Dissolved organic phosphorus promotes Cyclotella growth and adaptability in eutrophic tropical estuaries.

Dissolved organic phosphorus (DOP) is an important nutrient for phytoplankton growth in oligotrophic oceans. However, little is known about the impact of DOP on phytoplankton growth in eutrophic waters. In the present study, we conducted field monitoring as well as in situ and laboratory experiments in the Pearl River estuary (PRE). Field observations showed an increase in the nitrogen-to-phosphorus ratio and DOP in recent years in the PRE. The phytoplankton community was dominated by nanophytoplankton Cyclotella in the upper and middle estuary, with high concentrations of DOP and light limitation during the ebb stage of the spring to neap tide in summer. The relative abundance of Cyclotella in natural waters was higher after enrichment with estuarine water with a background of 0.40-0.46 µM DOP, even when dissolved inorganic phosphorus was sufficient (0.55-0.76 µM). In addition, the relative abundance of Cyclotella in natural waters was higher after enrichment with phosphoesters. Laboratory culture results also confirmed that phosphoesters can enhance the growth rate of Cyclotella cryptica. Our study highlights that Cyclotella can become the dominant species in estuaries with increased levels of phosphoesters and low and fluctuating light adaptability and under the joint effect of dynamic processes such as upwelling and tides. Our results provide new insights into the role of Cyclotella in biogeochemical cycles affected by DOP utilization and potential applications in relieving the hypoxia of tropical eutrophic estuaries.IMPORTANCEThis study provides evidence that Cyclotella can become the dominant species in estuaries with increased levels of phosphoesters and low and fluctuating light adaptability and under the joint effect of dynamic processes such as upwelling and tides. Our study provides new insights into the role of Cyclotella in biogeochemical cycles affected by dissolved organic phosphorus utilization, especially affected by anthropogenic inputs and climate change. Potential applications include relieving the hypoxia of tropical eutrophic estuaries.

Labyrinthulomycetes thrives in organic matter-rich waters with ecological partitioning in the Pearl River Estuary.

Labyrinthulomycetes play an important role in marine biogeochemical cycles, but their diversity, distribution patterns, and key regulatory factors remain unclear. This study measured the abundance and diversity of Labyrinthulomycetes in the Pearl River Estuary (PRE) to understand its distribution pattern and relationship with environmental and biological factors. The abundance of Labyrinthulomycetes ranged from 24 to 500 cells·mL-1, with an average of 144.37 ± 94.65 cells·mL-1, and its community composition showed obvious ecological partitioning in the PRE. The results of statistical analysis indicated that CDOM, salinity, and chlorophyll a contributed significantly (P < 0.01) to the community composition, explaining 46.59%, 11.34%, and 4.38% of the variance, respectively. The Labyrinthulomycetes distribution pattern combined with the niches of dominant species was revealed; low-salinity species mainly use terrigenous organic matter occupied dominant positions in the upper estuary and showed the highest abundance; moderate-salinity species that can use phytoplankton-derived resources thrived in the middle estuary; and seawater species dominated the lower estuary with the highest diversity but the lowest abundance. In addition, the results of phylogenetic tree analysis indicated that the existence of a novel lineage, and further study on the diversity and ecological functions of Labyrinthulomycetes is needed.IMPORTANCELabyrinthulomycetes play important roles in organic matter remineralization, carbon sinks, and food webs. However, the true diversity of Labyrinthulomycetes is still unclear due to limitations in isolation and culture methods. In addition, previous studies on their relationship with environmental factors are inconsistent and even contradictory, and it is speculated that their community composition may have spatial heterogeneity along the environmental gradient. In this study, the distribution pattern and key regulators of Labyrinthulomycetes in the PRE were revealed. Combining the niche of dominant species, it is suggested that salinity determines the spatial differences in Labyrinthulomycetes diversity, and the resources of substrate (terrestrial input or phytoplankton-derived) determine the dominant species, and its abundance is mainly determined by organic matter concentrations. Our study provided new information on the Labyrinthulomycetes diversity and verified the spatial heterogeneity of Labyrinthulomycetes community composition, providing reliable explanations for the inconsistencies in previous studies.

Alternatives Exert Higher Health Risks than Bisphenol A on Indo-Pacific Humpback Dolphins.

The detrimental effects of bisphenol (BP) exposure are a concern for vulnerable species, Indo-Pacific humpback dolphins (Sousa chinensis). To investigate the characteristics of BP profiles and their adverse impact on humpback dolphins, we assessed the concentrations of six BPs, including bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF), bisphenol AF (BPAF), bisphenol B (BPB), and bisphenol P (BPP) in blubber (n = 26) and kidney (n = 12) of humpback dolphins stranded in the Pearl River Estuary, China. BPS accounted for the largest proportion of the total bisphenols (∑BPs) in blubber (55%) and kidney (69%). The concentration of ∑BP in blubber was significantly higher than that in the kidney and liver. The EC50 values of five BPA alternatives were lower than those of BPA in humpback dolphin skin fibroblasts (ScSF) and human skin fibroblasts (HSF). ScSF was more sensitive to BPS, BPAF, BPB, and BPP than HSF. The enrichment pathway of BPA was found to be associated with inflammation and immune dysregulation, while BPP and BPS demonstrated a preference for genotoxicity. BPA, BPP, and BPS, which had risk quotients (RQs) > 1, were found to contribute to subhealth and chronic disease in humpback dolphins. According to the EC50-based risk assessment, BPS poses a higher health risk than BPA for humpback dolphins. This study successfully evaluated the risks of bisphenols in rare and endangered cetacean cell lines using a noninvasive method. More in vivo and in field observations are necessary to know whether the BPA alternatives are likely to be regrettable substitutions.

Numerical study of the upwelling and downwelling effects of artificial reefs along tidal cycles in the Pearl River Estuary.

Artificial reefs (ARs) are a preferred option for managers due to their distinctive hydrodynamic properties, which support a highly productive local ecosystem. However, the hydrodynamics characteristics of ARs in natural marine environments have not been conducted. Being the first to explore the spatiotemporal characteristic of flow fields around ARs along tidal cycles in marine environments, this study redefined the upwelling and downwelling of ARs, based on natural vertical velocities, and separated the upwelling into co-direction upwelling and re-direction upwelling, and the downwelling into co-direction downwelling and re-direction downwelling. This study simulated the flow field in the Wanshan ARs area of the Pearl River Estuary along the tidal cycles using the MIKE3-FM. Numerical simulations revealed that (1) co-direction upwelling and co-direction downwelling were the dominant components of the vertical flow field effects of ARs; (2) the areas sum of upwelling and downwelling were largest in the medium water column, with about 1.6 and 1.03 times as large as the bottom and surface water column, respectively, while the fluxes sum of the upwelling and downwelling were largest in bottom water column, with approximately 1.3 and 2.2 times larger than those in the middle and surface water columns; (3) the area and volume of the upwelling and downwelling gradually decreased along neap-spring tide, exhibited significantly negative correlations with current speeds; while the upwelling flux and downwelling flux gradually increased along neap-spring tide; exhibited a significantly positive correlation with current speed; (4) the effects of tide to upwelling and downwelling of AR are forced by the northward velocity of current speed, the net flux of upwelling and downwelling showed a significant positive correlation with the northward velocity of current speed (r = 0.94). These results could provide a reference for assessing the flow field effect of ARs and a guide for the configuration and management of ARs.

Ectobacillus ponti sp. nov., a novel bacterium isolated from Pearl River Estuary.

A Gram-staining-positive, aerobic, motile, and rod-shaped strain, designated SYSU M60031T, was isolated from a Pearl River Estuary sediment sample, Guangzhou, Guangdong, China. The isolate could grow at pH 5.0-8.0 (optimum, pH 7.0), 25-37 °C (optimum, 28 °C) and in the presence of 0-1 % (w/v) NaCl (optimum, 0 %). The predominant respiratory menaquinone of SYSU M60031T was MK-7. The cellular polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, one unidentified aminophospholipid, and one unidentified aminolipid. The major fatty acids (>10 % of total) were iso-C14 : 0, iso-C15 : 0, anteiso-C15 : 0, iso-C16 : 0, and C16 : 0. The genomic DNA G+C content was 51.2 %. Phylogenetic analyses based on 16S rRNA gene sequences and core genes indicated that strain SYSU M60031T belonged to the genus Ectobacillus and showed the highest sequence similarity to Ectobacillus funiculus NAF001T (96.16%), followed by Ectobacillus antri SYSU K30001T (95.08 %). Based on the phenotypic, genotypic, and phylogenetic data, strain SYSU M60031T should be considered to represent a novel species of the genus Ectobacillus, for which the name Ectobacillus ponti sp. nov. is proposed. The type strain of the proposed novel isolate is SYSU M60031T (=CGMCC 1.19243T =NBRC 115614T).

Impact of climate change on coastal water quality and its interaction with pollution prevention efforts.

The impact of climate change on nearshore coastal water quality and its interaction with pollution prevention efforts (e.g., the development of green and gray water infrastructure) still lack systematic investigation. This study performed a holistic analysis of the impact of climate change on the salinity and concentrations of total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl.a) in Shenzhen Bay between Shenzhen and Hong Kong, the two most developed megacities in South China, based on three-dimensional hydrodynamic and water quality modeling. The major study findings were as follows. First, Chl.a was the most sensitive parameter, and its bay-wide average concentration in 2100 was predicted to be approximately 13% and 46% higher than those in 2015 under mild and rapid climate change scenarios, respectively. Second, sea level rise was found to be a major driver of all four water quality parameters, while temperature and radiation mainly influenced Chl.a and precipitation mainly influenced nutrients. Third, water quality responses to climate change were highly heterogeneous over the bay. Even under a mild climate change scenario, the highest location-specific changes (2100 vs. 2015) in salinity and TN, TP and Chl.a concentrations were projected to be approximately 21%, 19%, 25%, and 65%, respectively. Fourth, changes in seasonal variation due to climate change may lead to an enhanced ecological risk of algal blooms. Finally, the effect of reducing TN and TP concentrations by proposed water infrastructure development was found to be significantly weakened (nearly 40% and 20% for TN and TP, respectively, under a mild climate change scenario), while the negative effect (i.e., increase in the Chl.a concentration) was notably accelerated. Regional cooperation is critical for protecting the water quality of the bay, particularly under climate change. The insights obtained in this study are applicable to other coastal water zones around the world with similar socioeconomic backgrounds and climatic conditions.

Source Apportionment, Hydrodynamic Influence, and Environmental Stress of Pharmaceuticals in a Microtidal Estuary with Multiple Outlets in South China.

Pharmaceutical residues in the environment are of great concern as ubiquitous emerging contaminants. This study investigated the presence of 40 pharmaceuticals in water and sediment of the Pearl River Estuary (PRE) in the wet season of 2020. Among psychiatric drugs, only diazepam was found in water samples while six of them were detected in the sediment. The Σantibiotics levels ranged from 6.18 to 35.9 ng/L and 2.63 to 140 ng/g dry weight in water and sediment samples, respectively. Fluoroquinolones and tetracyclines were found well settling in the outlet sediment, while sulfonamides could be released from disturbed sediment under stronger tidal wash-out conditions. After entering the marine waters, pharmaceuticals tended to deposit at the PRE mouth by the influence of the plume bulge and onshore invasion of deep shelf waters. Low ecological risks to the aquatic organisms and of causing antimicrobial resistance were identified. Likewise, hydrological modeling results revealed insignificant risks: erythromycin-H2O and sulfamethoxazole discharged through the outlets constituted 30.8% and 6.74% of their environmental capacity, respectively. Source apportionment revealed that pharmaceutical discharges through the Humen and Yamen outlets were predominantly of animal origin. Overall, our findings provide strategic insights on environmental regulations to further minimize the environmental stress of pharmaceuticals in the PRE.

Deinococcus aestuarii sp. nov. and Deinococcus aquaedulcis sp. nov., two novel resistant bacteria isolated from pearl river estuary.

Two novel species of the genus Deinococcus, designated SYSU M49105T and SYSU M42101T, were isolated from freshwater samples of the Pearl River estuary in Guangdong, China. Phylogenetic analysis using 16S rRNA gene sequence indicated that strains SYSU M49105T and SYSU M42101T showed the highest sequence similarities to Deinococcus aetherius JCM 11751 T (93.6%) and Deinococcus multiflagellatus NBRC 112888 T (97.3%), respectively. Cells of both strains were Gram-staining positive, aerobic, coccus-shaped, oxidase-negative and non-motile. The cell wall contained meso-diaminopimelic acid as their diagnostic diamino acid. MK-8 was the predominant respiratory quinone for both strains. The polar lipid profile of SYSU M49105T contained two unidentified phosphoglycolipids, nine unidentified glycolipids, and five unidentified polar lipids. SYSU M42101T had one unidentified phosphoglycolipid, nine unidentified glycolipids, one unidentified aminophospholipid and four unidentified polar lipids. The major fatty acids of strains SYSU M49105T and SYSU M42101T were summed feature 3 (C16:1 ω7c and/ or C16:1 ω6c) and C16:0. The G + C contents of the novel isolates based on genomic DNAs were 69.6% and 67.4%, respectively. On the basis of phenotypic, genotypic and phylogenetic data, strains SYSU M49105T and SYSU M42101T should be considered to represent two novel species in the genus Deinococcus, for which the names Deinococcus aestuarii sp. nov. and Deinococcus aquaedulcis sp. nov. were proposed with the type strains SYSU M49105T (= KCTC 43258 T = CGMCC 1.18609 T) and SYSU M42101T (= KCTC 43257 T = CGMCC 1.18614 T), respectively.

Roseomonas ponticola sp. nov., a novel bacterium isolated from Pearl River estuary.

A novel species of the genus Roseomonas, designated SYSU M41301T, was isolated from water sample of the Pearl River estuary in Guangdong, China. Polyphasic, taxonomic and phylogenomic analyses were used to determine the taxonomy position of the strain. Phylogenetic analysis using 16S rRNA gene sequence indicated that strain SYSU M41301T showed the highest sequence similarity to Roseomonas stagni KCTC 22213T (97.9 %) and Roseomonas riguiloci KCTC 23339T (96.4 %). The novel species could be differentiated from other species of the genus Roseomonas by its distinct phenotypic and genotypic characteristics. The isolate was Gram-staining-negative, aerobic, short rod-shape, oxidase-positive and non-motile. The predominant respiratory quinone was ubiquinone 8 (Q-8). The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, and one unidentified polar lipid. The major fatty acids (>10 % of total) were 11-methyl C18 : 1 ω7c, summed feature 3 (C16 : 1 ω7c and/ or C16 : 1 ω6c) and summed feature 8 (C18:  :1 ω7c and/or C18 : 1 ω6c). The G+C content of the novel isolate based on genomic DNA was 72.0 mol%. On the basis of phenotypic, genotypic and phylogenetic data, strain SYSU M41301T should be considered to represent a novel species in the genus Roseomonas, for which the name Roseomonas ponticola sp. nov. is proposed with the type strain SYSU M41301T (=KCTC 72726T=CGMCC 1.18613T).

Degradation and Aging of Terrestrial Organic Carbon within Estuaries: Biogeochemical and Environmental Implications.

Estuaries are action zones for organic carbon (OC) degradation and aging. These processes influence the nature of terrestrial OC (OCterr) export and the magnitude of OCterr burial in marginal seas, with important environmental implications such as CO2 release and hypoxia. In this study, we determined the contents and carbon isotopic compositions (13C and 14C) of bulk OC and fatty acids (FAs) as well as the sedimentological characteristics of suspended particulate matter (SPM) samples collected from two sites over four seasons and of surface sediment samples from three sites in the Pearl River estuary (PRE) to evaluate processes controlling OCterr degradation and aging along an estuarine gradient. We found that the abundance-weighted average C24-32FA 14C ages increased by an average of ∼1170 years for SPM and by an average of ∼3440 years in PR/PRE sediments, along the ∼60 km PRE transect. These increases in the FA age coincided with an 86% decrease in the corresponding mineral surface area-normalized FA loading along the sediment transport pathway, implying that selective degradation of labile and younger OC resulted in apparent OC aging. These measurements reveal an important shift in the nature of OC, with implications for biogeochemical cycling within estuaries and for regional environmental changes.

Characteristics of expanded polystyrene microplastics on island beaches in the Pearl River Estuary: abundance, size, surface texture and their metals-carrying capacity.

While expanded polystyrene (EPS) microplastics have been widely recognized as one of the most important components of plastic litter in the intertidal zones of the global ocean, our understanding of their environmental fate on island beaches is insufficient. In this study, we intended to reveal that the latest EPS microplastic pollution status on 5 island beaches in the Pearl River Estuary, China, by comprehensively assessing the abundance, distribution, size, surface texture and carrying capacity of heavy metals (Cd, As, Cr, Ni, Cu, Pb, Mn, Fe, Al). High level of EPS microplastic abundance ranged from 328 to 82,276 particles m-2 was found, with the highest abundance at Guishan Island and the lowest at Dong'ao Island. Spatial distribution of EPS microplastic abundance was significantly different among different islands. EPS microplastics in the size range of 1-2 mm were the most abundant. The content of heavy metals in EPS microplastics collected on the beaches was greater than that in the new EPS products. The average concentrations of heavy metals in EPS microplastics from 5 islands are Cd (0.27 ± 0.19 µg g-1), As (5.50 ± 3.84 µg g-1), Cr (14.9 ± 8.25 µg g-1), Cu (15.0 ± 7.66 µg g-1), Ni (17.2 ± 17.6 µg g-1), Pb (24.8 ± 7.39 µg g-1), Mn (730 ± 797 µg g-1), Fe (8340 ± 4760 µg g-1), and Al (9624 ± 6187 µg g-1), respectively. The correlation between heavy metals in EPS microplastics and sediments was better than that between heavy metals in EPS microplastics and seawater. The study results indicated that EPS microplastics could act as a carrier for the transport of heavy metals, which might pose a threat to biological and human health.

Fluorene degradation by Rhodococcus sp. A2-3 isolated from hydrocarbon contaminated sediment of the Pearl River estuary, China.

The pollution of polycyclic aromatic hydrocarbons was serious in sediments of the Pearl River estuary, China. A fluorene-degrading bacterium, strain A2-3, was isolated from hydrocarbon contaminated sediment of this estuary and identified as Rhodococcus sp. based on the analyses of 16S rRNA gene sequence and morphology. Rhodococcus sp. A2-3 can take naphthalene, p-Teropheny, fluorene, pyrene, salicylic acid, citric acid, acetic acid, diethyletheranhydrous, methanol or 4,4'-dibromodiphenyl ether as sole carbon source. 100% of 100 mg/L fluorene or 89% of 400 mg/L fluorene was removed in 7 days by strain A2-3 at 30 °C and pH 7.5. The strain A2-3 showed a high degradation efficiency of fluorene when pH values ranged from 5.5 to 8.5. The proposed pathway of fluorene catabolism by strain A2-3 was initially attacked by 3,4 dioxygenation. Our results suggested Rhodococcus sp. A2-3 can degrade PAHs under aerobic conditions and can function in bioremediation, particularly for weakly acid environment.

Roseibium aestuarii sp. nov., isolated from Pearl River Estuary.

A novel bacterium, designated strain SYSU M00256-3T, was isolated from a water sample collected from Pearl River Estuary at Guangzhou, PR China. Its taxonomic position was determined by using a polyphasic approach. Cells of the strain were Gram-staining-negative, motile, aerobic and rod-shaped with peritrichous flagella. It could grow at 15-45 °C, pH 4.0-10.0 and in the presence of 0-7.5 % (w/v) NaCl. The chemotaxonomic features of strain SYSU M00256-3T included ubiquinone-10 (Q-10) as the sole respiratory quinone; phosphatidylcholine, phosphatidylmethylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and an unidentified phospholipid as major polar lipids; summed feature 8 (C18 : 1 ω7c and C18 : 1 ω6c) as the predominant fatty acids (>70 %). On the basis of 16S rRNA gene sequence analysis, strain SYSU M00256-3T was most closely related to the type strains of Roseibium hamelinense CGMCC 1.12584T (97.7 %) and R. aquae CGMCC 1.12426T (97.2 %), R. sediminis KCTC 52373T (96.7 %), R. denhamense CGMCC 1.12583T (96.4 %). The average nucleotide identity (ANI) values between R. aestuarii SYSU M00256-3T and R. hamelinense CGMCC 1.12584T, R. aquae CGMCC 1.12426T, R. denhamense CGMCC 1.12583T and R. sediminis KCTC 52373T were 78.0, 78.2, 77.7 and 78.8, and the dDDH value is 20.0, 20.8, 20.1 and 20.6 correspondingly. Based on the analyses of the phenotypic, genotypic and phylogenetic characteristics, strain SYSU M00256-3T is characterized to represent a novel species of the genus Roseibium, for which the name Roseibium aestuarii sp. nov. is proposed. The type strain is SYSU M00256-3T (=NBRC 112946T=CGMCC 1.16156T).

Population dynamics of methanogens and methanotrophs along the salinity gradient in Pearl River Estuary: implications for methane metabolism.

Methane, a major greenhouse gas, plays an important role in global carbon cycling and climate change. Methanogenesis is identified as an important process for methane formation in estuarine sediments. However, the metabolism of methane in the water columns of estuaries is not well understood. The goal of this research was to examine the dynamics in abundance and community composition of methanogens and methanotrophs, and to examine whether and how they take part in methane metabolism in the water columns from the lower Pearl River (freshwater) to the coastal South China Sea (seawater). Quantitative PCR (qPCR) and high-throughput sequencing results showed that the abundance of methanogens decreased with increasing salinity, suggesting that growth of these methanogens in the Pearl River Estuary may be influenced by high salinity. Also, the methane concentration in surface waters was lower than that in near-bottom waters at most sites, suggesting sediment methanogens are a likely source of methane. In the estuarine mixing zone, significantly high methane concentrations existed with the presence of salt-tolerant methanogens (e.g., Methanomicrobiaceae, Methanocella, Methanosaeta and Methanobacterium) and methanotrophs (e.g., Methylocystis and Methylococcaceae), which were found in brackish habitats. Furthermore, a number of methanotrophic OTUs (from pmoA gene sequence data) had specific positive correlations with methanogenic OTUs (from mcrA gene sequence data), and some of these methanogenic OTUs were correlated with concentrations of particulate organic carbon (POC). The results indicate that methanotrophs and methanogens may be intimately linked in methane metabolism attached with particles in estuarine waters.

Ecological characteristics and teratogenic retinal determination of Cochlodinium geminatum blooms in Pearl River Estuary, South China.

Since 2006, harmful dinoflagellate blooms of Cochlodinium geminatum have infrequently occurred in the Pearl River Estuary, South China. During late October to early November in 2018, C. geminatum blooms occurred again in the region. To investigate the blooming mechanism in certain temporal conditions, we analysed the changes in the environmental parameters and phytoplankton community structure during and after the bloom. The results indicated that the water temperature and salinity had large impacts on the bloom. During the C. geminatum bloom, the phytoplankton community structure changed and the number of dominant species decreased. After the bloom, the species number and abundance of diatoms increased, as the species diversity was recovering. Retinal was detected in the field samples and cultured C. geminatum. It has been demonstrated to exist in some algae species (e.g. Cyanophyta, Chlorophyta, Bacillariophyta, and Euglenophyt), and our results indicates that such teratogens also exist in dinoflagellates. The highest concentration of retinal was detected during the bloom. This result indicates that the retinal content may accumulate during a bloom. Retinal has been demonstrated to be a teratogenic agent and may therefore present a potential risk to aquatic organisms during a bloom episode. This research provided more comprehensive information concerning the ecological influences of C. geminatum blooms.

Aestuariivirga litoralis gen. nov., sp. nov., a proteobacterium isolated from a water sample, and proposal of Aestuariivirgaceae fam. nov.

A Gram-stain-negative, non-motile, short rod and aerobic bacterium, designated strain SYSU M10001T, was isolated from a water sample collected from the coastal region of Pearl River Estuary, Guangdong Province, PR China. Strain SYSU M10001T showed optimal growth at 28 °C, pH 7.0 and in the absence of NaCl. Phylogenetic analyses based on 16S rRNA gene sequences and concatenation of 20 protein markers revealed a distinct lineage for strain SYSU M10001T in the order Rhizobiales. Strain SYSU M10001T showed highest 16S rRNA gene sequence similarities to Hyphomicrobium nitrativorans NL23T (91.1 %) and Hyphomicrobium hollandicum IFAM KB-677T (91.1 %). The respiratory ubiquinone was Q-8. The polar lipids of the strain comprised diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminophospholipid, two unidentified phospholipids and three unidentified lipids. The predominant cellular fatty acids identified were C19 : 0cyclo ω8c, summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. The G+C content was determined to be 65.5 % (genome). On the basis of differences in the phenotypic, physiological and biochemical characteristics, and results of the phylogenetic analyses, strain SYSU M10001T is proposed to represent a novel species in a novel genus for which the name Aestuariivirga litoralis gen. nov., sp. nov. The type strain of the type species Aestuariivirga litoralis is SYSU M10001T (=NBRC 112960T=KCTC 52945T). Besides, the distinct phylogenetic lineage and the distinct chemotaxonomic profile among the families in the order Rhizobiales indicated that strain SYSU M10001T should represent a new family for which the name Aestuariivirgaceae fam. nov. is proposed.

Impacts of Freshwater and Seawater Mixing on the Production and Decay of Virioplankton in a Subtropical Estuary.

Virioplankton is an important component of the aquatic ecosystem and plays multiple ecological and biogeochemical roles. Although the spatial and temporal distributions and dynamics of virioplankton have been well investigated in riverine and marine environments, little is known about the dynamics and environmental controlling mechanisms of virioplankton in estuaries. In this study, viral abundance, production and decay were examined in the Pearl River Estuary (PRE), one of the largest estuaries in China. The influences of freshwater and seawater mixing on viral ecological dynamics were evaluated with several cross-transplant experiments. In PRE, viral abundance, production and decay rates varied from 2.72 ± 0.09 to 27.5 ± 1.07 × 106 viruses ml-1, 7.98 ± 2.33 to 16.27 ± 2.85% h-1 and 0.80 ± 0.23 to 3.74 ± 0.98% h-1, respectively. When the riverine and marine microbial community were transferred into simulated brackish water, viral production rates were markedly inhibited by 83.8% and 47.3%, respectively. The decay of riverine and marine virioplankton was inhibited by 21.1% and 34.2%, respectively, in simulated brackish water. These results indicate change of estuarine environmental factors significantly alters the dynamics of riverine and marine virioplankton. In addition, the effects of mixing on viral production and decay differed between high- and low-fluorescence viruses. High-fluorescence viruses seemed more resistant to decay than low-fluorescence viruses, whereas the production of marine low-fluorescence viruses seemed more resistant to inhibition than that of marine high-fluorescence viruses. Together, these results provide new insights into the ecological dynamics of virioplankton in estuarine environments.

Aestuariisphingobium litorale gen. nov., sp. nov., a novel proteobacterium isolated from a water sample of Pearl River estuary.

Strain SYSU M10002T was isolated from a water sample collected from the coastal region of Pearl River estuary, Guangdong Province, southern China. The taxonomic position of the isolate was investigated by polyphasic taxonomic approaches. The isolate was found to be Gram-negative, non-motile, short rods and aerobic. The strain was able to grow at 14-37 °C, pH 6.0-10.0 and in the presence of up to 0.5% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain SYSU M10002T is a member of the family Sphingomonadaceae, with high sequence similarity to Sphingorhabdus buctiana T5T (95.1%). Overall genomic related indices between the genome of strain SYSU M10002T and those of related strains were low to moderate (AAI values < 64.3%; POCP values < 58%), indicating that strain SYSU M10002T represents a novel lineage within the family Sphinogomonadaceae. Strain SYSU M10002T contained homospermidine as its polyamine. The major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid, two unidentified phospholipids and an unidentified aminolipid. Ubiquinone Q-9 (44.9%) and Q-10 (43.2%) were the dominant respiratory quinones, along with a minor amount of Q-8 (11.9%). The predominant cellular fatty acids (> 10%) identified were summed feature 3 (C16:1ω7c and/or C16:1ω6c), summed feature 8 (C18:1ω7c) and C14:0 2-OH. The genomic DNA G+C content was 64.0%. Based on the analyses of the phenotypic, genotypic and phylogenetic characteristics, strain SYSU M10002T is determined to represent a novel species of a novel genus, for which the name Aestuariisphingobium litorale gen. nov., sp. nov. is proposed. The type strain of the species is SYSU M10002T (= KCTC 52944T = NBRC 112961T).

Mercury methylation-related microbes and genes in the sediments of the Pearl River Estuary and the South China Sea.

Methylmercury (MeHg) is a toxicant that mainly originates from in situ microbial methylation of inorganic mercury (Hg) in the environment and poses a severe health risk to the public. However, the characteristics of the Hg-methylating microbial community and its relationship with MeHg production in various environments remain to be understood. In the present study, Hg-methylating microbial communities and genes (hgcAB cluster) in the sediments of the Pearl River (PR), Pearl River Estuary (PRE) and South China Sea (SCS) were investigated at a large spatial scale using high-throughput sequencing-based approaches. The results showed that sulfur-reducing bacteria (SRB) and iron-reducing bacteria (IRB) were consistently the dominant microbial strains responsible for the methylation of inorganic Hg in all three regions investigated. The abundance and diversity of Hg-methylating communities and genes were both found to be higher in the PR sediments compared to that in the PRE and SCS sediments, and in good agreement with the spatial distribution of MeHg. Furthermore, a significant correlation was observed between the MeHg concentration and the abundance of both hgcA and hgcB genes in the sediments of the PR, PRE and SCS regions. Overall, the present study suggested that there was the presence of a close link between MeHg and Hg-methylating communities or genes in the ambient aquatic environment, which could be used to reflect the potential of in situ MeHg production.

Normalized Method for Land Surface Temperature Monitoring on Coastal Reclaimed Areas.

The temporal analysis of land surface temperature (LST) has generally been studied using data from the same season, as temperature varies greatly over time. However, the cloud cover in thermal remotely sensed images and the coarse resolution of passive sensor system significantly limits data availability of same season for comparative temporal analysis in many parts of the world. To address this problem, we propose a new method for temporal monitoring of surface temperature based on LST normalization (LSTn); deploying the average open water temperature to normalize LST when monitoring temporal change in the surface temperature of newly coastal reclaimed areas. This method was applied in the Lingding Bay area, Guangdong Province, Southern China. Original LST and LSTn values were calculated for years 1987, 1997, 2007, and 2017. In contrast to the original LST, results show that LSTn can reduce seasonal variability when monitoring temporal change in surface temperatures. Additionally, LSTn revealed pronounced differences between the temperature of impervious surfaces and other land cover types. This method offers more robust detection of surface urban heat islands than original LST in newly developed coastal areas.