Relationship between the persistence of mer operon sequences in Escherichia coli and their resistance to mercury

Molecular characterization of resistance determinants and mobile genetic elements of ESBL producing multidrug-resistant bacteria from freshwater lakes in Kashmir, India

BACKGROUND

Antibiotic resistance conceded as a global concern is a phenomenon that emerged from the bacterial response to the extensive utilization of antimicrobials. The expansion of resistance determinants through horizontal transfer is linked with mobile genetic elements (MGEs) like transposons, insertion sequences, and integrons. Heavy metals also create consequential health hazards. Metal resistance gene in alliance with antibiotic resistance genes (ARGs) and MGEs is assisting bacteria to attain exalted quantity of resistance.

METHODOLOGY

The present work was carried out to study ARGs blaCTX-M, AmpC, qnrS, MGEs like ISecp1, TN3, TN21, and Int I by performing PCR and sequencing from Wular and Dal lakes of Kashmir; India. The genetic environment analysis of blaCTX-M-15 was carried out using PCR amplification, and sequencing approach followed by in-silico docking and mutational studies. Co-occurrence of ARGs and HMRGs was determined. Plasmid typing was done using PCR-based replicon typing (PBRT) and conjugation assay was also performed.

RESULTS

Out of 201 isolates attained from 16 locations, 33 were ESBLs producers. 30 ESBL displaying isolates were perceived positive for CTX-M gene, followed by AmpC (17), qnrS (13), ISecp1 (15), TN3 (11), TN21 (11), Int I (18), and SulI (14). The genetic environment of blaCTX-M-15 was observed as (ISEcp1-blaCTX-M-15-orf477), classical promoter-10 TACAAT and -35 TTGAA was found at the 3' region. The 3D structure of CTX-M-15 and ISEcp1 was generated and CTX-M-15-ISEcp1 (R299L) docking and mutation showed a reduction in hydrogen bonds. Co-occurrence of antibiotics and HMRGs (mer, sil, and ars) was found in 18, 14, and 8 isolates. PBRT analysis showed the presence of Inc. groups- B/O, F, I1, HI1, FIA, HI2, N, FIB, L/M. Molecular analysis of transconjugants showed the successful transfer of ARGs, MGEs, and HMRGs in the E. coli J53 AZ^R strain.

CONCLUSION

This study highlights the occurrence of ESBL producing bacteria in the aquatic environment of Kashmir India that can serve as a reservoir of ARGs. It also discussed the molecular mechanisms of MGEs which can help in containing the spread of antibiotic resistance.

Bacterial isolates harboring antibiotics and heavy-metal resistance genes co-existing with mobile genetic elements in natural aquatic water bodies

The rise in antibiotic-resistant bacteria and contamination of water bodies is a serious issue that demands immense attention of scientific acumen. Here, we examined the pervasiveness of ESBL producing bacteria in Dal Lake and Wular Lake of Kashmir valley, India. Isolates were screened for antibiotic, heavy metal resistant elements, and their coexistence with mobile genetic elements. Out of two hundred one isolates screened, thirty-eight were found positive for ESBL production. Antibiotic profiling of ESBL positive isolates with 16 different drugs representing β-lactam or -non-β-lactam, exhibited multidrug resistance phenotype among 55% isolates. Molecular characterization revealed the occurrence of drug resistance determinants blaTEM, AmpC, qnrS, and heavy metal resistance genes (MRGs) merB, merP, merT, silE, silP, silS, and arsC. Furthermore, mobile genetic elements IntI, SulI, ISecp1, TN3, TN21 were also detected. Conjugation assay confirmed the transfer of different ARGs, HMRGs, and mobile elements in recipient Escherichia coli J53 AZ^R strain. Plasmid incompatibility studies showed blaTEM to be associated with Inc groups B/O, HI1, HI2, I1, N, FIA, and FIB. Co-occurrence of blaTEM, HMRGs, and mobile elements from the aquatic milieu of Kashmir, India has not been reported so far. From this study, the detection of the blaTEM gene in the bacteria Bacillus simplex and Brevibacterium frigoritolerans are found for the first time. Considering all the facts it becomes crucial to conduct studies in natural aquatic environments that could help depict the epidemiological situations in which the resistance mechanism might have clinical relevance.

The metagenomic landscape of xenobiotics biodegradation in mangrove sediments

Metagenomics is a powerful approach to study microorganisms present in any given environment and their potential to maintain and improve ecosystem health without the need of cultivating these microorganisms in the laboratory. In this study, we combined a cultivation-independent metagenomics approach with functional assays to identify the detoxification potential of microbial genes evaluating their potential to contribute to xenobiotics resistance in oil-impacted mangrove sediments. A metagenomic fosmid library containing 12,960 clones from highly contaminated mangrove sediment was used in this study. For assessment of metal resistance, clones were grown in culture medium with increasing concentrations of mercury. The analyses metagenomic library sequences revealed the presence of genes related to heavy metals and antibiotics resistance in the oil-impacted mangrove microbiome. The taxonomic profiling of these sequences suggests that at the genus level, Geobacter was the most abundant genus in our dataset. A functional screening assessment of the metagenomic library successfully detected 24 potential heavy metal tolerant clones, six of which were capable of growing with increased concentrations of mercury. The genetic characterization of selected clones allowed the detection of genes related to detoxification processes, such as chromate transport protein ChrA, haloacid dehalogenase-like hydrolase, lipopolysaccharide transport system, and 3-oxoacyl-[acyl-carrier-protein] reductase. Clones were capable of growing in medium containing increased concentrations of metals and antibiotics, but none manifested strong mercury removal from culture medium characteristic of mercuric reductase activity. These results suggest that resistance to xenobiotic stress varies greatly and that additional studies to elucidate the potential of metal biotransformation need to be carried out with the goal of improving bioremediation application.

Enhanced cadmium resistance and accumulation in Pseudomonas putida KT2440 expressing the phytochelatin synthase gene of Schizosaccharomyces pombe

Phytochelatins (PCs) are cysteine-rich peptides with high binding affinity for toxic metals. Expressing the PC synthase gene (PCS) in plant growth-promoting bacteria may enhance its metal resistance and accumulation, consequently increasing phytoremediation efficiency in heavy metal pollution. In this study, PCS from Schizosaccharomyces pombe was cloned and expressed in Pseudomonas putida KT2440, which was confirmed by real-time RT-PCR through an increase in SpPCS mRNA expression level when induced by 20 μmol of CdCl2 in the transformed Ps. putida cells. The recombined strain KT2440-SpPCS exhibited enhanced Cd, Ag and Hg resistance. Compared with the original strain, KT2440-SpPCS also displayed a threefold to fivefold increase in Cd accumulation (14·32 μmol g(-1) to 17·38 μmol g(-1) ; dry weight) when grown in 30 and 50 μmol CdCl2 , along with an increase in nonprotein thiols. Further experiments showed significantly enhanced germination rates and growth of wheat seeds in 0·1 mmol to 1·0 mmol Cd when inoculated with KT2440-SpPCS. This study shows potential use of Ps. putida KT2440-SpPCS in plants to construct a symbiotic system for an enhanced phytoremediation of heavy metal-contaminated environments.

SIGNIFICANCE AND IMPACT OF THE STUDY

The symbiotic system of using plant growth-promoting bacteria Pseudomonas putida to express phytochelatin synthase gene of Schizosaccharomyces pombe together in plants resulted in high heavy metal resistance and high accumulation capacity, suggesting potential enhancement in phytoremediation of heavy metal-contaminated environments.

Prevalence of heavy metal resistance in bacteria isolated from tannery effluents and affected soil

In the present study, a total of 198 bacteria were isolated, 88 from the tannery effluents and 110 from agricultural soil irrigated with the tannery effluents. Tannery effluents and soils were analyzed for metal concentrations by atomic absorption spectrophotometer. The tannery effluents and soil samples were found to be contaminated with chromium, nickel, zinc, copper, and cadmium. All isolates were tested for their resistance against Cr(6+ ), Cr(3+ ), Ni(2+ ), Zn(2+ ), Cu(2+ ), Cd(2+ ), and Hg(2+ ). From the total of 198 isolates, maximum bacterial isolates were found to be resistant to Cr(6+ ) 178 (89.9%) followed by Cr(3+ ) 146 (73.7%), Cd(2+ ) 86 (43.4%), Zn(2+ ) 83 (41.9%), Ni(2+ ) 61 (30.8%), and Cu(2+ ) 51 (25.6%). However, most of the isolates were sensitive to Hg(2+ ). Among the isolates from tannery effluents, 97.8% were resistant to Cr(6+ ) and 64.8% were resistant to Cr(3+ ). Most of the soil isolates were resistant against Cr(6+ ) (83.6%) and Cr(3+ ) (81.8%). All isolates were categorized into Gram-positive and Gram-negative bacteria. In a total of 114 Gram-positive isolates, 91.2% were resistant to Cr(6+ ) followed by 73.7% to Cr(3+ ), 42.1% to Zn(2+ ), 40.4% to Cd(2+ ), and 32.5% to Ni(2+ ). Among Gram-negative isolates, 88.1% were found showing resistance to Cr(6+ ), 75.0% to Cr(3+ ), and 47.6% were resistant to Cd(2+ ). Majority of these metal-resistant isolates were surprisingly found sensitive to the ten commonly used antibiotics. Out of 198 isolates, 114 were found sensitive to all antibiotics whereas only two isolates were resistant to maximum eight antibiotics at a time. Forty-one and 40 isolates which constitute 20.7% and 20.2% were resistant to methicilin and amoxicillin, respectively.

Conjugative plasmids in multi-resistant bacterial isolates from Indian soil

AIMS

Determination of heavy metal and antibiotic resistance and presence of conjugative plasmids in bacteria isolated from soil irrigated with wastewater.

METHODS AND RESULTS

Composite soil samples were collected from Ghaziabad, Uttar Pradesh, India. Forty different bacteria were selected from nutrient agar and characterized by morphological, cultural and biochemical tests. All the isolates were tested for their resistance to different heavy metals and antibiotics. The DNA derived from multiple metal and antibiotic-resistant bacterial isolates was PCR amplified and plasmid-specific sequences (IncP, IncN, IncW, IncQ and pMV158-type) were analysed by dot blot hybridization. All isolates gave PCR products with trfA2 and oriT primers of the IncP group. These PCR products also hybridized with the RP4-derived probes. However, the samples were negative for all the other investigated plasmids as proved by PCR and dot blots.

CONCLUSIONS

The presence of conjugative/mobilizable IncP plasmids in the isolates indicates that these bacteria have gene-mobilizing capacity with implications for potential dissemination of introduced recombinant DNA.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of IncP plasmids in all the bacterial isolates is another proof for the prevalence of these plasmids. We propose that IncP plasmids are mainly responsible for the spread of multi-resistant bacteria in these soils.

Molecular cloning and genetic analysis of functional merB gene from indian isolates of Escherichia coli

Studies were carried out to characterize organomercurial lyase genes from wild type mercury-resistant Escherichia coli isolates, previously collected from five geographically distinct regions of the Indian subcontinent. PCR amplification followed by DNA sequencing of amplified fragments showed three merB identical to the previously characterized mer B from E. coli pR831b that were thus considered as the same gene. The remaining two genes derived from E. coli isolates of an almost mercury-free site (Dal lake, Kashmir) and designated as pIAAD3 merB and pIAAD14 merB showed slight variation (2%) at base. However, this variation in pIAAD3 due to the absence of base "T" at 479 position results in complete frame shift and the predicted MerB-like polypeptide derived from it showed 21.53% divergent at its C terminal end from the previously characterized pR831b MerB. The expression profile of pIAAD3 merB in pQE30 and pUC18 vectors each demonstrated 22.2 kDa proteins. The induced DH5alpha E. coli cells possessing pIAAD3 merB cloned in pUC18 vector split phenyl mercuric acetate (PMA) into benzene and inorganic mercury efficiently, thus giving a clue that the expressed gene product is biologically active. The current study suggests that such genetic changes may take place in the continued absence of mercury pressure, and with such modifications, they finally break down to act as vestigial remnants. Further work is going on in our lab to exploit pIAAD3 merB for the bioremediation of mercury-polluted sites.