The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Joanne M. Santini - One of the best experts on this subject based on the ideXlab platform.
-
characterization of a two component signal transduction system that controls arsenite oxidation in the chemolithoautotroph nt 26
Fems Microbiology Letters, 2010Co-Authors: Sunita Sardiwal, Joanne M. Santini, Thomas H Osborne, Snezana DjordjevicAbstract:NT-26 is a chemolithoautotrophic arsenite oxidizer. Understanding the mechanisms of arsenite signalling, tolerance and oxidation by NT-26 will have significant implications for its use in bioremediation and arsenite sensing. We have identified the histidine kinase (AroS) and the cognate response regulator (AroR) involved in the arsenite-dependent transcriptional regulation of the arsenite oxidase aroBA operon. AroS contains a single periplasmic sensory domain that is linked through transmembrane helices to the HAMP domain that transmits the signal to the kinase core of the protein. AroR belongs to a family of AAA+ transcription regulators that interact with DNA through a helix-turn-helix domain. The presence of the AAA+ domain as well as the RNA polymerase σ54-interaction sequence motif suggests that this protein regulates transcription through interaction with RNA polymerase in a σ54-dependent fashion. The kinase core of AroS and the receiver domain of AroR were heterologously expressed and purified and their autophosphorylation and transphosphorylation activities were confirmed. Using site-directed mutagenesis, we have identified the phosphorylation sites on both proteins. Mutational analysis in NT-26 confirmed that both proteins are essential for arsenite oxidation and the AroS mutant affected growth with arsenite, also implicating it in the regulation of arsenite tolerance. Lastly, arsenite sensing does not appear to involve thiol chemistry.
-
Microbial oxidation of arsenite in a subarctic environment: diversity of arsenite oxidase genes and identification of a psychrotolerant arsenite oxidiser.
BMC Microbiology, 2010Co-Authors: Thomas H Osborne, Heather E. Jamieson, Stephen R. Walker, Seamus A. Ward, Karen A. Hudson-edwards, D. Kirk Nordstrom, Joanne M. SantiniAbstract:Background: Arsenic is toxic to most living cells. The two soluble inorganic forms of arsenic are arsenite (+3) and arsenate (+5), with arsenite the more toxic. Prokaryotic metabolism of arsenic has been reported in both thermal and moderate environments and has been shown to be involved in the redox cycling of arsenic. No arsenic metabolism (either dissimilatory arsenate reduction or arsenite oxidation) has ever been reported in cold environments (i.e. < 10°C). Results: Our study site is located 512 kilometres south of the Arctic Circle in the Northwest Territories, Canada in an inactive gold mine which contains mine waste water in excess of 50 mM arsenic. Several thousand tonnes of arsenic trioxide dust are stored in underground chambers and microbial biofilms grow on the chamber walls below seepage points rich in arsenite-containing solutions. We compared the arsenite oxidisers in two subsamples (which differed in arsenite concentration) collected from one biofilm. ‘Species’ (sequence) richness did not differ between subsamples, but the relative importance of the three identifiable clades did. An arsenite-oxidising bacterium (designated GM1) was isolated, and was shown to oxidise arsenite in the early exponential growth phase and to grow at a broad range of temperatures (4-25°C). Its arsenite oxidase was constitutively expressed and functioned over a broad temperature range. Conclusions: The diversity of arsenite oxidisers does not significantly differ from two subsamples of a microbial biofilm that vary in arsenite concentrations. GM1 is the first psychrotolerant arsenite oxidiser to be isolated with the ability to grow below 10°C. This ability to grow at low temperatures could be harnessed for arsenic bioremediation in moderate to cold climates.
-
Arsenite oxidation by the heterotroph Hydrogenophaga sp. str. NT-14: the arsenite oxidase and its physiological electron acceptor.
Biochimica et biophysica acta, 2004Co-Authors: Rachel N Vanden Hoven, Joanne M. SantiniAbstract:Heterotrophic arsenite oxidation by Hydrogenophaga sp. str. NT-14 is coupled to the reduction of oxygen and appears to yield energy for growth. Purification and partial characterization of the arsenite oxidase revealed that it (1). contains two heterologous subunits, AroA (86 kDa) and AroB (16 kDa), (2). has a native molecular mass of 306 kDa suggesting an alpha(3)beta(3) configuration, and (3). contains molybdenum and iron as cofactors. Although the Hydrogenophaga sp. str. NT-14 arsenite oxidase shares similarities to the arsenite oxidases purified from NT-26 and Alcaligenes faecalis, it differs with respect to activity and overall conformation. A c-551-type cytochrome was purified from Hydrogenophaga sp. str. NT-14 and appears to be the physiological electron acceptor for the arsenite oxidase. The cytochrome can also accept electrons from the purified NT-26 arsenite oxidase. A hypothetical electron transport chain for heterotrophic arsenite oxidation is proposed.
-
Arsenite oxidation by the heterotroph Hydrogenophaga sp. str. NT-14: the arsenite oxidase and its physiological electron acceptor
Biochimica et Biophysica Acta, 2004Co-Authors: Rachel N. Vanden Hoven, Joanne M. SantiniAbstract:Abstract Heterotrophic arsenite oxidation by Hydrogenophaga sp. str. NT-14 is coupled to the reduction of oxygen and appears to yield energy for growth. Purification and partial characterization of the arsenite oxidase revealed that it (1) contains two heterologous subunits, AroA (86 kDa) and AroB (16 kDa), (2) has a native molecular mass of 306 kDa suggesting an α3β3 configuration, and (3) contains molybdenum and iron as cofactors. Although the Hydrogenophaga sp. str. NT-14 arsenite oxidase shares similarities to the arsenite oxidases purified from NT-26 and Alcaligenes faecalis, it differs with respect to activity and overall conformation. A c-551-type cytochrome was purified from Hydrogenophaga sp. str. NT-14 and appears to be the physiological electron acceptor for the arsenite oxidase. The cytochrome can also accept electrons from the purified NT-26 arsenite oxidase. A hypothetical electron transport chain for heterotrophic arsenite oxidation is proposed.
-
Molybdenum-Containing Arsenite Oxidase of the Chemolithoautotrophic Arsenite Oxidizer NT-26
Journal of Bacteriology, 2004Co-Authors: Joanne M. Santini, Rachel N. Vanden HovenAbstract:The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an α2β2 configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per α2β2 unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of Alcaligenes faecalis, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of Aeropyrum pernix, Sulfolobus tokodaii, and Chloroflexus aurantiacus. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome bc1 and b6f complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an aroA mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate.
Srinivasa D Sarma - One of the best experts on this subject based on the ideXlab platform.
-
geology and geochemistry of Arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes
Precambrian Research, 2002Co-Authors: S M Naqvi, C Manikyamba, Nirmal S Charan, V Balaram, Srinivasa D SarmaAbstract:Abstract Detailed geological, petrological and geochemical studies have been carried out on an Arenite–quartzwacke suite of rocks constituting a part of the Late Archaean Sandur schist belt in Dharwar craton, southern India for understanding the nature of provenance for these sedimentary rocks. The Arenite–quartzwacke consists of rounded to sub-rounded and angular fragments of monocrystalline–polycrystalline quartz, quartzite and chert embedded in a fine-grained matrix of quartz and sericite. While Arenites are more siliceous (SiO 2 , 80–92 wt.%), the quartzwacke have relatively lower silica content (ca. 69–78 wt.%). The Arenites and quartzwackes have CIA values ranging from 76 to 96 which suggest intense chemical weathering. This is further corroborated by the positive correlation between Al 2 O 3 and TiO 2 in both these rock types. The ACNK modeling of Arenites and quartzwackes show evidence for addition of K 2 O during later metasomatic alteration. In the ACNKFM ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during K-metasomatism and the presence of mafic rocks in the source. The high concentration of HFSE such as Zr, Hf, Nb and Ta and the trace element ratios Th/Sc, La/Sc, Th/U and Ce/Th in the Arenite–quartzwacke indicate a mixed provenance. The rare earth element modeling of quartzwackes considering tonalite, granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members. A composition comprising of 25% tonalite+25% granite+50% amphibolite in the provenance appears to match with the observed range of REE patterns of quartzwackes. The presence of higher proportions of granite in the provenance is evidenced by the large negative Eu anomalies in these sediments. Field evidence and structural discordance suggest that the Arenite–quartzwacke suite is an allochthonous part of the Sandur schist belt.
S M Naqvi - One of the best experts on this subject based on the ideXlab platform.
-
geology and geochemistry of Arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes
Precambrian Research, 2002Co-Authors: S M Naqvi, C Manikyamba, Nirmal S Charan, V Balaram, Srinivasa D SarmaAbstract:Abstract Detailed geological, petrological and geochemical studies have been carried out on an Arenite–quartzwacke suite of rocks constituting a part of the Late Archaean Sandur schist belt in Dharwar craton, southern India for understanding the nature of provenance for these sedimentary rocks. The Arenite–quartzwacke consists of rounded to sub-rounded and angular fragments of monocrystalline–polycrystalline quartz, quartzite and chert embedded in a fine-grained matrix of quartz and sericite. While Arenites are more siliceous (SiO 2 , 80–92 wt.%), the quartzwacke have relatively lower silica content (ca. 69–78 wt.%). The Arenites and quartzwackes have CIA values ranging from 76 to 96 which suggest intense chemical weathering. This is further corroborated by the positive correlation between Al 2 O 3 and TiO 2 in both these rock types. The ACNK modeling of Arenites and quartzwackes show evidence for addition of K 2 O during later metasomatic alteration. In the ACNKFM ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during K-metasomatism and the presence of mafic rocks in the source. The high concentration of HFSE such as Zr, Hf, Nb and Ta and the trace element ratios Th/Sc, La/Sc, Th/U and Ce/Th in the Arenite–quartzwacke indicate a mixed provenance. The rare earth element modeling of quartzwackes considering tonalite, granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members. A composition comprising of 25% tonalite+25% granite+50% amphibolite in the provenance appears to match with the observed range of REE patterns of quartzwackes. The presence of higher proportions of granite in the provenance is evidenced by the large negative Eu anomalies in these sediments. Field evidence and structural discordance suggest that the Arenite–quartzwacke suite is an allochthonous part of the Sandur schist belt.
-
Geology and geochemistry of Arenite-quartzwacke from the Late Archaean Sandur schist belt—implications for provenance and accretion processes
Precambrian Research, 2002Co-Authors: S M Naqvi, C Manikyamba, V Balaram, S. Nirmal Charan, D. Srinivasa SarmaAbstract:Abstract Detailed geological, petrological and geochemical studies have been carried out on an Arenite–quartzwacke suite of rocks constituting a part of the Late Archaean Sandur schist belt in Dharwar craton, southern India for understanding the nature of provenance for these sedimentary rocks. The Arenite–quartzwacke consists of rounded to sub-rounded and angular fragments of monocrystalline–polycrystalline quartz, quartzite and chert embedded in a fine-grained matrix of quartz and sericite. While Arenites are more siliceous (SiO 2 , 80–92 wt.%), the quartzwacke have relatively lower silica content (ca. 69–78 wt.%). The Arenites and quartzwackes have CIA values ranging from 76 to 96 which suggest intense chemical weathering. This is further corroborated by the positive correlation between Al 2 O 3 and TiO 2 in both these rock types. The ACNK modeling of Arenites and quartzwackes show evidence for addition of K 2 O during later metasomatic alteration. In the ACNKFM ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during K-metasomatism and the presence of mafic rocks in the source. The high concentration of HFSE such as Zr, Hf, Nb and Ta and the trace element ratios Th/Sc, La/Sc, Th/U and Ce/Th in the Arenite–quartzwacke indicate a mixed provenance. The rare earth element modeling of quartzwackes considering tonalite, granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members. A composition comprising of 25% tonalite+25% granite+50% amphibolite in the provenance appears to match with the observed range of REE patterns of quartzwackes. The presence of higher proportions of granite in the provenance is evidenced by the large negative Eu anomalies in these sediments. Field evidence and structural discordance suggest that the Arenite–quartzwacke suite is an allochthonous part of the Sandur schist belt.
V N Kozhevnikov - One of the best experts on this subject based on the ideXlab platform.
-
an archean quartz Arenite andesite association in the eastern baltic shield russia implications for assemblage types and shield history
Precambrian Research, 2000Co-Authors: P C Thurston, V N KozhevnikovAbstract:Abstract Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe an unusual quartz Arenite-subaerial andesite association within the Archean Hisovaara greenstone belt, a fragment of the Parandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists of several lithotectonic assemblages: (1) a komatiite-tholeiite assemblage>2803 Ma (based on ages of cross-cutting dikes); (2) an andesite-quartz Arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks, and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. The andesite-quartz Arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental andesites overlain by massive andesites, then amygdaloidal and plagioclase phyric andesites. Unconformably overlying the andesite is a unit of quartz-rich sandstones (6–40 m thick) dominated by quartz Arenite extending several km along strike. At the north end, the quartz Arenite succession consists of basal andesite overlain by quartz Arenite exhibiting hummocky cross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite/komatiite unit. At the south end, the succession is basal andesite, regolith, cross-bedded quartz Arenite, weathered andesites, a second quartz Arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry has been obtained on the rocks of the andesite-quartz Arenite assemblage. The quartz Arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz Arenites. The andesites display moderately fractionated spidergrams with negative anomalies at Ti, Ta and Nb typical of arc volcanism. The andesite-quartz Arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerial andesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaara andesite-quartz Arenite assemblage provides a linkage in Archean greenstones between assemblages representing continental volcanism and a platform-to-rift setting. The presence of an erosional interval in>2.8 Ga greenstones suggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada.
-
An Archean quartz Arenite–andesite association in the eastern Baltic Shield, Russia: implications for assemblage types and shield history
Precambrian Research, 2000Co-Authors: P C Thurston, V N KozhevnikovAbstract:Abstract Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe an unusual quartz Arenite-subaerial andesite association within the Archean Hisovaara greenstone belt, a fragment of the Parandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists of several lithotectonic assemblages: (1) a komatiite-tholeiite assemblage>2803 Ma (based on ages of cross-cutting dikes); (2) an andesite-quartz Arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks, and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. The andesite-quartz Arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental andesites overlain by massive andesites, then amygdaloidal and plagioclase phyric andesites. Unconformably overlying the andesite is a unit of quartz-rich sandstones (6–40 m thick) dominated by quartz Arenite extending several km along strike. At the north end, the quartz Arenite succession consists of basal andesite overlain by quartz Arenite exhibiting hummocky cross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite/komatiite unit. At the south end, the succession is basal andesite, regolith, cross-bedded quartz Arenite, weathered andesites, a second quartz Arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry has been obtained on the rocks of the andesite-quartz Arenite assemblage. The quartz Arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz Arenites. The andesites display moderately fractionated spidergrams with negative anomalies at Ti, Ta and Nb typical of arc volcanism. The andesite-quartz Arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerial andesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaara andesite-quartz Arenite assemblage provides a linkage in Archean greenstones between assemblages representing continental volcanism and a platform-to-rift setting. The presence of an erosional interval in>2.8 Ga greenstones suggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada.
V Balaram - One of the best experts on this subject based on the ideXlab platform.
-
geology and geochemistry of Arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes
Precambrian Research, 2002Co-Authors: S M Naqvi, C Manikyamba, Nirmal S Charan, V Balaram, Srinivasa D SarmaAbstract:Abstract Detailed geological, petrological and geochemical studies have been carried out on an Arenite–quartzwacke suite of rocks constituting a part of the Late Archaean Sandur schist belt in Dharwar craton, southern India for understanding the nature of provenance for these sedimentary rocks. The Arenite–quartzwacke consists of rounded to sub-rounded and angular fragments of monocrystalline–polycrystalline quartz, quartzite and chert embedded in a fine-grained matrix of quartz and sericite. While Arenites are more siliceous (SiO 2 , 80–92 wt.%), the quartzwacke have relatively lower silica content (ca. 69–78 wt.%). The Arenites and quartzwackes have CIA values ranging from 76 to 96 which suggest intense chemical weathering. This is further corroborated by the positive correlation between Al 2 O 3 and TiO 2 in both these rock types. The ACNK modeling of Arenites and quartzwackes show evidence for addition of K 2 O during later metasomatic alteration. In the ACNKFM ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during K-metasomatism and the presence of mafic rocks in the source. The high concentration of HFSE such as Zr, Hf, Nb and Ta and the trace element ratios Th/Sc, La/Sc, Th/U and Ce/Th in the Arenite–quartzwacke indicate a mixed provenance. The rare earth element modeling of quartzwackes considering tonalite, granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members. A composition comprising of 25% tonalite+25% granite+50% amphibolite in the provenance appears to match with the observed range of REE patterns of quartzwackes. The presence of higher proportions of granite in the provenance is evidenced by the large negative Eu anomalies in these sediments. Field evidence and structural discordance suggest that the Arenite–quartzwacke suite is an allochthonous part of the Sandur schist belt.
-
Geology and geochemistry of Arenite-quartzwacke from the Late Archaean Sandur schist belt—implications for provenance and accretion processes
Precambrian Research, 2002Co-Authors: S M Naqvi, C Manikyamba, V Balaram, S. Nirmal Charan, D. Srinivasa SarmaAbstract:Abstract Detailed geological, petrological and geochemical studies have been carried out on an Arenite–quartzwacke suite of rocks constituting a part of the Late Archaean Sandur schist belt in Dharwar craton, southern India for understanding the nature of provenance for these sedimentary rocks. The Arenite–quartzwacke consists of rounded to sub-rounded and angular fragments of monocrystalline–polycrystalline quartz, quartzite and chert embedded in a fine-grained matrix of quartz and sericite. While Arenites are more siliceous (SiO 2 , 80–92 wt.%), the quartzwacke have relatively lower silica content (ca. 69–78 wt.%). The Arenites and quartzwackes have CIA values ranging from 76 to 96 which suggest intense chemical weathering. This is further corroborated by the positive correlation between Al 2 O 3 and TiO 2 in both these rock types. The ACNK modeling of Arenites and quartzwackes show evidence for addition of K 2 O during later metasomatic alteration. In the ACNKFM ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during K-metasomatism and the presence of mafic rocks in the source. The high concentration of HFSE such as Zr, Hf, Nb and Ta and the trace element ratios Th/Sc, La/Sc, Th/U and Ce/Th in the Arenite–quartzwacke indicate a mixed provenance. The rare earth element modeling of quartzwackes considering tonalite, granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members. A composition comprising of 25% tonalite+25% granite+50% amphibolite in the provenance appears to match with the observed range of REE patterns of quartzwackes. The presence of higher proportions of granite in the provenance is evidenced by the large negative Eu anomalies in these sediments. Field evidence and structural discordance suggest that the Arenite–quartzwacke suite is an allochthonous part of the Sandur schist belt.
