Diverse bacterial hosts and potential risk of antibiotic resistomes in ship ballast water revealed by metagenomic binning

Ship ballast water promoting the long-range migration of antibiotic resistance genes (ARGs) has raised a great concern. This study attempted to reveal ARGs profile in ballast water and decipher their hosts and potential risk using metagenomic approaches. In total, 710 subtypes across 26 ARG types were identified among the ballast water samples from 13 ships of 11 countries and regions, and multidrug resistance genes were the most dominant ARGs. The composition of ARGs were obviously different across samples, and only 5% of the ARG subtypes were shared by all samples. Procrustes analysis showed the bacterial community contributed more than the mobile genetic elements (MGEs) in shaping the antibiotic resistome. Further, 79 metagenome-assembled genomes (46 genera belong to four phyla) were identified as ARG hosts, with predominantly affiliated with the Proteobacteria. Notably, potential human pathogens (Alcaligenes, Mycolicibacterium, Rhodococcus and Pseudomonas) were also recognized as the ARG hosts. Above 30% of the ARGs hosts contained the MGEs simultaneously, supporting a pronounced horizontal gene transfer capability. A total of 43 subtypes (six percent of overall ARGs) of ARGs were assessed with high-risk, of which 23 subtypes belonged to risk Rank I (including rsmA, ugd, etc.) and 20 subtypes to the risk Rank II (including aac(6)-I, sul1, etc.). In addition, antibiotic resistance risk index indicated the risk of ARGs in ballast water from choke points of maritime trade routes was significantly higher than that from other regions. Overall, this study offers insights for risk evaluation and management of antibiotic resistance in ballast water.

Viral community distribution, assembly mechanism, and associated hosts in an industrial park wastewater treatment plant

Viruses manipulate bacterial community composition and impact wastewater treatment efficiency. Some viruses pose threats to the environment and human populations through infection. Improving the efficiency of wastewater treatment and ensuring the health of the effluent and receptor pools requires an understanding of how viral communities assemble and interact with hosts in wastewater treatment plants (WWTPs). We used metagenomic analysis to study the distribution, assembly mechanism, and sensitive hosts for the viral communities in raw water, anaerobic tanks, and returned activated sludge units of a large-scale industrial park WWTP. Uroviricota (53.42% ± 0.14%) and Nucleocytoviricota (26.1% ± 0.19%) were dominant in all units. Viral community composition significantly differed between units, as measured by β diversity (P = 0.005). Compared to raw water, the relative viral abundance decreased by 29.8% in the anaerobic tank but increased by 9.9% in the activated sludge. Viral community assembly in raw water and anaerobic tanks was predominantly driven by deterministic processes (MST <0.5) versus stochastic processes (MST >0.5) in the activated sludge, indicating that differences in diffusion limits may fundamentally alter the assembly mechanisms of viral communities between the solid and liquid-phase environments. Acidobacteria was identified as the sensitive host contributing to viral abundance, exhibiting strong interactions and a mutual dependence (degree = 59). These results demonstrate the occurrence and prevalence of viruses in WWTPs, their different assembly mechanism, and sensitive hosts. These observations require further study of the mechanisms of viral community succession, ecological function, and roles in the successive wastewater treatment units.

Prevalence of antibiotic and metal resistance genes in phytoremediated cadmium and zinc contaminated soil assisted by chitosan and Trichoderma harzianum

Heavy metal in soil have been shown to be toxic with high concentrations and acts as selective pressure on both bacterial metal and antibiotic resistance determinants, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) were applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of antibiotic and metal resistance genes (ARGs and MRGs) in the soil was also evaluated using metagenomic approach. Results indicated that the phytoremediation of Cd and Zn contaminated soil was promoted by Chi, and Tri further reinforced this effect, along with the increased availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and β-lactam resistance genes) and maintained a high level of MRGs (e.g., chromium, copper) in soil. Soil available Zn and Cd fractions were the main factors contributing to ARGs profile by co-selection, while boosted bacterial hosts (e.g., Mitsuaria, Solirubrobacter, Ramlibacter) contributed to prevalence of most MRGs (e.g., Cd). These findings indicate the potential risk of ARGs and MRGs propagation in phytoremediation of metal contaminated soils assisted by organic and biological agents.

Guidelines to Compose an Ideal Bacteriophage Cocktail

Properly designed bacteriophage therapeutics are the cornerstone for a successful outcome of bacteriophage therapy. Here we present an overview of the different strategies and steps that can be taken to develop a bacteriophage cocktail that complies with relevant quality and safety requirements. It is based on empirical bacteriophage therapy knowledge from over a century of experience, more recently performed studies, and emerging technologies. We emphasize the selection of adequate bacteriophages and describe a modified Appelmans' method to improve the overall performance of therapeutic bacteriophages individually and collectively in the cocktail. We present two versions of the method, which differ from each other by the employed techniques to evaluate phage activity and synergy: photometric assessment of bacterial growth versus measurement of bacterial respiration via the Omnilog® system.

Enhanced expression and solubility of main protease (Mpro) of SARS-CoV-2 from E. coli

The main protease (Mpro) of SARS-CoV-2 is a essential enzyme that facilitates viral transcription and replication. Furthermore, the conservation of Mpro across different variants and its non-overlapping nature with human proteases make it an appealing target for therapeutic interventions against SARS-CoV-2. Multiple inhibitors specifically target Mpro to mitigate the infection caused by SARS-CoV-2. In the current study, successful cloning and expression of SARS-CoV-2 Mpro were achieved using two E. coli hosts, namely BL21-DE3 and BL21-DE3-RIL. By optimizing the conditions for induction, the expression of Mpro in the soluble fraction of E. coli was improved. Subsequently, Mpro was purified using affinity chromatography, yielding significantly higher quantities from the BL21-DE3-RIL strain compared to the BL21-DE3 strain, with the former producing nearly twice as much as the latter. The purified Mpro was further characterized by mass spectrometry, fluorescence spectroscopy and circular dichroism (CD). Through fluorescence quenching studies, it was discovered that both GC376 and chitosan, which are inhibitors of Mpro, induced structural changes in the purified Mpro protein. This indicates that the protein retained its functional activity even after being expressed in a bacterial host. Further, FRET-based assay highlighted that the enzymatic activity of Mpro was significantly reduced in presence of both GC376 and chitosan. Consequently, the utilization of optimal conditions and the BL21-DE3-RIL bacterial host facilitates the cost-effective production of Mpro on a large scale, enabling high yields. This production approach can be applied for the screening of potent therapeutic drugs, making it a valuable resource for drug development endeavors.

Reduction of mobile genetic elements determines the removal of antibiotic resistance genes during pig manure composting after thermal pretreatment

Animal manure is a primary repository of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). This work explored the efficiency of ARGs and MGEs removal during pig manure composting after thermal pretreatment (TPC) and the underlying mechanisms. TPC resulted in a decrease of 94.7% and 92.3% in the relative abundance of ARGs and MGEs which was 48.9% and 76.6% lower than control, respectively. Network analysis indicated that reductions of ARGs and MGEs in TPC were relevant to decrease in the amount and abundance of bacterial hosts. Furthermore, total ARGs abundance in TPC was correlated with that of intI1 and Tn916/1545 (P < 0.001). Redundancy analysis supported a leading role of MGEs in ARGs dynamics in TPC. Reduction of MGEs rather than bacterial hosts contributed mainly to ARGs removal in TPC, as revealed by structural equation modeling. In conclusion, TPC was an effective method to treat animal manure containing ARGs.

Metagenomic analysis reveals patterns and hosts of antibiotic resistance in different pig farms

In actual production environments, antibiotic-resistant genes (ARGs) are abundant in pig manure, which can form transmission chains through animals, the environment, and humans, thereby threatening human health. Therefore, based on metagenomic analysis methods, ARGs and mobile genetic elements (MGEs) were annotated in pig manure samples from 6 pig farms in 3 regions of Shanxi Province, and the potential hosts of ARGs were analyzed. The results showed that a total of 14 ARG types were detected, including 182 ARG subtypes, among which tetracycline, phenol, aminoglycoside, and macrolide resistance genes were the main ones. ARG profiles, MGE composition, and microbial communities were significantly different in different regions as well as between different pig farms. In addition, Anaerobutyricum, Butyrivibrio, and Turicibacter were significantly associated with multiple ARGs, and bacteria such as Prevotella, Bacteroides, and the family Oscillospiraceae carried multiple ARGs, suggesting that these bacteria are potential ARG hosts in pig manure. Procrustes analysis showed that bacterial communities and MGEs were significantly correlated with ARG profiles. Variation partitioning analysis results indicated that the combined effect of MGEs and bacterial communities accounted for 64.08% of resistance variation and played an important role in ARG profiles. These findings contribute to our understanding of the dissemination and persistence of ARGs in actual production settings, and offer some guidance for the prevention and control of ARGs contamination.

Xenogenetic evolutionary of integrons promotes the environmental pollution of antibiotic resistance genes - Challenges, progress and prospects

Environmental pollution of antibiotic resistance genes (ARGs) has been a great public concern. Integrons, as mobile genetic elements, with versatile gene acquisition systems facilitate the horizontal gene transfer (HGT) and pollution disseminations of ARGs. However, little is understood about the characteristics of ARGs mediated by integrons, which hampers our monitoring and control of the mobile antimicrobial resistance risks. To address these issues, we reviewed 3,322 publications concerning detection methods and pipeline, ARG diversity and evolutionary progress, environmental and geographical distribution, bacterial hosts, gene cassettes arrangements, and based on which to identify ARGs with high risk levels mediated by integrons. Diverse ARGs of 516 subtypes attributed to 12 types were capable of being carried by integrons, with 62 core ARG subtypes prevalent in pollution source, natural and human-related environments. Hosts of ARG-carrying integrons reached 271 bacterial species, most frequently carried by opportunistic pathogens Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. Moreover, the observed emergence of ARGs together with their multiple arrangements indicated the accumulation of ARGs mediated by integrons, and thus pose increasing HGT risks under modern selective agents. With the concerns of public health, we urgently call for a better monitoring and control of these high-risk ARGs. Our identified Risk Rank I ARGs (aacA7, blaOXA10, catB3, catB8, dfrA5) with high mobility, reviewed key trends and noteworthy advancements, and proposed future directions could be reference and guidance for standard formulation.

Organic fertilizer potentiates the transfer of typical antibiotic resistance gene among special bacterial species

The propagation of antibiotic resistance genes (ARGs) in environments has evoked many attentions, however, how to identify their host pathogenic bacteria in situ remains a great challenge. Here we explored the bacterial host distribution and dissemination of a typical ARG, sul1 gene, in agricultural soils through the simultaneous detection of sul1 and its host 16S rRNA gene by emulsion paired isolation and concatenation PCR (epicPCR). Compared to chemical fertilizer, organic fertilizer (chicken manure) led to a higher prevalence of sul1 gene in the soil, and dominant bacterial hosts of sul1 gene were classified into Proteobacteria and Bacteroidetes phyla. Additionally, significant higher diversity of antibiotic resistance bacteria (ARB), higher rate of horizontal gene transfer (HGT), higher rate of mobile genetic elements (MGE) and higher proportion of pathogens were all observed in the treatment of organic fertilizer. This study alerts potential health risks of manure applications in agricultural soils.

Risks of antibiotic resistance genes and antimicrobial resistance under chlorination disinfection with public health concerns

As a widely used disinfection technology, the effects of chlorination on antibiotic resistome and bacterial community received great scientific concerns, while the pathogens associated health risks kept largely unknown. With this concern, the present study used metagenomic analysis combined with culture method to reveal chlorination effects on antibiotic resistance genes (ARGs) and their bacterial hosts (total microbes and Escherichia coli) through simulating the chlorination dosage with human health concerns (drinking water and swimming pool). The resistome profiling showed that chlorination process could significantly decrease both abundance and diversity of total ARGs, while with limited removal rates of 6.0-8.7% for opportunistic pathogens E. coli isolates. Of all the observed 515 ARG subtypes, 105 core subtypes were identified and persistent during chlorination for both total microbes and E. coli. Antibiotic susceptibility test showed that chlorination treatment could efficiently remove multi-resistant E. coli isolates but select for tetracycline resistant isolates. Five ARG-carrying genomes (assigned to Bacteroidetes, Firmicutes, Actinobacteria) enriched by 18.1-102% after chlorination were retrieved by using metagenomic binning strategies. Bray-Curtis dissimilarity, network and procrustes analyses all indicated the remained antibiotic resistome and bacterial community were mainly chlorination-driven. Furthermore, a systematic pipeline for monitoring chlorination-associated antimicrobial resistance risks was proposed. These together enhance our knowledge of chlorination treatment associated public concerns, as important reference and guidance for surveillance and control of antibiotic resistance.