Conformational Entropy as a Means to Control the Behavior of Poly(diketoenamine) Vitrimers In and Out of Equilibrium.

Control of equilibrium and non-equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg ), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network.

Poly(oxime-ester) Vitrimers with Catalyst-Free Bond Exchange.

Vitrimers are network polymers that undergo associative bond exchange reactions in the condensed phase above a threshold temperature, dictated by the exchangeable bonds comprising the vitrimer. For vitrimers, chemistries reliant on poorly nucleophilic bond exchange partners (e.g., hydroxy-functionalized alkanes) or poorly electrophilic exchangeable bonds, catalysts are required to lower the threshold temperature, which is undesirable in that catalyst leaching or deactivation diminishes its influence over time and may compromise reuse. Here we show how to access catalyst-free bond exchange reactions in catalyst-dependent polyester vitrimers by obviating conventional ester bonds in favor of oxime-esters. Poly(oxime-ester) (POE) vitrimers are synthesized using thiol-ene click chemistry, affording high stretchability and malleability. POE vitrimers are readily recycled with little degradation of their initial mechanical properties, suggesting exciting opportunities for sustainable plastics.

Microplastics in the Coral Reef Systems from Xisha Islands of South China Sea.

The impacts of microplastics on coral reefs are gaining attention due to findings that microplastics affect coral health. This work investigated the distribution and characteristics of microplastics in the seawater, fish, and corals in 3 atolls from the Xisha Islands of South China Sea. In the seawater samples, microplastics were detected in the outer reef slopes, reef flats, and lagoons with abundances ranging from 0.2 to 11.2, 1.0 to 12.2, and 1.0 to 45.2 items L-1, respectively. Microplastic abundance was 0-12.0 items individual-1 (0-4.7 items g-1) in fish and 1.0-44.0 items individual-1(0.02-1.3 items g-1) in coral. The predominant shape and polymer of microplastics in seawater, fish, and coral were fibrous rayon and polyethylene terephthalate (PET). Microplastic sizes primarily ranged from 20-330 µm in both the seawater and fish, while there were relatively more 1-5 mm microplastics in the corals. The shape, size, color, and polymer type distribution patterns of microplastics in seawater more closely resembled those in fish gills than those in fish gastrointestinal tracts or coral samples. This study shows that microplastics are abundant in these coral reef systems and they are captured by fish or "trapped" by corals.

Atomic Force Microscopy Nanomechanical Mapping Visualizes Interfacial Broadening between Networks Due to Chemical Exchange Reactions.

The interfacial broadening between two different epoxy networks having different moduli was nanomechanically mapped. The interfacial broadening of the two networks produced an interfacial zone having a gradient in the concentration and, hence, properties of the original two networks. This interfacial broadening of the networks leads to the generation of a new network with a segmental composition corresponding to a mixture of the original two network segments. The intermixing of the two, by nature of the exchange reactions, was on the segmental level. By mapping the time dependence of the variation in the modulus at different temperatures, the kinetics of the exchange reaction was measured and, by varying the temperature, the activation energy of the exchange reaction was determined.

Study on immobilization of marine oil-degrading bacteria by carrier of algae materials.

This study investigated the immobilizations with of bacteria two kinds of algal materials, Enteromorpha residue and kelp residue. The lipophilicity of them were compared by diesel absorption rates. The immobilization efficiency of Bacillus sp. E3 was measured to evaluate whether these carriers would satisfy the requirement for biodegradation of oil spills. The bacteria were immobilized through adsorption with the sterilized and non-sterilized carriers to compare the differences between the two treatments. Oil degradation rates were determined using gravimetric and GC-MS methods. Results showed the absorption rates of Enteromorpha residue and kelp residue for diesel were 411 and 273% respectively and remained approximately 105 and 120% after 2 h of erosion in simulated seawater system. After immobilized of Bacillus sp. E3, the oil degradation rates of them were higher than 65% after 21 days biodegradations. GC-MS analysis showed that two immobilizations degraded higher than 70% of the total alkane and the total PAHs, whereas the free bacteria degraded 63% of the total alkane and 66% the total PAHs. And the bacteria immobilized with the carriers degraded more HMW-alkanes and HMW-PAHs than the free bacteria. The bacteria immobilized by non-sterilized kelp residue showed a considerably higher degradation rate than that using sterilized kelp residue. A considerably higher cells absorption rate of immobilization was obtained when using kelp residue, and the preparation of immobilization was low cost and highly efficient. The experiments show the two algae materials, especially the kelp residue, present potential application in bioremediation of marine oil spills.

A pilot study suggests the correspondence between SAR202 bacteria and dissolved organic matter in the late stage of a year-long microcosm incubation.

SAR202 bacteria are abundant in the marine environment and they have been suggested to contribute to the utilization of recalcitrant organic matter (RDOM) within the ocean's biogeochemical cycle. However, this functional role has only been postulated by metagenomic studies. During a one-year microcosm incubation of an open ocean microbial community with lysed Synechococcus and its released DOM, SAR202 became relatively more abundant in the later stage (after day 30) of the incubation. Network analysis illustrated a high degree of negative associations between SAR202 and a unique group of molecular formulae (MFs) in phase 2 (day 30 to 364) of the incubation, which is empirical evidence that SAR202 bacteria are major consumers of the more oxygenated, unsaturated, and higher-molecular-weight MFs. Further investigation of the SAR202-associated MFs suggested that they were potentially secondary products arising from initial heterotrophic activities following the amendment of labile Synechococcus-derived DOM. This pilot study provided a preliminary observation on the correspondence between SAR202 bacteria and more resistant DOM, further supporting the hypothesis that SAR202 bacteria play important roles in the degradation of RDOM and thus the ocean's biogeochemical cycle.

Flexible, transparent, and sustainable cellulose-based films for organic solar cell substrates.

Cellulose, often considered a highly promising substitute for petroleum-based plastics, offers several compelling advantages, including abundant availability, cost-effectiveness, environmental friendliness, and biodegradability. However, its inherent highly crystalline structure and extensive hydrogen-bonded network pose challenges for processing and recycling. In this study, we introduce the concept of cellulose vitrimers (CVs), wherein dynamic bonds are incorporated to reconfigure the hydrogen-bonded network, resulting in a mechanically robust, highly transparent material. CVs exhibit exceptional malleability, thermal stability, and noteworthy resistance to water and solvents. Due to the dynamic bond disassociation, CVs can be effectively chemically recycled using a well-established "dissolution-and-reforming" process. Moreover, CVs have proven successful as flexible substrate materials for organic solar cells, outperforming traditional petroleum-based polyethylene naphthalate (PEN). Given these advantages, CVs have the potential to replace conventional petroleum-based materials as recyclable and environmentally friendly alternatives, particularly within the realm of electronic devices and displays.

Deep metagenomic sequencing unveils novel SAR202 lineages and their vertical adaptation in the ocean.

SAR202 bacteria in the Chloroflexota phylum are abundant and widely distributed in the ocean. Their genome coding capacities indicate their potential roles in degrading complex and recalcitrant organic compounds in the ocean. However, our understanding of their genomic diversity, vertical distribution, and depth-related metabolisms is still limited by the number of assembled SAR202 genomes. In this study, we apply deep metagenomic sequencing (180 Gb per sample) to investigate microbial communities collected from six representative depths at the Bermuda Atlantic Time Series (BATS) station. We obtain 173 SAR202 metagenome-assembled genomes (MAGs). Intriguingly, 154 new species and 104 new genera are found based on these 173 SAR202 genomes. We add 12 new subgroups to the current SAR202 lineages. The vertical distribution of 20 SAR202 subgroups shows their niche partitioning in the euphotic, mesopelagic, and bathypelagic oceans, respectively. Deep-ocean SAR202 bacteria contain more genes and exhibit more metabolic potential for degrading complex organic substrates than those from the euphotic zone. With deep metagenomic sequencing, we uncover many new lineages of SAR202 bacteria and their potential functions which greatly deepen our understanding of their diversity, vertical profile, and contribution to the ocean's carbon cycling, especially in the deep ocean.

Variation in Bacterial Community Structures and Functions as Indicators of Response to the Restoration of Suaeda salsa: A Case Study of the Restoration in the Beidaihe Coastal Wetland.

Microbes play an essential role in the restoration of degraded coastal wetlands. However, few studies have focused on the role of key bacteria in the restoration process. Here, Suaeda salsa was planted to recover the biodiversity in the degraded Beidaihe coastal wetland. We monitored omics and soil environmental factors to understand the complex relationship between the bacterial community and wetland health during the restoration period. After planting S. salsa in the degraded area, the soil quality was improved in the later stage of restoration (LPR). Bacterial α-diversity increased with restoration and was positively correlated with TOC. Proteobacteria is the dominant bacterial phylum during the restoration period, and Bacteroidetes, Planctomycetes, Gemmatimonadetes, and Acidobacteria were sensitive to the planting restoration. Random forest analysis picked 30 key OTUs, showing the key bacterial variation of successful restoration. The result indicated that the sum of the relative abundances of key bacterial OTUs was more than 2% in the health wetland. The ß-diversity showed that the growth of S. salsa reshaped the soil bacterial community structure and function in the LPR, which recovered to the level in the control area. Putative biogeochemical functions showed that symbionts and aromatic compound degradation were dominant bacterial functions in the growth period of S. salsa. Our study proposed a new indicator to assess wetland health and the planting restoration of S. salsa increased bacteria groups with the ability of symbionts and aromatic compound degradation in the Beidaihe coastal wetland. This study expanded our knowledge of coastal wetland restoration and its ecological contributions.

Atmospheric microplastics in the Northwestern Pacific Ocean: Distribution, source, and deposition.

Microplastic pollution is recognized as a ubiquitous global issue. However, limited information is available concerning microplastics in the marine air. Here we present the occurrence and distribution of atmospheric microplastics in the Northwestern Pacific Ocean, with abundance ranging from 0.0046 to 0.064 items/m3. The microplastics were in various shapes and polymer types, of which fibrous rayon (67%) and polyethylene terephthalate (PET, 23%) accounted for the majority. The atmospheric microplastics in the pelagic area showed higher abundance and smaller size compared to those in the nearshore area, indicating smaller-sized microplastics in the atmosphere might travel long distances over the ocean. The atmospheric microplastic distribution was not only affected by weather conditions but might also be related to the microplastic sources. The microplastic polymer types combined with the backward trajectory model analysis showed that atmospheric microplastics in the Northwestern Pacific Ocean mainly originated from the land and the adjacent oceanic atmosphere. Spearman's correlation coefficient of the relationship between the features of microplastics in the atmosphere and surface seawater tended to increase with increasing offshore distances. Our field-based research revealed that atmospheric microplastics were a non-negligible source of marine microplastic pollution.

Diversity and functions of quorum sensing bacteria in the root environment of the Suaeda glauca and Phragmites australis coastal wetlands.

The quorum sensing (QS) system plays a significant role in the bacteria-bacteria or plant-bacteria relationships through signal molecules. However, little is known about the distribution and functional diversity of QS bacteria in the root environment of Suaeda glauca and Phragmites australis in coastal wetlands. We explored the bacterial community by amplicon sequencing and isolated 1050 strains from the rhizosphere soil and root tissues of S. glauca and P. australis in northern China to investigate the bacterial community and AHL producers. AHL activity was found in 76 isolates, and 22 distinct strains were confirmed by 16S rRNA gene sequencing. A substantial number of AHL producers clustered in rhizobiales and sphingomonadale, which derived from the root tissues. AHL producers in the rhizosphere soil mostly belonged to rhodobacterales. The different taxa of AHL producers in the rhizosphere soil and root tissues resulted in a variation of AHL profiles that C6-HSL dominated the AHL profiles in root bacteria compared to the C8-HSL in rhizobacteria, implying different ecological roles for AHL producers in the rhizosphere soil and root tissues. Many AHL producers may form biofilms, and some can degrade DMSP and oil, demonstrating that QS bacteria in the root environment have a wide ecological roles. In our study, for one of the first times here, we explore the distribution and functional variety of AHL producers in the root environment of S. glauca-P. australis. This study expands current knowledge of the relationship between QS bacteria and coastal plants (S. glauca and P. australis), and vital roles of QS bacterial in maintaining the health of coastal wetlands.

Metagenomic evidence for the microbial transformation of carboxyl-rich alicyclic molecules: A long-term macrocosm experiment.

Carboxyl-rich alicyclic molecules (CRAMs) widely exist in the ocean and constitute the central part of the refractory dissolved organic matter (RDOM) pool. Although a consensus has been reached that microbial activity forms CRAMs, the detailed molecular mechanisms remain largely unexplored. To better understand the underlying genetic mechanisms driving the microbial transformation of CRAM, a long-term macrocosm experiment spanning 220 days was conducted in the Aquatron Tower Tank at Dalhousie University, Halifax, Canada, with the supply of diatom-derived DOM as a carbon source. The DOM composition, community structure, and metabolic pathways were characterised using multi-omics approaches. The addition of diatom lysate introduced a mass of labile DOM into the incubation seawater, which led to a low degradation index (IDEG) and refractory molecular lability boundary (RMLB) on days 1 and 18. The molecular compositions of the DOM molecules in the later incubation period (from day 120 to day 220) were more similar in composition to those on day 0, suggesting a rapid turnover of phytoplankton debris by microbial communities. Taxonomically, while Alpha proteobacteria dominated during the entire incubation period, Gamma proteobacteria became more sensitive and abundant than the other bacterial groups on days 1 and 18. Recalcitrant measurements such as IDEG and RMLB were closely related to the DOM molecules, bacterial community, and Kyoto encyclopaedia of Genes and Genomes (KEGG) modules, suggesting close associations between RDOM accumulation and microbial metabolism. KEGG modules that showed strong positive correlation with CRAMs were identified using a microbial ecological network approach. The identified KEGG modules produced the substrates, such as the acetyl-CoA or 3­hydroxy-3-methylglutaryl-CoA, which could participate in the mevalonate pathway to generate the precursor of CRAM analogues, isopentenyl-PP, suggesting a potential generation pathway of CRAM analogues in bacteria and archaea. This study revealed the potential genetic and molecular processes involved in the microbial origin of CRAM analogues, and thus indicated a vital ecological role of bacteria and archaea in RDOM production. This study also offered new perspectives on the carbon sequestration in the ocean.

Microplastics in four bivalve species and basis for using bivalves as bioindicators of microplastic pollution.

Microplastics in bivalves have caused widespread concern due to their potential health risk to humans. In this study, microplastics in the digestive systems of four locally cultured bivalve species (scallop Chlamys farreri, mussel Mytilus galloprovincialis, oyster Crassostrea gigas, and clam Ruditapes philippinarum) in Qingdao, China, were analyzed and detected in 233 out of 290 bivalve samples (80%) over four seasons. The microplastic abundance in four species of bivalves ranged between 0.5 and 3.3 items/individual or 0.3 and 20.1 items/g wet weight digestive system, with significant species-specific and region-specific differences but no season-specific differences. Microfiber was the most predominant shape of all microplastics found. Eighteen types of polymer with diameters between 7 and 5000 µm were identified by µ-FT-IR (505 of 587 suspected items identified as microplastics) with polyvinyl chloride (PVC) and rayon being the most abundant ones. Bivalves collected in summer contained more larger-sized microplastics. R. philippinarum accumulated more smaller-sized microplastics and showed different microplastic features compared with the other three species of bivalves. By comparing and analyzing the microplastic polymer types between each bivalve species and the ambient environment, microplastic in clam can best reflect the variability of microplastic polymer types in sediment among different areas. Mussels can reflect the variability of microplastic polymer types in water to an extent. Therefore, clam and mussel are recommended to serve as bioindicators for microplastic pollution in the sediment and water, respectively. The occurrence of microplastics pollution in bivalves worldwide is wide, and bivalves can act as the transporter of microplastics to humans. Our results suggest that bivalves have an important role as environmental bioindicators and the pollution of microplastics in bivalves needs attention.

An examination of the occurrence and potential risks of microplastics across various shellfish.

The ingestion of microplastics by shellfish pose a potential health risk for human via seafood consumption. This study investigated and compared the contamination levels and potential human health risks of microplastics in the digestive system of commercial shellfish from North (Qingdao) and South (Xiamen) China. Microplastics were detected in 70%-100% of shellfish samples from Qingdao and 70%-90% of shellfish samples from Xiamen, with abundances ranging from 1.2 to 4.1 items/individual (or 0.8-4.4 items/g, wet weight of digestive system) in shellfish from Qingdao and 1.3-6.0 items/individual (or 2.1-4.0 items/g) in shellfish from Xiamen. The microplastic composition was dominated by rayon and tended to be fibrous in shape, and white, black, and transparent in color. Microplastics <500 µm were the dominant size range, in which the size range of 100-200 µm was the most abundant size. Features of microplastics in the water-dwelling shellfish were different from those of the sediment-dwelling shellfish, and the microplastic features in the shellfish correlated with the sampling region, shellfish length, total wet body weight, and wet weight of the digestive system. Risk assessment results revealed that the potential human health risk posed by microplastics from the digestive system of commercial shellfish was higher in Qingdao than Xiamen.

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

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

Marine microplastic-associated bacterial community succession in response to geography, exposure time, and plastic type in China's coastal seawaters.

Microplastics have emerged as new pollutants in oceans. Nevertheless, information of the long-term variations in the composition of plastic-associated microbial communities in coastal waters remains limited. This study applied high-throughput sequencing to investigate the successional stages of microbial communities attached to polypropylene and polyvinyl chloride microplastics exposed for one year in the coastal seawater of China. The composition of plastisphere microbial communities varied remarkably across geographical locations and exposure times. The dominant bacteria in the plastisphere were affiliated with the Alphaproteobacteria class, particularly Rhodobacteraceae, followed by the Gammaproteobacteria class. Scanning electron microscopy analysis revealed that the microplastics showed signs of degradation. Microbial communities showed adaptations to plastisphere including more diverse microbial community and greater "xenobiotics biodegradation and metabolism" in metabolic pathway analysis. The findings elucidate the long-term changes in the community composition of microorganisms that colonize microplastics and expand the understanding of plastisphere microbial communities present in the marine environment.

Complete Genome Sequence of a Quorum-Sensing Bacterium, Oceanicola sp. Strain D3, Isolated from a Microplastic Surface in Coastal Water of Qingdao, China.

Oceanicola sp. strain D3 was isolated from the plastisphere of polyvinyl chloride (PVC) in coastal water of Qingdao, China. Here, we present the complete genome sequence of strain D3, which consists of a chromosome of 3,926,685 bp with a G+C content of 64.49% and 4,964 coding DNA sequences. This is the first report of a quorum-sensing (QS) system in an Oceanicola sp. strain.

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

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