Diversity in transcripts and translational pattern of stress proteins in marine extremophiles

Biological functions at high pressure: transcriptome response of Shewanella oneidensis MR-1 to hydrostatic pressure relevant to Titan and other icy ocean worlds

High hydrostatic pressure (HHP) is a key driver of life's evolution and diversification on Earth. Icy moons such as Titan, Europa, and Enceladus harbor potentially habitable high-pressure environments within their subsurface oceans. Titan, in particular, is modeled to have subsurface ocean pressures ≥ 150 MPa, which are above the highest pressures known to support life on Earth in natural ecosystems. Piezophiles are organisms that grow optimally at pressures higher than atmospheric (0.1 MPa) pressure and have specialized adaptations to the physical constraints of high-pressure environments - up to ~110 MPa at Challenger Deep, the highest pressure deep-sea habitat explored. While non-piezophilic microorganisms have been shown to survive short exposures at Titan relevant pressures, the mechanisms of their survival under such conditions remain largely unelucidated. To better understand these mechanisms, we have conducted a study of gene expression for Shewanella oneidensis MR-1 using a high-pressure experimental culturing system. MR-1 was subjected to short-term (15 min) and long-term (2 h) HHP of 158 MPa, a value consistent with pressures expected near the top of Titan's subsurface ocean. We show that MR-1 is metabolically active in situ at HHP and is capable of viable growth following 2 h exposure to 158 MPa, with minimal pressure training beforehand. We further find that MR-1 regulates 264 genes in response to short-term HHP, the majority of which are upregulated. Adaptations include upregulation of the genes argA, argB, argC, and argF involved in arginine biosynthesis and regulation of genes involved in membrane reconfiguration. MR-1 also utilizes stress response adaptations common to other environmental extremes such as genes encoding for the cold-shock protein CspG and antioxidant defense related genes. This study suggests Titan's ocean pressures may not limit life, as microorganisms could employ adaptations akin to those demonstrated by terrestrial organisms.

Effect of salinity on genes involved in the stress response in mangrove soils

Mangroves are a challenging ecosystem for the microorganisms that inhabit them, considering they are subjected to stressful conditions such as high and fluctuating salinity. Metagenomic analysis of mangrove soils under contrasting salinity conditions was performed at the mouth of the Ranchera River to the Caribbean Sea in La Guajira, Colombia, using shotgun sequencing and the Illumina Hiseq 2500 platform. Functional gene analysis demonstrated that salinity could influence the abundance of microbial genes involved in osmoprotectant transport, DNA repair, heat shock proteins (HSP), and Quorum Sensing, among others. In total, 135 genes were discovered to be linked to 12 pathways. Thirty-four genes out of 10 pathways had statistical differences for a p-value and FDR < 0.05. UvrA and uvrB (nucleotide excision repair), groEL (HSP), and secA (bacterial secretion system) genes were the most abundant and were enriched by high salinity. The results of this study showed the prevalence of diverse genetic mechanisms that bacteria use as a response to survive in the challenging mangrove, as well as the presence of various genes that are recruited in order to maintain bacterial homeostasis under conditions of high salinity.

Optimization, partial purification, and characterization of a novel high molecular weight alkaline protease produced by Halobacillus sp. HAL1 using fish wastes as a substrate

BACKGROUND

Hydrolytic enzymes from halophilic microorganisms have a wide range of industrial applications. Herein, we report the isolation of Halobacillus sp. HAL1, a moderately halophilic bacterium that produces a novel high molecular weight extracellular alkaline protease when grown in fish processing wastes as a substrate.

RESULTS

Results showed that the isolated strain belonged to the genus Halobacillus, and it was designated as Halobacillus sp. HAL1 with the GenBank accession number OK001470. The strain secreted an extracellular alkaline protease, and the highest yield was obtained when it was grown in a medium with fish wastes substrate as the sole nutritional source (10 g/L) and incubated at 25 °C under shaking conditions. The enzyme was partially purified by Sephadex G-100 column chromatography. Zymographic analysis showed two casein degrading bands of about 190 and 250 KDa. The optimum enzyme activity was at a temperature of 50 °C at pH 8. The proteolytic activity was enhanced in the presence of metal ions (Ca²⁺, Mg²⁺, and Mn²⁺), surfactants (Tween 80, SDS, and Triton-X100), H₂O₂, and EDTA.

CONCLUSION

Our study indicates that Haobacillus sp. HAL1 is a moderately halophilic strain and secrets a novel high molecular wight alkaline protease that is suitable for detergent formulation.

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.

Transcriptomic Analysis Reveals Common Adaptation Mechanisms Under Different Stresses for Moderately Piezophilic Bacteria

Piezophiles, by the commonly accepted definition, grow faster under high hydrostatic pressure (HHP) than under ambient pressure and are believed to exist only in pressurized environments where life has adapted to HHP during evolution. However, recent findings suggest that piezophiles have developed a common adaptation strategy to cope with multiple types of stresses including HHP. These results raise a question on the ecological niches of piezophiles: are piezophiles restricted to habitats with HHP? In this study, we observed that the bacterial strains Sporosarcina psychrophila DSM 6497 and Lysinibacillus sphaericus LMG 22257, which were isolated from surface environments and then transferred under ambient pressure for half a century, possess moderately piezophilic characteristics with optimal growth pressures of 7 and 20 MPa, respectively. Their tolerance to HHP was further enhanced by MgCl₂ supplementation under the highest tested pressure of 50 MPa. Transcriptomic analysis was performed to compare gene expression with and without MgCl₂ supplementation under 50 MPa for S. psychrophila DSM 6497. Among 4390 genes or transcripts obtained, 915 differentially expressed genes (DEGs) were identified. These DEGs are primarily associated with the antioxidant defense system, intracellular compatible solute accumulation, and membrane lipid biosynthesis, which have been reported to be essential for cells to cope with HHP. These findings indicate no in situ pressure barrier for piezophile isolation, and cells may adopt a common adaptation strategy to cope with different stresses.

The metabolic pathways of polyhydroxyalkanoates and exopolysaccharides synthesized by Haloferax mediterranei in response to elevated salinity

How polymer synthesis is mobilized or activated as a biological response of Haloferax mediterranei against hypertonic conditions remains largely unexplored. This study investigated the protein expression of H. mediterranei in response to high salinity by using isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis. The microbes were harvested at end of fermentation at the NaCl salinity of 75 and 250 g L^-1. Among the identified 2123 proteins, 170 proteins were differentially expressed. Gene ontology annotation revealed that the highest number of proteins was annotated in biological process category, which was responsible for metabolic process, cellular component and catalytic activity. Differentially expressed proteins were belonged to the class of response to stimulus as well as catalytic activity and binding. Under high salinity conditions, three pathways were established as key responses of PHA and EPS production to hypertonic pressure. Two overexpressed proteins, beta-ketoacyl-ACP reductase and 3-hydroxyacyl-CoA dehydrogenase, enhanced the synthesis of PHAs. The serine-pyruvate transaminase and serine-glyoxylate transaminase were upregulated, thereby increasing the conversion of glucose to PHA. Downregulated levels of sulfate-adenylyl transferase and adenylyl-sulfate kinase could cause diminished EPS synthesis. This study could contribute to better understanding of the proteomic mechanisms of the synthesized polymers in defending against salt stress. SIGNIFICANCE: Haloferax mediterranei, a family member of halophilic archaea, is well known for its fermentative production of poly-β-hydroxyalkanoates (PHAs). PHAs are natural polymers that exhibit great potential in a wide range of applications such as a good alternative to petroleum-based plastics and the biocompatible material. For decades, the functional role of PHAs synthesized by H. mediterranei is deemed to be carbon and energy reservations. The finding proved that differential production of PHA and EPS in H. mediterranei exposed to elevated salinity was caused by differential protein expression. This is the first report on how PHA and EPS synthesized by H. mediterranei is mobilized as the response of increased salinity, contributing to the understanding of halophilic archaea's response to hypertonic stress and the precise control of fermentation production. Despite its advantages as a PHA cell factory, H. mediterranei synthesized EPS simultaneously, thereby lowering the maximum yield of PHA production. Overall, salinity can be used as a vital microbial fermentation parameter to obtain the highest harvest of PHA, as well as the lowest EPS synthesis in industrial fermentation.

Cross-Stress Adaptation in a Piezophilic and Hyperthermophilic Archaeon From Deep Sea Hydrothermal Vent

Hyperthermophiles, living in environments above 80°C and usually coupling with multi-extreme environmental stresses, have drawn great attention due to their application potential in biotechnology and being the primitive extant forms of life. Studies on their survival and adaptation mechanisms have extended our understanding on how lives thrive under extreme conditions. During these studies, the "cross-stress" behavior in various organisms has been observed between the extreme high temperature and other environmental stresses. Despite the broad observation, the global view of the cross-stress behavior remains unclear in hyperthermophiles, leaving a knowledge gap in our understanding of extreme adaptation. In this study, we performed a global quantitative proteomic analysis under extreme temperatures, pH, hydrostatic pressure (HP), and salinity on an archaeal strain, Thermococcus eurythermalis A501, which has outstanding growth capability on a wide range of temperatures (50-100°C), pH (4-9), and HPs (0.1-70 MPa), but a narrow range of NaCl (1.0-5.0 %, w/v). The proteomic analysis (79.8% genome coverage) demonstrated that approximately 61.5% of the significant differentially expressed proteins (DEPs) responded to multiple stresses. The responses to most of the tested stresses were closely correlated, except the responses to high salinity and low temperature. The top three enriched universal responding processes include the biosynthesis and protection of macromolecules, biosynthesis and metabolism of amino acids, ion transport, and binding activities. In addition, this study also revealed that the specific dual-stress responding processes, such as the membrane lipids for both cold and HP stresses and the signal transduction for both hyperosmotic and heat stresses, as well as the sodium-dependent energetic processes might be the limiting factor of the growth range in salinity. The present study is the first to examine the global cross-stress responses in a piezophilic hyperthermophile at the proteomic level. Our findings provide direct evidences of the cross-stress adaptation strategy (33.5% of coding-genes) to multiple stresses and highlight the specific and unique responding processes (0.22-0.63% of coding genes for each) to extreme temperature, pH, salinity, and pressure, which are highly relevant to the fields of evolutionary biology as well as next generation industrial biotechnology (NGIB).

De novo transcriptome analysis of halotolerant bacterium Staphylococcus sp. strain P-TSB-70 isolated from East coast of India: In search of salt stress tolerant genes

In the present study, we identified salt stress tolerant genes from the marine bacterium Staphylococcus sp. strain P-TSB-70 through transcriptome sequencing. In favour of whole-genome transcriptome profiling of Staphylococcus sp. strain P-TSB-70 (GenBank Accn. No. KP117091) which tolerated upto 20% NaCl stress, the strain was cultured in the laboratory condition with 20% NaCl stress. Transcriptome analyses were performed by SOLiD4.0 sequencing technology from which 10280 and 9612 transcripts for control and treated, respectively, were obtained. The coverage per base (CPB) statistics were analyzed for both the samples. Gene ontology (GO) analysis has been categorized at varied graph levels based on three primary ontology studies viz. cellular components, biological processes, and molecular functions. The KEGG analysis of the assembled transcripts using KAAS showed presumed components of metabolic pathways which perhaps implicated in diverse metabolic pathways responsible for salt tolerance viz. glycolysis/gluconeogenesis, oxidative phosphorylation, glutathione metabolism, etc. further involving in salt tolerance. Overall, 90 salt stress tolerant genes were identified as of 186 salt-related transcripts. Several genes have been found executing normally in the TCA cycle pathway, integral membrane proteins, generation of the osmoprotectants, enzymatic pathway associated with salt tolerance. Recognized genes fit diverse groups of salt stress genes viz. abc transporter, betaine, sodium antiporter, sodium symporter, trehalose, ectoine, and choline, that belong to different families of genes involved in the pathway of salt stress. The control sample of the bacterium showed elevated high proportion of transcript contigs (29%) while upto 20% salt stress treated sample of the bacterium showed a higher percentage of transcript contigs (31.28%). A total of 1,288 and 1,133 transcript contigs were measured entirely as novel transcript contigs in both control and treated samples, respectively. The structure and function of 10 significant salt stress tolerant genes of Staphylococcus sp. have been analyzed in this study. The information acquired in the present study possibly used to recognize and clone the salt stress tolerant genes and support in developing the salt stress-tolerant plant varieties to expand the agricultural productivity in the saline system.

Properties and Applications of Extremozymes from Deep-Sea Extremophilic Microorganisms: A Mini Review

The deep sea, which is defined as sea water below a depth of 1000 m, is one of the largest biomes on the Earth, and is recognised as an extreme environment due to its range of challenging physical parameters, such as pressure, salinity, temperature, chemicals and metals (such as hydrogen sulphide, copper and arsenic). For surviving in such extreme conditions, deep-sea extremophilic microorganisms employ a variety of adaptive strategies, such as the production of extremozymes, which exhibit outstanding thermal or cold adaptability, salt tolerance and/or pressure tolerance. Owing to their great stability, deep-sea extremozymes have numerous potential applications in a wide range of industries, such as the agricultural, food, chemical, pharmaceutical and biotechnological sectors. This enormous economic potential combined with recent advances in sampling and molecular and omics technologies has led to the emergence of research regarding deep-sea extremozymes and their primary applications in recent decades. In the present review, we introduced recent advances in research regarding deep-sea extremophiles and the enzymes they produce and discussed their potential industrial applications, with special emphasis on thermophilic, psychrophilic, halophilic and piezophilic enzymes.

Isolation and characterization of marine bacteria from East Coast of India: functional screening for salt stress tolerance

Soil salinization has become a severe constraint for crop production world-wide which necessitated development or induced enhancement of salt stress tolerance in plant life to sustain production in saline lands. Recognition and prospecting of valuable stress tolerant genes from natural microbial resources of saline habitat is obscure to date. Therefore, the investigation was towards isolation and characterization of marine salt stress tolerant microbes along the East coast of India for revelation of effective salt stress tolerant genes. Salt stress tolerance was assessed from 98 bacterial isolates obtained from 28 water and soil samples. Among them, 35 isolates which failed to grow beyond 4% salt were discarded and remainder 63 isolates were selected for further functional analysis and only seven isolates recorded ≥8% NaCl stress tolerance. Phylogeny revealed that four isolates belong to Firmicutes and three isolates were members of Proteobacteria. Ribosomal Database Project Release-11 and SILVA SSU database based genotyping and taxonomic identity analysis confirmed that the higher (20%) salt stress tolerant bacteria were Staphylococcus sp., Enterococcus sp., Enterobacter sp. and Proteus sp. To investigate candidate, as well as, novel salt stress tolerant genes, the seven bacterial isolates would provide new horizon to focus on the recent developments of salinity stress tolerance. In addition, the findings evidently point out the diversity of salt stress tolerant marine bacteria in coastal Odisha and West Bengal, India.

Comparative transcriptome analysis of Eogammarus possjeticus at different hydrostatic pressure and temperature exposures

Hydrostatic pressure is an important environmental factor affecting the vertical distribution of marine organisms. Laboratory-based studies have shown that many extant shallow-water marine benthic invertebrates can tolerate hydrostatic pressure outside their known natural distributions. However, only a few studies have focused on the molecular mechanisms of pressure acclimatisation. In the present work, we examined the pressure tolerance of the shallow-water amphipod Eogammarus possjeticus at various temperatures (5, 10, 15, and 20 °C) and hydrostatic pressures (0.1–30 MPa) for 16 h. Six of these experimental groups were used for transcriptome analysis. We found that 100% of E. possjeticus survived under 20 MPa at all temperature conditions for 16 h. Sequence assembly resulted in 138, 304 unigenes. Results of differential expression analysis revealed that 94 well-annotated genes were up-regulated under high pressure. All these findings indicated that the pressure tolerance of E. possjeticus was related to temperature. Several biological processes including energy metabolism, antioxidation, immunity, lipid metabolism, membrane-related process, genetic information processing, and DNA repair are probably involved in the acclimatisation in deep-sea environments.

Enhancing the Adaptability of the Deep-Sea Bacterium Shewanella piezotolerans WP3 to High Pressure and Low Temperature by Experimental Evolution under H2O2 Stress

Oxidative stresses commonly exist in natural environments, and microbes have developed a variety of defensive systems to counteract such events. Although increasing evidence has shown that high hydrostatic pressure (HHP) and low temperature (LT) induce antioxidant defense responses in cells, there is no direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT. In this study, using the wild-type (WT) strain of a deep-sea bacterium, Shewanella piezotolerans WP3, as an ancestor, we obtained a mutant, OE100, with an enhanced antioxidant defense capacity by experimental evolution under H₂O₂ stress. Notably, OE100 exhibited better tolerance not only to H₂O₂ stress but also to HHP and LT (20 MPa and 4°C, respectively). Whole-genome sequencing identified a deletion mutation in the oxyR gene, which encodes the transcription factor that controls the oxidative stress response. Comparative transcriptome analysis showed that the genes associated with oxidative stress defense, anaerobic respiration, DNA repair, and the synthesis of flagella and bacteriophage were differentially expressed in OE100 compared with the WT at 20 MPa and 4°C. Genetic analysis of oxyR and ccpA2 indicated that the OxyR-regulated cytochrome c peroxidase CcpA2 significantly contributed to the adaptation of WP3 to HHP and LT. Taken together, these results confirmed the inherent relationship between antioxidant defense mechanisms and the adaptation of a benthic microorganism to HHP and LT.IMPORTANCE Oxidative stress exists in various niches, including the deep-sea ecosystem, which is an extreme environment with conditions of HHP and predominantly LT. Although previous studies have shown that HHP and LT induce antioxidant defense responses in cells, direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT is lacking. In this work, using the deep-sea bacterium Shewanella piezotolerans WP3 as a model, we proved that enhancement of the adaptability of WP3 to HHP and LT can benefit from its antioxidant defense mechanism, which provided useful insight into the ecological roles of antioxidant genes in a benthic microorganism and contributed to an improved understanding of microbial adaptation strategies in deep-sea environments.

B-DNA model systems in non-terran bio-solvents: implications for structure, stability and replication

We have computationally analyzed a comprehensive series of Watson–Crick and mismatched B-DNA base pairs, in the gas phase and in several solvents, including toluene, chloroform, ammonia, methanol and water, using dispersion-corrected density functional theory and implicit solvation.

Global transcriptome analysis of Halolamina sp. to decipher the salt tolerance in extremely halophilic archaea

Extremely halophilic archaea survive in the hypersaline environments such as salt lakes or salt mines. Therefore, these microorganisms are good sources to investigate the molecular mechanisms underlying the tolerance to high salt concentrations. In this study, a global transcriptome analysis was conducted in an extremely halophilic archaeon, Halolamina sp. YKT1, isolated from a salt mine in Turkey. A comparative RNA-seq analysis was performed using YKT1 isolate grown either at 2.7M NaCl or 5.5M NaCl concentrations. A total of 2149 genes were predicted to be up-regulated and 1638 genes were down-regulated in the presence of 5.5M NaCl. The salt tolerance of Halolamina sp. YKT1 involves the up-regulation of genes related with membrane transporters, CRISPR-Cas systems, osmoprotectant solutes, oxidative stress proteins, and iron metabolism. On the other hand, the genes encoding the proteins involved in DNA replication, transcription, translation, mismatch and nucleotide excision repair were down-regulated. The RNA-seq data were verified for seven up-regulated genes as well as six down-regulated genes via qRT-PCR analysis. This comprehensive transcriptome analysis showed that the halophilic archaeon canalizes its energy towards keeping the intracellular osmotic balance minimizing the production of nucleic acids and peptides.

Characterization of the interaction between superoxide dismutase and 2-oxoisovalerate dehydrogenase

Thermophiles are attractive microorganisms to study the adaptation of life in high temperature environment. It is revealed that superoxide dismutase (SOD) is essential for thermoadaptation of thermophiles. However, the SOD-mediated pathway of thermoadaptation remains unclear. To address this issue, the proteins interacted with SOD were characterized in Thermus thermophilus in this study. Based on co-immunoprecipitation and Western blot analyses, the results showed that 2-oxoisovalerate dehydrogenase α subunit was bound to SOD. The isothermal titration calorimetry analysis showed the existence of the interaction between SOD and 2-oxoisovalerate dehydrogenase α subunit. The bacterial two-hybrid data indicated that SOD was directly interacted with 2-oxoisovalerate dehydrogenase α subunit. Gene site-directed mutagenesis analysis revealed that the intracellular interaction between SOD and 2-oxoisovalerate dehydrogenase α subunit was dependent on their whole molecules. Therefore our study presented a novel aspect of SOD in the thermoadaptation of thermophiles by interaction with dehydrogenase, a key enzyme of tricarboxylic acid cycle.

Marine extremophiles: a source of hydrolases for biotechnological applications

The marine environment covers almost three quarters of the planet and is where evolution took its first steps. Extremophile microorganisms are found in several extreme marine environments, such as hydrothermal vents, hot springs, salty lakes and deep-sea floors. The ability of these microorganisms to support extremes of temperature, salinity and pressure demonstrates their great potential for biotechnological processes. Hydrolases including amylases, cellulases, peptidases and lipases from hyperthermophiles, psychrophiles, halophiles and piezophiles have been investigated for these reasons. Extremozymes are adapted to work in harsh physical-chemical conditions and their use in various industrial applications such as the biofuel, pharmaceutical, fine chemicals and food industries has increased. The understanding of the specific factors that confer the ability to withstand extreme habitats on such enzymes has become a priority for their biotechnological use. The most studied marine extremophiles are prokaryotes and in this review, we present the most studied archaea and bacteria extremophiles and their hydrolases, and discuss their use for industrial applications.

Omics profiles used to evaluate the gene expression of Exiguobacterium antarcticum B7 during cold adaptation

BACKGROUND

Exiguobacterium antarcticum strain B7 is a Gram-positive psychrotrophic bacterial species isolated in Antarctica. Although this bacteria has been poorly studied, its genome has already been sequenced. Therefore, it is an appropriate model for the study of thermal adaptation. In the present study, we analyzed the transcriptomes and proteomes of E. antarcticum B7 grown at 0°C and 37°C by SOLiD RNA-Seq, Ion Torrent RNA-Seq and two-dimensional difference gel electrophoresis tandem mass spectrometry (2D-DIGE-MS/MS).

RESULTS

We found expression of 2,058 transcripts in all replicates from both platforms and differential expression of 564 genes (absolute log2FC≥1, P-value<0.001) comparing the two temperatures by RNA-Seq. A total of 73 spots were differentially expressed between the two temperatures on 2D-DIGE, 25 of which were identified by MS/MS. Some proteins exhibited patterns of dispersion in the gel that are characteristic of post-translational modifications.

CONCLUSIONS

Our findings suggest that the two sequencing platforms yielded similar results and that different omic approaches may be used to improve the understanding of gene expression. To adapt to low temperatures, E. antarcticum B7 expresses four of the six cold-shock proteins present in its genome. The cold-shock proteins were the most abundant in the bacterial proteome at 0°C. Some of the differentially expressed genes are required to preserve transcription and translation, while others encode proteins that contribute to the maintenance of the intracellular environment and appropriate protein folding. The results denote the complexity intrinsic to the adaptation of psychrotrophic organisms to cold environments and are based on two omic approaches. They also unveil the lifestyle of a bacterial species isolated in Antarctica.

Proteomics of arsenic stress in the gram-positive organism Exiguobacterium sp. PS NCIM 5463

The general responses of microorganisms to environmental onslaughts are modulated by altering the gene expression pattern to reduce damage in the cell and produce compensating stress responses. The present study attempts to unravel the response of the Gram-positive Exiguobacterium sp. PS NCIM 5463 in the presence of [As(III)] and arsenate [As(V)] using comparative proteomics via two-dimension gel electrophoresis (2-DE) coupled with identification of proteins using matrix-assisted laser desorption/ionisation (MALDI-TOF/MALDI-TOF/TOF). Out of 926 Coomassie-stained proteins, 45 were differentially expressed (p < 0.05). Considering the resolution and abundance level, 24 spots (peptides) were subjected to MALDI analysis, identified and categorised into several functional categories, viz., nitrogen metabolism, energy and stress regulators, carbohydrate metabolism, protein synthesis components and others. A functional role of each protein is discussed in Exiguobacterium sp. PS 5463 under arsenic stress and validated at their transcript level using a quantitative real-time polymerase chain reaction. Unlike previous reports that unravel the responses toward arsenic stress in Gram-negative organisms, the present study identified new proteins under arsenic stress in a Gram-positive organism, Exiguobacterium sp. PS NCIM 5463, which could elucidate the physiology of organisms under arsenic stress.

Proteogenomic insights into salt tolerance by a halotolerant alpha-proteobacterium isolated from an Andean saline spring

Tistlia consotensis is a halotolerant Rhodospirillaceae that was isolated from a saline spring located in the Colombian Andes with a salt concentration close to seawater (4.5%w/vol). We cultivated this microorganism in three NaCl concentrations, i.e. optimal (0.5%), without (0.0%) and high (4.0%) salt concentration, and analyzed its cellular proteome. For assigning tandem mass spectrometry data, we first sequenced its genome and constructed a six reading frame ORF database from the draft sequence. We annotated only the genes whose products (872) were detected. We compared the quantitative proteome data sets recorded for the three different growth conditions. At low salinity general stress proteins (chaperons, proteases and proteins associated with oxidative stress protection), were detected in higher amounts, probably linked to difficulties for proper protein folding and metabolism. Proteogenomics and comparative genomics pointed at the CrgA transcriptional regulator as a key-factor for the proteome remodeling upon low osmolarity. In hyper-osmotic condition, T. consotensis produced in larger amounts proteins involved in the sensing of changes in salt concentration, as well as a wide panel of transport systems for the transport of organic compatible solutes such as glutamate. We have described here a straightforward procedure in making a new environmental isolate quickly amenable to proteomics.

BIOLOGICAL SIGNIFICANCE

The bacterium Tistlia consotensis was isolated from a saline spring in the Colombian Andes and represents an interesting environmental model to be compared with extremophiles or other moderate organisms. To explore the halotolerance molecular mechanisms of the bacterium T. consotensis, we developed an innovative proteogenomic strategy consisting of i) genome sequencing, ii) quick annotation of the genes whose products were detected by mass spectrometry, and iii) comparative proteomics of cells grown in three salt conditions. We highlighted in this manuscript how efficient such an approach can be compared to time-consuming genome annotation when pointing at the key proteins of a given biological question. We documented a large number of proteins found produced in greater amounts when cells are cultivated in either hypo-osmotic or hyper-osmotic conditions. This article is part of a Special Issue entitled: Trends in Microbial Proteomics.

Radiation-resistant extremophiles and their potential in biotechnology and therapeutics

Extremophiles are organisms able to thrive in extreme environmental conditions. Microorganisms with the ability to survive high doses of radiation are known as radioresistant or radiation-resistant extremophiles. Excessive or intense exposure to radiation (i.e., gamma rays, X-rays, and particularly UV radiation) can induce a variety of mutagenic and cytotoxic DNA lesions, which can lead to different forms of cancer. However, some populations of microorganisms thrive under different types of radiation due to defensive mechanisms provided by primary and secondary metabolic products, i.e., extremolytes and extremozymes. Extremolytes (including scytonemin, mycosporine-like amino acids, shinorine, porphyra-334, palythine, biopterin, and phlorotannin, among others) are able to absorb a wide spectrum of radiation while protecting the organism's DNA from being damaged. The possible commercial applications of extremolytes include anticancer drugs, antioxidants, cell-cycle-blocking agents, and sunscreens, among others. This article aims to review the strategies by which microorganisms thrive in extreme radiation environments and discuss their potential uses in biotechnology and the therapeutic industry. The major challenges that lie ahead are also discussed.