Microplastics Biodegradation by Estuarine and Landfill Microbiomes.

Plastic pollution poses a worldwide environmental challenge, affecting wildlife and human health. Assessing the biodegradation capabilities of natural microbiomes in environments contaminated with microplastics is crucial for mitigating the effects of plastic pollution. In this work, we evaluated the potential of landfill leachate (LL) and estuarine sediments (ES) to biodegrade polyethylene (PE), polyethylene terephthalate (PET), and polycaprolactone (PCL), under aerobic, anaerobic, thermophilic, and mesophilic conditions. PCL underwent extensive aerobic biodegradation with LL (99 ± 7%) and ES (78 ± 3%) within 50-60 days. Under anaerobic conditions, LL degraded 87 ± 19% of PCL in 60 days, whereas ES showed minimal biodegradation (3 ± 0.3%). PE and PET showed no notable degradation. Metataxonomics results (16S rRNA sequencing) revealed the presence of highly abundant thermophilic microorganisms assigned to Coprothermobacter sp. (6.8% and 28% relative abundance in anaerobic and aerobic incubations, respectively). Coprothermobacter spp. contain genes encoding two enzymes, an esterase and a thermostable monoacylglycerol lipase, that can potentially catalyze PCL hydrolysis. These results suggest that Coprothermobacter sp. may be pivotal in landfill leachate microbiomes for thermophilic PCL biodegradation across varying conditions. The anaerobic microbial community was dominated by hydrogenotrophic methanogens assigned to Methanothermobacter sp. (21%), pointing at possible syntrophic interactions with Coprothermobacter sp. (a H2-producer) during PCL biodegradation. In the aerobic experiments, fungi dominated the eukaryotic microbial community (e.g., Exophiala (41%), Penicillium (17%), and Mucor (18%)), suggesting that aerobic PCL biodegradation by LL involves collaboration between fungi and bacteria. Our findings bring insights on the microbial communities and microbial interactions mediating plastic biodegradation, offering valuable perspectives for plastic pollution mitigation.

Acidification Offset Warming-Induced Increase in N2O Production in Estuarine and Coastal Sediments.

Global warming and acidification, induced by a substantial increase in anthropogenic CO2 emissions, are expected to have profound impacts on biogeochemical cycles. However, underlying mechanisms of nitrous oxide (N2O) production in estuarine and coastal sediments remain rarely constrained under warming and acidification. Here, the responses of sediment N2O production pathways to warming and acidification were examined using a series of anoxic incubation experiments. Denitrification and N2O production were largely stimulated by the warming, while N2O production decreased under the acidification as well as the denitrification rate and electron transfer efficiency. Compared to warming alone, the combination of warming and acidification decreased N2O production by 26 ± 4%, which was mainly attributed to the decline of the N2O yield by fungal denitrification. Fungal denitrification was mainly responsible for N2O production under the warming condition, while bacterial denitrification predominated N2O production under the acidification condition. The reduced site preference of N2O under acidification reflects that the dominant pathways of N2O production were likely shifted from fungal to bacterial denitrification. In addition, acidification decreased the diversity and abundance of nirS-type denitrifiers, which were the keystone taxa mediating the low N2O production. Collectively, acidification can decrease sediment N2O yield through shifting the responsible production pathways, partly counteracting the warming-induced increase in N2O emissions, further reducing the positive climate warming feedback loop.

Metagenomics-Based Microbial Ecological Community Threshold and Indicators of Anthropogenic Disturbances in Estuarine Sediments.

Assessing the impacts of cumulative anthropogenic disturbances on estuarine ecosystem health is challenging. Using spatially distributed sediments from the Pearl River Estuary (PRE) in southern China, which are significantly influenced by anthropogenic activities, we demonstrated that metagenomics-based surveillance of benthic microbial communities is a robust approach to assess anthropogenic impacts on estuarine benthic ecosystems. Correlational and threshold analyses between microbial compositions and environmental conditions indicated that anthropogenic disturbances in the PRE sediments drove the taxonomic and functional variations in the benthic microbial communities. An ecological community threshold of anthropogenic disturbances was identified, which delineated the PRE sediments into two groups (H and L) with distinct taxa and functional traits. Group H, located nearshore and subjected to a higher level of anthropogenic disturbances, was enriched with pollutant degraders, putative human pathogens, fecal pollution indicators, and functional traits related to stress tolerance. In contrast, Group L, located offshore and subjected to a lower level of anthropogenic disturbances, was enriched with halotolerant and oligotrophic taxa and functional traits related to growth and resource acquisition. The machine learning random forest model identified a number of taxonomic and functional indicators that could differentiate PRE sediments between Groups H and L. The identified ecological community threshold and microbial indicators highlight the utility of metagenomics-based microbial surveillance in assessing the adverse impacts of anthropogenic disturbances in estuarine sediments, which can assist environmental management to better protect ecosystem health.

River-estuary continuum highlighted by variabilities in carbon and nitrogen stable isotope ratios of the catadromous eel Anguilla japonica.

Estuaries exhibit high physicochemical variability and the properties of estuaries and the constituent segments are not yet systematically understood. This study aims to reveal the spatial heterogeneity of predominant organic sources using carbon and nitrogen stable isotope ratios (δ13C and δ15N, respectively) of Japanese eels (Anguilla japonica), one of the ideal natural samplers. In the Miyakoda River, Japan, our study site, the effectiveness of eel δ13C and δ15N values as standard indices of predominant organic sources was tested by employing the River Continuum Concept. This study then extended the application of these indices to the estuary, i.e., the Hamana Lake system, into which the Miyakoda River flows. Once in the upper estuary, eel δ13C and δ15N values became high, with the latter peaking in this river-estuary continuum, indicating that artificial labile subsidies (nutrients and organic matter) with high δ15N values were rapidly assimilated into the food web. Eel δ15N values decreased again in the middle estuary. Nevertheless, the influence of terrestrial organic subsidies extended into this segment, as evidenced by the low δ13C values of eels. These results suggest that refractory organic matter with low δ15N values, such as plant-derived ones, is slowly assimilated into the food web in the downstream estuarine segments. The higher δ13C values in the lower estuary suggested that the contribution of eelgrass or macroalgae occurred in addition to benthic microalgae. Thus, our results emphasize the need to consider the multiple energy flows to understand the estuary as a continuum.

Picocyanobacterial-bacterial interactions sustain cyanobacterial blooms in nutrient-limited aquatic environments.

Cyanobacterial blooms (CBs) and concomitant water quality issues in oligotrophic/mesotrophic waters have been recently reported, challenging the conventional understanding that CBs are primarily caused by eutrophication. To elucidate the underlying mechanism of CBs in nutrition-deficient waters, the changes in Chlorophyll a (Chl-a), cyanobacterial-bacterial community composition, and certain microbial function in Qingcaosha Reservoir, the global largest tidal estuary storage reservoir, were analyzed systematically and comprehensively after its pilot run (2011-2019) in this study. Although the water quality was improved and stabilized, more frequent occurrences of bloom level of Chl-a (>20 µg L-1) in warm seasons were observed during recent years. The meteorological changes (CO2, sunshine duration, radiation, precipitation, evaporation, and relative humidity), water quality variations (pH, total organic carbon content, dissolved oxygen, and turbidity), accumulated sediments as an endogenous source, as well as unique estuarine conditions collectively facilitated picocyanobacterial-bacterial coexistence and community functional changes in this reservoir. A stable and tight co-occurrence pattern was established between dominant cyanobacteria (Synechococcus, Cyanobium, Planktothrix, Chroococcidiopsis, and Prochlorothrix) and certain heterotrophic bacteria (Proteobacteria, Actinobacteria, and Bacteroidetes), which contributed to the remineralization of organic matter for cyanobacteria utilization. The relative abundance of chemoorganoheterotrophs and bacteria related to nitrogen transformation (Paracoccus, Rhodoplanes, Nitrosomonas, and Zoogloea) increased, promoting the emergence of CBs in nutrient-limited conditions through enhanced nutrient recycling. In environments with limited nutrients, the interaction between photosynthetic autotrophic microorganisms and heterotrophic bacteria appears to be non-competitive. Instead, they adopt complementary roles within their ecological niche over long-term succession, mutually benefiting from this association. This long-term study confirmed that enhanced nutrient cycling, facilitated by cyanobacterial-bacterial symbiosis following long-term succession, could promote CBs in oligotrophic aquatic environments devoid of external nutrient inputs. This study advances understanding of the mechanisms that trigger and sustain CBs under nutritional constraints, contributing to developing more effective mitigation strategies, ensuring water safety, and maintaining ecological balance.

Enhancement of per- and Polyfluoroalkyl Substances (PFAS) quantification on surface waters from marinas in the douro river, Portugal.

PFAS, known as "forever" compounds, are prevalent in various environments, including soils and aquatic systems, due to extensive usage. Surface waters in several European countries, especially marinas and ports with high boat traffic, require further study as potential contamination sources. Reliable methods for the extraction and quantification of these emergent compounds are essential. This study aimed to improve an existent solid phase extraction method to analyse marinas and ports' surface waters with variable salinities (2, 9 and 17 PSU). The objectives were to: 1) optimise the solid phase extraction method, considering matrix salinity effects and cross-contaminations, 2) validate the extraction and quantification method of 18 EPA 537.1 PFAS in estuarine surface waters, using the Ultra-High Performance Liquid Chromatography - Quadrupole Time - Of - Flight - Tandem Mass spectrometry, and 3) apply the optimised method for PFAS quantification in three Portuguese marinas. All ICH criteria were successfully validated considering 9 PSU. Limits of quantification ranged from 117.80 ng/L to 385 ng/L, except for PFHpA (645.85 ng/L). PFAS levels (PFOA, HFPO-DA, PFBS, PFHxS and PFOS) were relatively low, reaching a maximum of 0.32 ng/L only for the PFOA. In Freixo marina, total average concentrations were slightly higher (∑PFAS = 1.02 ng/L) when compared to the ones found in Cais da Ribeira Port (∑PFAS = 0.94 ng/L) and Afurada marina (∑PFAS = 0.81 ng/L). PFOS concentrations are below the limit values set by the Environmental Quality Standards (36000 ng/L of PFOS for inland surface water, respectively), similar to other Portuguese river studies. This study enabled the development of a precise and reliable extraction and quantification method to quantify PFAS in estuarine surface waters, particularly from marinas. This method can be readily applied to analyse PFAS in other estuarine samples.

Haplosporidium nelsoni and Perkinsus marinus occurrence in waters of Great Bay Estuary, New Hampshire.

In Great Bay Estuary, New Hampshire, USA, Haplosporidium nelsoni and Perkinsus marinus are 2 active pathogens of the eastern oyster Crassostrea virginica (Gmelin), that cause MSX (multinucleated sphere with unknown affinity 'X') and dermo mortalities, respectively. Whereas studies have quantified infection intensities in oyster populations and determined whether these parasites exist in certain planktonic organisms, no studies thus far have examined both infectious agents simultaneously in water associated with areas that do and do not have oyster populations. As in other estuaries, both organisms are present in estuarine waters throughout the Bay, especially during June through November, when oysters are most active. Waters associated with oyster habitats had higher, more variable DNA concentrations from these pathogenic organisms than waters at a non-oyster site. This finding allows for enhanced understanding of disease-causing organisms in New England estuaries, where oyster restoration is a priority.

Pharmacokinetic disposition of marbofloxacin after intramuscular administration in estuarine crocodiles (Crocodylus porosus).

To date, the pharmacokinetics of fluoroquinolones in estuarine crocodiles (Crocodylus porosus) have been reported for enrofloxacin but not for marbofloxacin (MBF), which is a broad-spectrum antibiotic used only in veterinary medicine. This study investigated the pharmacokinetics of MBF after intramuscular administration at two difference dosages (2 and 4 mg/kg body weight) in estuarine crocodiles and estimated pharmacokinetic/pharmacodynamic (PK/PD) surrogate parameters for the optimization of dosage regimens. Ten treated estuarine crocodiles were divided into two groups (n = 5) using a randomization procedure according to a parallel study design. Blood samples were collected at assigned times up to 168 h. MBF plasma samples were cleaned up using liquid-liquid extraction and analyzed using a validated high-performance liquid chromatography method with fluorescence detection. A non-compartment approach was used to fit the plasma concentration of MBF vs time curve for each crocodile. The plasma concentrations of MBF were quantifiable for up to 168 h in both groups. The elimination half-life values of MBF were long (33.99 and 39.28 h for 2 and 4 mg/kg, respectively) with no significant differences between the groups. The average plasma protein binding of MBF was 30.85%. According to the surrogated PK/PD parameter (AUC0-24 -to-MIC ratio >100-125), the 2 and 4 mg/kg dosing rates should be effective for bacteria with MIC values lower than 0.125 µg/mL and 0.35 µg/mL, respectively.

Histological structure of the digestive tract, liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland.

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is in the secondary trophic level with a carnivorous nature. Studies on digestive system will help us further identify the niche of this species in the food web/food chain. The present study therefore aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained using beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall comprised four layers, namely mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal oesophagus. The stomach had many gastric folds, with height and width being 649.76 ± 85.15 and 370.30 ± 68.56 µm, respectively. Gastric glands were found in the anterior stomach but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-developed secretory granules of varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of the goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge of the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species.

Life cycles and challenges for fish species that breed in South African estuaries.

The literature currently recognizes four guilds of estuarine resident fish species, namely solely estuarine, estuarine and marine, estuarine and freshwater, and estuarine migrant. In this review the life cycles of actual representatives from these four guilds are assessed to determine whether the current definitions, which have never been formally tested, are appropriate to fish species resident in South African estuaries. Detailed information and diagrammatic life cycles are provided for the selected species covered by this review. A potential new estuarine resident guild category is also identified, namely, those taxa that are primarily estuarine but also have subpopulations recorded in both adjacent marine and freshwater habitats. The full range of reproductive characteristics employed by estuary resident species is examined, ranging from live bearers, pouch and nest brooders, to a suite of oviparous taxa that attach their ova to estuarine rocks, shells, and submerged vegetation, all of which assists with larval retention within the estuarine environment. The small size and early reproductive maturity of most estuarine resident species is highlighted, with reduced vulnerability to predation in shallow, sheltered, often turbid estuary waters offering considerable protection during spawning events when compared to the open ocean. In addition, these small fish would not have to move considerable distances at any stage of their life cycle, since egg, larval, juvenile, and adult stages all occur in the same place. The existence of contingent subpopulations within many estuarine resident species is noted, physico-chemical stresses on these species are highlighted, and the eurytopic nature of these small fish taxa emphasized.

Interdecadal changes in ichthyofauna in a tropical bay with high anthropogenic influences: functional stability despite turnover predominance.

Functional characteristics of species are of great importance for understanding their roles in ecosystems and can be used to detect long-term chances in the environment. We evaluated temporal changes (1983-1985 and 2017-2019) in taxonomic and functional indices of the fish fauna in shallow areas of a tropical bay heavily impacted by anthropogenic activities in recent decades. The hypothesis that functional indices change over time as a result of environmental degradation was tested. Our results showed a significant decrease in species richness and abundance over time, and in functional richness, while others functional diversity indices (divergency, evenness, and originality) remained stable. Thirteen functional groups were detected, some of which contained only one species, raising concerns about the loss of ecosystem functions due to ongoing changes. We also observed an increase in beta diversity over time, which may be the result of a decrease in local richness without leading to regional extinctions. Turnover was the most important process in structuring the fish fauna at the evaluated time scale. The relative stability of the functional structure and the higher levels of turnover seem to be related to the dominance of functional groups, within which species replace each other according to their responses to environmental filters that select for specific functional traits. Incorporating functional diversity indices and beta diversity variations in the fish community helped to enhance the existing information about this coastal system by offering improved estimates of biological diversity through diverse approaches. The predominance of turnover identified in the preset study suggests a dynamic and fluctuating species composition within the habitat. In this sense, habitat preservation should prioritize the protection of diverse habitats to accommodate a broad spectrum of species.

Differential modulation of digestive enzymes and energy reserves at different times after feeding in juveniles of the marine estuarine-dependent flatfish Paralichthys orbignyanus (Valenciennes, 1839).

Integrative studies are lacking on the responses of digestive enzymes and energy reserves in conjunction with morphological traits at distinct postprandial times in marine estuarine-dependent flatfishes of ecological and economic importance, such as Paralichthys orbignyanus. We determined total weight (TW), hepato-somatic index (IH), activities of digestive enzymes in the intestine, and the concentration of energy reserves in the liver and the muscle at 0, 24, 72, and 360 h after feeding in juveniles of P. orbignyanus. Amylase activity decreased at 72 h (about 30%). Maltase, sucrose, and lipase activities reached peak at 24 h (67%, 600%, and 35%, respectively). Trypsin and aminopeptidase-N activities at 24 and 72 h, respectively, were lower than those at t = 0 (53% and 30%). A peak increase in the concentration of glycogen and triglycerides in the liver (24 h) (86% and 89%, respectively) occurred. In muscle, glycogen and triglyceride concentrations were unchanged at 24 h and higher at 72 and 360 h (100% and 60%). No changes were found in TW, IH, free glucose in the liver and muscle, and protein in the liver. The protein concentration in the muscle sharply increased at 24 and 360 h after feeding (60%). The results indicate a distinct and specific response of central components of carbohydrate, lipid, and protein metabolism that could be adjustments at the biochemical level upon periods of irregular feeding and even of long-term food deprivation inside coastal lagoons or estuaries. The distinct responses of digestive enzymes in the intestine and energy reserves in the liver and muscle suggest the differential modulation of tissue-specific anabolic and catabolic pathways that would allow the maintenance of physical conditions.

Population dynamics of the long-snouted seahorse (Hippocampus guttulatus Cuvier, 1829) in the Mar Menor coastal lagoon.

A 10-year monitoring program was developed to quantify the population dynamics of the long-snouted seahorse population in the Mar Menor coastal lagoon. Based on 985 underwater visual censuses, we estimated the long-snouted seahorse (Hippocampus guttulatus Cuvier, 1829) population size in the Mar Menor lagoon and its reduction in size in the last decades, as well as the effect of eutrophication crises in 2016 and 2019 on the species. The annual recruitment for the 2013-2020 period was estimated by comparing the relative abundance of early seahorse life stages in the ichthyoplankton. The density ranged from 0.0458 specimens/m3 at the beginning of the sampling period to 0.0004 at the end, showing a statistically significant difference between the three analyzed periods (Hgl=2 = 14.0, p = 0.001). The long-snouted seahorse population from the Mar Menor lagoon exemplifies the impact of fishing activities and human pressure, especially euxinic episodes and habitat destruction. As a result of this, the Mar Menor population has decreased from several million specimens to a few thousand, in only three decades. This species showed considerable resilience, the seahorse population began to recover once fishing activity stopped. In contrast, the long-snouted seahorse showed high vulnerability to habitat loss and an episodic flooding event. Adult seahorses showed preferences for highly complex habitats, especially Caulerpa prolifera-Cymodocea nodosa mixed meadows and habitats of high complexity and anthropogenic origin, such as harbors, jetties, or breakwaters. In contrast, juvenile seahorses preferred monotonous seabeds with low complexity, such as the sandy beds that are characteristic of the Mar Menor lagoon littoral.

Fish community structure and functional guild composition in an anthropogenically impacted, temporarily closed sandbar estuary.

This study investigates the fish assemblage in a temporarily-closed sandbar estuary along India's west coast, across different zones and seasons. Moderate species diversity (54 species), low species abundance, varying fish diversity from lower to upper estuarine gradient (higher counts in lower zones, and decreasing from middle to upper zones), and higher prevalence of marine migrants (estuarine use) and piscivorous species (feeding mode) were the significant characteristics of the estuary. Distinct spatial, seasonal, and estuarine mouth state-based variations were recorded in the estuary, based on diversity indices and count of taxa. Peak diversity and abundance were noted during the pre-monsoon, and during the open mouth state of the estuary. The entire estuarine gradient is anthropogenically impacted by a multitude of stressors, except at the estuarine mouth region, which is favored by marine connectivity. The fish assemblage structure in Poonthura estuary (PE) has thus far remained unaffected by anthropogenic disturbances. Nevertheless, growth and nursery function of the estuary have been significantly compromised. The predominance of juvenile fish in the ecosystem, and prevailing anthropogenic stressors from point and non-point sources underscore the necessity for long-term maintenance of the population of coastal species, as well as a need for developing and implementing urgent management strategies for this fragile ecosystem.

Warming and hypoxia reduce the performance and survival of northern bay scallops (Argopecten irradians irradians) amid a fishery collapse.

Warming temperatures and diminishing dissolved oxygen (DO) concentrations are among the most pervasive drivers of global coastal change. While regions of the Northwest Atlantic Ocean are experiencing greater than average warming, the combined effects of thermal and hypoxic stress on marine life in this region are poorly understood. Populations of the northern bay scallop, Argopecten irradians irradians across the northeast United States have experienced severe declines in recent decades. This study used a combination of high-resolution (~1 km) satellite-based temperature records, long-term temperature and DO records, field and laboratory experiments, and high-frequency measures of scallop cardiac activity in an ecosystem setting to quantify decadal summer warming and assess the vulnerability of northern bay scallops to thermal and hypoxic stress across their geographic distribution. From 2003 to 2020, significant summer warming (up to ~0.2°C year-1 ) occurred across most of the bay scallop range. At a New York field site in 2020, all individuals perished during an 8-day estuarine heatwave that coincided with severe diel-cycling hypoxia. Yet at a Massachusetts site with comparable DO levels but lower daily mean temperatures, mortality was not observed. A 96-h laboratory experiment recreating observed daily temperatures of 25 or 29°C, and normoxia or hypoxia (22.2% air saturation), revealed a 120-fold increased likelihood of mortality in the 29°C-hypoxic treatment compared with control conditions, with scallop clearance rates also reduced by 97%. Cardiac activity measurements during a field deployment indicated that low DO and elevated daily temperatures modulate oxygen consumption rates and likely impact aerobic scope. Collectively, these findings suggest that concomitant thermal and hypoxic stress can have detrimental effects on scallop physiology and survival and potentially disrupt entire fisheries. Recovery of hypoxic systems may benefit vulnerable fisheries under continued warming.

Sinisalibacter aestuarii sp. nov., isolated from estuarine sediment of the Arakawa River.

A Gram-stain-negative, rod-shaped, non-motile and strictly aerobic bacterium, which showed biofilm-forming ability on polystyrene, designated as strain B-399T, was isolated from the estuarine sediment of the Arakawa River near Tokyo Bay. It grew at pH 6.0-8.5, at 15-35 °C and in the presence of 0-7.5 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B-399T was clustered in the genus Sinisalibacter and has 96.94 % sequence similarity to Sinisalibacter lacisalsi X12M-4T, which was the only validly described species in this genus. On the basis of our genome sequencing analyses, the average nucleotide identity and digital DNA-DNA hybridization values between strains B-399T and S. lacisalsi X12M-4T were 79.54 and 22.30 %, respectively, which confirms that strain B-399T represents a novel species of the genus Sinisalibacter. The draft genome size and the DNA G+C content of strain B-399T were 4.12 Mb and 65.2 mol%, respectively. The major fatty acids (>10 %) of strain B-399T were C16 : 0, summed feature 8 (C18 : 1 ω6c and/or C18 : 1 ω7c) and C19 : 0 cyclo ω8c. The polar lipids were phosphatidylcholine, phosphatidylglycerol, an unidentified phospholipid, an unidentified aminolipid and unidentified lipids. The respiratory quinone was Q-10. These chemotaxonomic features were almost coincident with those of the genus Sinisalibacter. Therefore, strain B-399T should be classified as representing a new species of the genus Sinisalibacter, for which the name Sinisalibacter aestuarii sp. nov. is proposed. The type strain is B-399T (=NBRC 115629T=DSM 114148T).

Spatiotemporal Dynamics of Bacterial Taxonomic and Functional Profiles in Estuarine Intertidal Soils of China Coastal Zone.

Bacteria play an important role in regulating carbon (C), nitrogen (N), and sulfur (S) in estuarine intertidal wetlands. To gain insights into the ecological and metabolic modes possessed by bacteria in estuarine intertidal wetlands, a total of 78 surface soil samples were collected from China's coastal intertidal wetlands to examine the spatial and seasonal variations of bacterial taxonomic composition, assembly processes, and ecological system functions through shotgun metagenomic and 16S rRNA gene sequencing. Obvious spatiotemporal dynamic patterns in the bacterial community structure were identified, with more pronounced seasonal rather than spatial variations. Dispersion limitation was observed to act as a critical factor affecting community assembly, explaining approximately half of the total variation in the bacterial community. Functional bacterial community structure exhibited a more significant latitudinal change than seasonal variability, highlighting that functional stability of the bacterial communities differed with their taxonomic variability. Identification of biogeochemically related links between C, N, and S cycles in the soils showed the adaptive routed metabolism of the bacterial communities and the strong interactions between coupled metabolic pathways. Our study broadens the insights into the taxonomic and functional profiles of bacteria in China's estuarine intertidal soils and helps us understand the effects exerted by environmental factors on the ecological health and microbial diversity of estuarine intertidal flats.

Bioaccumulation and Trophic Transfer of Organophosphate Flame Retardants and Their Metabolites in the Estuarine Food Web of the Pearl River, China.

The accumulation and trophodynamics of organophosphate flame retardants (OPFRs) and their metabolites were investigated in the estuarine food web of the Pearl River, China. The mean ∑OPFR concentration among the investigated species increased in the following order: fish [431 ± 346 ng/g lipid weight (lw)] < snail (1310 ± 621 ng/g lw) < shrimp (1581 ± 1134 ng/g lw) < crab (1744 ± 1397 ng/g lw). The di-alkyl phosphates (DAPs) of di-(n-butyl) phosphate (DNBP), bis(2-butoxyethyl) phosphate (BBOEP), and diphenyl phosphate (DPHP) were the most abundant metabolites, with concentrations same as or even higher than their corresponding parent compounds. The log bioaccumulation factors for most OPFRs were lower than 3.70, and significant biomagnification was only found for trisphenyl phosphate [TPHP, with the trophic magnification factors (TMFs) > 1]. The TMFs of OPFRs, except for TPHP and tributyl phosphate had a positive correlation with lipophilicity (log KOW, p ≤ 0.05) and a negative correlation with the biotransformation rate (log KM, p ≤ 0.05). The mean TMF > 1 was observed for all of the OPFR metabolites based on the bootstrap regression method. The "pseudo-biomagnification" of OPFR metabolites might be attributed to the biotransformation of OPFRs in organisms at high trophic levels.

Increased Nitrogen Loading Facilitates Nitrous Oxide Production through Fungal and Chemodenitrification in Estuarine and Coastal Sediments.

Estuarine and coastal environments are assumed to contribute to nitrous oxide (N2O) emissions under increasing nitrogen loading. However, isotopic and molecular mechanisms underlying N2O production pathways under elevated nitrogen concentration remain poorly understood. Here we used microbial inhibition, isotope mass balance, and molecular approaches to investigate N2O production mechanisms in estuarine and coastal sediments through a series of anoxic incubations. Site preference of the N2O molecule increased due to increasing nitrate concentration, suggesting the changes in N2O production pathways. Enhanced N2O production under high nitrate concentration was not mediated by bacterial denitrification, but instead was mainly regulated by fungal denitrification. Elevated nitrate concentration increased the contribution of fungal denitrification to N2O production by 11-25%, whereas it decreased bacterial N2O production by 16-33%. Chemodenitrification was also enhanced by high nitrate concentration, contributing to 13-28% of N2O production. Elevated nitrate concentration significantly mediated nirK-type denitrifiers structure and abundance, which are the keystone taxa driving N2O production. Collectively, these results suggest that increasing nitrate concentration can shift N2O production pathways from bacterial to fungal and chemodenitrification, which are mainly responsible for the enhanced N2O production and have widespread implications for N2O projections under ongoing nitrogen pollution in estuarine and coastal ecosystems.

Exploring the Complexities of Dissolved Organic Matter Photochemistry from the Molecular Level by Using Machine Learning Approaches.

Dissolved organic matter (DOM) sustains a substantial part of the organic matter transported seaward, where photochemical reactions significantly affect its transformation and fate. The irradiation experiments can provide valuable information on the photochemical reactivity (photolabile, photoresistant, and photoproduct) of molecules. However, the inconsistency of the fate of irradiated molecules among different experiments curtailed our understanding of the roles the photochemical reactions have played, which cannot be properly addressed by traditional approaches. Here, we conducted irradiation experiments for samples from two large estuaries in China. Molecules that occurred in irradiation experiments were characterized by the Fourier transform ion cyclotron resonance mass spectrometry and assigned probabilistic labels to define their photochemical reactivity. These molecules with probabilistic labels were used to construct a learning database for establishing a suitable machine learning (ML) model. We further applied our well-trained ML model to "un-matched" (i.e., not detected in our irradiation experiments) molecules from five estuaries worldwide, to predict their photochemical reactivity. Results showed that numerous molecules with strong photolability can be captured solely by the ML model. Moreover, comparing DOM photochemical reactivity in five estuaries revealed that the riverine DOM chemistry largely determines their subsequent photochemical transformation. We offer an expandable and renewable approach based on ML to compatibly integrate existing irradiation experiments and shed insight into DOM transformation and degradation processes.