial and temporal dynamics of nitrogen and phosphorus exports, and the response of nitrogen and phosphorus exports to land use change and precipitation change were analyzed between 2000 and 2015. The results show that the amount of N and P exports increased during 2000-2015, and the N and P exports are mainly distributed around Bosten Lake. The N and P exports are greatly affected by cultivated land, built-up areas and grassland, while they are less affected by other land use types. The high precipitation areas with small exports of N and P are mainly distributed in mountain areas, while small precipitation areas with large exports of N and P are distributed in plains where the cultivated land and built-up areas are concentrated. The InVEST model can be used in Northwest China, and the statistical downscaling of reanalysis precipitation data can be used in the InVEST model to improve the simulation accuracy in the data scarce regions of Northwest China.