# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 5133 | 0 | 0.9854 | Draft genome sequence of Marinobacter sp. DUT-3, a manganese-oxidizing and potential antibiotic-resistant bacterium from Bohai coastal sediments. A manganese-oxidizing bacterium, Marinobacter sp. DUT-3, was isolated from Bohai coastal sediments. A total of 24 contigs with GC content of 57.91% and 3,817 protein-coding genes were obtained by genome sequencing. Isolation of this strain suggests potential for synergistic antibiotics removal via biogenic manganese oxides and intrinsic resistance. | 2025 | 41081498 |
| 6147 | 1 | 0.9853 | Cadmium accumulation and DNA homology with metal resistance genes in sulfate-reducing bacteria. Cadmium resistance (0.1 to 1.0 mM) was studied in four pure and one mixed culture of sulfate-reducing bacteria (SRB). The growth of the bacteria was monitored with respect to carbon source (lactate) oxidation and sulfate reduction in the presence of various concentrations of cadmium chloride. Two strains Desulfovibrio desulfuricans DSM 1926 and Desulfococcus multivorans DSM 2059 showed the highest resistance to cadmium (0.5 mM). Transmission electron microscopy of the two strains showed intracellular and periplasmic accumulation of cadmium. Dot blot DNA hybridization using the probes for the smtAB, cadAC, and cadD genes indicated the presence of similar genetic determinants of heavy metal resistance in the SRB tested. DNA sequencing of the amplified DNA showed strong nucleotide homology in all the SRB strains with the known smtAB genes encoding synechococcal metallothioneins. Protein homology with the known heavy metal-translocating ATPases was also detected in the cloned amplified DNA of Desulfomicrobium norvegicum I1 and Desulfovibrio desulfuricans DSM 1926, suggesting the presence of multiple genetic mechanisms of metal resistance in the two strains. | 2005 | 16085855 |
| 6098 | 2 | 0.9847 | Isolation and Characterization of Multi-Metal-Resistant Halomonas sp. MG from Tamil Nadu Magnesite Ore Soil in India. The aim of the study was to isolate and characterize potential multi-metal-resistant bacteria from ore soils. A total of three bacteria were isolated and assayed for resistance to arsenic (As), copper (Cu), and lead (Pb). Isolate Halomonas sp. MG exhibited maximum resistance to 1000 mg Pb/L, 800 mg As/L, and 500 mg Cu/L and it was identified as Halomonas sp. based on the partial 16S rDNA sequences. The metal(loid)s resistance mechanisms were further confirmed by amplification of arsC (As) copAU (Cu), and pbrT (Pb) genes. Biological transmission electron micrographs and XRD studies showed that the isolate Halomonas sp. MG transformed and/or biomineralized the metals either intracellularly or extracellularly. These results suggest that the isolate could be used as a potential candidate for the bioremediation of As, Cu, and Pb. | 2015 | 26298269 |
| 7967 | 3 | 0.9846 | Ciprofloxacin degradation in anaerobic sulfate-reducing bacteria (SRB) sludge system: Mechanism and pathways. Ciprofloxacin (CIP), a fluoroquinolone antibiotic, removal was examined for the first time, in an anaerobic sulfate-reducing bacteria (SRB) sludge system. About 28.0% of CIP was biodegraded by SRB sludge when the influent CIP concentration was 5000 μg/L. Some SRB genera with high tolerance to CIP (i.e. Desulfobacter), were enriched at CIP concentration of 5000 μg/L. The changes in antibiotic resistance genes (ARGs) of SRB sludge coupled with CIP biodegradation intermediates were used to understand the mechanism of CIP biodegradation for the first time. The percentage of efflux pump genes associated with ARGs increased, while the percentage of fluoroquinolone resistance genes that inhibit the DNA copy of bacteria decreased during prolonged exposure to CIP. It implies that some intracellular CIP was extruded into extracellular environment of microbial cells via efflux pump genes to reduce fluoroquinolone resistance genes accumulation caused by exposure to CIP. Additionally, the degradation products and the possible pathways of CIP biodegradation were also examined using the new method developed in this study. The results suggest that CIP was biodegraded intracellularly via desethylation reaction in piperazinyl ring and hydroxylation reaction catalyzed by cytochrome P450 enzymes. This study provides an insight into the mechanism and pathways of CIP biodegradation by SRB sludge, and opens-up a new opportunity for the treatment of CIP-containing wastewater using sulfur-mediated biological process. | 2018 | 29494897 |
| 6114 | 4 | 0.9846 | Uranium and other heavy metal resistance and accumulation in bacteria isolated from uranium mine wastes. Ten bacterial strains isolated from uranium mine wastes were characterized in terms of their uranium and other metal resistance and accumulation. 16S rRNA gene sequence analysis identified the strains as members of genera Bacillus, Serratia, and Arthrobacter. Strains were able to utilize various carbon sources, particularly aromatic hydrocarbons, grow at broad pH and temperature ranges and produce non specific acid phosphatase relevant for metal phosphate precipitation in contaminated environment. The isolates exhibited high uranium and other heavy metals (Ni, Co, Cu and Cd) resistance and accumulation capacities. Particularly, Arthrobacter sp. J001 and Bacillus sp. J003 were superior in terms of U resistance at low pH (pH 4.0) along with metals and actinides (U and Th) removal with maximum cell loading of 1088 μmol U, 1293 μmol Th, 425 μmol Cu, 305 μmol Cd, 377 μmol Zn, 250 μmol Ni g(-1) cell dry wt. Genes encoding P(1B)-type ATPases (Cu-CPx and Zn-CPx) and ABC transporters (nik) as catalytic tools for maintaining cellular metal homeostasis were detected within several Bacillus spp., with possible incidence of horizontal gene transfer for the later gene showing phylogenetic lineage to α Proteobacteria members. The study provides evidence on intrinsic abilities of indigenous bacteria from U-mine suitable for survival and cleaning up of contaminated mine sites. | 2012 | 22375546 |
| 3612 | 5 | 0.9846 | Copper resistance in Desulfovibrio strain R2. A sulfate-reducing bacterium, designated as strain R2, was isolated from wastewater of a ball-bearing manufacturing facility in Tomsk, Western Siberia. This isolate was resistant up to 800 mg Cu/l in the growth medium. By comparison, Cu-resistance of reference cultures of sulfate-reducing bacteria ranged from 50 to 75 mg Cu/l. Growth experiments with strain R2 showed that Cu was an essential trace element and, on one hand, enhanced growth at concentrations up to 10 mg/l but, on the other hand, the growth rate decreased and lag-period extended at copper concentrations of >50 mg/l. Phenotypic characteristics and a 1078 bp nucleotide sequence of the 16S rDNA placed strain R2 within the genus Desulfovibrio. Desulfovibrio R2 carried at least one plasmid of approximately of 23.1 kbp. A 636 bp fragment of the pcoR gene of the pco operon that encodes Cu resistance was amplified by PCR from plasmid DNA of strain R2. The pco genes are involved in Cu-resistance in some enteric and aerobic soil bacteria. Desulfovibrio R2 is a prospective strain for bioremediation purposes and for developing a homologous system for transformation of Cu-resistance in sulfate-reducing bacteria. | 2003 | 12755486 |
| 3021 | 6 | 0.9843 | Sequencing and comparative analysis of IncP-1α antibiotic resistance plasmids reveal a highly conserved backbone and differences within accessory regions. Although IncP-1 plasmids are important for horizontal gene transfer among bacteria, in particular antibiotic resistance spread, so far only three plasmids from the subgroup IncP-1α have been completely sequenced. In this study we doubled this number. The three IncP-1α plasmids pB5, pB11 and pSP21 were isolated from bacteria of two different sewage treatment plants and sequenced by a combination of next-generation and capillary sequencing technologies. A comparative analysis including the previously analysed IncP-1α plasmids RK2, pTB11 and pBS228 revealed a highly conserved plasmid backbone (at least 99.9% DNA sequence identity) comprising 54 core genes. The accessory elements of the plasmid pB5 constitute a class 1 integron interrupting the parC gene and an IS6100 copy inserted into the integron. In addition, the tetracycline resistance genes tetAR and the ISTB11-like element are located between the klc operon and the trfA-ssb operon. Plasmid pB11 is loaded with a Tn5053-like mercury resistance transposon between the parCBA and parDE operons and contains tetAR that are identical to those identified in plasmid pB5 and the insertion sequence ISSP21. Plasmid pSP21 harbours an ISPa7 element in a Tn402 transposon including a class 1 integron between the partitioning genes parCBA and parDE. The IS-element ISSP21 (99.89% DNA sequence identity to ISSP21 from pB11), inserted downstream of the tetR gene and a copy of ISTB11 (identical to ISTB11 on pTB11) inserted between the genes pncA and pinR. On all three plasmids the accessory genes are almost always located between the backbone modules confirming the importance of the backbone functions for plasmid maintenance. The striking backbone conservation among the six completely sequenced IncP-1α plasmids is in contrast to the much higher diversity within the IncP-1β subgroup. | 2011 | 21115076 |
| 3566 | 7 | 0.9843 | Transfer of antibiotic multiresistant plasmid RP4 from escherichia coli to activated sludge bacteria. In situ transfer of a self-transmissible, antibiotic-multiresistant plasmid RP4 from a laboratory Escherichia coli strain C600 to indigenous activated sludge bacteria was investigated using filter mating. The transfer frequency of RP4 from the donor E. coli to the bacteria that was sampled from two wastewater treatment plants was 5.1x10(-2) to 7.5x10(-1) and 4.6x10(-3) to 1.3x10(-2)/potential recipient. The isolated transconjugants showed resistance to Ap, Km, and Tc and the presence of a plasmid with a similar size to RP4. The traG gene on RP4 was also detected from all transconjugants. Reverse-transfer experiments from the transconjugants to E. coli HB101 indicated that RP4 maintained self-transmissibility in the transconjugants. The transconjugant strains were dominant bacteria in activated sludge including Pseudomonas fluorescens, P. putida, and Ochrobactrum anthropi and minor populations of enteric bacterial strains including Citrobacter freundii, E. coli, Enterobacter cloacae, E. asburiae, and Klebsiella pneumoniae ssp. pneumoniae. The transconjugant strains K. pneumoniae ssp. pneumonia, E. cloacae, and E. asburiae had several naturally occurring plasmids. These results suggest that in situ transfer of plasmids and the exchange of antibiotic-resistant genes can occur between released and indigenous bacteria in activated sludge. | 2008 | 18930008 |
| 5843 | 8 | 0.9843 | Genome sequences of copper resistant and sensitive Enterococcus faecalis strains isolated from copper-fed pigs in Denmark. Six strains of Enterococcus faecalis (S1, S12, S17, S18, S19 and S32) were isolated from copper fed pigs in Denmark. These Gram-positive bacteria within the genus Enterococcus are able to survive a variety of physical and chemical challenges by the acquisition of diverse genetic elements. The genome of strains S1, S12, S17, S18, S19 and S32 contained 2,615, 2,769, 2,625, 2,804, 2,853 and 2,935 protein-coding genes, with 41, 42, 27, 42, 32 and 44 genes encoding antibiotic and metal resistance, respectively. Differences between Cu resistant and sensitive E. faecalis strains, and possible co-transfer of Cu and antibiotic resistance determinants were detected through comparative genome analysis. | 2015 | 26203344 |
| 2766 | 9 | 0.9842 | Identification of new bacteria harboring qnrS and aac(6')-Ib/cr and mutations possibly involved in fluoroquinolone resistance in raw sewage and activated sludge samples from a full-scale WWTP. Wastewater treatment plants (WWTPs) harbor bacteria and antimicrobial resistance genes, favoring gene exchange events and resistance dissemination. Here, a culture-based and metagenomic survey of qnrA, qnrB, qnrS, and aac(6')-Ib genes from raw sewage (RS) and activated sludge (AS) of a full-scale municipal WWTP was performed. A total of 96 bacterial isolates were recovered from nalidixic acid-enrichment cultures. Bacteria harboring the aac(6')-Ib gene predominated in RS, whereas qnrS-positive isolates were specific to AS. Novel qnrS- and aac(6')-Ib-cr positive species were identified: Morganella morganii, Providencia rettgeri, and Pseudomonas guangdongensis (qnrS), and Alcaligenes faecalis and P. rettgeri (aac(6')-Ib-cr). Analysis of qnrS and aac(6')-Ib sequences from isolates and clone libraries suggested that the diversity of qnrS is wider than that of aac(6')-Ib. A large number of amino acid mutations were observed in the QnrS and AAC(6')-Ib proteins at previously undetected positions, whose structural implications are not clear. An accumulation of mutations at the C72, Q73, L74, A75 and M76 positions of QnrS, and D181 of AAC(6')-Ib might be important for resistance. These findings add significant information on bacteria harboring qnrS and aac(6')-Ib genes, and the presence of novel mutations that may eventually emerge in clinical isolates. | 2017 | 27984803 |
| 6788 | 10 | 0.9841 | Release and Constancy of an Antibiotic Resistance Gene in Seawater under Grazing Stress by Ciliates and Heterotrophic Nanoflagellates. Extracellular DNA (exDNA) is released from bacterial cells through various processes. The antibiotic resistance genes (ARGs) coded on exDNA may be horizontally transferred among bacterial communities by natural transformation. We quantitated the released/leaked tetracycline resistance gene, tet(M) over time under grazing stress by ciliates and heterotrophic nanoflagellates (HNFs), and found that extracellular tet(M) (ex-tetM) increased with bacterial grazing. Separate microcosms containing tet(M)-possessing bacteria with ciliates or HNFs were prepared. The copy number of ex-tetM in seawater in the ciliate microcosm rapidly increased until 3 d after the incubation, whereas that in the HNF microcosm showed a slower increase until 20 d. The copy number of ex-tetM was stable in both cases throughout the incubation period, suggesting that extracellular ARGs are preserved in the environment, even in the presence of grazers. Additionally, ARGs in bacterial cells were constant in the presence of grazers. These results suggest that ARGs are not rapidly extinguished in a marine environment under grazing stress. | 2017 | 28592722 |
| 5856 | 11 | 0.9841 | Amplification of DNA from native populations of soil bacteria by using the polymerase chain reaction. Specific DNA sequences from native bacterial populations present in soil, sediment, and sand samples were amplified by using the polymerase chain reaction with primers for either "universal" eubacterial 16S rRNA genes or mercury resistance (mer) genes. With standard amplification conditions, 1.5-kb rDNA fragments from all 12 samples examined and from as little as 5 micrograms of soil were reproducibly amplified. A 1-kb mer fragment from one soil sample was also amplified. The identity of these amplified fragments was confirmed by DNA-DNA hybridization. | 1992 | 1444376 |
| 6756 | 12 | 0.9841 | Conjugative Gene Transfer between Nourished and Starved Cells of Photobacterium damselae ssp. damselae and Escherichia coli. Horizontal gene transfer (HGT) between bacteria with different habitats and nutritional requirements is important for the spread of antibiotic resistance genes (ARG). The objective of the present study was to clarify the effects of organic matter on HGT between nourished and starved bacteria. We demonstrated that conjugation ability is affected by the nutritional conditions of the cell and environment. A filter mating HGT experiment was performed using Photobacterium damselae ssp. damselae, strain 04Ya311, a marine-origin bacterium possessing the multidrug-resistance plasmid pAQU1, as the donor, and Escherichia coli as the recipient. The donor and recipient were both prepared as nutrient-rich cultured and starved cells. Filter mating was performed on agar plates with and without organic nutrients. The transcription of the plasmid-borne genes tet(M) and traI was quantitated under eutrophic and oligotrophic conditions. The donor P. damselae transferred the plasmid to E. coli at a transfer rate of 10(-4) under oligotrophic and eutrophic conditions. However, when the donor was starved, HGT was not detected under oligotrophic conditions. The addition of organic matter to starved cells restored conjugative HGT even after 6 d of starvation. The transcription of traI was not detected in starved cells, but was restored upon the addition of organic matter. The HGT rate appears to be affected by the transcription of plasmid-associated genes. The present results suggest that the HGT rate is low in starved donors under oligotrophic conditions, but is restored by the addition of organic matter. | 2019 | 31631079 |
| 7782 | 13 | 0.9840 | Degradation of Extracellular Antibiotic Resistance Genes with UV(254) Treatment. Disinfected wastewater effluent contains a complex mixture of biomolecules including DNA. If intact genes conveying antibiotic resistance survive the disinfection process, environmental bacteria may take them up. We treated plasmid pWH1266, which contains ampicillin resistance gene bla(TEM-1) and tetracycline resistance gene tetA, with UV(254) doses up to 430 mJ/cm(2) and studied the ability of those genes to be acquired by Acinetobacter baylyi. The plasmids required approximately 20-25 mJ/cm(2) per log(10) loss of transformation efficiency. We monitored plasmid DNA degradation using gel electrophoresis and qPCR with both short amplicons (∼200 bps, representative of ARG amplicon lengths commonly used for environmental monitoring) and long amplicons (800-1200 bps, designed to cover the entire resistance genes). The rate of transformability loss due to UV(254) treatment was approximately 20× and 2× larger than the rate of gene degradation measured with the short and long amplicons qPCR, respectively. When extrapolated to account for the length of the entire pWH1266 plasmid, the qPCR rate constants were 2-7× larger than the rate constants measured with transformation assays. Gel electrophoresis results confirmed that DNA cleavage was not a major inactivating mechanism. Overall, our results demonstrate that qPCR conservatively measures the potential for a gene to be transformed by environmental bacteria following UV(254) treatment. | 2017 | 28475324 |
| 6157 | 14 | 0.9840 | Molecular identification of arsenic-resistant estuarine bacteria and characterization of their ars genotype. In the present study, 44 arsenic-resistant bacteria were isolated through serial dilutions on agar plate with concentrations ≥0.05 mM of sodium arsenite and ≥10 mM of sodium arsenate from Mandovi and Zuari--estuarine water systems. The ars genotype characterization in 36 bacterial isolates (resistant to 100 mM of sodium arsenate) revealed that only 17 isolates harboured the arsA (ATPase), B (arsenite permease) and C (arsenate reductase) genes on the plasmid DNA. The arsA, B and C genes were individually detected using PCR in 16, 9 and 13 bacterial isolates respectively. Molecular identification of the 17 isolates bearing the ars genotype was carried using 16S rDNA sequencing. A 1300 bp full length arsB gene encoding arsenite efflux pump and a 409 bp fragment of arsC gene coding for arsenate reductase were isolated from the genera Halomonas and Acinetobacter. Phylogenetic analysis of arsB and arsC genes indicated their close genetic relationship with plasmid borne ars genes of E. coli and arsenate reductase of plant origin. The putative arsenate reductase gene isolated from Acinetobacter species complemented arsenate resistance in E. coli WC3110 and JM109 validating its function. This study dealing with isolation of native arsenic-resistant bacteria and characterization of their ars genes might be useful to develop efficient arsenic detoxification strategies for arsenic contaminated aquifers. | 2012 | 21879358 |
| 6239 | 15 | 0.9839 | Viability and transcriptional responses of multidrug resistant E. coli to chromium stress. The viability of multidrug resistant (MDR) bacteria in environment is critical for the spread of antimicrobial resistance. In this study, two Escherichia coli strains, MDR LM13 and susceptible ATCC25922, were used to elucidate differences in their viability and transcriptional responses to hexavalent chromium (Cr(VI)) stress. The results show that the viability of LM13 was notably higher than that of ATCC25922 under 2-20 mg/L Cr(VI) exposure with bacteriostatic rates of 3.1%-57%, respectively, for LM13 and 0.9%-93.1%, respectively, for ATCC25922. The levels of reactive oxygen species and superoxide dismutase in ATCC25922 were much higher than those in LM13 under Cr(VI) exposure. Additionally, 514 and 765 differentially expressed genes were identified from the transcriptomes of the two strains (log(2)|FC| > 1, p < 0.05). Among them, 134 up-regulated genes were enriched in LM13 in response to external pressure, but only 48 genes were annotated in ATCC25922. Furthermore, the expression levels of antibiotic resistance genes, insertion sequences, DNA and RNA methyltransferases, and toxin-antitoxin systems were generally higher in LM13 than in ATCC25922. This work shows that MDR LM13 has a stronger viability under Cr(VI) stress, and therefore may promote the dissemination of MDR bacteria in environment. | 2023 | 36868548 |
| 6117 | 16 | 0.9839 | Isolation and characterization of the heavy metal resistant bacteria CCNWRS33-2 isolated from root nodule of Lespedeza cuneata in gold mine tailings in China. A total of 108 strains of bacteria were isolated from root nodules of wild legumes growing in gold mine tailings in northwest of China and were tested for heavy metal resistance. The results showed that the bacterial strain CCNWRS33-2 isolated from Lespedeza cuneata was highly resistant to copper, cadmium, lead and zinc. The strain had a relatively high mean specific growth rate under each heavy metal stress test and exhibited a high degree of bioaccumulation ability. The partial sequence of the copper resistance gene copA was amplified from the strain and a sequence comparison with our Cu-resistant PCR fragment showed a high homology with Cu-resistant genes from other bacteria. Phylogenetic analysis based on the 16S rRNA gene sequence showed that CCNWRS33-2 belongs to the Rhizobium-Agrobacterium branch and it had 98.9% similarity to Agrobactrium tumefaciens LMG196. | 2009 | 18562095 |
| 466 | 17 | 0.9838 | High diversity of bacterial mercuric reductase genes from surface and sub-surface floodplain soil (Oak Ridge, USA). DNA was extracted from different depth soils (0-5, 45-55 and 90-100 cm below surface) sampled at Lower East Fork Poplar Creek floodplain (LEFPCF), Oak Ridge (TN, USA). The presence of merA genes, encoding the mercuric reductase, the key enzyme in detoxification of mercury in bacteria, was examined by PCR targeting Actinobacteria, Firmicutes or beta/gamma-Proteobacteria. beta/gamma-Proteobacteria merA genes were successfully amplified from all soils, whereas Actinobacteria were amplified only from surface soil. merA clone libraries were constructed and sequenced. beta/gamma-Proteobacteria sequences revealed high diversity in all soils, but limited vertical similarity. Less than 20% of the operational taxonomic units (OTU) (DNA sequences > or = 95% identical) were shared between the different soils. Only one of the 62 OTU was > or = 95% identical to a GenBank sequence, highlighting that cultivated bacteria are not representative of what is found in nature. Fewer merA sequences were obtained from the Actinobacteria, but these were also diverse, and all were different from GenBank sequences. A single clone was most closely related to merA of alpha-Proteobacteria. An alignment of putative merA genes of genome sequenced mainly marine alpha-Proteobacteria was used for design of merA primers. PCR amplification of soil alpha-Proteobacteria isolates and sequencing revealed that they were very different from the genome-sequenced bacteria (only 62%-66% identical at the amino-acid level), although internally similar. In light of the high functional diversity of mercury resistance genes and the limited vertical distribution of shared OTU, we discuss the role of horizontal gene transfer as a mechanism of bacterial adaptation to mercury. | 2007 | 18043664 |
| 5262 | 18 | 0.9838 | High abundances of class 1 integrase and sulfonamide resistance genes, and characterisation of class 1 integron gene cassettes in four urban wetlands in Nigeria. There is little information about environmental contamination with antibiotic resistance genes (ARG) in Sub-Saharan Africa, home to about 1 billion people. In this study we measured the abundance of three genes (sul1, sul2, and intI1) used as indicators of environmental contamination with ARGs in the sediments of four urban wetlands in southwestern Nigeria by qPCR. In addition, we characterised the variable regions of class 1 integrons in sulfamethoxazole/trimethoprim (SMX/TRI)-resistant bacteria isolated from the wetlands by PCR and DNA sequencing. The indicator ARGs were present in all wetlands with mean absolute copy numbers/gram of sediment ranging between 4.7x106 and 1.2x108 for sul1, 1.1x107 and 1x108 for sul2, and 5.3x105 and 1.9x107 for intI1. The relative abundances (ARG/16S rRNA copy number) ranged from about 10-3 to 10-1. These levels of ARG contamination were similar to those previously reported for polluted environments in other parts of the world. The integrase genes intI1 and intI2 were detected in 72% and 11.4% SMX/TRI-resistant isolates, respectively. Five different cassette array types (dfrA7; aadA2; aadA1|dfrA1; acc(6')lb-cr|arr3|dfrA27; arr3|acc(6')lb-cr|dfrA27) were detected among 34 (59.6%) intI1-positive isolates. No gene cassettes were found in the nine intI2-positive isolates. These results show that African urban ecosystems impacted by anthropogenic activities are reservoirs of bacteria harbouring transferable ARG. | 2018 | 30496274 |
| 6354 | 19 | 0.9838 | Genetic and transcriptional analysis of a novel plasmid-encoded copper resistance operon from Lactococcus lactis. A plasmid-borne copper resistance operon (lco) was identified from Lactococcus lactis subsp. lactis LL58-1. The lco operon consists of three structural genes lcoABC. The predicted products of lcoA and lcoB were homologous to chromosomally encoded prolipoprotein diacylglyceral transferases and two uncharacterized proteins respectively, and the product of lcoC is similar to several multicopper oxidases, which are generally plasmid-encoded. This genetic organization represents a new combination of genes for copper resistance in bacteria. The three genes are co-transcribed from a copper-inducible promoter, which is controlled by lcoRS encoding a response regulator and a kinase sensor. The five genes are flanked by two insertion sequences, almost identical to IS-LL6 from L. lactis. Transposon mutagenesis and subcloning analysis indicated that the three structural genes were all required for copper resistance. Copper assay results showed that the extracellular concentration of copper of L. lactis LM0230 containing the lco operon was significantly higher than that of the host strain when copper was added at concentrations from 2 to 3 mM. The results suggest that the lco operon conferred copper resistance by reducing the intracellular accumulation of copper ions in L. lactis. | 2002 | 12384305 |