Diversity of mercury resistance determinants amongBacillusstrains isolated from sediment of Minamata Bay

Abstract

Thirty mercury-resistant (Hg R ) Bacillus strains were isolated from mercury-polluted sediment of Minamata Bay, Japan. Mercury resistance phenotypes were classified into broad-spectrum (resistant to inorganic Hg 2þ and organomercurials) and narrow-spectrum (resistant to inorganic Hg 2þ and sensitive to organomercurials) groups. Polymerase chain reaction (PCR) product sizes and the restriction nuclease site maps of mer operon regions from all broad-spectrum Hg R Bacillus were identical to that of Bacillus megaterium MB1. On the other hand, the PCR products of the targeted merP (extracellular mercury-binding protein gene) and merA (intracellular mercury reductase protein gene) regions from the narrow-spectrum Hg R Bacillus were generally smaller than those of the B. megaterium MB1 mer determinant. Diversity of gene structure configurations was also observed by restriction fragment length polymorphism (RFLP) profiles of the merA PCR products from the narrow-spectrum Hg R Bacillus. The genetic diversity of narrow-spectrum mer operons was greater than that of broad-spectrum ones. ß

Diversity of Mercury Resistant Escherichia coli Strains Isolated from Aquatic Systems in Rio de Janeiro, Brazil

“…In our study, this methodology allowed the detection of variability in the 285 bp merA fragment among 14 E. coli strains (Figure 3). These results are in agreement with previous findings regarding the widespread occurrence and diversity of mercury resistance markers among distinct microbial populations from several environments, including soils and sediments, aquatic systems, animals, and clinical isolates [13,14,27,28,31,32]. The high plasticity found in the bacterial genome contributes to the diversity and dissemination of genetic markers favoring its circulation in geographically dispersed environments, even between distinct evolutionary lineages.…”

“…Many studies have been conducted in order to determine the mercury resistance in environmental bacteria by testing the minimum inhibitory concentration [25][26][27][28]. There is not a standard protocol for determining the MIC of heavy metals.…”

“…The genetic system evolved as mer operon is the only well-known bacterial mercury resistance system with high yield transformation of its toxic target into volatile nontoxic forms [27,31,[33][34][35], particularly in Gram-negative bacteria [14,22]. The mer locus is found to be widely distributed among bacterial lineages, and mer-like sequences have been described.…”

“…The increased complexity of mer operons can be attributed to the gradual addition of functions involved in the regulation of the operon by Hg, Hg transport, and organomercury resistance [17]. The diversity of merA gene in Gram-negative and Gram-positive bacteria has been accessed by several approaches including those using restriction fragment assays [27,31,33,34]. In all these studies, a high genetic variability was detected in merA determinant carried by bacterial species from different environments.…”

Splicing of a Bacterial Group II Intron from Bacillus megaterium Is Independent of Intron-Encoded Protein

“…The gene transfer is often relating to the bacterial resistance such as heavy metal resistance (18) or antibiotic resistance (22). Conjugative plasmids, bacteriophages and transposons are well known as the vectors for the mobilization.…”