Distribution of DNA Sequences Encoding Narrow- and Broad-Spectrum Mercury Resistance

Mercury resistant (Hg(R)) Bacillus were isolated from soil at a mercury contaminated site on the banks of the River Mersey, in Northwest England. The frequency of Hg(R) bacteria in the culturable Bacillus population in soil samples ranged from 4.4 to 5.4. No Hg(R) Bacillus could be isolated from a sediment sample taken close to the contaminated soil sample in 1994. DNA sequences homologous to a merA probe from the Hg(R) isolate Bacillus sp. strain RC607 were found to be chromosomally located in 98 of the Hg(R) Bacillus isolates from the soil site. Oligonucleotide primers designed to the merA gene of RC607 were used to amplify the sequences present in the isolates, and also merA determinants present in bacterial DNA directly extracted from soil. Classification of cultured Bacillus merA products and of 40 merA determinants amplified directly from extracted soil bacterial DNA was based on restriction fragment length polymorphism patterns. This technique revealed a total of 22 classes of amplification products. Unweighted paired group mean analysis was used to examine the relationships between these classes and indicated the presence of microsites in Fiddlers Ferry soil containing distinct Hg(R) populations. API identification of the Hg(R) Bacillus isolates revealed that diversity of merA between these microsites is not simply due to the divergent evolution of differing Bacillus species. Lack of a more substantial class correlation between cultured samples taken at different times indicated significant temporal variation in the genetic composition of Bacillus merA in soil. Copyright (C) 1998 Federation of European Microbiological Societies

Section: Discussionsupporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Diversity amongst Bacillus merA genes amplified from mercury resistant isolates and directly from mercury polluted soil

Hart

1998

“…The proportion of Bacillus strains that are mercury resistant within Fiddlers Ferry soil, at around 5%, is within the range of mercury resistant bacteria isolated in studies previously cited by Rochelle et al [6]. With the total culturable Bacillus population, the viable counts from sediment were significantly lower than those from soil, and so the failure to isolate Hg R Bacillus strains from Fiddlers Ferry sediment is therefore not surprising.…”

Section: Discussionsupporting

confidence: 66%

“…Resistance to these toxic compounds can be found in a diverse range of bacterial species, which have been isolated from different environments across the globe [2–4]. The presence of such mercury resistant (Hg R ) bacteria is often correlated with the level of mercury contamination in an environment [5, 6], although Hg R bacteria have been isolated from ‘uncontaminated’ environments [7].…”

Section: Introductionmentioning

confidence: 99%

Diversity amongst Bacillus merA genes amplified from mercury resistant isolates and directly from mercury polluted soil

Hart

Elliott

Osborn

et al. 1998

Mercury resistant (HgR) Bacillus were isolated from soil at a mercury contaminated site on the banks of the River Mersey, in Northwest England. The frequency of HgR bacteria in the culturable Bacillus population in soil samples ranged from 4.4% to 5.4%. No HgRBacillus could be isolated from a sediment sample taken close to the contaminated soil sample in 1994. DNA sequences homologous to a merA probe from the HgR isolate Bacillus sp. strain RC607 were found to be chromosomally located in 98% of the HgRBacillus isolates from the soil site. Oligonucleotide primers designed to the merA gene of RC607 were used to amplify the sequences present in the isolates, and also merA determinants present in bacterial DNA directly extracted from soil. Classification of cultured Bacillus merA products and of 40 merA determinants amplified directly from extracted soil bacterial DNA was based on restriction fragment length polymorphism patterns. This technique revealed a total of 22 classes of amplification products. Unweighted paired group mean analysis was used to examine the relationships between these classes and indicated the presence of microsites in Fiddlers Ferry soil containing distinct HgR populations. API identification of the HgRBacillus isolates revealed that diversity of merA between these microsites is not simply due to the divergent evolution of differing Bacillus species. Lack of a more substantial class correlation between cultured samples taken at different times indicated significant temporal variation in the genetic composition of Bacillus merA in soil.

“…The short term incubation of soil with Hg(II) did not result in a change in the numbers of VH bacteria nor in the numbers of total bacteria determined by direct microscopy (data not shown) but induced an increase in Hg R colonies ( Table 2). Such an enrichment of resistant strains is a common observation in metal-contaminated soils or aquatic systems [6,7,11,30,31].…”

Section: Impact Of Hg(ii) Spiking On Bacteria In Unfractionated Soilmentioning

confidence: 93%

A soil microscale study to reveal the heterogeneity of Hg(II) impact on indigenous bacteria by quantification of adapted phenotypes and analysis of community DNA fingerprints

Ranjard

2000

The short term impact of 50 WM Hg(II) on soil bacterial community structure was evaluated in different microenvironments of a silt loam soil in order to determine the contribution of bacteria located in these microenvironments to the overall bacterial response to mercury spiking. Microenvironments and associated bacteria, designated as bacterial pools, were obtained by successive soil washes to separate the outer fraction, containing loosely associated bacteria, and the inner fraction, containing bacteria retained into aggregates, followed by a physical fractionation of the inner fraction to separate aggregates according to their size (size fractions). Indirect enumerations of viable heterotrophic (VH) and resistant (Hg R ) bacteria were performed before and 30 days after mercury spiking. A ribosomal intergenic spacer analysis (RISA), combined with multivariate analysis, was used to compare modifications at the community level in the unfractionated soil and in the microenvironments. The spatial heterogeneity of the mercury impact was revealed by a higher increase of Hg R numbers in the outer fraction and in the coarse size fractions. Furthermore, shifts in RISA patterns of total community DNA indicated changes in the composition of the dominant bacterial populations in response to Hg(II) stress in the outer and in the clay size fractions. The heterogeneity of metal impact on indigenous bacteria, observed at a microscale level, is related to both the physical and chemical characteristics of the soil microenvironments governing mercury bioavailability and to the bacterial composition present before spiking. ß