An antibiotic-resistance enzyme from a deep-sea bacterium

Global quantification and distribution of antibiotic resistance genes in oceans and seas: Anthropogenic impacts and regional variability

The global spread of antibiotic resistance genes (ARGs) in the marine environment poses a significant threat to public health and natural ecosystems. This study quantified and analysed the distribution and co-occurrence patterns of ARGs in a wide range of oceans and high seas, including the Atlantic, Arctic and Indian Ocean, the Mediterranean Sea and the Persian Gulf. Focusing on beta-lactamases (blaOXA-48, blaCTX-M-1 group, and blaTEM), sulfonamides (sul1) and tetracycline (tetA), our results showed that sul1 was ubiquitous, indicating widespread dissemination. Notably, the Mediterranean Sea exhibited higher levels of multiple ARGs in single samples, suggesting significant anthropogenic impact. Interestingly, the Arctic Ocean, particularly around the Svalbard Islands, also showed the presence of multiple ARGs, highlighting the pervasive occurrence of antibiotic resistance in remote areas. We employed two clustering approaches to explore ARG patterns, primarily focusing on identifying geographic trends and differences in ARG abundance. Additionally, we investigated potential sources of contamination, including proximity to wastewater treatment plants, ports, marine traffic, and currents. These findings clearly demonstrate that antibiotic resistance gene contamination is widespread across diverse marine environments, with significant regional variations. This underscores the urgent need for tailored intervention strategies and global collaboration to mitigate the spread of ARGs and manage their complex dynamics in marine ecosystems.

Transmission and control strategies of antimicrobial resistance from the environment to the clinic: A holistic review

The environment serves as a significant reservoir of antimicrobial resistance (AMR) microbes and genes and is increasingly recognized as key source of clinical AMR. Modern human activities impose an additional burden on environmental AMR, promoting its transmission to clinical setting and posing a serious threat to human health and welfare. Therefore, a comprehensive review of AMR transmission from the environment to the clinic, along with proposed effective control strategies, is crucial. This review systematically summarized current research on the transmission of environmental AMR to clinical settings. Furthermore, the transmission pathways, horizontal gene transfer (HGT) mechanisms, as well as the influential drivers including triple planetary crisis that may facilitate AMR transfer from environmental species to clinical pathogens are highlighted. In response to the growing trend of AMR transmission, we propose insightful mitigation strategies under the One Health framework, integrating advanced surveillance and tracking technologies, interdisciplinary knowledge, multisectoral interventions, alongside multiple antimicrobial use and stewardship approaches to tacking development and spread of AMR.

Sediment microbial diversity, functional potentials, and antibiotic resistance pattern: a case study of Cochin Estuary core sediment

Marine sediments are an important part of the marine environment and the world's greatest organic carbon source. Sediment microorganisms are important regulators of major geochemical and eco-environmental processes in marine environments, especially nutrient dynamics and biogeochemical cycles. Despite their importance, core marine microorganisms are virtually unknown due to a lack of consensus on how to identify them. Most core microbiotas have been characterized thus far based on species abundance and occurrence. The combined effects of habitat and depth on benthic bacterial communities and ecological functions were studied using "Next-Generation sequencing (NGS) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) predictive functional profiling" at the surface (0.2 cm) and bottom depth (250 cm) in a sediment core sample from Cochin Estuary, Kerala, India. The results showed that bacterial diversity and richness were significantly higher in the surface sediment sample with the most abundant phyla being Proteobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes. The major metabolic functions were metabolism, followed by environmental information processing and genetic information processing. Antibiotic resistance genes between the surface and bottom samples help to understand the resistance pattern among multidrug resistance is the most prominent one. Among viruses, Siphoviridae is the dominant family, followed by Myoviridae. In the case of Archea, Crenarchaeota is dominant, whereas among eukaryotes phyla Streptophyta and Chordata were dominant in the surface and the bottom samples respectively.

Pseudomonas aeruginosa Isolates from Water Samples of the Gulf of Mexico Show Similar Virulence Properties but Different Antibiotic Susceptibility Profiles than Clinical Isolates

Pseudomonas aeruginosa is an opportunistic pathogen found in a wide variety of environments, including soil, water, and habitats associated with animals, humans, and plants. From a One Health perspective, which recognizes the interconnectedness of human, animal, and environmental health, it is important to study the virulence characteristics and antibiotic susceptibility of environmental bacteria. In this study, we compared the virulence properties and the antibiotic resistance profiles of seven isolates collected from the Gulf of Mexico with those of seven clinical strains of P. aeruginosa. Our results indicate that the marine and clinical isolates tested exhibit similar virulence properties; they expressed different virulence factors and were able to kill Galleria mellonella larvae, an animal model commonly used to analyze the pathogenicity of many bacteria, including P. aeruginosa. In contrast, the clinical strains showed higher antibiotic resistance than the marine isolates. Consistently, the clinical strains exhibited a higher prevalence of class 1 integron, an indicator of anthropogenic impact, compared with the marine isolates. Thus, our results indicate that the P. aeruginosa marine strains analyzed in this study, isolated from the Gulf of Mexico, have similar virulence properties, but lower antibiotic resistance, than those from hospitals.

Comparative analysis of characteristics of antibiotic resistomes between Arctic soils and representative contaminated samples using metagenomic approaches

Antibiotic resistance is one of the most concerned global health issues. However, comprehensive profiles of antibiotic resistance genes (ARGs) in various environmental settings are still needed to address modern antibiotic resistome. Here, Arctic soils and representative contaminated samples from ARG pollution sources were analyzed using metagenomic approaches. The diversity and abundance of ARGs in Arctic soils were significantly lower than those in contaminated samples (p < 0.01). ARG profiles in Arctic soils were featured with the dominance of vanF, ceoB, and bacA related to multidrug and bacitracin, whereas those from ARG pollution sources were characterized by prevalent resistance to anthropogenic antibiotics such as sulfonamides, tetracyclines, and beta-lactams. Mobile genetic elements (MGEs) were found in all samples, and their abundance and relatedness to ARGs were both lower in Arctic soils than in polluted samples. Significant relationships between bacterial communities and ARGs were observed (p < 0.01). Cultural bacteria in Arctic soils had clinically-concerned resistance to erythromycin, vancomycin, ampicillin, etc., but ARGs relevant to those antibiotics were undetectable in their genomes. Our results suggested that Arctic environment could be an important reservoir of novel ARGs, and antibiotic stresses could cause ARG pollution via horizontal gene transfer and enrichment of resistant bacteria.

Novel spore-forming species exhibiting intrinsic resistance to third- and fourth-generation cephalosporins and description of Tigheibacillus jepli gen. nov., sp. nov

A comprehensive microbial surveillance was conducted at NASA's Mars 2020 spacecraft assembly facility (SAF), where whole-genome sequencing (WGS) of 110 bacterial strains was performed. One isolate, designated 179-BFC-A-HST, exhibited less than 80% average nucleotide identity (ANI) to known species, suggesting a novel organism. This strain demonstrated high-level resistance [minimum inhibitory concentration (MIC) >256 mg/L] to third-generation cephalosporins, including ceftazidime, cefpodoxime, combination ceftazidime/avibactam, and the fourth-generation cephalosporin cefepime. The results of a comparative genomic analysis revealed that 179-BFC-A-HST is most closely related to Virgibacillus halophilus 5B73CT, sharing an ANI of 78.7% and a digital DNA-DNA hybridization (dDDH) value of 23.5%, while their 16S rRNA gene sequences shared 97.7% nucleotide identity. Based on these results and the recent recognition that the genus Virgibacillus is polyphyletic, strain 179-BFC-A-HST is proposed as a novel species of a novel genus, Tigheibacillus jepli gen. nov., sp. nov (type strain 179-BFC-A-HST = DSM 115946T = NRRL B-65666T), and its closest neighbor, V. halophilus, is proposed to be reassigned to this genus as Tigheibacillus halophilus comb. nov. (type strain 5B73CT = DSM 21623T = JCM 21758T = KCTC 13935T). It was also necessary to reclassify its second closest neighbor Virgibacillus soli, as a member of a novel genus Paracerasibacillus, reflecting its phylogenetic position relative to the genus Cerasibacillus, for which we propose Paracerasibacillus soli comb. nov. (type strain CC-YMP-6T = DSM 22952T = CCM 7714T). Within Amphibacillaceae (n = 64), P. soli exhibited 11 antibiotic resistance genes (ARG), while T. jepli encoded for 3, lacking any known β-lactamases, suggesting resistance from variant penicillin-binding proteins, disrupting cephalosporin efficacy. P. soli was highly resistant to azithromycin (MIC >64 mg/L) yet susceptible to cephalosporins and penicillins.

IMPORTANCE

The significance of this research extends to understanding microbial survival and adaptation in oligotrophic environments, such as those found in SAF. Whole-genome sequencing of several strains isolated from Mars 2020 mission assembly cleanroom facilities, including the discovery of the novel species Tigheibacillus jepli, highlights the resilience and antimicrobial resistance (AMR) in clinically relevant antibiotic classes of microbes in nutrient-scarce settings. The study also redefines the taxonomic classifications within the Amphibacillaceae family, aligning genetic identities with phylogenetic data. Investigating ARG and virulence factors (VF) across these strains illuminates the microbial capability for resistance under resource-limited conditions while emphasizing the role of human-associated VF in microbial survival, informing sterilization practices and microbial management in similar oligotrophic settings beyond spacecraft assembly cleanrooms such as pharmaceutical and medical industry cleanrooms.

β-Lactams from the Ocean

The title of this essay is as much a question as it is a statement. The discovery of the β-lactam antibiotics-including penicillins, cephalosporins, and carbapenems-as largely (if not exclusively) secondary metabolites of terrestrial fungi and bacteria, transformed modern medicine. The antibiotic β-lactams inactivate essential enzymes of bacterial cell-wall biosynthesis. Moreover, the ability of the β-lactams to function as enzyme inhibitors is of such great medical value, that inhibitors of the enzymes which degrade hydrolytically the β-lactams, the β-lactamases, have equal value. Given this privileged status for the β-lactam ring, it is therefore a disappointment that the exemplification of this ring in marine secondary metabolites is sparse. It may be that biologically active marine β-lactams are there, and simply have yet to be encountered. In this report, we posit a second explanation: that the value of the β-lactam to secure an ecological advantage in the marine environment might be compromised by its close structural similarity to the β-lactones of quorum sensing. The steric and reactivity similarities between the β-lactams and the β-lactones represent an outside-of-the-box opportunity for correlating new structures and new enzyme targets for the discovery of compelling biological activities.

Watershed urbanization enhances the enrichment of pathogenic bacteria and antibiotic resistance genes on microplastics in the water environment

Microplastics (MPs) serve as vectors for microorganisms and antibiotic resistance genes (ARGs) and contribute to the spread of pathogenic bacteria and ARGs across various environments. Patterns of microbial communities and ARGs in the biofilm on the surface of MPs, also termed as plastisphere, have become an issue of global concern. Although antibiotic resistome in the plastisphere has been detected, how watershed urbanization affects patterns of potential pathogens and ARGs in the microplastic biofilms is still unclear. Here, we compared the bacterial communities, the interaction between bacterial taxa, pathogenic bacteria, and ARGs between the plastisphere and their surrounding water, and revealed the extensive influence of urbanization on them. Our results showed that bacterial communities and interactions in the plastisphere differed from those in their surrounding water. Microplastics selectively enriched Bacteroidetes from water. In non-urbanized area, the abundance of Oxyphotobacteria was significantly (p < 0.05) higher in plastisphere than that in water, while α-Proteobacteria was significantly (p < 0.05) higher in plastisphere than those in water of urbanized area. Pathogenic bacteria, ARGs, and mobile genetic elements (MGEs) were significantly (p < 0.05) higher in the urbanized area than those in non-urbanized area. MPs selectively enriched ARG-carrying potential pathogens, i.e., Klebsiella pneumoniae and Enterobacter cloacae, and exhibited a distinct effect on the relative abundance of ARG and pathogens in water with different urbanization levels. We further found ARGs were significantly correlated to MGEs and pathogenic bacteria. These results suggested that MPs would promote the dissemination of ARGs among microbes including pathogenic bacteria, and urbanization would affect the impact of MPs on microbes, pathogens, and ARGs in water. A high level of urbanization could enhance the enrichment of pathogens and ARGs by MPs in aquatic systems and increase microbial risk in aquatic environments. Our findings highlighted the necessity of controlling the spread of ARGs among pathogens and the usage of plastic products in ecosystems of urban areas.

Metagenomic analysis reveals the diversity and distribution of antibiotic resistance genes in thermokarst lakes of the Yellow River Source Area

Thermokarst lakes form as the results of ice-rich permafrost thawing and act as important water resources in cold regions. However, the distributions of antibiotic resistance genes (ARGs) in thermokarst lakes are far less studied. Using metagenomic sequencing approach, we provided the first study to document ARGs in thermokarst lakes of the Yellow River Source Area on the Qinghai-Tibet Plateau (QTP). The results revealed that both sediment and water of the thermokarst lakes harbor diverse ARGs. Multidrug resistance genes were the most diverse, while rifamycin resistance genes were the most abundant with rpoB2 and rpoB genes having the highest proportion. Sediment samples contained more ARGs than water samples, but their composition differed between the two types of samples. However, the composition variations of sediment and water ARGs were closely correlated. The Sorensen dissimilarities of ARGs were controlled by strong turnover processes in sediment samples, and by turnover and nestedness in water samples. High contributions of nestedness were found between sediment and water samples. Moreover, ARGs in water had more significant relationships with environmental variables than that in sediment. Given the role of thermokarst lakes as important water resources in permafrost landscape, as well as intensifying influences of climate change and anthropogenetic activities, thermokarst lakes could bring potential ARG risks, warranting further investigation and evaluation.

Abundance and diversity of antibiotic resistance genes and bacterial communities in the western Pacific and Southern Oceans

This study investigated the abundance and diversity of antibiotic resistance genes (ARGs) and the composition of bacterial communities along a transect covering the western Pacific Ocean (36°N) to the Southern Ocean (74°S) using the Korean icebreaker R/V Araon (total cruise distance: 14,942 km). The relative abundances of ARGs and bacteria were assessed with quantitative PCR and next generation sequencing, respectively. The absolute abundance of ARGs was 3.0 × 10⁶ ± 1.6 × 10⁶ copies/mL in the western Pacific Ocean, with the highest value (7.8 × 10⁶ copies/mL) recorded at a station in the Tasman Sea (37°S). The absolute abundance of ARGs in the Southern Ocean was 1.8-fold lower than that in the western Pacific Ocean, and slightly increased (0.7-fold) toward Terra Nova Bay in Antarctica, possibly resulting from natural terrestrial sources or human activity. β-Lactam and tetracycline resistance genes were dominant in all samples (88-99%), indicating that they are likely the key ARGs in the ocean. Correlation and network analysis showed that Bdellovibrionota, Bacteroidetes, Cyanobacteria, Margulisbacteria, and Proteobacteria were positively correlated with ARGs, suggesting that these bacteria are the most likely ARG carriers. This study highlights the latitudinal profile of ARG distribution in the open ocean system and provides insights that will help in monitoring emerging pollutants on a global scale.

Antibiotic resistance genes on the Qinghai-Tibet Plateau above an elevation of 5,000 m

Antibiotic resistance genes (ARGs) widely occur in both anthropogenic and remote environments. Several studies have investigated the distribution of antibiotic resistance in natural environments. However, the occurrence and diversity of ARGs in remote environments at high elevations have not yet been well elucidated. Abundance, diversity, as well as influencing factors of ARGs in different ecosystems on the Qinghai-Tibet Plateau beyond elevation 5,000 m were explored, using high-throughput quantitative PCR. Totally, 197 ARGs and 12 mobile genetic elements (MGEs) were determined with abundances ranging from 3.75 × 10⁶ to 2.39 × 10⁷ and from 2.21 × 10⁴ to 1.62 × 10⁶ copies g^-1, respectively. Both the absolute and relative abundances of ARGs in farmland were lower than those in wetland and grassland. The diversity and dominant resistance mechanism of ARG profiles showed obvious differences among these ecosystems. Bacterial communities and MGEs significantly correlated with ARG profiles, while physico-chemical factors showed little impact. The high abundance and strong positive correlation between integron intI-1 and ARGs suggested a high potential horizontal ARG transfer. Based on the results, the Qinghai-Tibet Plateau can be regarded as a considerable ARG gene pool. This study provides insights into the provenance of ARGs at high elevations.

Mutation of the conserved Asp-Asp pair impairs the structure, function, and inhibition of CTX-M Class A β-lactamase

The Asp233-Asp246 pair is highly conserved in Class A β-lactamases, which hydrolyze β-lactam antibiotics. Here, we characterize its function using CTX-M-14 β-lactamase. The D233N mutant displayed decreased activity that is substrate-dependent, with reductions in k_cat /K_m ranging from 20% for nitrocefin to 6-fold for cefotaxime. In comparison, the mutation reduced the binding of a known reversible inhibitor by 10-fold. The mutant structures showed movement of the 213-219 loop and the loss of the Thr216-Thr235 hydrogen bond, which was restored by inhibitor binding. Mutagenesis of Thr216 further highlighted its contribution to CTX-M activity. These results demonstrate the importance of the aspartate pair to CTX-M hydrolysis of substrates with bulky side chains, while suggesting increased protein flexibility as a means to evolve drug resistance.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

Inhibition of the Clostridioides difficile Class D β-Lactamase CDD-1 by Avibactam

Avibactam is a potent diazobicyclooctane inhibitor of class A and C β-lactamases. The inhibitor also exhibits variable activity against some class D enzymes from Gram-negative bacteria; however, its interaction with recently discovered class D β-lactamases from Gram-positive bacteria has not been studied. Here, we describe microbiological, kinetic, and mass spectrometry studies of the interaction of avibactam with CDD-1, a class D β-lactamase from the clinically important pathogen Clostridioides difficile, and show that avibactam is a potent irreversible mechanism-based inhibitor of the enzyme. X-ray crystallographic studies at three time-points demonstrate the rapid formation of a stable CDD-1-avibactam acyl-enzyme complex and highlight differences in the anchoring of the inhibitor by class D enzymes from Gram-positive and Gram-negative bacteria.

Abundance, diversity and mobility potential of antibiotic resistance genes in pristine Tibetan Plateau soil as revealed by soil metagenomics

Widespread occurrence of antibiotic resistance genes (ARGs) has become an important clinical issue. Studying ARGs in pristine soil environments can help to better understand the intrinsic soil resistome. In this study, 10 soil samples were collected from a high elevation and relatively pristine Tibetan area, and metagenomic sequencing and bioinformatic analyses were conducted to investigate the microbial diversity, the abundance and diversity of ARGs and the mobility potential of ARGs as indicated by different mobile genetic elements (MGEs). A total of 48 ARG types with a relative abundance of 0.05-0.28 copies of ARG/copy of 16S rRNA genes were detected in Tibetan soil samples. The observed ARGs were mainly associated with antibiotics that included glycopeptide and rifamycin; the most abundant ARGs were vanRO and vanSO. Low abundance of MGEs and potentially plasmid-related ARGs indicated a low horizontal gene transfer risk of ARGs in the pristine soil. Pearson correlation and redundancy analyses showed that temperature and total organic carbon were the major environmental factors controlling both microbial diversity and ARG abundance and diversity.

Characterization of the novel OXA-213-like β-lactamase OXA-822 from Acinetobacter calcoaceticus

OBJECTIVES

This study analysed the novel carbapenem-hydrolysing class D β-lactamase OXA-822 identified in the clinical Acinetobacter calcoaceticus isolate AC_2117.

METHODS

WGS was employed for identification of β-lactamases. Micro-broth dilution was used for evaluation of antibiotic susceptibility of AC_2117 and transformants containing blaOXA-822. After heterologous purification of OXA-822, OXA-359 and OXA-213, enzyme kinetics were determined using spectrometry. The effect of OXA-822 upon meropenem treatment was analysed in the Galleria mellonella in vivo infection model.

RESULTS

OXA-822 is a member of the intrinsic OXA-213-like family found in A. calcoaceticus and Acinetobacter pittii. Amino acid sequence similarity to the nearest related OXA-359 was 97%. Production of OXA-822, OXA-359 and OXA-213 in Acinetobacter baumannii ATCC® 19606T resulted in elevated MICs for carbapenems (up to 16-fold). Penicillinase activity of the purified OXA-822 revealed high KM values, in the millimolar range, combined with high turnover numbers. OXA-822 showed the highest affinity to carbapenems, but affinity to imipenem was ∼10-fold lower compared with other carbapenems. Molecular modelling revealed that imipenem does not interact with a negatively charged side chain of OXA-822, as doripenem does, leading to the lower affinity. Presence of OXA-822 decreased survival of infected Galleria mellonella larvae after treatment with meropenem. Only 52.7% ± 7.7% of the larvae survived after 24 h compared with 90.9% ± 3.7% survival in the control group.

CONCLUSIONS

The novel OXA-822 from a clinical A. calcoaceticus isolate displayed penicillinase and carbapenemase activity in vitro, elevated MICs in different species and decreased carbapenem susceptibility in A. baumannii in vivo.

Insights into factors driving the transmission of antibiotic resistance from sludge compost-amended soil to vegetables under cadmium stress

Sludge compost is often used as a fertilizer for crops, although it might be enriched with antibiotic resistance genes (ARGs) and heavy metals that cannot be removed through composting. A robust understanding of the factors affecting the transmission of ARGs to vegetables grown in soils treated with sludge products is lacking. In this study, target ARGs in the bulk and rhizosphere soils and endophytes of shallots under heavy metal stress (i.e., Cd) were assessed, and the factors driving the transmission of ARGs were identified. Cd stress resulted in an increase in the relative abundances of target ARGs in the bulk and rhizosphere soils and endophytes. The driving factors were different in soils and plants under different degrees of Cd stress. The fungal community composition was the main driving factor of ARG variation in both bulk and rhizosphere soils. Moreover, endophytic bacteria played a crucial role in transferring ARGs to plants. Higher Cd stress promoted the transfer of most target ARGs from the below-ground plant parts to the above-ground parts. These findings indicate that application of sludge contaminated with heavy metals, such as Cd, can facilitate the dissemination of ARGs into vegetables, which must be considered while assessing the risks to public health.

Metagenomic characterization of antibiotic resistance genes in Antarctic soils

Antibiotic resistance genes (ARGs) are considered environmental pollutants. Comprehensive characterization of the ARGs in pristine environments is essential towards understanding the evolution of antibiotic resistance. Here, we analyzed ARGs in soil samples collected from relatively pristine Antarctica using metagenomic approaches. We identified 79 subtypes related to 12 antibiotic classes in Antarctic soils, in which ARGs related to multidrug and polypeptide were dominant. The characteristics of ARGs in Antarctic soils were significantly different from those in active sludge, chicken feces and swine feces, in terms of composition, abundance and potential transferability. ARG subtypes (e.g., bacA, ceoB, dfrE, mdtB, amrB, and acrB) were more abundant than others in Antarctic soils. Approximately 60% of the ARGs conferred antibiotic resistance via an efflux mechanism, and a low fraction of ARGs (∼16%) might be present on plasmids. Culturable bacterial consortiums isolated from Antarctic soils were consistently susceptible to most of the tested antibiotics frequently used in clinical therapies. The amrB and ceoB carried by culturable species did not express the resistance to aminoglycoside and fluoroquinolone at the levels of clinical concern. Our results suggest that the wide use of antibiotics may have contributed to developing higher antibiotic resistance and mobility.

Antibacterial and anticancer activities of orphan biosynthetic gene clusters from Atlantis II Red Sea brine pool

BACKGROUND

Cancer and infectious diseases are problematic because of continuous emergence of drug resistance. One way to address this enormous global health threat is bioprospecting the unlikeliest environments, such as extreme marine niches, which have tremendous biodiversity that is barely explored. One such environment is the Red Sea brine pool, Atlantis II Deep (ATII). Here, we functionally screened a fosmid library of metagenomic DNA isolated from the ATII lower convective layer (LCL) for antibacterial and anticancer activities.

RESULTS

Selected clones, 14-7E and 10-2G, displayed antibacterial effects on the marine strain Bacillus sp. Cc6. Moreover, whole cell lysates from 14-7E and 10-2G exhibited decreased cell viability against MCF-7 (39.1% ± 6.6, 42% ± 8.1 at 50% v/v) and U2OS cells (35.7% ± 1.9, 79.9% ± 5.9 at 50% v/v), respectively. By sequencing the insert DNA from 14-7E and 10-2G, we identified two putative orphan biosynthetic gene clusters. Both clusters harbored putative ATP-binding cassette (ABC) transporter permeases and S-adenosylmethionine-related genes. Interestingly, the biosynthetic gene cluster identified on 14-7E is of archaeal origin and harbors a putative transcription factor. Several identified genes may be responsible for the observed antibacterial and anticancer activities. The 14-7E biosynthetic gene cluster may be encoding enzymes producing a specialized metabolite (effect of detected genes involved in C-C bond formation and glycosylation). The bioactivity may also be due to predicted subtilases encoded by this cluster. The 10-2G cluster harbored putative glycosyltransferase and non-ribosomal peptide synthase genes; thus the observed activity of this clone could be caused by a bioactive peptide.

CONCLUSIONS

The ATII LCL prokaryotic metagenome hosts putative orphan biosynthetic gene clusters that confer antibiotic and anticancer effects. Further biochemical studies should characterize the detected bioactive components, and the potential use of 14-7E metabolite for antibiosis and 10-2G metabolite as a selective anti-breast cancer drug.

Bactericidal assessment of nano-silver on emerging and re-emerging human pathogens

With the threat of the growing number of bacteria resistant to antibiotics, the re-emergence of previously deadly infections and the emergence of new infections, there is an urgent need for novel therapeutic agent. Silver in the nano form, which is being used increasingly as antibacterial agents, may extend its antibacterial application to emerging and re-emerging multidrug-resistant pathogens, the main cause of nosocomial diseases worldwide. In the present study, a completely bottom up method to prepare green nano-silver was used. To explore the action of nano-silver on emerging Bacillus megaterium MTCC 7192 and re-emerging Pseudomonas aeruginosa MTCC 741 pathogenic bacteria, the study includes an analysis of the bacterial membrane damage through Scanning Electron Microscope (SEM) as well as alternation of zeta potential and intracellular leakages. In this work, we observed genuine bactericidal property of nano-silver as compare to broad spectrum antibiotics against emerging and re-emerging mode. After being exposed to nano-silver, the membrane becomes scattered from their original ordered arrangement based on SEM observation. Moreover, our results also suggested that alternation of zeta potential enhanced membrane permeability, and beyond a critical point, it leads to cell death. The leakages of intracellular constituents were confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). In conclusion, the combine results suggested that at a specific dose, nano-silver may destroy the structure of bacterial membrane and depress its activity, which causes bacteria to die eventually.

Comparative mangrove metagenome reveals global prevalence of heavy metals and antibiotic resistome across different ecosystems

The mangrove ecosystem harbors a complex microbial community that plays crucial role in biogeochemical cycles. In this study, we analyzed mangrove sediments from India using de novo whole metagenome next generation sequencing (NGS) and compared their taxonomic and functional community structures to mangrove metagenomics samples from Brazil and Saudi Arabia. The most abundant phyla in the mangroves of all three countries was Proteobacteria, followed by Firmicutes and Bacteroidetes. A total of 1,942 genes were found to be common across all the mangrove sediments from each of the three countries. The mangrove resistome consistently showed high resistance to fluoroquinolone and acriflavine. A comparative study of the mangrove resistome with other ecosystems shows a higher frequency of heavy metal resistance in mangrove and terrestrial samples. Ocean samples had a higher abundance of drug resistance genes with fluoroquinolone and methicillin resistance genes being as high as 28.178% ± 3.619 and 10.776% ± 1.823. Genes involved in cobalt-zinc-cadmium resistance were higher in the mangrove (23.495% ± 4.701) and terrestrial (27.479% ± 4.605) ecosystems. Our comparative analysis of samples collected from a variety of habitats shows that genes involved in resistance to both heavy metals and antibiotics are ubiquitous, irrespective of the ecosystem examined.

Arctic antibiotic resistance gene contamination, a result of anthropogenic activities and natural origin

The increasing global prevalence of antibiotic resistance genes (ARGs) in the environment is attributed to anthropogenic activities, particularly the misuse of antimicrobial drugs in human care and animal production. In the present study, we first examined Arctic/sub-Arctic (polar) sediments for the abundance and diversity of 30 ARGs against sulfonamide, tetracycline, aminoglycoside, quinolone, macrolide, and β-lactam antibiotics. Polar sediment ARGs were detected by qPCR at relatively low levels (10^-9 to 10^-5 copies/16S rRNA gene copies) compared to the reference sites, which were heavily impacted regions of China (the Haihe River, the Tianjin Water Park water and the Qilihai Wetland water, at 10^-8 to 10^-2 copies/16S rRNA gene copies). A human mitochondrial gene target, Hmt, was first used to aid in the identification of ARGs associated with anthropogenic activities, being relatively persistent, in high copy number and a human-specific molecular marker. Hmt was consistently present in easily quantifiable amounts in the polar sediment samples, indicating their relationship with human-impact, and it was also positively correlated with the relative abundance of ARGs and to the concentrations of modern-day antibiotics. Phylogenetic analyses of resistance sequences from both the Arctic marine sediments and a major database of human pathogens indicated that the ARGs in polar region were the result of a mix of human influence and natural origins. To our knowledge, this is the first study to show that ARGs in Arctic marine sediments appear to be a mixture of both natural origins and recent human influence. This study provides a significant reference regarding the global reach of antibiotic resistance, which is associated with anthropogenic activities.

Distribution of ARGs and MGEs among glacial soil, permafrost, and sediment using metagenomic analysis

Antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) can be identified with metagenomic analyses comparing relatively pristine and human-impacted environments. We collected samples from 3 different environments: glacial soil little affected by anthropogenic activity, deep permafrost dated to 5821 BP (before human antibiotics), and sediment from the Pearl River. Sulfonamides, tetracyclines, and fluoroquinolones were common in the sediment samples. Sulfonamides and tetracycline were not found in permafrost; tetracycline was also not found in glacial soil. ARGs from the sediment were more abundant and diverse than those from glacial soil and permafrost. More types of resistance mechanisms were also present in the sediment. The diversity of MGEs was significantly correlated with the abundance and diversity of ARGs. The result will help future workers to better understand the distribution of ARGs among environments more or less impacted by anthropogenic activities.

The Prevalence of Antibiotic Resistant Diarrhogenic Bacterial Species in Surface Waters, South Eastern Nigeria

Background

This study assessed the bacteriological qualities of surface waters in Afikpo, between April and September 2016.

Methods

Surface water samples were collected from three streams for bacteriological analysis. Bacteria species were isolated using standard microbiological and biochemical techniques. Antibiotic susceptibility study was carried out using Kirby Bauer disc diffusion method.

Results

The result of the mean heterotrophic bacteria count from the streams showed that Okpu stream had 209.5CFU/100 mL, Ohino Ngodo 162.5 CFU/100mL, and Ngwogo stream 162.0 CFU/100mL respectively. Out of the twenty-six (26) isolates obtained, E. coli and Staphylococcus species had the highest percentage occurrence (23.1%) respectively. Klebsiella, Shigella and Enterobacter sp had (11.5%) each, Pseudomonas spp (7.7%), while Salmonella and Streptococcus sp had the least percentage occurrence of (3.8%). The antibiotic susceptibility studies showed that large proportions of isolates were resistant to sulphamethaxoid (SUL), cephalothin (CEP), tetracycline (TET), penicillin G (PEN), oxytetracycline (OXY), cefotaxime (CEF), nalidixic acid (NAL) and cefuroxime sodium (CXM). The most effective antibiotic was azithromycin followed by imipenem.

Conclusion

The presence of these multi-drug resistant strains in water samples could facilitate transmission of antibiotic resistance. This emphasizes the need for proper treatment of water in the study area.

Astrobiology as a framework for investigating antibiotic susceptibility: a study of Halomonas hydrothermalis

Physical and chemical boundaries for microbial multiplication on Earth are strongly influenced by interactions between environmental extremes. However, little is known about how interactions between multiple stress parameters affect the sensitivity of microorganisms to antibiotics. Here, we assessed how 12 distinct permutations of salinity, availability of an essential nutrient (iron) and atmospheric composition (aerobic or microaerobic) affect the susceptibility of a polyextremotolerant bacterium, Halomonas hydrothermalis, to ampicillin, kanamycin and ofloxacin. While salinity had a significant impact on sensitivity to all three antibiotics (as shown by turbidimetric analyses), the nature of this impact was modified by iron availability and the ambient gas composition, with differing effects observed for each compound. These two parameters were found to be of particular importance when considered in combination and, in the case of ampicillin, had a stronger combined influence on antibiotic tolerance than salinity. Our data show how investigating microbial responses to multiple extremes, which are more representative of natural habitats than single extremes, can improve our understanding of the effects of antimicrobial compounds and suggest how studies of habitability, motivated by the desire to map the limits of life, can be used to systematically assess the effectiveness of antibiotics.

Novel thermostable antibiotic resistance enzymes from the Atlantis II Deep Red Sea brine pool

The advent of metagenomics has greatly facilitated the discovery of enzymes with useful biochemical characteristics for industrial and biomedical applications, from environmental niches. In this study, we used sequence-based metagenomics to identify two antibiotic resistance enzymes from the secluded, lower convective layer of Atlantis II Deep Red Sea brine pool (68°C, ~2200 m depth and 250‰ salinity). We assembled > 4 000 000 metagenomic reads, producing 43 555 contigs. Open reading frames (ORFs) called from these contigs were aligned to polypeptides from the Comprehensive Antibiotic Resistance Database using BLASTX. Two ORFs were selected for further analysis. The ORFs putatively coded for 3'-aminoglycoside phosphotransferase [APH(3')] and a class A beta-lactamase (ABL). Both genes were cloned, expressed and characterized for activity and thermal stability. Both enzymes were active in vitro, while only APH(3') was active in vivo. Interestingly, APH(3') proved to be thermostable (T_m  = 61.7°C and ~40% residual activity after 30 min of incubation at 65°C). On the other hand, ABL was not as thermostable, with a T_m  = 43.3°C. In conclusion, we have discovered two novel AR enzymes with potential application as thermophilic selection markers.

Metagenomic Analysis Revealing Antibiotic Resistance Genes (ARGs) and Their Genetic Compartments in the Tibetan Environment

Comprehensive profiles of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in a minimally impacted environment are essential to understanding the evolution and dissemination of modern antibiotic resistance. Chemical analyses of the samples collected from Tibet demonstrated that the region under investigation was almost devoid of anthropogenic antibiotics. The soils, animal wastes, and sediments were different from each other in terms of bacterial community structures, and in the typical profiles of ARGs and MGEs. Diverse ARGs that encoded resistance to common antibiotics (e.g., beta-lactams, fluoroquinolones, etc.) were found mainly via an efflux mechanism completely distinct from modern antibiotic resistome. In addition, a very small fraction of ARGs in the Tibetan environment were carried by MGEs, indicating the low potential of these ARGs to be transferred among bacteria. In comparison to the ARG profiles in relatively pristine Tibet, contemporary ARGs and MGEs in human-impacted environments have evolved substantially since the broad use of anthropogenic antibiotics.

Self-resistance in Streptomyces, with Special Reference to β-Lactam Antibiotics

Antibiotic resistance is one of the most serious public health problems. Among bacterial resistance, β-lactam antibiotic resistance is the most prevailing and threatening area. Antibiotic resistance is thought to originate in antibiotic-producing bacteria such as Streptomyces. In this review, β-lactamases and penicillin-binding proteins (PBPs) in Streptomyces are explored mainly by phylogenetic analyses from the viewpoint of self-resistance. Although PBPs are more important than β-lactamases in self-resistance, phylogenetically diverse β-lactamases exist in Streptomyces. While class A β-lactamases are mostly detected in their enzyme activity, over two to five times more classes B and C β-lactamase genes are identified at the whole genomic level. These genes can subsequently be transferred to pathogenic bacteria. As for PBPs, two pairs of low affinity PBPs protect Streptomyces from the attack of self-producing and other environmental β-lactam antibiotics. PBPs with PASTA domains are detectable only in class A PBPs in Actinobacteria with the exception of Streptomyces. None of the Streptomyces has PBPs with PASTA domains. However, one of class B PBPs without PASTA domain and a serine/threonine protein kinase with four PASTA domains are located in adjacent positions in most Streptomyces. These class B type PBPs are involved in the spore wall synthesizing complex and probably in self-resistance. Lastly, this paper emphasizes that the resistance mechanisms in Streptomyces are very hard to deal with, despite great efforts in finding new antibiotics.

Antibiotic Resistome: Improving Detection and Quantification Accuracy for Comparative Metagenomics

The unprecedented rise of life-threatening antibiotic resistance (AR), combined with the unparalleled advances in DNA sequencing of genomes and metagenomes, has pushed the need for in silico detection of the resistance potential of clinical and environmental metagenomic samples through the quantification of AR genes (i.e., genes conferring antibiotic resistance). Therefore, determining an optimal methodology to quantitatively and accurately assess AR genes in a given environment is pivotal. Here, we optimized and improved existing AR detection methodologies from metagenomic datasets to properly consider AR-generating mutations in antibiotic target genes. Through comparative metagenomic analysis of previously published AR gene abundance in three publicly available metagenomes, we illustrate how mutation-generated resistance genes are either falsely assigned or neglected, which alters the detection and quantitation of the antibiotic resistome. In addition, we inspected factors influencing the outcome of AR gene quantification using metagenome simulation experiments, and identified that genome size, AR gene length, total number of metagenomics reads and selected sequencing platforms had pronounced effects on the level of detected AR. In conclusion, our proposed improvements in the current methodologies for accurate AR detection and resistome assessment show reliable results when tested on real and simulated metagenomic datasets.

Halophilic Protein Adaptation Results from Synergistic Residue-Ion Interactions in the Folded and Unfolded States

Halophilic organisms thrive in environments with extreme salt concentrations and have adapted by allowing molar quantities of cosolutes, mainly KCl, to accumulate in their cytoplasm. To cope with this high intracellular salinity, halophilic organisms modified the chemical composition of their proteins to enrich their surface with acidic and short polar side chains, while lysines and bulky hydrophobic residues got depleted. We have emulated the evolutionary process of haloadaptation with natural and designed halophilic polypeptides and applied novel nuclear magnetic resonance (NMR) methodology to study the different mechanisms contributing to protein haloadaptation at a per residue level. Our analysis of an extensive set of NMR observables, determined over several proteins, allowed us to disentangle the synergistic contributions of protein haloadaptation: cation exclusion and electrostatic repulsion between negatively charged residues destabilize the denatured state ensemble while cumulative weak cation-protein interactions stabilize the folded conformations.

Occurrences and distribution of sulfonamide and tetracycline resistance genes in the Yangtze River Estuary and nearby coastal area

The role of highly impacted estuaries needs to be examined with respect to the spread of antibiotic resistance genes in the environment. In the present study, sulfonamide resistance (sul), tetracycline resistance (tet) and class I integron (int1) genes were ubiquitous in the sediments of the Yangtze Estuary (YE) and nearby coastal area, and exhibited a declining trend from the inner estuary to the coast. Good relationships were only observed between int1 and sul1 genes, implying that int1 gene is essential to the proliferation of sul1 gene. A non-significant correlation between int1 and 16S rRNA genes indicated that the int1 gene came from pollution sources of ARGs instead of being intrinsic in environmental bacterial populations. Sulfonamides were rarely detected in the sediments of this region, so could not result in the production of sul genes in the local environment.

Class D β-lactamases do exist in Gram-positive bacteria

Production of β-lactamases of the four molecular classes (A, B, C, and D) is the major mechanism of bacterial resistance to β-lactams, the largest class of antibiotics that have saved countless lives since their inception 70 years ago. Although several hundred efficient class D enzymes have been identified in Gram-negative pathogens over the last four decades, they have not been reported in Gram-positive bacteria. Here we demonstrate that efficient class D β-lactamases capable of hydrolyzing a wide array of β-lactam substrates are widely disseminated in various species of environmental Gram-positive organisms. Class D enzymes of Gram-positive bacteria have a distinct structural architecture and employ a unique substrate binding mode quite different from that of all currently known class A, C, and D β-lactamases. They constitute a novel reservoir of antibiotic resistance enzymes.

Characterization of a novel metallo-β-lactamases fold hydrolase from Pelagibacterium halotolerans, a marine halotolerant bacterium isolated from East China Sea

In this study, a novel metallo-β-lactamases fold hydrolase PH-1 was identified from Pelagibacterium halotolerans B2(T). This novel member of the family Hyphomicrobiaceae was isolated from the East China Sea. In silico analysis demonstrated that PH-1 and its relative homologues cluster in a unique branch and constitute a new subgroup among MBLs. PH-1 was cloned and overexpressed in Escherichia coli BL21 in a soluble form. SDS-PAGE, MALDI-TOF/TOF-MS, and size-exclusion chromatography analysis demonstrated that the PH-1 was a monomer with molecular weight of about 29 kDa. Substrate specificity study showed PH-1 preferred penicillin type β-lactams and exhibited maximum activity toward penicillin-G. Additionally, our experiments also revealed that PH-1 was a halotolerant enzyme since it is active under 4 M NaCl. The enzyme activity of PH-1 was negatively affected by 1 mM Mn(2+) and EDTA. These observations lay a foundation for further study of MBLs from marine bacterium.

Ligand-Induced Proton Transfer and Low-Barrier Hydrogen Bond Revealed by X-ray Crystallography

Ligand binding can change the pKa of protein residues and influence enzyme catalysis. Herein, we report three ultrahigh resolution X-ray crystal structures of CTX-M β-lactamase, directly visualizing protonation state changes along the enzymatic pathway: apo protein at 0.79 Å, precovalent complex with nonelectrophilic ligand at 0.89 Å, and acylation transition state (TS) analogue at 0.84 Å. Binding of the noncovalent ligand induces a proton transfer from the catalytic Ser70 to the negatively charged Glu166, and the formation of a low-barrier hydrogen bond (LBHB) between Ser70 and Lys73, with a length of 2.53 Å and the shared hydrogen equidistant from the heteroatoms. QM/MM reaction path calculations determined the proton transfer barrier to be 1.53 kcal/mol. The LBHB is absent in the other two structures although Glu166 remains neutral in the covalent complex. Our data represents the first X-ray crystallographic example of a hydrogen engaged in an enzymatic LBHB, and demonstrates that desolvation of the active site by ligand binding can provide a protein microenvironment conducive to LBHB formation. It also suggests that LBHBs may contribute to stabilization of the TS in general acid/base catalysis together with other preorganized features of enzyme active sites. These structures reconcile previous experimental results suggesting alternatively Glu166 or Lys73 as the general base for acylation, and underline the importance of considering residue protonation state change when modeling protein-ligand interactions. Additionally, the observation of another LBHB (2.47 Å) between two conserved residues, Asp233 and Asp246, suggests that LBHBs may potentially play a special structural role in proteins.

The role of class I integrons in the dissemination of sulfonamide resistance genes in the Pearl River and Pearl River Estuary, South China

Antibiotic resistance genes (ARGs), as a newly emerging contaminant, are unique because they are disseminated through horizontal gene transfer in the environment. In the present study, a class 1 integron gene (int1) and various ARGs (sul1, sul2, sul3, qnrS, and ermB) were measured in water and sediment samples from the Pearl River (PR) to the Pearl River Estuary (PRE), where there is a distinct gradient in anthropogenic impact. The int1, sul1, and sul2 genes were detected in all samples, and their concentrations exhibited a clear trend of decline consistent with anthropogenic impact. Both the int1 and sul genes had dynamically migrated between water and sediments. The relative abundance of the int1 gene normalized to the 16S rRNA gene correlated significantly with the total concentrations of antibiotics in water and sediments. Good correlations were also observed between the abundance of int1 and each type of sul gene in the samples. However, the sul1 gene showed a much stronger relationship with int1 in different seasons, probably due to the presence of sul1 in the conserved region of class 1 integron. Our results strongly support that integrons play an important role in the dissemination of ARGs in human-impacted aquatic environments.

Evolution of conformational dynamics determines the conversion of a promiscuous generalist into a specialist enzyme

β-Lactamases are produced by many modern bacteria as a mechanism of resistance toward β-lactam antibiotics, the most common antibiotics in use. β-Lactamases, however, are ancient enzymes that originated billions of years ago. Recently, proteins corresponding to 2- to 3-Gy-old Precambrian nodes in the evolution of Class A β-lactamases have been prepared and shown to be moderately efficient promiscuous catalysts, able to degrade a variety of antibiotics with catalytic efficiency levels similar to those of an average modern enzyme. Remarkably, there are few structural differences (in particular at the active-site regions) between the resurrected enzymes and a penicillin-specialist modern β-lactamase. Here, we propose that the ancestral promiscuity originates from conformational dynamics. We investigate the differences in conformational dynamics of the ancient and extant β-lactamases through MD simulations and quantify the contribution of each position to functionally related dynamics through Dynamic Flexibility Index. The modern TEM-1 lactamase shows a comparatively rigid active-site region, likely reflecting adaptation for efficient degradation of a specific substrate (penicillin), whereas enhanced deformability at the active-site neighborhood in the ancestral resurrected proteins likely accounts for the binding and subsequent degradation of antibiotic molecules of different size and shape. Clustering of the conformational dynamics on the basis of Principal Component Analysis is in agreement with the functional divergence, as the ancient β-lactamases cluster together, separated from their modern descendant. Finally, our analysis leads to testable predictions, as sites of potential relevance for the evolution of dynamics are identified and mutations at those sites are expected to alter substrate-specificity.

Permanent draft genome sequence of Bacillus flexus strain T6186-2, a multidrug-resistant bacterium isolated from a deep-subsurface oil reservoir

Previous studies suggest that antibiotic resistance genes have an ancient origin, which is not always linked to the use of antibiotics but can be enhanced by human activities. Bacillus flexus strain T6186-2 was isolated from the formation water sample of a deep-subsurface oil reservoir. Interestingly, antimicrobial susceptibility testing showed that this strain is susceptible to kanamycin, however, resistant to ampicillin, erythromycin, gentamicin, vancomycin, fosfomycin, fosmidomycin, tetracycline and teicoplanin. To explore our knowledge about the origins of antibiotic resistance genes (ARGs) in the relatively pristine environment, we sequenced the genome of B. flexus strain T6186-2 as a permanent draft. It represents the evidence for the existence of a reservoir of ARGs in nature among microbial populations from deep-subsurface oil reservoirs.

Metagenomic profiles of antibiotic resistance genes (ARGs) between human impacted estuary and deep ocean sediments

Knowledge of the origins and dissemination of antibiotic resistance genes (ARGs) is essential for understanding modern resistomes in the environment. The mechanisms of the dissemination of ARGs can be revealed through comparative studies on the metagenomic profiling of ARGs between relatively pristine and human-impacted environments. The deep ocean bed of the South China Sea (SCS) is considered to be largely devoid of anthropogenic impacts, while the Pearl River Estuary (PRE) in south China has been highly impacted by intensive human activities. Commonly used antibiotics (sulfamethazine, norfloxacin, ofloxacin, tetracycline, and erythromycin) have been detected through chemical analysis in the PRE sediments, but not in the SCS sediments. In the relatively pristine SCS sediments, the most prevalent and abundant ARGs are those related to resistance to macrolides and polypeptides, with efflux pumps as the predominant mechanism. In the contaminated PRE sediments, the typical ARG profiles suggest a prevailing resistance to antibiotics commonly used in human health and animal farming (including sulfonamides, fluoroquinolones, and aminoglycosides), and higher diversity in both genotype and resistance mechanism than those in the SCS. In particular, antibiotic inactivation significantly contributed to the resistance to aminoglycosides, β-lactams, and macrolides observed in the PRE sediments. There was a significant correlation in the levels of abundance of ARGs and those of mobile genetic elements (including integrons and plasmids), which serve as carriers in the dissemination of ARGs in the aquatic environment. The metagenomic results from the current study support the view that ARGs naturally originate in pristine environments, while human activities accelerate the dissemination of ARGs so that microbes would be able to tolerate selective environmental stress in response to anthropogenic impacts.

Antimicrobial use in aquaculture re-examined: its relevance to antimicrobial resistance and to animal and human health

The worldwide growth of aquaculture has been accompanied by a rapid increase in therapeutic and prophylactic usage of antimicrobials including those important in human therapeutics. Approximately 80% of antimicrobials used in aquaculture enter the environment with their activity intact where they select for bacteria whose resistance arises from mutations or more importantly, from mobile genetic elements containing multiple resistance determinants transmissible to other bacteria. Such selection alters biodiversity in aquatic environments and the normal flora of fish and shellfish. The commonality of the mobilome (the total of all mobile genetic elements in a genome) between aquatic and terrestrial bacteria together with the presence of residual antimicrobials, biofilms, and high concentrations of bacteriophages where the aquatic environment may also be contaminated with pathogens of human and animal origin can stimulate exchange of genetic information between aquatic and terrestrial bacteria. Several recently found genetic elements and resistance determinants for quinolones, tetracyclines, and β-lactamases are shared between aquatic bacteria, fish pathogens, and human pathogens, and appear to have originated in aquatic bacteria. Excessive use of antimicrobials in aquaculture can thus potentially negatively impact animal and human health as well as the aquatic environment and should be better assessed and regulated.

On 3LEZ, a deep-sea halophilic protein with in vitro class-a β-lactamase activity: molecular-dynamics, docking, and reactivity simulations

This work shows that a deep-sea protein, 3LEZ, with known in vitro β-lactamase activity, proved stable, substantially in the conformation detected by X-ray diffraction of the crystal, when subjected to molecular-dynamics (MD) simulations under conditions compatible with shallow seas. Docking simulations showed that the β-lactamase active site S85 of 3LEZ (S70 in Ambler numbering) is the preferential binding pocket for not only β-lactam antibiotics and inhibitors, but, surprisingly, also for a wide variety of other biologically active compounds in various chemical classes, including marine metabolites. In line with the in vitro β-lactamase activity, a) affinities on docking β-lactam antibiotics and inhibitors onto 3LEZ were found to roughly parallel published K(m) and K(i) values, obtained from MichaelisMenten kinetics under room conditions, and b) DFT calculations agreed with experiments that the irreversible reaction of the β-lactamase inhibitor clavulanic acid with the whole S85 catalytic center of 3LEZ is spontaneous. These observations must be viewed in the light that a) the compounds in other chemical classes showed comparable affinities, and, in some cases, even higher than β-lactams, for the S85 active site, b) K(m) and K(i) data are not available at the high hydrostatic pressure of the deep sea, where 3LEZ is believed to have evolved, c) an inverse order of affinities for the β-lactams, with respect to both experimentation and simulations at room conditions, was observed from comparative docking simulations with 3LEZ derived from MD under high hydrostatic pressure. Although MD requires a general assessment for high hydrostatic pressure before c) above is given the same weight as all other observations, this work questions the conclusion that the in vitro determined β-lactamase activity represents the ecological role of 3LEZ.

Hyperstability and substrate promiscuity in laboratory resurrections of Precambrian β-lactamases

We report a sequence reconstruction analysis targeting several Precambrian nodes in the evolution of class-A β-lactamases and the preparation and experimental characterization of their encoded proteins. Despite extensive sequence differences with the modern enzymes (~100 amino acid differences), the proteins resurrected in the laboratory properly fold into the canonical lactamase structure. The encoded proteins from 2-3 billion years (Gyr)-old β-lactamase sequences undergo cooperative two-state thermal denaturation and display very large denaturation temperature enhancements (~35 °C) relative to modern β-lactamases. They degrade different antibiotics in vitro with catalytic efficiencies comparable to that of an average modern enzyme. This enhanced substrate promiscuity is not accompanied by significant changes in the active-site region as seen in static X-ray structures, suggesting a plausible role for dynamics in the evolution of function in these proteins. Laboratory resurrections of 2-3 Gyr-old β-lactamases also endowed modern microorganisms with significant levels of resistance toward a variety of antibiotics, opening up the possibility of performing laboratory replays of the molecular tape of lactamase evolution. Overall, these results support the notions that Precambrian life was thermophilic and that proteins can evolve from substrate-promiscuous generalists into specialists during the course of natural evolution. They also highlight the biotechnological potential of laboratory resurrection of Precambrian proteins, as both high stability and enhanced promiscuity (likely contributors to high evolvability) are advantageous features in protein scaffolds for molecular design and laboratory evolution.

Antibiotic resistance is prevalent in an isolated cave microbiome

Antibiotic resistance is a global challenge that impacts all pharmaceutically used antibiotics. The origin of the genes associated with this resistance is of significant importance to our understanding of the evolution and dissemination of antibiotic resistance in pathogens. A growing body of evidence implicates environmental organisms as reservoirs of these resistance genes; however, the role of anthropogenic use of antibiotics in the emergence of these genes is controversial. We report a screen of a sample of the culturable microbiome of Lechuguilla Cave, New Mexico, in a region of the cave that has been isolated for over 4 million years. We report that, like surface microbes, these bacteria were highly resistant to antibiotics; some strains were resistant to 14 different commercially available antibiotics. Resistance was detected to a wide range of structurally different antibiotics including daptomycin, an antibiotic of last resort in the treatment of drug resistant Gram-positive pathogens. Enzyme-mediated mechanisms of resistance were also discovered for natural and semi-synthetic macrolide antibiotics via glycosylation and through a kinase-mediated phosphorylation mechanism. Sequencing of the genome of one of the resistant bacteria identified a macrolide kinase encoding gene and characterization of its product revealed it to be related to a known family of kinases circulating in modern drug resistant pathogens. The implications of this study are significant to our understanding of the prevalence of resistance, even in microbiomes isolated from human use of antibiotics. This supports a growing understanding that antibiotic resistance is natural, ancient, and hard wired in the microbial pangenome.

Epidemiological expansion, structural studies, and clinical challenges of new β-lactamases from gram-negative bacteria

β-Lactamase evolution presents to the infectious disease community a major challenge in the treatment of infections caused by multidrug-resistant gram-negative bacteria. Because over 1,000 of these naturally occurring β-lactamases exist, attempts to correlate structure and function have become daunting. Although new enzymes in the extended-spectrum β-lactamase (ESBL) families are frequently identified, the older CTX-M-14 and CTX-M-15 enzymes have become the most prevalent ESBLs in global surveillance. Carbapenemases with either serine-based or zinc-facilitated hydrolysis mechanisms are posing some of the most critical problems. Most geographical regions now report KPC serine carbapenemases and the metallo-β-lactamases VIM, IMP, and NDM-1, even though NDM-1 was only recently identified. The rapid emergence of these newer enzymes, with multiple β-lactamases appearing in a single organism, makes the design of new β-lactamase inactivators or β-lactamase-stable β-lactams all the more difficult. Combination therapy will likely be required to counteract the continuing evolution of these insidious enzymes in multidrug-resistant pathogens.

Identification of products of inhibition of GES-2 beta-lactamase by tazobactam by x-ray crystallography and spectrometry

The GES-2 β-lactamase is a class A carbapenemase, the emergence of which in clinically important bacterial pathogens is a disconcerting development as the enzyme confers resistance to carbapenem antibiotics. Tazobactam is a clinically used inhibitor of class A β-lactamases, which inhibits the GES-2 enzyme effectively, restoring susceptibility to β-lactam antibiotics. We have investigated the details of the mechanism of inhibition of the GES-2 enzyme by tazobactam. By the use of UV spectrometry, mass spectroscopy, and x-ray crystallography, we have documented and identified the involvement of a total of seven distinct GES-2·tazobactam complexes and one product of the hydrolysis of tazobactam that contribute to the inhibition profile. The x-ray structures for the GES-2 enzyme are for both the native (1.45 Å) and the inhibited complex with tazobactam (1.65 Å). This is the first such structure of a carbapenemase in complex with a clinically important β-lactam inhibitor, shedding light on the structural implications for the inhibition process.

An unexpected similarity between antibiotic-resistant NDM-1 and beta-lactamase II from Erythrobacter litoralis

NDM-1 (New Delhi metallo-beta-lactamase) gene encodes a metallo-beta-lactamase (MBL) with high carbapenemase activity, which makes the host bacterial strain easily dispatch the last-resort antibiotics known as carbapenems and cause global concern. Here we present the bioinformatics data showing an unexpected similarity between NDM-1 and beta-lactamase II from Erythrobacter litoralis, a marine microbial isolate. We have further expressed these two mature proteins in E. coli cells, both of which present as a monomer with a molecular mass of 25 kDa. Antimicrobial susceptibility assay reveals that they share similar substrate specificities and are sensitive to aztreonam and tigecycline. The conformational change accompanied with the zinc binding visualized by nuclear magnetic resonance, Zn(2+)-bound NDM-1, adopts at least some stable tertiary structure in contrast to the metal-free protein. Our work implies a close evolutionary relationship between antibiotic resistance genes in environmental reservoir and in the clinic, challenging the antimicrobial resistance monitoring.

Fungal community analysis in the deep-sea sediments of the Central Indian Basin by culture-independent approach

Few studies have addressed the occurrence of fungi in deep-sea sediments, characterized by elevated hydrostatic pressure, low temperature, and fluctuating nutrient conditions. We evaluated the diversity of fungi at three locations of the Central Indian Basin (CIB) at a depth of ~5,000 m using culture-independent approach. Community DNA isolated from these sediments was amplified using universal and fungal-specific internal transcribed spacers and universal 18S rDNA primer pairs. A total of 39 fungal operational taxonomic units, with 32 distinct fungal taxa were recovered from 768 clones generated from 16 environmental clone libraries. The application of multiple primers enabled the recovery of eight sequences that appeared to be new. The majority of the recovered sequences belonged to diverse phylotypes of Ascomycota and Basidiomycota. Our results suggested the existence of cosmopolitan marine fungi in the sediments of CIB. This study further demonstrated that diversity of fungi varied spatially in the CIB. Individual primer set appeared to amplify different fungal taxa occasionally. This is the first report on culture-independent diversity of fungi from the Indian Ocean.