High pressure conditions stimulate expression of chloramphenicol acetyltransferase regulated by the lac promoter in Escherichia coli

Effects of Hydrostatic Pressure on the Thermodynamics of CspB-Bs Interactions with the ssDNA Template

Understanding the thermodynamic mechanisms of adaptation of biomacromolecules to high hydrostatic pressure can help shed light on how piezophilic organisms can survive at pressures reaching over 1000 atmospheres. Interaction of proteins with nucleic acids is one of the central processes that allow information flow encoded in the sequence of DNA. Here, we report the results of a study on the interaction of cold shock protein B from Bacillus subtilis (CspB-Bs) with heptadeoxythymine template (pDT7) as a function of temperature and hydrostatic pressure. Experimental data collected at different CspB-Bs:pDT7 ratios were analyzed using a thermodynamic linkage model that accounts for both protein unfolding and CspB-Bs:pDT7 binding. The global fit to the model provided estimates of the stability of CspB-Bs, ΔG_Prot^o, the volume change upon CspB-Bs unfolding, ΔV_Prot, the association constant for CspB-Bs:pDT7 complex, K_a^o, and the volume changes upon pDT7 single-stranded DNA (ssDNA) template binding, ΔV_Bind. The protein, CspB-Bs, unfolds with an increase in hydrostatic pressure (ΔV_Prot < 0). Surprisingly, our study showed that ΔV_Bind < 0, which means that the binding of CspB-Bs to ssDNA is stabilized by an increase in hydrostatic pressure. Thus, CspB-Bs binding to pDT7 represents a case of linked equilibrium in which folding and binding react differently upon an increase in hydrostatic pressure: protein folding/unfolding equilibrium favors the unfolded state, while protein-ligand binding equilibrium favors the bound state. These opposing effects set a "maximum attainable" pressure tolerance to the protein-ssDNA complex under given conditions.

Design and modelling of an engineered bacteria-based, pressure-sensitive soil

In this paper, we describe the first steps in the design of a synthetic biological system based on the use of genetically modified bacteria to detect elevated pressures in soils and respond by cementing soil particles. Such a system might, for example, enable a self- constructed foundation to form in response to load using engineered bacteria which could be seeded and grown in the soils. This process would reduce the need for large-scale excavations and may be the basis for a new generation of self-assembling and responsive bio-based materials. A prototype computational model is presented which integrates experimental data from a pressure sensitive gene within Escherichia coli bacteria with geotechnical models of soil loading and pore water pressure. The results from the integrated model are visualised by mapping expected gene expression values onto the soil volume. We also use our experimental data to design a two component system where one type of bacteria acts as a sensor and signals to another material synthesis bacteria. The simulation demonstrates the potential of computational models which integrate multiple scales from macro stresses in soils to the expression of individual genes to inform new types of design process. The work also illustrates the combination of in silico (silicon based computing) computation with in vivo (in the living) computation.

Impact of high hydrostatic pressure on bacterial proteostasis

High hydrostatic pressure (HHP) is an important factor that limits microbial growth in deep-sea ecosystems to specifically adapted piezophiles. Furthermore, HHP treatment is used as a novel food preservation technique because of its ability to inactivate pathogenic and spoilage bacteria while minimizing the loss of food quality. Disruption of protein homeostasis (i.e. proteostasis) as a result of HHP-induced conformational changes in ribosomes and proteins has been considered as one of the limiting factors for both microbial growth and survival under HHP conditions. This work therefore reviews the effects of sublethal (≤100MPa) and lethal (>100MPa) pressures on protein synthesis, structure, and functionality in bacteria. Furthermore, current understanding on the mechanisms adopted by piezophiles to maintain proteostasis in HHP environments and responses developed by atmospheric-adapted bacteria to protect or restore proteostasis after HHP exposure are discussed.

Effects of hydrostatic pressure on growth and luminescence of a moderately-piezophilic luminous bacteria Photobacterium phosphoreum ANT-2200

Bacterial bioluminescence is commonly found in the deep sea and depends on environmental conditions. Photobacterium phosphoreum ANT-2200 has been isolated from the NW Mediterranean Sea at 2200-m depth (in situ temperature of 13°C) close to the ANTARES neutrino telescope. The effects of hydrostatic pressure on its growth and luminescence have been investigated under controlled laboratory conditions, using a specifically developed high-pressure bioluminescence system. The growth rate and the maximum population density of the strain were determined at different temperatures (from 4 to 37°C) and pressures (from 0.1 to 40 MPa), using the logistic model to define these two growth parameters. Indeed, using the growth rate only, no optimal temperature and pressure could be determined. However, when both growth rate and maximum population density were jointly taken into account, a cross coefficient was calculated. By this way, the optimum growth conditions for P. phosphoreum ANT-2200 were found to be 30°C and, 10 MPa defining this strain as mesophile and moderately piezophile. Moreover, the ratio of unsaturated vs. saturated cellular fatty acids was found higher at 22 MPa, in agreement with previously described piezophile strains. P. phosphoreum ANT-2200 also appeared to respond to high pressure by forming cell aggregates. Its maximum population density was 1.2 times higher, with a similar growth rate, than at 0.1 MPa. Strain ANT-2200 grown at 22 MPa produced 3 times more bioluminescence. The proposed approach, mimicking, as close as possible, the in situ conditions, could help studying deep-sea bacterial bioluminescence and validating hypotheses concerning its role into the carbon cycle in the deep ocean.

Psychromonas hadalis sp. nov., a novel piezophilic bacterium isolated from the bottom of the Japan Trench

An obligately piezophilic bacterium was isolated from sediment collected from the bottom of the Japan Trench at a depth of 7542 m. The isolated strain, designated K41G(T), was closely affiliated with members of the genus Psychromonas on the basis of 16S rRNA gene sequence analysis. Levels of DNA-DNA relatedness between strain K41G(T) and Psychromonas reference strains were significantly lower than that accepted as the phylogenetic definition of a species. The optimal temperature and pressure for growth of strain K41G(T) were 6 degrees C and 60 MPa, respectively. The DNA G+C content was 39.1 mol%. Whole-cell fatty acids consisted of significant amounts of unsaturated fatty acids C(16 : 1) (37 %) and C(14 : 1) (17 %), saturated fatty acid C(16 : 0) (31 %) and polyunsaturated fatty acid C(22 : 6) (8 %). Based on the taxonomic differences observed, strain K41G(T) is considered to represent a novel obligately piezophilic Psychromonas species. The name Psychromonas hadalis (type strain, K41G(T)=JCM 11830(T)=ATCC BAA-638(T)) is proposed. This is the second species of obligately piezophilic bacteria to be proposed in the genus Psychromonas.

Viability and cellulose synthesizing ability of Gluconacetobacter xylinus cells under high-hydrostatic pressure

The effect of pressure on viability and the synthesis of bacterial cellulose (BC) by Gluconacetobacter xylinus ATCC53582 were investigated. G. xylinus was statically cultivated in a pressurized vessel under 0.1, 30, 60, and 100 MPa at 25 degrees C for 6 days. G. xylinus cells remained viable and retained cellulose producing ability under all the conditions tested, though the production of cellulose decreased with increasing the pressure. The BCs produced at each pressure condition were analyzed by field emission scanning electron microscopy (FE-SEM) and Fourier Transform Infrared (FT-IR). FE-SEM revealed that the widths of BC fibers produced under high pressure decreased as compared with those produced under the atmospheric pressure. By FT-IR, all the BCs were found to be of Cellulose type I, as the same as typical native cellulose. Our findings evidently showed that G. xylinus possessed a piezotolerant (barotolerant) feature adapting to 100 MPa without losing its BC producing ability. This was the first attempt in synthesizing BC with G. xylinus under elevated pressure of 100 MPa, which corresponded to the deep sea at 10,000 m.

Colwellia piezophila sp. nov., a novel piezophilic species from deep-sea sediments of the Japan Trench

Two strains of obligately piezophilic bacteria were isolated from sediment collected from the bottom surface of a small canyon on the seaward slope of the Japan Trench at a depth of 6278 m. The isolated strains, Y223GT and Y251E, are closely affiliated with members of the genus Colwellia on the basis of 16S rRNA gene sequence analysis. The G+C contents of both strains were about 39 mol%. DNA–DNA hybridization values between these strains and Colwellia reference strains were significantly lower than those accepted as the phylogenetic definition of a species. The novel strains are Gram-negative, polarly flagellated and facultatively anaerobic. The optimal pressure for growth was 60 MPa at both 4 and 10 °C; the most rapid growth rate was observed at 10 °C and 60 MPa. No growth occurred at 15 °C under any pressure studied. The major isoprenoid quinone is Q-8. The predominant cellular fatty acids are C16 : 0 and C16 : 1. Based on the taxonomic differences observed, the isolated strains appear to represent a novel obligately piezophilic Colwellia species. The name Colwellia piezophila sp. nov. (type strain Y223GT=JCM 11831T=ATCC BAA-637T) is proposed.

Analysis of hydrostatic pressure effects on transcription in Escherichia coli by DNA microarray procedure

Hydrostatic pressure is a well-known physical stimulus, but its effects on cell physiology have not been clarified. To investigate pressure effects on Escherichia coli, we carried out DNA microarray analysis of the entire E. coli genome. The microarray results showed pleiotropic effects on gene expression. In particular, heat- and cold-stress responses were induced simultaneously by the elevated pressure. Upon temperature stress (including both temperature up- and down-shifts) and other environmental stresses, gene expression adjusts to adapt to such environmental changes through regulations by several DNA-binding proteins. An E. coli mutant, which deleted the hns gene encoding one of the regulator proteins, exhibited great pressure sensitivity. The result suggested that the H-NS protein was a possible transcriptional regulator for adaptation of the high-pressure stress.

Heat shock protein-mediated resistance to high hydrostatic pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i). the expression of rpoH, encoding the heat shock-specific sigma factor sigma(32), was also induced by high pressure; (ii). heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii). basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.

In vitro stability and expression of green fluorescent protein under high pressure conditions

AIMS

The objective of this work was to evaluate the use of wild-type GFP and mutant forms thereof as reporter for gene expression under high pressure conditions.

METHODS AND RESULTS

The intensity of fluorescence after high pressure treatment was checked by subjecting cells, crude protein extracts containing GFPs and purified GFPs to pressures ranging from 100 MPa to 900 MPa. All tested GFP's retained fluorescence up to 600 MPa without loss of intensity. Expression of GFP under sublethal conditions was investigated in Escherichia coli with plasmid pQBI63, in which rsGFP is placed downstream of the T7 RNA polymerase binding site. T7 RNA polymerase is controlled in E. coli BL21 (DE3) pLysS by an IPTG inducible lacUV5 promoter. A pressure induced increase of GFP expression was monitored at 50 Mpa and 70 MPa.

CONCLUSION

Fluorescence of GFPs is not influenced at pressures at which protein expression still occurs. We showed that the expression system used is inducible by pressurized conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study proved GFP to be a suitable reporter for gene expression studies capable to detect pressure induced gene expression.

The biotechnological potential of piezophiles

Microorganisms that prefer high-pressure conditions are termed piezophiles (previously termed barophiles). The molecular basis of piezophily is now being investigated extensively focusing on aspects of gene regulation and the function of certain proteins in deep-sea isolates. Little attention has been paid, however, to the potential biotechnological applications of piezophiles compared with other extremophiles. Based on the fundamental knowledge available, we will try to answer the following questions: How can we exploit the biotechnological potential of piezophiles? What can be understood by the application of high-pressure in biological systems?

RecD function is required for high-pressure growth of a deep-sea bacterium

A genomic library derived from the deep-sea bacterium Photobacterium profundum SS9 was conjugally delivered into a previously isolated pressure-sensitive SS9 mutant, designated EC1002 (E. Chi and D. H. Bartlett, J. Bacteriol. 175:7533-7540, 1993), and exconjugants were screened for the ability to grow at 280-atm hydrostatic pressure. Several clones were identified that had restored high-pressure growth. The complementing DNA was localized and in all cases found to possess strong homology to recD, a DNA recombination and repair gene. EC1002 was found to be deficient in plasmid stability, a phenotype also seen in Escherichia coli recD mutants. The defect in EC1002 was localized to a point mutation that created a stop codon within the recD gene. Two additional recD mutants were constructed by gene disruption and were both found to possess a pressure-sensitive growth phenotype, although the magnitude of the defect depended on the extent of 3' truncation of the recD coding sequence. Surprisingly, the introduction of the SS9 recD gene into an E. coli recD mutant had two dramatic effects. At high pressure, SS9 recD enabled growth in the E. coli mutant strain under conditions of plasmid antibiotic resistance selection and prevented cell filamentation. Both of these effects were recessive to wild-type E. coli recD. These results suggest that the SS9 recD gene plays an essential role in SS9 growth at high pressure and that it may be possible to identify additional aspects of RecD function through the characterization of this activity.

Barophiles: deep-sea microorganisms adapted to an extreme environment

The deep-sea environment is characterized by high pressure and low temperature but in the vicinity of hydrothermal vents regions of extremely high temperature exist. Deep-sea microorganisms have specially adapted features that enable them to live and grow in this extreme environment. Recent research on the physiology and molecular biology of deep-sea barophilic bacteria has identified pressure-regulated operons and shown that microbial growth is influenced by the relationship between temperature and pressure in the deep-sea environment.

Identification of a regulatory protein required for pressure-responsive gene expression in the deep-sea bacterium Photobacterium species strain SS9

Here, we report the characterization of a gene necessary for hydrostatic pressure regulation of gene expression in the deep-sea bacterium Photobacterium species strain SS9. The deduced amino acid sequence of the gene product shares extensive similarity to ToxR, a transmembrane DNA-binding protein first discovered as a virulence determinant in the pathogenic bacterium Vibrio cholerae. Changes in hydrostatic pressure induce changes in both the abundance and the activity of the SS9 ToxR protein (or the activity of a ToxR-regulated protein). As with other high-pressure-inducible phenomena observed in higher organisms, anaesthetics antagonize high-pressure signalling mediated by ToxR. It is suggested that SS9 ToxR has evolved the ability to respond to pressure-mediated alterations in membrane structure. V. cholerae and SS9 also share similarity in a ToxR-regulated protein, indicating that part of the ToxR regulon is conserved in diverse members of the family Vibrionaceae. The SS9 ToxR system represents a useful model for studies of signal transduction and environmental adaptation in the largest portion of the biosphere, the deep sea.

Isolating and characterizing deep-sea marine microorganisms

We have isolated several microorganisms that are adapted to living in the extremes of the deep-sea environment. They include barophilic bacteria, which are able to grow at high hydrostatic pressure, but that are unable to grow at atmospheric pressure, and organic-solvent-tolerant bacteria, which are able to grow in the presence of toxic organic solvents such as toluene or benzene. In this review, we describe how to isolate such extremophiles, and we outline the characteristics of several strains that have been recovered from the deep-sea environment.

High pressure represses expression of the malB operon in Escherichia coli

The formation of plaques by lambda phage in Escherichia coli was prevented by elevated hydrostatic pressure; phage plaques were not detected at 30 MPa. Furthermore, using promoter fragments derived from the malB operon, we showed that gene expression initiated from both promoters (malK-lamB and malEFG) was repressed by elevated hydrostatic pressure. Our findings suggest that high pressure affects gene expression directed by the malB regulatory interval, and this may cause a decrease in the quantities of lambda receptor protein, LamB.

High pressure influences on gene and protein expression

Elevated hydrostatic pressure can influence gene and protein expression in both 1 atmosphere-adapted and high pressure-adapted microorganisms. Here we review experiments documenting these effects and describe their significance towards understanding the molecular bases of life in deep-sea high pressure environments.