Molecular cloning, sequencing, and expression of a chemoreceptor gene from Leptospirillum ferrooxidans

Metabolic diversity and adaptive mechanisms of iron- and/or sulfur-oxidizing autotrophic acidophiles in extremely acidic environments

Many studies have investigated the mechanisms underlying the survival and growth of certain organisms in extremely acidic environments known to be harmful to most prokaryotes and eukaryotes. Acidithiobacillus and Leptospirillum spp. are dominant bioleaching bacteria widely used in bioleaching systems, which are characterized by extremely acidic environments. To survive and grow in such settings, these acidophiles utilize shared molecular mechanisms that allow life in extreme conditions. In this review, we have summarized the results of published genomic analyses, which underscore the ability of iron- and/or sulfur-oxidizing autotrophic acidophiles belonging to the genera Acidithiobacillus and Leptospirillum to adapt to acidic environmental conditions. Several lines of evidence point at the metabolic diversity and multiplicity of pathways involved in the survival of these organisms. The ability to thrive in adverse environments requires versatile activation of structural and functional adaptive responses, including bacterial adhesion, motility, and resistance to heavy metals. We have highlighted recent developments centered on the key survival mechanisms employed by dominant extremophiles, and have laid the foundation for future studies focused on the ability of acidophiles to thrive in extremely acidic environments.

Helicobacter pylori strain ATCC700392 encodes a methyl-accepting chemotaxis receptor protein (MCP) for arginine and sodium bicarbonate

Helicobacter pylori ATCC43504 responds chemotactically to aspartic acid and serine, but not to arginine, nor to sodium bicarbonate. In contrast, H. pylori ATCC700392 (strain 26695) shows chemotaxis to all four attractants. Open reading frame HP0099 from H. pylori 26695 is predicted to encode one of three methyl-accepting chemotaxis receptor proteins (MCPs). When Escherichia coli is transformed with a plasmid carrying HP0099 from strain 26695, the recombinants acquire chemotaxis to arginine, bicarbonate, and urea. In H. pylori 43504, the HP0099 gene is interrupted with a mini-IS605 insertion, which accounts for its inability to recognize arginine and bicarbonate as attractants. Together, these results argue that the H. pylori HP0099 gene encodes an MCP for arginine and bicarbonate.

Heavy metal mining using microbes

The use of acidiphilic, chemolithotrophic iron- and sulfur-oxidizing microbes in processes to recover metals from certain types of copper, uranium, and gold-bearing minerals or mineral concentrates is now well established. During these processes insoluble metal sulfides are oxidized to soluble metal sulfates. Mineral decomposition is believed to be mostly due to chemical attack by ferric iron, with the main role of the microorganisms being to reoxidize the resultant ferrous iron back to ferric iron. Currently operating industrial biomining processes have used bacteria that grow optimally from ambient to 50 degrees C, but thermophilic microbes have been isolated that have the potential to enable mineral biooxidation to be carried out at temperatures of 80 degrees C or higher. The development of higher-temperature processes will extend the variety of minerals that can be commercially processed.

The superfamily of chemotaxis transducers: from physiology to genomics and back

Chemotaxis transducers are specialized receptors that microorganisms use in order to sense the environment in directing their motility to favorable niches. The Escherichia coli transducers are models for studying the sensory and signaling events at the molecular level. Extensive studies in other organisms and the arrival of genomics has resulted in the accumulation of sequences of many transducer genes, but they are not fully understood. In silico analysis provides some assistance in classification of various transducers from different species and in predicting their function. All transducers contain two structural modules: a conserved C-terminal multidomain module, which is a signature element of the transducer superfamily, and a variable N-terminal module, which is responsible for the diversity within the superfamily. These structural modules have two distinct functions: the conserved C-terminal module is involved in signaling and adaptation, and the N-terminal module is involved in sensing various stimuli. Both C-terminal and N-terminal modules appear to be mobile genetic elements and subjects of duplication and lateral transfer. Although chemotaxis transducers are found exclusively in prokaryotic organisms that have some type of motility (flagellar, gliding or pili-based), several types of domains that are found in their N-terminal modules are also present in signal transduction proteins from eukaryotes, including humans. This indicates that basic principles of sensory transduction are conserved throughout the phylogenetic tree and that the chemotaxis transducer superfamily is a valuable source of novel sensory elements yet to be discovered.

Membrane topology of CadA homologous P-type ATPase of Helicobacter pylori as determined by expression of phoA fusions in Escherichia coli and the positive inside rule

The only experimental data available on the membrane topology of transition metal ATPases are from in vitro studies on two distinct P-type ATPases (CadA and CopA) of a gastric bacterium, Helicobacter pylori, both postulated to contain eight transmembrane domains (H1 to H8). In this study, H. pylori CadA ATPase was subjected to analysis of membrane topology in vivo by expression of ATPase-alkaline phosphatase (AP) hybrid proteins in Escherichia coli using a novel vector, pBADphoA. This vector contains an inducible arabinose promoter and unique restriction sites for fusion of DNA fragments to phoA. The phoA gene lacking sequences encoding its N-terminal signal peptide was linked to the C-terminal regions of the postulated five cytoplasmic and four periplasmic segments of the H. pylori pump. The results obtained by heterologous expression of ATPase-AP hybrid proteins showed consistence with a model of eight transmembrane domains. They also demonstrated that the H. pylori ATPase sequences are well assembled in the cytoplasmic membrane of E. coli, a neutralophilic bacterium. Cloning and amino acid sequence analysis of the homologous ATPase of Helicobacter felis further verified the topological model for the H. pylori pump analyzed here, although the degree of amino acid sequence identity varied between the corresponding transmembrane segments, from 25% for H1 up to 100% for H6. It was found that the topology of ATPase follows the 'positive inside rule'. With respect to the bioenergetic capacities of H. pylori, we discuss here the membrane potential as a possible factor directing insertion of ATPases in the cytoplasmic membrane of gastric bacteria.