The abuse or misuse of antibiotics is directly linked to the emergence of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs) in the environment. Most fish farms located on Jeju Island operate a flow-through system that pumps in seawater for fish farming and discharges it back to the ocean. To investigate the amount of ARGs that these fish farm effluents discharge into the marine environment, we conducted a metagenomic-based resistome analysis. We observed higher levels of ARGs in fish farm effluents than in seawater at beach and residential areas. A greater proportion of ARGs was found on plasmid rather than on chromosomal DNA, especially for sulfonamide and phenicol classes. The distribution of ARGs did not differ between summer and winter, but the microbial community did. In addition, fish farm samples contained significantly more opportunistic pathogens (i.e., Vibrio, Photobacterium, Aliivibrio, and Tenacibaculum) and virulence factors than non-fish farm samples. Vibrio was the most frequently identified host of ARGs and virulence factors. The presence of Vibrio in the coastal area has been increasing owing to the recent rise in the temperature of seawater. This study suggests the need for actions to treat or monitor ARGs in the coastal areas where fish farms operating a flow-through system are located.

The green turtle (Chelonia mydas) is listed as a globally endangered species and is vulnerable to anthropogenic threats, including environmental pollution. This study investigated the antimicrobial resistance of Gram-negative bacteria isolated from wild green turtles admitted to a sea turtle rehabilitation center in Taiwan. For this investigation, cloacal and nasal swab samples were collected from 28 green turtles between 2018 and 2020, from which a total of 47 Gram-negative bacterial isolates were identified. Among these, Vibrio spp. were the most dominant isolate (31.91%), and 89.36% of the 47 isolates showed resistance to at least one of 18 antimicrobial agents tested. Isolates resistant to one (6.38%), two (8.51%), and multiple (74.47%) antimicrobials were observed. The antimicrobial agents to which isolates showed the greatest resistance were penicillin (74.47%), followed by spiramycin, amoxicillin, and cephalexin. The antimicrobial-resistance profiles identified in this study provide useful information for the clinical treatment of sea turtles in rehabilitation facilities. The results of our study also imply that wild green turtles may be exposed to polluting effluents containing antimicrobials when the turtles traverse migratory corridors or forage in feeding habitats. To benefit sea turtle conservation, future research should focus on (1) how to prevent pollution from antimicrobials in major green turtle activity areas and (2) identifying sources of antimicrobial-resistant bacterial strains in coastal waters of Taiwan.

Aromatic halogenated chemicals are an unregulated class of byproducts (DBPs) generated from disinfection processes in the water environment. Information on the toxicological interactions, such as antagonism and synergism, present in DBP mixtures remains limited. This study aimed to determine the toxicological effects of aromatic halogenated DBP mixtures on the freshwater bacterium Vibrio qinghaiensis sp.-Q67. The acute toxicities of seven DBPs and their binary mixtures toward V. qinghaiensis sp.-Q67 were determined through microplate toxicity analysis. The toxicities of single DBPs were ranked as follows: 2,5-dibromohydroquinone > 2,4-dibromophenol > 4-bromo-2-chlorophenol ≈ 2,6-dibromo-4-nitrophenol > 2,6-dichloro-4-nitrophenol > 2-bromo-4-chlorophenol > 4-bromophenol. The percentages of synergism (experimental values higher than the predicted concentration addition) on the levels of 50%, 20%, and 10% effective concentrations reached 61%, 41%, and 31%, respectively. These results indicated that the probability of synergism decreased as concentration levels decreased. The synergetic effects of the compounds were dependent on concentration levels and concentration ratios. The proposed quantitative structure–activity relationship model can be used to predict the interactive toxicities exerted by 105 binary DBP mixture rays of 21 DBP mixture systems.

Compound contamination and toxicity interaction necessitate the development of models that have an insight into the combined toxicity of chemicals. In this paper, a novel and simple model dependent only on the mixture information (MIM), was developed. Firstly, the concentration–response data of seven groups of binary and multi-component (pseudo-binary) mixtures with different mixture ratios to Vibrio qinghaiensis sp.-Q67 were determined using the microplate toxicity analysis. Then, a desirable non-linear function was selected to fit the data. It was found that there are good linear correlations between the location parameter (α) and mixture ratio (p) of a component and between the steepness (β) and p. Based on the correlations, a mixture toxicity model independent of pure component toxicity profiles was built. The model can be used to accurately estimate the toxicities of the seven groups of mixtures, which greatly simplified the predictive procedure of the combined toxicity.

Transformation products usually differ in environmental behaviors and toxicological properties from the parent contaminants, and probably cause potential risks to the environment. Toxicity evolution of a labile preservative, bronopol, upon primary aquatic degradation processes was investigated. Bronopol rapidly hydrolyzed in natural waters, and primarily produced more stable 2-bromo-2-nitroethanol (BNE) and bromonitromethane (BNM). Light enhanced degradation of the targeted compounds with water site specific photoactivity. The bond order analysis theoretically revealed that the reversible retroaldol reactions were primary degradation routes for bronopol and BNE. Judging from toxicity assays and the relative pesticide toxicity index, these degradation products (i.e., BNE and BNM), more persistent and higher toxic than the parent, probably accumulated in natural waters and resulted in higher or prolonging adverse impacts. Therefore, these transformation products should be included into the assessment of ecological risks of non-persistent and low toxic chemicals such as the preservative bronopol.

Many contaminants were carried by dust, a common environment media that is easy to contact with human beings, and antibiotic resistance genes (ARGs) as an emergency pollutant also harbor in dust and pose serious threats to human health especially those carried by opportunistic pathogens because inactivation of antibiotics caused by ARGs may enhance pathogenicity. Considering there is a gap of investigation of dust ARGs, 16 S rRNA gene sequences and high-throughput quantitative PCR were employed to obtain information of microbial communities and accumulated ARGs in dust from different urban places, including the malls, hospitals, schools and parks, to investigate the distribution and influencing factors of ARGs and discover the potential hosts of ARGs in dust. Here, 9 types of ARGs such as sulfonamide, tetracycline, and beta-lactamase and 71 subtypes of ARGs like sul1, tetM-01, and drfA1 were detected in dust. ARGs had varying distribution in different public places and seasons in dust. The abundances of total ARGs, MLSB and tetracycline genes were higher in spring than summer. The diversity of ARGs was highest in malls, follow by hospitals, schools, and parks. Additionally, multi-drug resistance genes in dust were more abundant in hospitals than in schools and parks. The microbes were distinguished as the most important driving factors for ARGs in dust, followed by the mobile genetic elements (MGEs) and different places, while dust physicochemical parameters only exert a negligible impact. Notably, several opportunistic pathogens like the Streptococcus, Vibrio, and Pseudomonas were inferred as potential hosts of high-risk ARGs such as mecA, tetM-02, and tetO-01 in dust because of strongly positive co-occurrence. These results imply that dust is likely an important reservoir of ARGs. We should realize that ARGs may be harbored in some opportunistic pathogens occur in dust and endanger human health because of dust contacting to human easily.

Microplastic ingestion has been documented in various aquatic species. This causes physical damage, and additionally contaminated microplastics transfer attached pollutants and microbial pathogens to ingesting organisms. Continued metal accumulation can lead to toxicity and adverse health effects; attached microbial pathogens can cause dysbiosis - which lowers host immunity and promotes infections. Catfish, Clarias gariepinus, are a major food source in Southeast Asia, a hotspot of plastic pollution. This study aimed to quantify the transfer of the trace metals copper (Cu) and lead (Pb) -at environmentally relevant concentrations-from microplastics (polyamide 12, PA12, and polylactic acid, PLA) to catfish. Fish were reared for three months and exposed to seven different combinations of feed, supplemented with plastics and metals. At monthly intervals, fish gills, intestines, liver, and edible muscles were analysed for Cu and Pb concentrations using ICP-OES, and the intestines content assessed for Vibrio sp.. Our results showed that biodegradable PLA transferred higher amounts of metals to catfish than expected and also led to increased Vibrio counts in the intestines compared to PA12. Trace metal accumulation was significantly different in varying tissues, with highest concentrations observed in the gills, followed by liver, intestines, and lastly edible muscles. The results of this study further support the existing evidence that microplastics act as efficient shuttles to concentrate and transfer metals. They also indicate that their uptake can cause dysbiosis (increased numbers of Vibrio sp.). Most importantly, however, our study highlights that biodegradable polymers, such as PLA, could actually pose a greater environmental threat when ingested compared to the more common polymers such as PA12.

Microplastics have emerged as a new anthropogenic substrate that can readily be colonized by microorganisms. Nevertheless, microbial community succession and assembly among different microplastics in nearshore mariculture cages remains poorly understood. Using an in situ incubation experiment, 16S rRNA gene amplicon sequencing, and the neutral model, we investigated the prokaryotic communities attached to polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) in a mariculture cage in Xiangshan Harbor, China. The α-diversities and compositions of microplastic-attached prokaryotic communities were significantly distinct from free-living and small particle-attached communities in the surrounding water but relatively similar to the large particle-attached communities. Although a distinct prokaryotic community was developed on each type of microplastic, the communities on PE and PP more closely resembled each other. Furthermore, the prokaryotic community dissimilarity among all media (microplastics and water fractions) tended to decrease over time. Hydrocarbon-degrading bacteria Alcanivorax preferentially colonized PE, and the genus Vibrio with opportunistically pathogenic members has the potential to colonize PET. Additionally, neutral processes dominated the prokaryotic community assembly on PE and PP, while selection was more responsible for the prokaryotic assembly on PET. The assembly of Planctomycetaceae and Thaumarchaeota Marine Group I taxa on three microplastics were mainly governed by selection and neutral processes, respectively. Our study provides further understanding of microplastic-associated microbial ecology in mariculture environments.