The behavior of mobile genetic elements (MGEs) in different environments

Characterization of antibiotic resistance genes and mobile genetic elements in Escherichia coli isolated from captive black bears

The objective of this study was to analyze the antimicrobial resistance (AMR) characteristics produced by antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and gene cassettes in Escherichia coli isolated from the feces of captive black bears. Antimicrobial susceptibility testing was performed by using the disk diffusion method, and both MGEs and integron gene cassettes were detected by polymerase chain reaction. Our results showed that 43.7% (62/142) of the isolates were multidrug resistant strains and 97.9% (139/142) of the isolates were resistant to at least one antibiotic. The highest AMR phenotype was observed for tetracycline (79.6%, 113/142), followed by ampicillin (50.0%, 71/142), trimethoprim-sulfamethoxazole (43.7%, 62/142) and cefotaxime (35.9%, 51/142). However, all isolates were susceptible to tobramycin. tetA had the highest occurrence in 6 ARGs in 142 E. coli isolates (76.8%, 109/142). Ten mobile genetic elements were observed and IS26 was dominant (88.0%, 125/142). ISECP1 was positively associated with five β-lactam antibiotics. ISCR3/14, IS1133 and intI3 were not detected. Seventy-five E. coli isolates (65 intI1-positive isolates, 2 intI2-positive isolates and 8 intI1 + intI2-positive isolates) carried integrons. Five gene cassettes (dfrA1, aadA2, dfrA17-aadA5, aadA2-dfrA12 and dfrA1-aadA1) were identified in the intI1-positive isolates and 2 gene cassettes (dfrA1-catB2-sat2-aadA1 and dfrA1-catB2-sat1-aadA1) were observed in the intI2-positive isolates. Monitoring of ARGs, MGEs and gene cassettes is important to understand the prevalence of AMR, which may help to introduce measures to prevent and control of AMR in E. coli for captive black bears.

Structure and dispersion of the conjugative mobilome in surface ocean bacterioplankton

Mobile genetic elements (MGEs), collectively referred to as the "mobilome", can have a significant impact on the fitness of microbial communities and therefore on ecological processes. Marine MGEs have mainly been associated with wide geographical and phylogenetic dispersal of adaptative traits. However, whether the structure of this mobilome exhibits deterministic patterns in the natural community is still an open question. The aim of this study was to characterize the structure of the conjugative mobilome in the ocean surface bacterioplankton by searching the publicly available marine metagenomes from the TARA Oceans survey, together with molecular markers, such as relaxases and type IV coupling proteins of the type IV secretion system (T4SS). The T4SS machinery was retrieved in more abundance than relaxases in the surface marine bacterioplankton. Moreover, among the identified MGEs, mobilizable elements were the most abundant, outnumbering self-conjugative sequences. Detection of a high number of incomplete T4SSs provides insight into possible strategies related to trans-acting activity between MGEs, and accessory functions of the T4SS (e.g. protein secretion), allowing the host to maintain a lower metabolic burden in the highly dynamic marine system. Additionally, the results demonstrate a wide geographical dispersion of MGEs throughout oceanic regions, while the Southern Ocean appears segregated from other regions. The marine mobilome also showed a high similarity of functions present in known plasmid databases. Moreover, cargo genes were mostly related to DNA processing, but scarcely associated with antibiotic resistance. Finally, within the MGEs, integrative and conjugative elements showed wider marine geographic dispersion than plasmids.

Lactococcus garvieae FUA009, a Novel Intestinal Bacterium Capable of Producing the Bioactive Metabolite Urolithin A from Ellagic Acid

Dietary polyphenol ellagic acid has anti-cancer and anti-inflammatory activities, and these biological activities require the conversion of ellagic acid to urolithins by intestinal microbes. However, few gut microbes are capable of metabolizing ellagic acid to produce urolithins, limiting the beneficial effects of ellagic acid on health. Here, we describe an intestinal bacterium Lactococcus garvieae FUA009 isolated from the feces of a healthy volunteer. It was demonstrated via HPLC and UPLC-MS analysis that the end product of ellagic acid metabolism of FUA009 was urolithin A. In addition, we also examined the whole genome sequence of FUA009 and then assessed the safety and probiotic properties of FUA009 based on a complete genome and phenotype analysis. We indicated that FUA009 was safe, which was confirmed by FUA009 being sensitive to multiple antibiotics, having no hemolytic activity, and being free of aggressive putative virulence factors. Moreover, 19 stress-responsive protein genes and 8 adhesion-related genes were predicted in the FUA009 genome. Furthermore, we demonstrated that FUA009 was tolerant to acid and bile salt by determining the cell viability in a stress environment. In summary, Lactococcus garvieae FUA009, as a novel UA-producing bacterium, not only contributes to the study of the metabolic pathway of ellagic acid but is also expected to be a novel probiotic candidate.

Occurrence and distribution of antibiotics and antibiotic resistance genes in the guts of shrimp from different coastal areas of China

With the continuous increase in shrimp (Litopenaeus vannamei) aquaculture production, the widespread use of antibiotics as a means of preventing and treating diseases has adversely affected the environment, animal health and symbiotic microorganisms in gut environments. At the same time, antibiotic resistance genes (ARGs) are widespread in aquaculture and pose a great threat to aquatic organisms and humans. Therefore, in the present study, the occurrence and distribution of 17 antibiotics, ARGs and mobile genetic elements (MGEs) were detected in the guts of shrimp collected from 12 coastal regions of China. The results showed that sulfadiazine, ciprofloxacin and norfloxacin were detectable in the guts of L. vannamei at all sampling sites. Sul1, sul2, floR and intI-1 were also detected in the guts of L. vannamei at all sampling sites. The total relative abundances of ARGs and MGEs were significantly positively correlated according to Pearson correlation analysis. Sulfonamide resistance genes (sul1 and sul2) were significantly positively correlated with intI-1. These results indicated that MGEs could increase the risk of horizontal gene transfer of ARGs in a gut environment. MGEs are the most important factors promoting the spread of ARGs. Correlation analysis showed that sulfadiazine was significantly positively correlated with sul1 and sul2 and that fluoroquinolone antibiotics were significantly positively correlated with floR, indicating that antibiotics could induce the production of ARGs. Network analysis indicated that Iamia and Alkaliphilus species may harbor the most antibiotic resistance genes, and these bacteria were closely related to the proliferation and spread of ARGs in a gut environment. Antibiotic use and the spread of ARGs in mariculture systems may have negative effects on shrimp and human health. The use of antibiotics should be strictly regulated to control contaminants in mariculture systems, including pathogens and ARGs, thereby reducing potential risks to human health.

Horizontal Transmission of Stress Resistance Genes Shape the Ecology of Beta- and Gamma-Proteobacteria

The transmissible locus of stress tolerance (tLST) is found mainly in beta- and gamma-Proteobacteria and confers tolerance to elevated temperature, pressure, and chlorine. This genomic island, previously referred to as transmissible locus of protein quality control or locus of heat resistance likely originates from an environmental bacterium thriving in extreme habitats, but has been widely transmitted by lateral gene transfer. Although highly conserved, the gene content on the island is subject to evolution and gene products such as small heat shock proteins are present in several functionally distinct sequence variants. A number of these genes are xenologs of core genome genes with the gene products to widen the substrate spectrum and to be highly (complementary) expressed thus their functionality to become dominant over core genome genes. In this review, we will present current knowledge of the function of core tLST genes and discuss current knowledge on selection and counter-selection processes that favor maintenance of the tLST island, with frequent acquisition of gene products involved in cyclic di-GMP signaling, in different habitats from the environment to animals and plants, processed animal and plant products, man-made environments, and subsequently humans.

Physiological and metagenomic strategies uncover the rhizosphere bacterial microbiome succession underlying three common environmental stresses in cassava

The most common environmental pollutants such as cadmium (Cd), glyphosate and tetracycline have led to profoundly adverse impacts on plant productivity. However, how tropical crops such as cassava sense these pollutants via roots and how rhizosphere microbiome interacts with the host and pollutants remain largely unknown. In this study, we found these stresses significantly inhibited plant growth and triggered cell damage in a dosage-dependent manner, and the toxic effect on redox homeostasis was correlated with antioxidant metabolism. Using metagenomics technique, we found the rhizosphere microbiomes dynamically altered as the dose of these stresses increased. We also identified stressor-associated metagenome-assembled genomes and microbial metabolic pathways as well as mobile genetic elements in the rhizosphere microbiomes. Next, a co-occurrence network of both physiological and microbiome features was constructed to explore how these pollutants derived oxidative damage through the microbiome succession. Notably, phyllosphere transplantation of Agrobacterium tumefaciens or Pseudomonas stutzeri can significantly alleviate the negative effects of stresses on cassava growth and redox homeostasis. Collectively, this study demonstrated the dynamics of rhizosphere bacterial microbiome of cassava under three common environmental stresses, and A. tumefaciens and P. stutzeri could be developed as potential beneficial bacteria to alleviate Cd, glyphosate and tetracycline-triggered damage to cassava.

Rhizomal Reclassification of Living Organisms

Living organisms interact with each other during their lifetime, leading to genomes rearrangement and sequences transfer. These well-known phenomena give these organisms mosaic genomes, which challenge their classification. Moreover, many findings occurred between the IXXth and XXIst century, especially the discovery of giant viruses and candidate phyla radiation (CPR). Here, we tried to provide an updated classification, which integrates 216 representative genomes of the current described organisms. The reclassification was expressed through a genetic network based on the total genomic content, not on a single gene to represent the tree of life. This rhizomal exploration represents, more accurately, the evolutionary relationships among the studied species. Our analyses show a separated branch named fifth TRUC (Things Resisting Uncompleted Classifications). This taxon groups CPRs together, independently from Bacteria, Archaea (which regrouped also Nanoarchaeota and Asgard members), Eukarya, and the giant viruses (recognized recently as fourth TRUC). Finally, the broadening of analysis methods will lead to the discovery of new organisms, which justify the importance of updating the classification at every opportunity. In this perspective, our pragmatic representation could be adjusted along with the progress of evolutionary studies.

Deposition of resistant bacteria and resistome through FMT in germ-free piglets

Faecal microbiota transplantation (FMT) has received considerable attention in recent years due to its remarkable efficacy in restoring a normal gut microbiome. Here, we established the groups of post-FMT recipient piglets using germ-free piglets during early life to characterize the colonization of gut microbiota composition and the enrichment of resistance gene acquisition. By metagenomic analysis, we identified 115 bacterial phyla and 2111 bacterial genera that were acquired by the FMT recipients. We found that early-life microbial colonization and the spread of resistomes in recipient piglets were age dependent. A total of 425, 425 and 358 AR genes primarily belonging to 114, 114 and 102 different types were detected in the donors, post-FMT recipients in the FMT-3D group and post-FMT recipients in the FMT-15D group respectively. Genes that encoded tetracycline, macrolide and chloramphenicol resistance proteins were the most dominant AR genes, and the results corresponded with the exposure of antibiotic consumption at farm. Bacteroides, Escherichia, Clostridium, Parabacteroides, Treponema, Lactobacillus and Enterococcus were significantly correlated with the distribution of AR genes. More importantly, the relative abundance of AR genes was positively correlated with the levels of mobile genetic elements. Our results indicate that early-life microbial colonization can persistently shape the gut microbiota and antibiotic resistome.

Mobile genetic elements mediate the mixotrophic evolution of novel Alicyclobacillus species for acid mine drainage adaptation

Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR-Cas systems, but had more GI, IS, and ICE, as well as more MGE-associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions.

Characterization of Proteus vulgaris Strain P3M, a Foodborne Multidrug-Resistant Bacterium Isolated from Penaeus vannamei in China

Proteus vulgaris is an important foodborne opportunistic pathogen, both environmentally and clinically. The use of appropriate antibiotics has significant therapeutic effects, but has led to the emergence and spread of drug-resistant strains. In this study, a P. vulgaris strain, designated "P3M," was isolated from Penaeus vannamei in Tianjin, China. The whole genome of P3M was sequenced, generating detailed information, including the key genes involved in important metabolic pathways and their physiological functions. A total of 218 antibiotic resistance genes (ARGs) were predicted in the genome. The determination of various minimum inhibitory concentrations indicated that P3M is a multidrug-resistant (MDR) bacterium, with significant resistance to 16 antibiotics in seven categories. Determination of fractional inhibitory concentration index showed that the combination of ciprofloxacin plus tetracycline exhibited synergistic antimicrobial activity. Bioinformatics and phylogenetic analyses detected the presence of two two-component systems that mediate multidrug resistance and several mobile genetic elements involved in the horizontal transfer of ARGs in P3M. P. vulgaris strains represent a serious challenge to clinicians and infection control teams for its ubiquity worldwide and close relevance with human life. To the best of our knowledge, we report the first isolation and characterization of an important foodborne MDR P. vulgaris strain, and this study will provide necessary theoretical basis for the selection and clinical use of the appropriate antibiotics.

Horizontal Gene Transfer and Its Association with Antibiotic Resistance in the Genus Aeromonas spp

The evolution of multidrug resistant bacteria to the most diverse antimicrobials known so far pose a serious problem to global public health. Currently, microorganisms that develop resistant phenotypes to multiple drugs are associated with high morbidity and mortality. This resistance is encoded by a group of genes termed ‘bacterial resistome’, divided in intrinsic and extrinsic resistome. The first one refers to the resistance displayed on an organism without previous exposure to an antibiotic not involving horizontal genetic transfer, and it can be acquired via mutations. The latter, on the contrary, is acquired exclusively via horizontal genetic transfer involving mobile genetic elements that constitute the ‘bacterial mobilome’. This transfer is mediated by three different mechanisms: transduction, transformation, and conjugation. Recently, a problem of public health due to implications in the emergence of multi-drug resistance in Aeromonas spp. strains in water environments has been described. This is derived from the genetic material transfer via conjugation events. This is important, since bacteria that have acquired antibiotic resistance in natural environments can cause infections derived from their ingestion or direct contact with open wounds or mucosal tissue, which in turn, by their resistant nature, makes their eradication complex. Implications of the emergence of resistance in Aeromonas spp. by horizontal gene transfer on public health are discussed.

Endogenous and Foreign Nucleoid-Associated Proteins of Bacteria: Occurrence, Interactions and Effects on Mobile Genetic Elements and Host's Biology

Mobile Genetic Elements (MGEs) are mosaics of functional gene modules of diverse evolutionary origin and are generally divergent from the hosts´ genetic background. Existing biases in base composition and codon usage of these elements` genes impose transcription and translation limitations that may affect the physical and regulatory integration of MGEs in new hosts. Stable appropriation of the foreign DNA depends on a number of host factors among which are the Nucleoid-Associated Proteins (NAPs). These small, basic, highly abundant proteins bind and bend DNA, altering its topology and folding, thereby affecting all known essential DNA metabolism related processes. Both chromosomally- (endogenous) and MGE- (foreign) encoded NAPs have been shown to exist in bacteria. While the role of host-encoded NAPs in xenogeneic silencing of both episomal (plasmids) and integrative MGEs (pathogenicity islands and prophages) is well acknowledged, less is known about the role of MGE-encoded NAPs in the foreign elements biology or their influence on the host's chromosome expression dynamics. Here we review existing literature on the topic, present examples on the positive and negative effects that endogenous and foreign NAPs exert on global transcriptional gene expression, MGE integrative and excisive recombination dynamics, persistence and transfer to suitable hosts and discuss the nature and relevance of synergistic and antagonizing higher order interactions between diverse types of NAPs.

Into the Thermus Mobilome: Presence, Diversity and Recent Activities of Insertion Sequences Across Thermus spp

A high level of transposon-mediated genome rearrangement is a common trait among microorganisms isolated from thermal environments, probably contributing to the extraordinary genomic plasticity and horizontal gene transfer (HGT) observed in these habitats. In this work, active and inactive insertion sequences (ISs) spanning the sequenced members of the genus Thermus were characterized, with special emphasis on three T. thermophilus strains: HB27, HB8, and NAR1. A large number of full ISs and fragments derived from different IS families were found, concentrating within megaplasmids present in most isolates. Potentially active ISs were identified through analysis of transposase integrity, and domestication-related transposition events of ISTth7 were identified in laboratory-adapted HB27 derivatives. Many partial copies of ISs appeared throughout the genome, which may serve as specific targets for homologous recombination contributing to genome rearrangement. Moreover, recruitment of IS1000 32 bp segments as spacers for CRISPR sequence was identified, pointing to the adaptability of these elements in the biology of these thermophiles. Further knowledge about the activity and functional diversity of ISs in this genus may contribute to the generation of engineered transposons as new genetic tools, and enrich our understanding of the outstanding plasticity shown by these thermophiles.

Divalent cations increase the conjugation efficiency of the incompatibility P-7 group plasmid pCAR1 among different Pseudomonas hosts

The incompatibility (Inc) P-7 group plasmid pCAR1 can be efficiently transferred among bacteria in artificial microcosms in the presence of divalent cations Ca²⁺ and Mg²⁺. One-on-one mating assays between Pseudomonas strains with different plasmids showed that the promotion of conjugation efficiency by divalent cations was exhibited in other plasmids, including pB10 and NAH7; however, this effect was larger in IncP-7 plasmids. The impact on pCAR1 conjugation differed according to donor-recipient pairs, and conjugation efficiency promotion was clearly detected between the donors P. resinovorans CA10dm4 and P. fluorescens Pf0-1 and the recipients P. putida KT2440 and CA10dm4. Transcriptome analyses showed that pCAR1 gene expression did not respond to cation changes, including the tra/trh genes involved in its transfer. However, the transcription of oprH genes, encoding putative outer-membrane proteins in both the donor and the recipient, were commonly upregulated under cation-limited conditions. The conjugation frequency of pCAR1 in the KT2440 oprH mutant was found not to respond to cations. This effect was partially recovered by complementation with the oprH gene, suggesting that OprH is involved in the increase of pCAR1 conjugation efficiency by divalent cations.

Different transferability of incompatibility (Inc) P-7 plasmid pCAR1 and IncP-1 plasmid pBP136 in stirring liquid conditions

Self-transmissible plasmids are classified into two types based on their sex pili: short and rigid pili, and long and flexible pili. The transferability of two plasmids with different types of sex pili, pBP136 and pCAR1, was compared in stirring liquid conditions with different cell density. The most probable number method to count transconjugants could detect differences in the transfer frequency with higher resolution in comparison with the conventional CFU counting method. Both plasmids showed higher transfer frequency in high stirring rates than static liquid conditions when the donor and recipient density was 10⁶−10⁷ CFU mL^-1. The probability of donor-initiated plasmid transfer was investigated by a single-cell-level analysis using a cell sorter. The probability was >36-fold higher for pBP136 than for pCAR1; thus, the simulated transfer frequency of pBP136 was much higher than that of pCAR1 in stirring liquid conditions. Nevertheless, the transfer frequency of pCAR1 was as high as that of pBP136 when the donor and recipient cell density was 10⁶ CFU mL^-1. This fact indicates that the lower probability of the donor pCAR1 to initiate transfer could be overcome by its high tolerance to the shearing force between donor and recipient cells under higher stirring liquid conditions. Our findings can explain the different survival strategies of these two types of plasmids based on their preferences of transfer conditions.