Energy transduction and transport processes in thermophilic bacteria

Bacterial diversity in 110 thermal hot springs of Indian Himalayan Region (IHR)

Thermal hot springs are present throughout the world and constitute a unique habitat for microbial diversity. The current investigation is conducted to study the bacterial diversity of thermophilic microorganisms in thermal hot springs of the Indian Himalayan Region (IHR). As of today, 110 geothermal hot springs have been explored for microbial diversity. In this study, we observed that the growth of thermophilic bacteria isolated from thermal hot springs of IHR ranges between 40 and 100 °C, and pH of 3.5-8 have been reported in the literature. The major bacterial species reported from the thermal hot springs of IHR are Bacillus spp., Geobacillus spp., Paenibacillus spp., Pseudomonas spp., Anoxybacillus, Paenibacillus, Brevibacillus, Aneurinibacillus, Thermus aquaticus, Aquimonas, Flavobacterium, etc. Furthermore, bacterial isolates from thermal hot springs of IHR have been reported to produce various enzymes and metabolites such as amylase, β-galactosidase, cellulase, nitrate reductase, acetoin, caffeine degradation enzymes, lipase, urease, and laccase. Metagenomic study and the entire genomic shotgun project have established the impact of physicochemical parameters (temperature and pH) on developing the microbiome. We have discussed the discoveries of microbiological data on the hot springs of IHR until the end of year 2021. As a whole, the microbiome adapts themselves as successful inhabitants to extreme environmental conditions and also serves as a diverse resource for potential applications in health, food, and environment.

Archaeal lipids forming a low energy-surface on air-water interface

Archaea or archaebacteria are the microorganism living in extreme environments such as hot springs and salt lakes. The membrane is featured universally by lipids which possess saturated polyisoprenoid chains in the hydrophobic moiety. This paper concerns the surface properties of Langmuir membranes made of archaeal lipid models (AL) bearing a phytanyl group or (3RS, 7R, 11R)-3,7,11,15-tetramethylhexadecyl group. All of the AL provide a Langmuir membrane on an air-water interface with an abnormally low surface tension (32-37 mN/m at 20-70 degrees C), while the conventional lipids having n-alkyl chains give membranes of 54-56 mN/m. The abnormally low energy surface of AL lipids is considered to arise from the bulky and fluid polyisoprenoid chain.

Characterization of a thermophilic P-type Ag+/Cu+-ATPase from the extremophile Archaeoglobus fulgidus

The thermophilic, sulfur metabolizing Archaeoglobus fulgidus contains two genes, AF0473 and AF0152, encoding for PIB-type heavy metal transport ATPases. In this study, we describe the cloning, heterologous expression, purification, and functional characterization of one of these ATPases, CopA (NCB accession number AAB90763), encoded by AF0473. CopA is active at high temperatures (75 degrees C; E(a) = 103 kJ/mol) and inactive at 37 degrees C. It is activated by Ag+ (ATPase V(max) = 14.82 micromol/mg/h) and to a lesser extent by Cu+ (ATPase V(max) = 3.66 micromol/mg/h). However, Cu+ interacts with the enzyme with higher apparent affinity (ATPase stimulation, Ag+ K(12) = 29.4 microm; Cu+ K(12) = 2.1 microm). This activation by Ag+ or Cu+ is dependent on the presence of millimolar amounts of cysteine. In the presence of ATP, these metals drive the formation of an acid-stable phosphoenzyme with apparent affinities similar to those observed in the ATPase activity determinations (Ag+, K(12) = 23.0 microm; Cu+, K(12) = 3.9 microm). However, comparable levels of phosphoenzyme are reached in the presence of both cations (Ag+, 1.40 nmol/mg; Cu+, 1.08 nmol/mg). The stimulation of phosphorylation by the cations suggests that CopA drives the outward movement of the metal. CopA presents additional functional characteristics similar to other P-type ATPases. ATP interacts with the enzyme with two apparent affinities (ATPase K(m) = 0.25 mm; phosphorylation K(m) = 4.81 microm), and the presence of vanadate leads to enzyme inactivation (IC(50) = 24 microm). This is the first Ag+/Cu+ -ATPase expressed and purified in a functional form. Thus, it provides a model for structure-functional studies of these transporters. Moreover, its characterization will also contribute to an understanding of thermophilic ion transporters.

The protein capsid of filamentous bacteriophage PH75 from Thermus thermophilus

The PH75 strain of filamentous bacteriophage (Inovirus) grows in the thermophilic bacterium Thermus thermophilus at 70 degrees C. We have characterized the viral DNA and determined the amino acid sequence of the major coat protein, p8. The p8 protein is synthesized without a leader sequence, like that of bacteriophage Pf3 but unlike that of bacteriophage Pf1, both of which grow in the mesophile Pseudomonas aeruginosa. X-ray diffraction patterns from ordered fibres of the PH75 virion are similar to those from bacteriophages Pf1 and Pf3, indicating that the protein capsid of the PH75 virion has the same helix symmetry and subunit shape, even though the primary structures of the major coat proteins are quite different and the virions assemble at very different temperatures. We have used this information to build a molecular model of the PH75 protein capsid based on that of Pf1, and refined the model by simulated annealing, using fibre diffraction data extending to 2.4 A resolution in the meridional direction and to 3.1 A resolution in the equatorial direction. The common design may reflect a fundamental motif of alpha-helix packing, although differences exist in the DNA packaging and in the means of insertion of the major coat protein of these filamentous bacteriophages into the membrane of the host bacterial cell. These may reflect differences in the assembly mechanisms of the virions.

Biooxidation capacity of the extremely thermoacidophilic archaeon metallosphaera sedula under bioenergetic challenge

The biooxidation capacity of an extremely thermoacidophilic archaeon Metallosphaera sedula (DSMZ 5348) was examined under bioenergetic challenges imparted by thermal or chemical stress in regard to its potential use in microbial bioleaching processes. Within the normal growth temperature range of M. sedula (70-79 degrees C) at pH 2.0, upward temperature shifts resulted in bioleaching rates that followed an Arrhenius-like dependence. When the cells were subjected to supraoptimal temperatures through gradual thermal acclimation at 81 degrees C (Han et al., 1997), cell densities were reduced but 3 to 5 times faster specific leaching rates (Fe3+ released from iron pyrite/cell/h) could be achieved by the stressed cells compared to cells at 79 degrees C and 73 degrees C, respectively. The respiration capacity of M. sedula growing at 74 degrees C was challenged by poisoning the cells with uncouplers to generate chemical stress. When the protonophore 2,4-dinitrophenol (5-10 μM) was added to a growing culture of M. sedula on iron pyrite, there was little effect on specific leaching rates compared to a culture with no protonophore at 74 degrees C; 25 μM levels proved to be toxic to M. sedula. However, a significant stimulation in specific rate was observed when the cells were subjected to 1 μM nigericin (+135%) and 2 μM (+63%); 5 μM levels of the ionophore completely arrested cell growth. The ionophore effect was further investigated in continuous culture growing on ferrous sulfate at 74 degrees C. When 1 μM nigericin was added as a pulse to a continuous culture, a 30% increase in specific iron oxidation rate was observed for short intervals, indicating a potential positive impact on leaching when periodic chemical stress is applied. This study suggests that biooxidation rates can be increased by strategic exposure of extreme thermoacidophiles to chemical or thermal stress, and this approach should be considered for improving process performance. Copyright 1998 John Wiley & Sons, Inc.

Energetic problems of extremely alkaliphilic aerobes

Over a decade of work on extremely alkaliphilic Bacillus species has clarified the extraordinary capacity that these bacteria have for regulating their cytoplasmic pH during growth at pH values well over 10. However, a variety of interesting energetic problems related to their Na(+)-dependent pH homeostatic mechanism are yet to be solved. They include: (1) the clarification of how cell surface layers play a role in a category of alkaliphiles for which this is the case; (2) identification of the putative, electrogenic Na+/H+ antiporter(s) that, in at least some alkaliphiles, may completely account for a cytoplasmic pH that is over 2 pH units lower than the external pH; (3) the determination of whether specific modules or accessory proteins are essential for the efficacy of such antiporters; (4) the mechanistic basis for the increase in the transmembrane electrical potential at the high external pH values at which the potential-consuming antiporter(s) must be most active; and (5) an explanation for the Na(+)-specificity of pH homeostasis in the extremely alkaliphilic bacilli as opposed to the almost equivalent efficacy of K+ for pH homeostasis in at least some non-alkaliphilic aerobes. The current status of such studies and future strategies will be outlined for this central area of alkaliphile energetics. Also considered, will be strategies to elucidate the basis for robust H(+)-coupled oxidative phosphorylation by alkaliphiles at pH values over 10. The maintenance of a cytoplasmic pH over 2 units below the high external pH results in a low bulk electrochemical proton gradient (delta p). To bypass this low delta p, Na(+)-coupling is used for solute uptake even by alkaliphiles that are mesophiles from environments that are not especially Na(+)-rich. This indicates that these bacteria indeed experience a low delta p, to which such coupling is an adaptation. Possible reasons and mechanisms for using a H(+)-coupled rather than a Na(+)-coupled ATP synthase under such circumstances will be discussed.

Stability and proton-permeability of liposomes composed of archaeal tetraether lipids

Liposomes composed of tetraether lipids originating from the thermoacidophilic archaeon Sulfolobus acidocaldarius were analyzed for their stability and proton permeability from 20 degrees C up to 80 degrees C. At room temperature, these liposomes are considerably more stable and have a much lower proton permeability than liposomes composed of diester lipids originating from the mesophilic bacterium Escherichia coli or the thermophilic bacterium Bacillus stearothermophilus. With increasing temperature, the stability decreased and the proton permeability increased for all liposomes. Liposomes composed from tetraether lipids, however, remain the most stable. These data suggest these liposomes retain the rigidity of the cytoplasmic membrane of S. acidocaldarius needed to endure extreme environmental growth conditions.