Biomedical subjects

John F Stolz

Publications and source records attributed to John F Stolz.

8 recordsLinked to original sources

PubMed2006

Arsenic and selenium in microbial metabolism.

Arsenic and selenium are readily metabolized by prokaryotes, participating in a full range of metabolic functions including assimilation, methylation, detoxification, and anaerobic respiration. Arsenic speciation and mobility is affected by microbes through oxidation/reduction reactions as part of resistance and respiratory processes. A robust arsenic cycle has been demonstrated in diverse environments. Respiratory arsenate reductases, arsenic methyltransferases, and new components in arsenic resistance have been recently described. The requirement for selenium stems primarily from its incorporation into selenocysteine and its function in selenoenzymes. Selenium oxyanions can serve as an electron acceptor in anaerobic respiration, forming distinct nanoparticles of elemental selenium that may be enriched in (76)Se. The biogenesis of selenoproteins has been elucidated, and selenium methyltransferases and a respiratory selenate reductase have also been described. This review highlights recent advances in ecology, biochemistry, and molecular biology and provides a prelude to the impact of genomics studies.

Amino Acid Sequence↗

PubMed2005

A microbial arsenic cycle in a salt-saturated, extreme environment.

Searles Lake is a salt-saturated, alkaline brine unusually rich in the toxic element arsenic. Arsenic speciation changed from arsenate [As(V)] to arsenite [As(III)] with sediment depth. Incubated anoxic sediment slurries displayed dissimilatory As(V)-reductase activity that was markedly stimulated by H2 or sulfide, whereas aerobic slurries had rapid As(III)-oxidase activity. An anaerobic, extremely haloalkaliphilic bacterium was isolated from the sediment that grew via As(V) respiration, using either lactate or sulfide as its electron donor. Hence, a full biogeochemical cycle of arsenic occurs in Searles Lake, driven in part by inorganic electron donors.

Aerobiosis↗

PubMed2005

Arsenic, microbes and contaminated aquifers.

The health of tens of millions of people world-wide is at risk from drinking arsenic-contaminated well water. In most cases this arsenic occurs naturally within the sub-surface aquifers, rather than being derived from identifiable point sources of pollution. The mobilization of arsenic into the aqueous phase is the first crucial step in a process that eventually leads to human arsenicosis. Increasing evidence suggests that this is a microbiological phenomenon.

Archaea↗

PubMed2005

Whither or wither geomicrobiology in the era of 'community metagenomics'.

Molecular techniques are valuable tools that can improve our understanding of the structure of microbial communities. They provide the ability to probe for life in all niches of the biosphere, perhaps even supplanting the need to cultivate microorganisms or to conduct ecophysiological investigations. However, an overemphasis and strict dependence on such large information-driven endeavours as environmental metagenomics could overwhelm the field, to the detriment of microbial ecology. We now call for more balanced, hypothesis-driven research efforts that couple metagenomics with classic approaches.

Bacteria↗

PubMed2004

Dissimilatory arsenate reduction with sulfide as electron donor: experiments with mono lake water and Isolation of strain MLMS-1, a chemoautotrophic arsenate respirer.

Anoxic bottom water from Mono Lake, California, can biologically reduce added arsenate without any addition of electron donors. Of the possible in situ inorganic electron donors present, only sulfide was sufficiently abundant to drive this reaction. We tested the ability of sulfide to serve as an electron donor for arsenate reduction in experiments with lake water. Reduction of arsenate to arsenite occurred simultaneously with the removal of sulfide. No loss of sulfide occurred in controls without arsenate or in sterilized samples containing both arsenate and sulfide. The rate of arsenate reduction in lake water was dependent on the amount of available arsenate. We enriched for a bacterium that could achieve growth with sulfide and arsenate in a defined, mineral medium and purified it by serial dilution. The isolate, strain MLMS-1, is a gram-negative, motile curved rod that grows by oxidizing sulfide to sulfate while reducing arsenate to arsenite. Chemoautotrophy was confirmed by the incorporation of H(14)CO(3)(-) into dark-incubated cells, but preliminary gene probing tests with primers for ribulose-1,5-biphosphate carboxylase/oxygenase did not yield PCR-amplified products. Alignment of 16S rRNA sequences indicated that strain MLMS-1 was in the delta-Proteobacteria, located near sulfate reducers like Desulfobulbus sp. (88 to 90% similarity) but more closely related (97%) to unidentified sequences amplified previously from Mono Lake. However, strain MLMS-1 does not grow with sulfate as its electron acceptor.

Arsenates↗

PubMed2003

The respiratory arsenate reductase from Bacillus selenitireducens strain MLS10.

The respiratory arsenate reductase from the Gram-positive, haloalkaliphile, Bacillus selenitireducens strain MLS10 was purified and characterized. It is a membrane bound heterodimer (150 kDa) composed of two subunits ArrA (110 kDa) and ArrB (34 kDa), with an apparent K(m) for arsenate of 34 microM and V(max) of 2.5 micromol min(-1) mg(-1). Optimal activity occurred at pH 9.5 and 150 g l(-1) of NaCl. Metal analysis (inductively coupled plasma mass spectrometry) of the holoenzyme and sequence analysis of the catalytic subunit (ArrA; the gene for which was cloned and sequenced) indicate it is a member of the DMSO reductase family of molybdoproteins.

Arsenates↗

PubMed2003

The ecology of arsenic.

Arsenic is a metalloid whose name conjures up images of murder. Nonetheless, certain prokaryotes use arsenic oxyanions for energy generation, either by oxidizing arsenite or by respiring arsenate. These microbes are phylogenetically diverse and occur in a wide range of habitats. Arsenic cycling may take place in the absence of oxygen and can contribute to organic matter oxidation. In aquifers, these microbial reactions may mobilize arsenic from the solid to the aqueous phase, resulting in contaminated drinking water. Here we review what is known about arsenic-metabolizing bacteria and their potential impact on speciation and mobilization of arsenic in nature.

Archaea↗

PubMed2002

Evolution of nitrate reductase: molecular and structural variations on a common function.

The biological transformation of nitrogen oxyanions is widespread in nature and gives rise to a robust biogeochemical cycle. The first step in nitrate reduction is carried out by the enzyme nitrate reductase (NR). Although NR always catalyzes the same chemical reaction (conversion of nitrate into nitrite), its location in the cell, structure, and function are organism-dependent. We use protein sequence data to determine phylogenetic relationships and to examine similarities in structure and function. Three distinct clades of NR are apparent: the eukaryotic assimilatory NR (Euk-NR) clade, the membrane-associated prokaryotic NR (Nar) clade, and a clade that includes both the periplasmic NR (Nap) and prokaryotic assimilatory NR (Nas). The high degree of sequence similarity and a phylogenetic distribution that follows taxonomic classification suggest a monophyletic origin for the Euk-NR early on in the evolution of eukaryotic cells. In contrast, sequence conservation, phylogenetic analysis, and physiology suggest that both Nar and Nap were acquired by horizontal gene transfer. Nap and Nas share a lesser degree of similarity, with Nap a subclade of Nas. Nap from strict anaerobic bacteria such as Desulfovibrio desulfuricans is ancestral to facultative species and may provide an evolutionary link between Nap and Nas. We observed conserved binding sites for molybdenum and pterin cofactors in all four proteins. In pathways involving Euk-NR, Nas, and Nar, for which ammonia is the end product, nitrite is reduced to ammonia by a siroheme nitrite reductase. Nap, however, is coupled to a pentaheme nitrite reductase. In denitrification, whether Nar or Nap is involved, nitrite is reduced to nitric oxide by either a cytochrome cd1 or a copper-containing nitrite reductase. This complexity underscores the importance of nitrate reduction as a key biological process.

Amino Acid Sequence↗