Analysis of a Bacteroides conjugative transposon using a novel "targeted capture" model system

The effect of synthetic silver nanoparticles on the antibiotic resistome and the removal efficiency of antibiotic resistance genes in a hybrid filter system treating municipal wastewater

Engineered nanoparticles, including silver nanoparticles (AgNPs), are released into the environment mainly through wastewater treatment systems. Knowledge of the impact of AgNPs on the abundance and removal efficiency of antibiotic resistance genes (ARGs) in wastewater treatment facilities, including constructed wetlands (CWs), is essential in the context of public health. This study evaluated the effect of increased (100-fold) collargol (protein-coated AgNPs) and ionic Ag⁺ in municipal wastewater on the structure, abundance, and removal efficiency of the antibiotic resistome, integron-integrase genes, and pathogens in a hybrid CW using quantitative PCR and metagenomic approaches. The abundance of ARGs in wastewater and the removal efficiency of ARGs in the hybrid system were significantly affected by higher Ag concentrations, especially with collargol treatment, resulting in an elevated ARG discharge of system effluent into the environment. The accumulated Ag in the filters had a more profound effect on the absolute and relative abundance of ARGs in the treated water than the Ag content in the water. This study recorded significantly enhanced relative abundance values for tetracycline (tetA, tetC, tetQ), sulfonamide (sul1, sul2), and aminoglycoside (aadA) resistance genes, which are frequently found on mobile genetic elements in collargol- and, to a lesser extent, AgNO₃-treated subsystems. Elevated plasmid and integron-integrase gene levels, especially intI1, in response to collargol presence indicated the substantial role of AgNPs in promoting horizontal gene transfer in the treatment system. The pathogenic segment of the prokaryotic community was similar to a typical sewage community, and strong correlations between pathogen and ARG proportions were recorded in vertical subsurface flow filters. Furthermore, the proportion of Salmonella enterica was positively related to the Ag content in these filter effluents. The effect of AgNPs on the nature and characteristics of prominent resistance genes carried by mobile genetic elements in CWs requires further investigation.

Genetic analysis of mobile tetQ elements in oral Prevotella species

Prevotella species are members of the bacterial oral flora and are opportunistic pathogens in polymicrobial infections of soft tissues. Antibiotic resistance to tetracyclines is common in these bacteria, and the gene encoding this resistance has been previously identified as tetQ. The tetQ gene is also found on conjugative transposons in the intestinal Bacteroides species; whether these related bacteria have transmitted tetQ to Prevotella is unknown. In this study, we describe our genetic analysis of mobile tetQ elements in oral Prevotella species. Our results indicate that the mobile elements encoding tetQ in oral species are distinct from those found in the Bacteroides. The intestinal bacteria may act as a reservoir for the tetQ gene, but Prevotella has incorporated this gene into an IS21-family transposon. This transposon is present in Prevotella species from more than one geographical location, implying that the mechanism of tetQ spread between oral Prevotella species is highly conserved.

Genetic and functional analyses of the mob operon on conjugative transposon CTn341 from Bacteroides spp

Bacteroides are Gram-negative anaerobes indigenous to the intestinal tract of humans, and they are important opportunistic pathogens. Mobile genetic elements, such as conjugative transposons (CTns), have contributed to an increase in antibiotic resistance in these organisms. CTns are self-transmissible elements that belong to the superfamily of integrative and conjugative elements (ICEs). CTn341 is 52 kb; it encodes tetracycline resistance and its transfer is induced by tetracycline. The mobilization region of CTn341 was shown to be comprised of a three-gene operon, mobABC, and the transfer origin, oriT. The three genes code for a nicking accessory protein, a relaxase, and a VirD4-like coupling protein, respectively. The Mob proteins were predicted to mediate the formation of the relaxosome complex, nick DNA at the oriT, and shuttle the DNA/protein complex to the mating-pore apparatus. The results of mutational studies indicated that the three genes are required for maximal transfer of CTn341. Mob gene transcription was induced by tetracycline, and this regulation was mediated through the two-component regulatory system, RteAB. The oriT region of CTn341 was located within 100 bp of mobA, and a putative Bacteroides consensus nicking site was observed within this region. Mutation of the putative nick site resulted in a loss of transfer. This study demonstrated a role of the mobilization region for transfer of Bacteroides CTns and that tetracycline induction occurs for the mob gene operon, as for the tra gene operon(s), as shown previously.

Genetic and structural analysis of the Bacteroides conjugative transposon CTn341

The genetic structure and functional organization of a Bacteroides conjugative transposon (CTn), CTn341, were determined. CTn341 was originally isolated from a tetracycline-resistant clinical isolate of Bacteroides vulgatus. The element was 51,993 bp long, which included a 5-bp coupling sequence that linked the transposon ends in the circular form. There were 46 genes, and the corresponding gene products fell into three major functional groups: DNA metabolism, regulation and antibiotic resistance, and conjugation. The G + C content and codon usage observed in the functional groups suggested that the groups belong to different genetic lineages, indicating that CTn341 is a composite, modular element. Mutational analysis of genes representing the different functional groups provided evidence for the gene assignments and showed that the basic conjugation and excision genes are conserved among Bacteroides spp. A group IIA1 intron, designated B.f.I1, was found to be inserted into the bmhA methylase gene. Reverse transcriptase PCR analysis of CTn341 RNA showed that B.fr.I1 was functional and was spliced out of the bmhA gene. Six related CTn-like elements were found in the genome sequences of Bacteroides fragilis NCTC9343 and Bacteroides thetaiotaomicron VPI5482. The putative elements were similar to CTn341 primarily in the tra and mob regions and in the exc gene, and several appeared to contain intron elements. Our data provide the first reported sequence for a complete Bacteroides CTn, and they should be of considerable benefit to further functional and genetic analyses of antibiotic resistance elements and genome evolution in Bacteroides.