S. Ray

Bio: S. Ray is an academic researcher from University of Calcutta. The author has contributed to research in topics: Mercury(II) reductase & Mercury (element). The author has an hindex of 5, co-authored 12 publications receiving 74 citations.

Effect of thiol compounds and flavins on mercury and organomercurial degrading enzymes in mercury resistant aquatic bacteria.

Abstract: Plasmid-determined mercuric and organomercurial resistance in microorganisms has been studied by several workers. Mercury reductase, catalyzing the reduction of mercury depends on sulfhydryl compounds. Organomercurial lyase that catalyzes the splitting of C-Hg linkages also needs thiol compounds for its activity. Until recently, no study has been reported on thiol specificity of these enzymes from various sources. In the present study, the authors report on enzymatic volatilization of HgCl{sub 2} by fourteen Hg-resistant bacterial strains. They have also studied thiol specificity of Hg-reductases and organomercurial lyases isolated from the above bacterial species. Hg-reductase is known to have FAD-moiety which stimulates enzyme activity whereas FMN and riboflavin are ineffective in this regard. The effect of flavins, namely FAD, FMN and riboflavin, on Hg-reductase and organomercurial lyase activity is also reported here.

Volatilization of mercury compounds and utilization of various aromatic compounds by a broad-spectrum mercury resistant Bacillus pasteurii strain

Abstract: Aquatic ecosystems may receive aromatic compounds through various routes These compounds can cause cancerous diseases in aquatic animals and enhance mutagenicity of the sediments The persistence of aromatic compounds deposited in sediments is affected by microbial degradation Plasmid-determined mercuric and organomercurial resistance in microorganisms has also been studied by several workers Utilization of various aromatic compounds as sole sources of carbon by an Hg-resistant bacterial strain has not been reported The author isolated a broad-spectrum Hg-resistant Bacillus pasteurii strain DR{sub 2} which could volatilize different mercury compounds and utilize various aromatic compounds as sole sources of carbon This strain preferentially utilized benzene in a medium containing both glucose and benzene To their knowledge, until recently there has been no report on preferential utilization of other compounds, particularly an aromatic compound to glucose in a mixture

Mercury resistance in nitrogen-fixing soil bacteria

Abstract: A large number of mercury-resistant nitrogen-fixing bacteria were isolated by screening soil samples from agricultural farms of West Bengal, India. All of the samples were found to contain significant quantities of mercury. Twenty five of the pure isolates were identified to the generic level following Bergey's Manual of Determinative Bacteriology, 8th edition. These organisms were resistant to HgCl2, and a few of them were resistant to phenylmercuric acetate (PMA) as well. Their mercury resistance was also associated with antibiotic resistance properties. Growth of two mercury-resistant N2-fixing organisms was monitored in liquid media supplemented with HgCl2. The mercury volatilizing capacity of four mercury-resistant bacterial strains was also determined.

Studies on mercury-detoxicating enzymes from a broad-spectrum mercury-resistant strain of Flavobacterium rigense

Abstract: Flavobacterium rigense strain PR2, a broad-spectrum mercury-resistant bacterium abundantly present in soil exhibited multiple metal resistance properties. Mercury resistance was due to the sequential action of two mercury-detoxicating enzymes, organomercurial lyase and mercuric reductase. The levels of these enzyme activities were determined using different mercury compounds as inducers and substrates. Mercuric reductase was partially purified from the bacterium and the physicochemical properties of the enzyme were studied. The effect of several enzyme inhibitors and heavy metal ions on the enzyme activity was also studied.

Studies on the mercury volatilizing enzymes in nitrogen-fixing Beijerinckia mobilis.

Abstract: Beijerinckia mobilis KDr2, a broad-spectrum, mercury-resistant nitrogen-fixing organism, possesses multiple metal-resistance properties. Mercuric reductase and organomercurial lyase activities of this bacterial strain were determined using different mercury compounds and heavy metal salts of copper, nickel, cobalt, cadmium, silver, zinc, lead and arsenate as inducers and substrates. Mercuric reductase was partially purified and the effect of some enzyme inhibitors and heavy metal ions on the enzyme activity was studied. The enzyme activity was completely inhibited by CdCl2, Bi(NO3)3 and KCN at 10-5M and by AgNO3, CoCl2 and CuSO4 at 10-4M.

Distribution, diversity and evolution of the bacterial mercury resistance (mer) operon

Abstract: Mercury and its compounds are distributed widely across the earth. Many of the chemical forms of mercury are toxic to all living organisms. However, bacteria have evolved mechanisms of resistance to several of these different chemical forms, and play a major role in the global cycling of mercury in the natural environment. Five mechanisms of resistance to mercury compounds have been identified, of which resistance to inorganic mercury (HgR) is the best understood, both in terms of the mechanisms of resistance to mercury and of resistance to heavy metals in general. Resistance to inorganic mercury is encoded by the genes of the mer operon, and can be located on transposons, plasmids and the bacterial chromosome. Such systems have a worldwide geographical distribution, and furthermore, are found across a wide range of both Gram-negative and Gram-positive bacteria from both natural and clinical environments. The presence of mer genes in bacteria from sediment cores suggest that mer is an ancient system. Analysis of DNA sequences from mer operons and genes has revealed genetic variation both in operon structure and between individual genes from different mer operons, whilst analysis of bacteria which are sensitive to inorganic mercury has identified a number of vestigial non-functional operons. It is hypothesised that mer, due to its ubiquity with respect to geographical location, environment and species range, is an ancient system, and that ancient bacteria carried genes conferring resistance to mercury in response to increased levels of mercury in natural environments, perhaps resulting from volcanic activity. Models for the evolution of both a basic mer operon and for the Tn21-related family of mer operons and transposons are suggested. The study of evolution in bacteria has recently become dominated by the generation of phylogenies based on 16S rRNA genes. However, it is important not to underestimate the roles of horizontal gene transfer and recombinational events in evolution. In this respect mer is a suitable system for evaluating phylogenetic methods which incorporate the effects of horizontal gene transfer. In addition, the mer operon provides a model system in the study of environmental microbiology which is useful both as an example of a genotype which is responsive to environmental pressures and as a generic tool for the development of new methodology for the analysis of bacterial communities in natural environments.

Glutathione in bacteria

Abstract: Glutathione metabolism and its role in vital functions of bacterial cells are considered, as well as common features and differences between the functions of glutathione in prokaryotic and eukaryotic cells. Particular attention is given to the recent data for the role of glutathione in bacterial redox-regulation and adaptation to stresses.

Mercury in aquatic ecosystems

Abstract: Mercury (Hg) is one of the most toxic heavy metals. From a biological perspective it has no redeeming virtue, for, unlike a number of other heavy metals, it is not known to perform any essential biochemical function (Bowen, 1966). Traces of Hg are ubiquitous in soils, natural waters, sediments, organisms and air (Jonasson and Boyle, 1972), and anomalously high Hg concentrations occur in many ecosystems owing to Hg pollution (a serious, widespread problem), natural Hg enrichment in certain rocks, distinctive properties of Hg such as its tendency to form highly stable complexes and compounds (including species that are easily taken up by organisms but not readily excreted), natural processes (e.g. methylation) which enhance the bioavailability of Hg, increased bioavailability of Hg due to environmental changes caused by human activities, and efficient accumulation of Hg by organisms and certain natural materials, such as soil organic matter and fine-grained sediments. Moreover, Hg is a relatively volatile element, and this accounts, in large part, for its wide distribution.

Mercury (II) removal by resistant bacterial isolates and mercuric (II) reductase activity in a new strain of Pseudomonas sp. B50A

Abstract: This study aimed to isolate mercury resistant bacteria, determine the minimum inhibitory concentration for Hg, estimate mercury removal by selected isolates, explore the mer genes, and detect and characterize the activity of the enzyme mercuric (II) reductase produced by a new strain of Pseudomonas sp. B50A. The Hg removal capacity of the isolates was determined by incubating the isolates in Luria Bertani broth and the remaining mercury quantified by atomic absorption spectrophotometry. A PCR reaction was carried out to detect the merA gene and the mercury (II) reductase activity was determined in a spectrophotometer at 340 nm. Eight Gram-negative bacterial isolates were resistant to high mercury concentrations and capable of removing mercury, and of these, five were positive for the gene merA. The isolate Pseudomonas sp. B50A removed 86% of the mercury present in the culture medium and was chosen for further analysis of its enzyme activity. Mercuric (II) reductase activity was detected in the crude extract of this strain. This enzyme showed optimal activity at pH 8 and at temperatures between 37°C and 45°C. The ions NH4+, Ba2+, Sn2+, Ni2+ and Cd2+ neither inhibited nor stimulated the enzyme activity but it decreased in the presence of the ions Ca2+, Cu+ and K+. The isolate and the enzyme detected were effective in reducing Hg(II) to Hg(0), showing the potential to develop bioremediation technologies and processes to clean-up the environment and waste contaminated with mercury.

Cadmium resistant Enterobacter cloacae and Klebsiella sp. isolated from industrial effluents and their possible role in cadmium detoxification

Abstract: Three bacterial strains, two of Klebsiella sp. and one Enterobacter cloacae were isolated from industrial effluents of chemical and textile industries. They showed high efficiency in removing cadmium (Cd2+) from the medium. When 100 μg/ml of Cd was added to the medium, the three isolates namely CMBL-Cd1, CMBL-Cd2 and CMBL-Cd3 removed or accumulated 86%, 87% and 85% of Cd, respectively, from the medium within 24h. Plasmids were detected in all the three strains. Plasmids of E. cloacae (pCBL1) and Klebsiella sp. (pCBL2 and pCBL3), estimated to be 6.6kb, were used to transform Escherichia coli C600. The transformed E. coli cells showed elevated resistance to Cd. Ethidium bromide curing indicated the presence of the Cd resistance gene on the plasmid. Resistance of the isolated strains against other metals like chromium (cr6+) and lead (pb2+) and a number of antibiotics was also checked. Cured strains showed lowered resistance against Cr and some antibiotics. This again supported the indication of the presence of Cd, Cr and some antibiotics resistance genes on plasmids.