Unraveling the nexus: Microplastics, antibiotics, and ARGs interactions, threats and control in aquaculture - A review

Synergistic effect of horizontal transfer of antibiotic resistance genes between bacteria exposed to microplastics and per/polyfluoroalkyl substances: An explanation from theoretical methods

Microplastics (MPs) and per/polyfluoroalkyl substances (PFASs), as emerging pollutants widely present in aquatic environments, pose a significant threat to human health through the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). Molecular dynamics simulations and machine learning can accurately capture the complex interactions between molecules. This study utilized them to identify the HGT risk between bacteria under MPs and PFASs stress. This study found that MPs and PFASs significantly increase the HGT risk between bacteria, up to 1.57 and 1.59 times, respectively. Notably, long-chain PFASs and perfluoroalkyl carboxylic acids increased the HGT risk by 1.38 and 1.40 times, respectively. Additionally, MPs primarily increase the HGT risk by enhancing hydrogen bonding interaction between key proteins in the HGT pathway and "active codons". The electronegativity and polarizability of PFASs critically influence the HGT risk, acting inversely and directly proportional, respectively. The HGT risk between bacteria under the combined stress from PP-MPs and PFASs exhibits a significant synergistic effect (synergistic effect value of 27.6), which markedly increases the HGT risk. Further analysis revealed that a smaller minimum distance and sharper RDF curve peaks between key proteins and "active codons" indicate higher HGT risk. This indicates that stronger interactions lead to higher HGT risk. This study identifies the characteristics of HGT risks between bacteria in aquatic environments under the individual and combined stresses from MPs and PFASs at the molecular level. It provides a theoretical basis for mitigating ARG transfer and comprehensively assessing the health risks posed by these emerging pollutants.

Phytoremediation of OTC-Cu/Zn contaminated sediment: Synergetic removal mechanism and microbial community response

Antibiotics and heavy metals (HMs) from aquiculture enter waters and eventually sink into sediments. However, sediments carrying excessive contaminants can become a source of contamination. Macrophytes are frequently employed to treat water contaminated with HMs due to their adaptability, rapid growth rate, and ability to extract contaminants. In this study, oxytetracycline (OTC), and copper (Cu)/zinc (Zn) were chosen to be the target contaminants of antibiotics and HMs in the sediment. A pot experiment was conducted to investigate the phytoremediation effect of two types of macrophytes, Canna indica and Iris pseudacorus. The removal percentages of OTC, Cu, and Zn range from 93.6 % to 97.6 %, 67.4-86.0 %, and 69.8-82.9 % from the sediment, respectively. Adding Cu/Zn facilitated the decomposition of OTC in the sediments, while the presence of OTC transformed Cu/Zn into a more stable form. Both macrophytes extracted HMs mainly through roots accumulation. Higher concentrations of bioavailable forms of Cu/Zn in sediments inhibited plant growth and development, while lower concentrations promoted that. The inhibitory of leaf chlorophyll a+b synthesis by various contaminant treatments showed that OTC>OTC-HMs>HMs and the stimulation of carotenoid synthesis indicated HMs≥OTC-HMs≥OTC. The dehydrogenase (DHA) activities, microbial diversity and abundance in sediment were severely inhibited by HMs, and the inhibition was alleviated by OTC-HMs with C. indica. Proteobacteria, Actinobacteria, and Firmicutes were the dominant bacterial phyla. This study expands the understanding of phytoremediation potential and outlines their physiological and microbial responses to combined antibiotics-HMs.

Comparative Study of Cell Nuclei Segmentation Based on Computational and Handcrafted Features Using Machine Learning Algorithms

Background: Nuclei segmentation is the first stage of automated microscopic image analysis. The cell nucleus is a crucial aspect in segmenting to gain more insight into cell characteristics and functions that enable computer-aided pathology for early disease detection, such as prostate cancer, breast cancer, brain tumors, and other diagnoses. Nucleus segmentation remains a challenging task despite significant advancements in automated methods. Traditional techniques, such as Otsu thresholding and watershed approaches, are ineffective in challenging scenarios. However, deep learning-based methods exhibit remarkable results across various biological imaging modalities, including computational pathology. Methods: This work explores machine learning approaches for nuclei segmentation by evaluating the quality of nuclei image segmentation. We employed several methods, including K-means clustering, Random Forest (RF), Support Vector Machine (SVM) with handcrafted features, and Logistic Regression (LR) using features derived from Convolutional Neural Networks (CNNs). Handcrafted features extract attributes like the shape, texture, and intensity of nuclei and are meticulously developed based on specialized knowledge. Conversely, CNN-based features are automatically acquired representations that identify complex patterns in nuclei images. To assess how effectively these techniques segment cell nuclei, their performance is evaluated. Results: Experimental results show that Logistic Regression based on CNN-derived features outperforms the other techniques, achieving an accuracy of 96.90%, a Dice coefficient of 74.24, and a Jaccard coefficient of 55.61. In contrast, the Random Forest, Support Vector Machine, and K-means algorithms yielded lower segmentation performance metrics. Conclusions: The conclusions suggest that leveraging CNN-based features in conjunction with Logistic Regression significantly enhances the accuracy of cell nuclei segmentation in pathological images. This approach holds promise for refining computer-aided pathology workflows, potentially leading to more reliable and earlier disease diagnoses.

A systematic review on aquaculture wastewater: Pollutants, impacts, and treatment technology

Aquaculture is the major way to solve the global food sacrcity. As the global population increases, the demand for aquaculture increases. Fish feed, drugs and chemicals, and metabolic waste or mortalities of aquatic organisms also increase, eventually resulting in the production of a large amount of aquaculture wastewater. These aquaculture discharges contain a variety of pollutants, such as conventional pollutants, organic compounds, heavy metals, and biological contaminants, inducing occupational hazards and risks, food security, the environment pollution. Proper wastewater treatment technologies are required to remove hazardous pollutants for minimizing their impacts on environmental and human health. Recirculating aquaculture systems, some biological and physicochemical methods have been applied to remove some pollutants from the aquaculture wastewater, but their efficiency in removing pollutants still requires to be further improved for achieving zero-waste discharge and ensuring sustainable aquaculture development. Meanwhile, sound regulation and legislation needs to be established for ensuring the normal operation of aquaculture industries and the standard discharge of wastewater. This review aims to provide comprehensive information of aquaculture wastewater for the researchers and promote the healthy development of aquaculture.

Genomic Insight into Zoonotic and Environmental Vibrio vulnificus: Strains with T3SS2 as a Novel Threat to Public Health

Vibrio vulnificus is a significant opportunistic pathogen with the highest fatality rate among foodborne microbes. However, due to a lack of comprehensive surveillance, the characteristics of isolates in China remain poorly understood. This study analyzed 60 strains of V. vulnificus isolated from diverse sources in Shanghai, including shellfish, crabs, shrimps, throat swabs of migratory birds, as well as seafood farming water and seawater. Identification of the genotypes was performed using PCR, and cytotoxicity was determined using an LDH assay. DNA was sequenced using Illumina NovaSeq followed by a bioinformatic analysis. The results demonstrated that a majority of the strains belonged to the 16S rRNA B-vcgC genotype. All strains carried five antibiotic resistance genes (ARGs), with some strains carrying over ten ARGs, mediating resistance to multiple antibiotics. Five strains possessed a highly abundant effector delivery system, which further investigations revealed to be a type III secretion system II (T3SS2), marking the first description of T3SS2 in V. vulnificus. Phylogenetic analysis indicated that it belonged to a different genetic lineage from T3SS2α and T3SS2β of V. parahaemolyticus. Bacteria with T3SS2 sequences were concentrated in coastal areas and mostly within the genus Vibrio in the global prevalence survey. Our study provides essential baseline information for non-clinical V. vulnificus and discovers the existence of T3SS2 in several strains which may be more virulent, thereby posing a new threat to human health.

Plastic Polymers and Antibiotic Resistance in an Antarctic Environment (Ross Sea): Are We Revealing the Tip of an Iceberg?

Microbial colonization of plastic polymers in Antarctic environments is an under-investigated issue. While several studies are documenting the spread of plastic pollution in the Ross Sea, whether the formation of a plastisphere (namely the complex microbial assemblage colonizing plastics) may favor the spread of antibiotic-resistant bacteria (ARB) in this marine environment is unknown yet. A colonization experiment was performed in this ecosystem, aiming at exploring the potential role of plastic polymers as a reservoir of antibiotic resistance. To this end, the biofilm-producing activity and the antibiotic susceptibility profiles of bacterial strains isolated from biofilms colonizing submerged polyvinylchloride and polyethylene panels were screened. The colonization experiment was carried out at two different sites of the Ross Sea, namely Road Bay and Tethys Bay. Most of bacterial isolates were able to produce biofilm; several multidrug resistances were detected in the bacterial members of biofilms associated to PVC and PE (also named as the plastisphere), as well as in the bacterial strains isolated from the surrounding water. The lowest percentage of ARB was found in the PE-associated plastisphere from the not-impacted (control) Punta Stocchino station, whereas the highest one was detected in the PVC-associated plastisphere from the Tethys Bay station. However, no selective enrichment of ARB in relation to the study sites or to either type of plastic material was observed, suggesting that resistance to antibiotics was a generalized widespread phenomenon. Resistance against to all the three classes of antibiotics assayed in this study (i.e., cell wall antibiotics, nucleic acids, and protein synthesis inhibitors) was observed. The high percentage of bacterial isolates showing resistance in remote environments like Antarctic ones, suffering increasing anthropic pressure, points out an emerging threat with a potential pathogenic risk that needs further deepening studies.

Comparison of pristine and aged poly-L-lactic acid and polyethylene terephthalate as microbe carriers in surface water: Displaying apparent differences

Microplastics (MPs) in water environment are potential carriers for many substances. In this study, pristine degradable poly-L-lactic acid (PLLA) and non-degradable polyethylene terephthalate (PET) MPs and their UV-aged counterparts were exposed to the Yuhangtang River (Y-River). The results showed that the surface morphology and structure of all MPs markedly changed after exposure. Oxygen-containing functional groups and hydrophilicity of aged MPs were higher compared with their pristine counterparts, and further increased after river exposure. The content of extracellular polymers (EPS) of biofilms on MPs increased with the exposure time, and was higher on aged MPs than on pristine ones. Similar results were obtained for most antibiotic resistance genes (ARGs) between pristine and aged MPs, and ARGs were positively related to pathogens. Dominant bacteria on all MPs were Proteobacteria (51.3 %-81.1 %), Chloroflexi (5.2 %-20.9 %) and Firmicutes (0.4 %-15.9 %), which markedly differed from the Y-River community. Aged MPs could enrich more microbes but relatively fewer bacterial species than pristine MPs, and higher enrichment and species diversity were observed on PLLA compared with PET. This study demonstrates that MPs are highly effective carriers for microbes, and the results provide valuable insights for evaluating the potential impact of bio-MPs on aquatic ecological environment.

Combined environmental pressure induces unique assembly patterns of micro-plastisphere biofilm microbial communities in constructed wetlands

The characteristics and dynamics of micro-plastisphere biofilm on the surface of microplastics (MPs) within artificial ecosystems, such as constructed wetlands (CWs), remain unclear, despite these ecosystems' potential to serve as sinks for MPs. This study investigates the dynamic evolution of micro-plastisphere biofilm in CWs, utilizing simulated wastewater containing sulfamethoxazole and humic acid, through physicochemical characterization and metagenomic analysis. Two different types of commercial plastics, including non-degradable polyethylene and degradable polylactic acid, were shredded into MPs and studied. The findings reveal that the types, shape and incubation time of MPs, along with humic acid content in wastewater, affected the quantity and quality of biofilms, such as the biofilm composition, spatial structure and microbial communities. After just 15 days into incubation, numerous microbials were observed on MP samples, with increases in biofilms content and enhanced humification of extracellular polymeric substances over time. Additionally, microbial communities on polylactic acid MPs, or those incubated for longer time, exhibit higher diversity, connectivity and stability, along with reduced vulnerability. Conversely, biofilms on polyethylene MPs were thicker, with higher potential for greenhouse gas emission and increased risk of antibiotic resistance genes. The addition of humic acid demonstrated opposite effects on biofilms across environmental interfaces, possibly due to its dual potential to produce light-induced free radicals and serve as a carbon source. Binning analysis further uncovered a unique assembly pattern of nutrients cycle genes and antibiotic resistance genes, significantly correlated within micro-plastisphere microbial communities, under the combined stress of nutrition and sulfamethoxazole. These results emphasize the shaping of micro-plastisphere biofilm characteristics by unique environmental conditions in artificial ecosystems, and the need to understand how DOM and other pollutants covary with MP pollution.

Mechanism insights into the histopathological changes of polypropylene microplastics induced gut and liver in zebrafish

Microplastics (MPs), emerging as significant pollutants, have been consistently detected in aquatic environments, with the Yangtze River experiencing a particularly severe level of microplastic pollution, exceeding all other watersheds in China. Polypropylene (PP), the plastic most abundantly found in the middle and lower reaches of the Yangtze River Basin, has less comprehensive research results into its toxic effects. Consequently, the present investigation employed zebrafish as a model organism to delve into the toxicological impacts of polypropylene microplastics (PP-MPs) with a diameter of 5 μm across varying concentrations (300 mg/L and 600 mg/L). Using histopathological, microbiota profiling, and transcriptomic approaches, we systematically evaluated the impact of PP-MPs exposure on the intestine and liver of zebrafish. Histopathological analysis revealed that exposure to PP-MPs resulted in thinner intestinal walls, damaged intestinal mucosa, and hepatic cellular damage. Intestinal microbiota profiling demonstrated that, the richness, uniformity, diversity, and homogeneity of gut microbes significantly increased after the PP-MPs exposure at high concentration. These alterations were accompanied by shifts in the relative abundance of microbiota associated with intestinal pathologies, suggesting a profound impact on the intestinal microbial community structure. Concurrently, hepatic transcriptome analysis and RT-qPCR indicated that the downregulation of pathways and genes associated with cell proliferation regulation and DNA damage repair mechanisms contributed to hepatic cellular damage, ultimately exerting adverse effects on the liver. Correlation analysis between the intestinal microbiota and liver transcriptome profiles further highlighted significant associations between intestinal microbiota and the downregulated hepatic pathways. Collectively, these results provide novel insights into the subacute toxicological mechanisms of PP-MPs in aquatic organisms and highlight the need for further research on the ecological and health risks associated with PP-MPs pollution.