Gene Determinants for Mercury Bioremediation as Revealed by Draft Genome Sequence Analysis of Stenotrophomonas sp. Strain MA5.
ABSTRACT: A soilborne Stenotrophomonas sp. strain (MA5) that is resistant to mercury was isolated. A draft genome sequence-based analysis revealed a suite of gene determinants to resist mercury and other heavy metals, multidrug efflux, stress response, and membrane transport, and these provide cues to a suite of mechanisms that underpin cellular survival in contaminated soil.
Project description:A largely understudied microbially mediated mercury (Hg) bioremediative pathway includes the volatilization of Hg2+ to Hg⁰. Therefore, studies on Hg resistant bacteria (HgR), isolated from historically long-term contaminated environments, can serve as models to understand mechanisms underpinning Hg cycling. Towards this end, a mercury resistant bacterial strain, identified as Stenotrophomonas sp., strain MA5, was isolated from Mill Branch on the Savannah River Site (SRS); an Hg-impacted ecosystem. Minimum inhibitory concentration (MIC) analysis showed Hg resistance of up to 20 µg/mL by MA5 with 95% of cells retaining viability. Microcosm studies showed that the strain depleted more than 90% of spiked Hg2+ within the first 24 h of growth and the detection of volatilized mercury indicated that the strain was able to reduce Hg2+ to Hg⁰. To understand molecular mechanisms of Hg volatilization, a draft whole genome sequence was obtained, annotated and analyzed, which revealed the presence of a transposon-derived mer operon (merRTPADE) in MA5, known to transport and reduce Hg2+ into Hg⁰. Based on the whole genome sequence of strain MA5, qRT-PCR assays were designed on merRTPADE, we found a ~40-fold higher transcription of mer T, P, A, D and E when cells were exposed to 5 µg/mL Hg2+. Interestingly, strain MA5 increased cellular size as a function of increasing Hg concentrations, which is likely an evolutionary response mechanism to cope with Hg stress. Moreover, metal contaminated environments are shown to co-select for antibiotic resistance. When MA5 was screened for antibiotic resistance, broad resistance against penicillin, streptomycin, tetracycline, ampicillin, rifampicin, and erythromycin was found; this correlated with the presence of multiple gene determinants for antibiotic resistance within the whole genome sequence of MA5. Overall, this study provides an in-depth understanding of the underpinnings of Stenotrophomonas-mercury interactions that facilitate cellular survival in a contaminated soil habitat.
Project description:Thirty-one mercury-resistant bacterial strains were isolated from the effluent discharge sites of the SIPCOT industrial area. Among them, only one strain (CASKS5) was selected for further investigation due to its high minimum inhibitory concentration of mercury and low antibiotic susceptibility. In accordance with 16S ribosomal RNA gene sequences, the strain CASKS5 was identified as Vibrio fluvialis. The mercury-removal capacity of V. fluvialis was analyzed at four different concentrations (100, 150, 200, and 250??g/ml). Efficient bioremediation was observed at a level of 250??g/ml with the removal of 60% of mercury ions. The interesting outcome of this study was that the strain V. fluvialis had a high bioremediation efficiency but had a low antibiotic resistance. Hence, V. fluvialis could be successfully used as a strain for the ecofriendly removal of mercury.
Project description:The gram negative bacterium Stenotrophomonas is rapidly evolving as a nosocomial pathogen in immuno-compromised patients. Treatment of Stenotrophomonas maltophilia infections is problematic because of their increasing resistance to multiple antibiotics. This article aims to review the multi-disciplinary role of Stenotrophomonas in our environment with special focus on their metabolic and genetic potential in relation to bioremediation and phytoremediation. Current and emerging treatments and diagnosis for patients infected with S. maltophilia are discussed besides their capability of production of novel bioactive compounds. The plant growth promoting characteristics of this bacterium has been considered with special reference to secondary metabolite production. Nano-particle synthesis by Stenotrophomonas has also been reviewed in addition to their applications as effective biocontrol agents in plant and animal pathogenesis.
Project description:Carriage of resistance genes can underpin bacterial survival, and by spreading these genes between species, mobile genetic elements (MGEs) can potentially protect diversity within microbial communities. The spread of MGEs could be affected by environmental factors such as selection for resistance, and biological factors such as plasmid host range, with consequences for individual species and for community structure. Here we cultured a focal bacterial strain, Pseudomonas fluorescens SBW25, embedded within a soil microbial community, with and without mercury selection, and with and without mercury resistance plasmids (pQBR57 or pQBR103), to investigate the effects of selection and resistance gene introduction on (1) the focal species; (2) the community as a whole; (3) the spread of the introduced mer resistance operon. We found that P. fluorescens SBW25 only escaped competitive exclusion by other members of community under mercury selection, even when it did not begin with a mercury resistance plasmid, due to its propensity to acquire resistance from the community by horizontal gene transfer. Mercury pollution had a significant effect on community structure, decreasing alpha diversity within communities while increasing beta diversity between communities, a pattern that was not affected by the introduction of mercury resistance plasmids by P. fluorescens SBW25. Nevertheless, the introduced merA gene spread to a phylogenetically diverse set of recipients over the 5 weeks of the experiment, as assessed by epicPCR. Our data demonstrates how the effects of MGEs can be experimentally assessed for individual lineages, the wider community, and for the spread of adaptive traits.
Project description:A Gram-stain negative, rod-shaped, aerobic bacterial strain, BII-R7T, was isolated during a study targeting the culture-dependent microbial diversity occurring in bentonite formations from southern Spain. Comparative 16S rRNA gene sequence analysis showed that BII-R7T represented a member of the genus Stenotrophomonas (class Gammaproteobacteria), and was related most closely to Stenotrophomonas rhizophila e-p10T (99.2?% sequence similarity), followed by Stenotrophomonas pavanii ICB 89T (98.5?%), Stenotrophomonas maltophilia IAM 12423T, Stenotrophomonas chelatiphaga LPM-5T and Stenotrophomonas tumulicola T5916-2-1bT (all 98.3?%). Pairwise sequence similarities to all other type strains of species of the genus Stenotrophomonas were below 98?%. Genome-based calculations (orthologous average nucleotide identity, original average nucleotide identity, genome-to-genome distance and DNA G+C percentage) indicated clearly that the isolate represents a novel species within this genus. Different phenotypic analyses, such as the detection of a quinone system composed of the major compound ubiquinone Q-8 and a fatty acid profile with iso-C15?:?0 and anteiso-C15?:?0 as major components, supported this finding at the same time as contributing to a comprehensive characterization of BII-R7T. Based on this polyphasic approach comprising phenotypic and genotypic/molecular characterization, BII-R7T can be differentiated clearly from its phylogenetic neighbours, establishing a novel species for which the name Stenotrophomonas bentonitica sp. nov. is proposed with BII-R7T as the type strain (=LMG 29893T=CECT 9180T=DSM 103927T).
Project description:The widespread distribution of mercury (Hg) threatens wildlife health, particularly piscivorous birds. Western North America is a diverse region that provides critical habitat to many piscivorous bird species, and also has a well-documented history of mercury contamination from legacy mining and atmospheric deposition. The diversity of landscapes in the west limits the distribution of avian piscivore species, complicating broad comparisons across the region. Mercury risk to avian piscivores was evaluated across the western United States and Canada using a suite of avian piscivore species representing a variety of foraging strategies that together occur broadly across the region. Prey fish Hg concentrations were size-adjusted to the preferred size class of the diet for each avian piscivore (Bald Eagle=36cm, Osprey=30cm, Common and Yellow-billed Loon=15cm, Western and Clark's Grebe=6cm, and Belted Kingfisher=5cm) across each species breeding range. Using a combination of field and lab-based studies on Hg effect in a variety of species, wet weight blood estimates were grouped into five relative risk categories including: background (<0.5?g/g), low (0.5-1?g/g), moderate (1-2?g/g), high (2-3?g/g), and extra high (>3?g/g). These risk categories were used to estimate potential mercury risk to avian piscivores across the west at a 1degree-by-1degree grid cell resolution. Avian piscivores foraging on larger-sized fish generally were at a higher relative risk to Hg. Habitats with a relatively high risk included wetland complexes (e.g., prairie pothole in Saskatchewan), river deltas (e.g., San Francisco Bay, Puget Sound, Columbia River), and arid lands (Great Basin and central Arizona). These results indicate that more intensive avian piscivore sampling is needed across Western North America to generate a more robust assessment of exposure risk.
Project description:Full title: Mercury-Induced Hepatotoxicity in Zebrafish: In Vivo Mechanistic Insights from Transcriptome Analysis, Phenotype Anchoring and Targeted Gene Expression Validation In this study, we performed microarray-based expression profiling on liver of zebrafish exposed to 200 µg/L of mercuric chloride for 8-96 h, to identify global transcriptional programs and biological pathways involved in mercury-induced adaptive responses under in vivo environment. Overall design: We analyzed 12 arrays for mercuric chloride treated zebrafish liver and 12 arrays for control liver.
Project description:Stenotrophomonas maltophilia is an emerging opportunistic human pathogen. In this report, we describe the isolation and genomic annotation of the S. maltophilia-infecting bacteriophage Mendera. A myophage of 159,961 base pairs, Mendera is T4-like and related most closely to Stenotrophomonas phage IME-SM1.
Project description:Prior studies addressing associations between mercury and blood pressure have produced inconsistent findings; some of this may result from measuring total instead of speciated mercury. This cross-sectional study of 263 pregnant women assessed total mercury, speciated mercury, selenium, and n-3 polyunsaturated fatty acids in umbilical cord blood and blood pressure during labor and delivery. Models with a) total mercury or b) methyl and inorganic mercury were evaluated. Regression models adjusted for maternal age, race/ethnicity, prepregnancy body mass index, neighborhood income, parity, smoking, n-3 fatty acids and selenium. Geometric mean total, methyl, and inorganic mercury concentrations were 1.40µg/L (95% confidence interval: 1.29, 1.52); 0.95µg/L (0.84, 1.07); and 0.13µg/L (0.10, 0.17), respectively. Elevated systolic BP, diastolic BP, and pulse pressure were found, respectively, in 11.4%, 6.8%, and 19.8% of mothers. In adjusted multivariable models, a one-tertile increase of methyl mercury was associated with 2.83mmHg (0.17, 5.50) higher systolic blood pressure and 2.99mmHg (0.91, 5.08) higher pulse pressure. In the same models, an increase of one tertile of inorganic mercury was associated with -1.18mmHg (-3.72, 1.35) lower systolic blood pressure and -2.51mmHg (-4.49, -0.53) lower pulse pressure. No associations were observed with diastolic pressure. There was a non-significant trend of higher total mercury with higher systolic blood pressure. We observed a significant association of higher methyl mercury with higher systolic and pulse pressure, yet higher inorganic mercury was significantly associated with lower pulse pressure. These results should be confirmed with larger, longitudinal studies.