Crystal structure of the reactive intermediate/imine deaminase A homolog from the Antarctic bacterium Psychrobacter sp. PAMC 21119.

The RidA subfamily proteins catalyze the deamination reaction of enamine/imine intermediates, which are metabolites of amino acids such as threonine and serine. Numerous structural and functional studies have been conducted on RidA isolated from mesophiles and thermophiles. However, little is known about the structure of the RidA proteins isolated from psychrophiles. In the present study, we elucidated the crystal structure of RidA from the Antarctic bacterium Psychrobacter sp. PAMC 21119 (Pp-RidA) at 1.6 Å resolution to identify the structural properties contributing to cold-adaptability. Although the overall structure of Pp-RidA is similar to those of its homologues, it exhibits specific structural arrangements of a loop positioned near the active site, which is assumed to play a role in covering the active site of catalysis. In addition, the surface electrostatic potential of Pp-RidA suggested that it exhibits stronger electrostatic distribution relative to its homologues. Our results provide novel insights into the key determinants of cold-adaptability.

Glycine Betaine Effect on Dormancy in Deinococcus sp. UDEC-P1 and Psychrobacter sp. UDEC-A5 Exposed to Hyperosmotic Stress.

Bacteria under stress increase the proportion of dormant cells to ensure their survival. Cold and osmotic stress are similar, because in both the availability of water is reduced. Glycine betaine (GB) is one of the most common osmoprotectants in bacteria and possesses cryoprotectant properties. Our aim was to determine whether GB modifies the proportion of dormant Deinococcus sp. UDEC-P1 and Psychrobacter sp. UDEC-A5 cells exposed to osmotic stress. Both bacterial strains were incubated in the presence of up to 1 M NaCl with or without GB. Active and dormant cells were evaluated by both spectrophotometric and flow cytometry analysis. Without GB, Deinococcus sp. UDEC-P1 grew in the presence of 0.05 M NaCl, but with 5 mM GB grew at 0.1 M NaCl. Psychrobacter sp. UDEC-A5 grew in the presence of up to 0.25 M NaCl, but with 5 mM GB grew at 0.5 M NaCl. Under osmotic stress, the proportion of dormant cells of Deinococcus sp. UDEC-P1 and Psychrobacter sp. UDEC-A5 increased significantly (about eightfold and fivefold, respectively). The addition of GB (5 mM) exerted a different effect on the two strains, since it avoided the entrance into the dormancy of Psychrobacter sp. UDEC-A5 cells, but not of Deinococcus sp. UDEC-P1 cells. Our results suggest that the effect of GB on bacterial metabolism is strain dependent. For bacteria in which GB avoids dormancy, such as Psychrobacter sp. UDEC-A5, it could be a "double-edged sword" by reducing the "seed bank" available to recover the active population when favorable conditions return.

A Novel Cold-Adapted and Salt-Tolerant RNase R from Antarctic Sea-Ice Bacterium Psychrobacter sp. ANT206.

A novel RNase R, psrnr, was cloned from the Antarctic bacterium Psychrobacter sp. ANT206 and expressed in Escherichia coli (E. coli). A bioinformatics analysis of the psrnr gene revealed that it contained an open reading frame of 2313 bp and encoded a protein (PsRNR) of 770 amino acids. Homology modeling indicated that PsRNR had reduced hydrogen bonds and salt bridges, which might be the main reason for the catalytic efficiency at low temperatures. A site directed mutation exhibited that His 667 in the active site was absolutely crucial for the enzyme catalysis. The recombinant PsRNR (rPsRNR) showed maximum activity at 30 °C and had thermal instability, suggesting that rPsRNR was a cold-adapted enzyme. Interestingly, rPsRNR displayed remarkable salt tolerance, remaining stable at 0.5-3.0 M NaCl. Furthermore, rPsRNR had a higher kcat value, contributing to its efficient catalytic activity at a low temperature. Overall, cold-adapted RNase R in this study was an excellent candidate for antimicrobial treatment.

Benefits and Drawbacks of Harboring Plasmid pP32BP2, Identified in Arctic Psychrophilic Bacterium Psychrobacter sp. DAB_AL32B.

Psychrobacter sp. DAB_AL32B, originating from Spitsbergen island (Arctic), carries the large plasmid pP32BP2 (54,438 bp). Analysis of the pP32BP2 nucleotide sequence revealed the presence of three predicted phenotypic modules that comprise nearly 30% of the plasmid genome. These modules appear to be involved in fimbriae synthesis via the chaperone-usher pathway (FIM module) and the aerobic and anaerobic metabolism of carnitine (CAR and CAI modules, respectively). The FIM module was found to be functional in diverse hosts since it facilitated the attachment of bacterial cells to abiotic surfaces, enhancing biofilm formation. The CAI module did not show measurable activity in any of the tested strains. Interestingly, the CAR module enabled the enzymatic breakdown of carnitine, but this led to the formation of the toxic by-product trimethylamine, which inhibited bacterial growth. Thus, on the one hand, pP32BP2 can enhance biofilm formation, a highly advantageous feature in cold environments, while on the other, it may prevent bacterial growth under certain environmental conditions. The detrimental effect of harboring pP32BP2 (and its CAR module) seems to be conditional, since this replicon may also confer the ability to use carnitine as an alternative carbon source, although a pathway to utilize trimethylamine is most probably necessary to make this beneficial. Therefore, the phenotype determined by this CAR-containing plasmid depends on the metabolic background of the host strain.

Fish-derived antimicrobial peptides: Activity of a chionodracine mutant against bacterial models and human bacterial pathogens.

The increasing resistance to conventional antibiotics is an urgent problem that can be addressed by the discovery of new antimicrobial drugs such as antimicrobial peptides (AMPs). AMPs are components of innate immune system of eukaryotes and are not prone to the conventional mechanisms that are responsible of drug resistance. Fish are an important source of AMPs and, recently, we have isolated and characterized a new 22 amino acid residues peptide, the chionodracine (Cnd), from the Antarctic icefish Chionodraco hamatus. In this paper we focused on a new Cnd-derived mutant peptide, namely Cnd-m3a, designed to improve the selectivity against prokaryotic cells and the antimicrobial activity against human pathogens of the initial Cnd template. Cnd-m3a was used for immunization of rabbits, which gave rise to a polyclonal antibody able to detect the peptide. The interaction kinetic of Cnd-m3a with the Antarctic bacterium Psychrobacter sp. (TAD1) was imaged using a transmission electron microscopy (TEM) immunogold method. Initially the peptide was associated with the plasma membrane, but after 180 min of incubation, it was found in the cytoplasm interacting with a DNA target inside the bacterial cells. Using fluorescent probes we showed that the newly designed mutant can create pores in the outer membrane of the bacteria E. coli and Psychrobacter sp. (TAD1), confirming the results of TEM analysis. Moreover, in vitro assays demonstrated that Cnd-m3a is able to bind lipid vesicles of different compositions with a preference toward negatively charged ones, which mimics the prokaryotic cell. The Cnd-m3a peptide showed quite low hemolytic activity and weak cytotoxic effect against human primary and tumor cell lines, but high antimicrobial activity against selected Gram - human pathogens. These results highlighted the high potential of the Cnd-m3a peptide as a starting point for developing a new human therapeutic agent.

Adaptations to marine versus terrestrial low temperature environments as revealed by comparative genomic analyses of the genus Psychrobacter.

While cold-adapted bacteria isolated from marine or terrestrial low temperature environments share many similarities, cold-adapted bacteria from terrestrial environments usually grow over a broader range of temperatures suggesting different constraints of these two low temperature environments. The diversity of habitats from which Psychrobacter have been isolated (e.g. cold marine environments, frozen soils, permafrost and humans) provides a unique opportunity to examine habitat specific adaptations while reducing phylogenetic effects. Here, comparative genomic analyses of 26 strains of Psychrobacter revealed several clusters with characteristics that correlated with habitat. Marine and terrestrial Psychrobacter have amino acid composition typical of psychrophiles (e.g. fewer proline and lysine, more acidic) when compared to Psychrobacter strains associated with warm hosts, and have many potentially cold-adapted core genes (e.g. ClpX, DsbC, GroEL/GroES and MutS2). Marine and terrestrial Psychrobacter share many genes (e.g. FadB) not found in warm host Psychrobacter, which had their own distinct gene content (e.g. collagenase-like protease). Furthermore, terrestrial Psychrobacter were differentiated from marine Psychrobacter by the use of different cold adaptations and more hydrophobic and aliphatic proteins. These data suggest that terrestrial and marine Psychrobacter evolved from a mesophilic ancestor and are accumulating adaptations for low temperatures as well as for their respective habitats.

Proteomic and transcriptomic investigations on cold-responsive properties of the psychrophilic Antarctic bacterium Psychrobacter sp. PAMC 21119 at subzero temperatures.

Psychrobacter sp. PAMC 21119, isolated from Antarctic permafrost soil, grows and proliferates at subzero temperatures. However, its major mechanism of cold adaptation regulation remains poorly understood. We investigated the transcriptomic and proteomic responses of this species to cold temperatures by comparing profiles at -5°C and 20°C to understand how extreme microorganisms survive under subzero conditions. We found a total of 2,906 transcripts and 584 differentially expressed genes (≥ twofold, P <0.005) by RNA-seq. Genes for translation, ribosomal structure and biogenesis were upregulated, and lipid transport and metabolism was downregulated at low temperatures. A total of 60 protein spots (≥ 1.8 fold, P < 0.005) showed differential expression on two-dimensional gel electrophoresis and the proteins were identified by mass spectrometry. The most prominent upregulated proteins in response to cold were involved in metabolite transport, protein folding and membrane fluidity. Proteins involved in energy production and conversion, and heme protein synthesis were downregulated. Moreover, isoform exchange of cold-shock proteins was detected at both temperatures. Interestingly, pathways for acetyl-CoA metabolism, putrescine synthesis and amino acid metabolism were upregulated. This study highlights some of the strategies and different physiological states that Psychrobacter sp. PAMC 21119 has developed to adapt to the cold environment in Antarctica.

Psychrobacter fjordensis sp. nov., a psychrotolerant bacterium isolated from an Arctic fjord in Svalbard.

A Gram-negative, non-motile, non-spore-forming, psychrotolerant and halotolerant bacterium designated BSw21516B(T), was obtained from seawater in Kongsfjorden, a glacial fjord in the Arctic Svalbard and subjected to taxonomic analysis using a polyphasic approach. This bacterium was observed to optimally grow at 25-29 °C; between at 4 and 34 °C, but not at >35 °C; and in the presence of 0-8 % (w/v) NaCl at an optimum concentration of 2-5 % (w/v) NaCl. Strain BSw21516B(T) was found to contain Ubiquinone-8 (Q-8) as a predominant respiratory lipoquinone and C18:1 ω9c and summed feature 3 (C16:1 ω7c and/or iso-C15:0 2-OH) as predominant cellular fatty acids. Phylogenetic analysis of 16S rRNA and gyrB gene sequences showed that this isolate belongs to the genus Psychrobacter and is closely related to Psychrobacter fozii LMG 21280(T), which was isolated from a sediment sample in Antarctica. DNA hybridization experiments revealed a low level of DNA-DNA relatedness (less than 58.6 %) between strain BSw21516B(T) and its closest relatives. Based on these results a new species Psychrobacter fjordensis sp. nov. is proposed (type strain BSw21516B(T) = KCTC 42279(T) = CCTCC AB 2014020(T)).

Molecular analysis of the diversity of genus Psychrobacter present within a temperate estuary.

Many members of the genus Psychrobacter are endemic in extremely cold and saline environments and the genus has been described as only marginally successful in warmer habitats. In a previous study the Psychrobacter genus was, unexpectedly, the most frequently isolated bacterial genus from the sea-surface microlayer (SML) and the underlying water (UW) of a temperate estuary (Ria de Aveiro, Portugal). Here we analysed the diversity in Psychrobacter populations inhabiting this estuary. Samples were collected at three dates and three locations from sea-SML and UW. Isolated Psychrobacter strains were well-adapted to temperatures and salt concentrations above the ones described as optimal for most members of this genus. Hydrocarbon-degrading potential was not confirmed for these strains. We developed and optimized a reliable and specific denaturing gradient gel electrophoresis (DGGE)-based method for the analysis of Psychrobacter populations in aquatic systems. DGGE profiles inferred that Psychrobacter populations were very stable in the estuary, a strong indication for the presence of well-adapted phylotypes. The analysis of genus-specific clone libraries revealed a surprisingly high diversity among Psychrobacter in Ria de Aveiro. Results indicated that novel species were probably cultivated. Significant differences between sea-SML and UW Psychrobacter communities were revealed. Observed diversity trends may be related to environmental factors such as salinity and/or anthropogenic pressures such as contamination with hydrocarbons.

p-Benzoquinone-mediated amperometric biosensor developed with Psychrobacter sp. for toxicity testing of heavy metals.

A rapid and reliable p-benzoquinone-mediated amperometric biosensor (ToxTell) incorporated with Psychrobacter sp. to detect toxicities of heavy metal ions has been developed. This ToxTell biosensor relied on the real-time monitoring of inhibition effect for metabolism by toxicant to provide early detection and assessment of the degree of toxicity to living cells. The effect of growth phase on the sensitivity of Psychrobacter sp. biosensor was studied. The results showed that at the middle of the logarithmic phase or transition from logarithmic to stationary phase, the Psychrobacter sp. ToxTell biosensor had a higher sensitivity to toxicants. The effects of pH, salinity in respiratory substrates and incubation time on the performance of Psychrobacter sp. biosensor were also investigated. EC(50) values of Cu(2+), Cd(2+), Zn(2+), Cr(6+), Hg(2+) and Pb(2+) to Psychrobacter sp. determined at incubation time 30 min were 2.6 mg/L, 47.3 mg/L, 10.9 mg/L, 14.0 mg/L, 0.8 mg/L and 110.1 mg/L, respectively. The ToxTell microbial biosensor developed in this work demonstrated excellent storage stability for more than 60 days. The biosensor could incorporate different microbial species as biocomponent to reflect the comprehensive values for toxicants in real samples and the results therefore had high degree of validity.

Biochemical characterization of a novel haloalkane dehalogenase from a cold-adapted bacterium.

A haloalkane dehalogenase, DpcA, from Psychrobacter cryohalolentis K5, representing a novel psychrophilic member of the haloalkane dehalogenase family, was identified and biochemically characterized. DpcA exhibited a unique temperature profile with exceptionally high activities at low temperatures. The psychrophilic properties of DpcA make this enzyme promising for various environmental applications.

Psychrobacter isolates of human origin, other than Psychrobacter phenylpyruvicus, are predominantly Psychrobacter faecalis and Psychrobacter pulmonis, with emended description of P. faecalis.

Human Psychrobacter isolates, other than Psychrobacter phenylpyruvicus, are predominantly designated Psychrobacter immobilis. Phenotypic and genotypic testing of Psychrobacter isolates that have been deposited in different culture collections as P. immobilis indicates that most of these human isolates belong to the species Psychrobacter faecalis and Psychrobacter pulmonis.

Psychrobacter sanguinis sp. nov., recovered from four clinical specimens over a 4-year period.

An analysis of 16S rRNA gene sequences from archived clinical reference specimens identified a novel species of the genus Psychrobacter, of which four strains have been independently isolated from human blood. On the basis of 16S rRNA gene sequence similarity, the closest relatives with validly published names were Psychrobacter arenosus R7(T) (98.7%), P. pulmonis CECT 5989(T) (97.7%), P. faecalis Iso-46(T) (97.6%) and P. lutiphocae IMMIB L-1110(T) (97.2%). Maximum-likelihood phylogenetic analysis of 16S rRNA gene sequences showed that the isolates belonged to the genus Psychrobacter and were members of a cluster associated with Psychrobacter sp. PRwf-1, isolated from a silk snapper fish. DNA-DNA relatedness and partial 23S rRNA gene sequences also supported the finding that the isolates belonged to a species distinct from its closest phylogenetic neighbours. The predominant cellular fatty acids were C(18:1)ω9c, C(16:0), summed feature 3 (C(16:1)ω7c and/or iso-C(15:0) 2-OH), summed feature 5 (C(18:2)ω6,9c and/or anteiso-C(18:0)) and C(18:0). Biochemical and morphological analysis further supported the assignment of the four isolates to a novel species. The name Psychrobacter sanguinis sp. nov. is proposed. The type strain is 13983(T) (=DSM 23635(T)=CCUG 59771(T)).

Manipulations of AMP metabolic genes increase growth rate and cold tolerance in Escherichia coli: implications for psychrophilic evolution.

Diverse organisms have adapted to thrive at low temperatures (i.e., <20 °C, termed psychrophiles), colonizing the majority of earth's biosphere. In contrast with mesophiles (20-40 °C thermal range), all observed psychrophiles increase intracellular adenosine 5'-triphosphate concentrations as temperatures decline; this phenomenon has been described as an important compensatory mechanism to deal with decreases in thermal energy and molecular motion. We considered purine metabolic pathways in class gammaproteobacteria (n = 115) to investigate metabolic and evolutionary bases of this process. A survey of the KEGG database indicated that psychrophilic purine metabolic pathways tend to be enriched with de novo adenosine 5'-monophosphate (AMP) synthetic enzymes, whereas mesophiles tend to be enriched with AMP degradative enzymes. Function of the observed psychrophilic pathway structure was tested by engineering the mesophilic gammaproteobacterium Escherichia coli to reflect psychrophilic purine metabolism, specifically by expressing adenylosuccinate synthetase (purA) from the psychrophilic gammaproteobacterium, Psychrobacter cryohalolentis, in an AMP nucleosidase (amn)-deficient background. Modified E. coli was capable of growing up to ∼70% faster at low temperatures and became up to ∼10-fold more cold tolerant relative to wild type. These findings highlight potentially important transitional steps in psychrophilic evolution.

The genome sequence of Psychrobacter arcticus 273-4, a psychroactive Siberian permafrost bacterium, reveals mechanisms for adaptation to low-temperature growth.

Psychrobacter arcticus strain 273-4, which grows at temperatures as low as -10 degrees C, is the first cold-adapted bacterium from a terrestrial environment whose genome was sequenced. Analysis of the 2.65-Mb genome suggested that some of the strategies employed by P. arcticus 273-4 for survival under cold and stress conditions are changes in membrane composition, synthesis of cold shock proteins, and the use of acetate as an energy source. Comparative genome analysis indicated that in a significant portion of the P. arcticus proteome there is reduced use of the acidic amino acids and proline and arginine, which is consistent with increased protein flexibility at low temperatures. Differential amino acid usage occurred in all gene categories, but it was more common in gene categories essential for cell growth and reproduction, suggesting that P. arcticus evolved to grow at low temperatures. Amino acid adaptations and the gene content likely evolved in response to the long-term freezing temperatures (-10 degrees C to -12 degrees C) of the Kolyma (Siberia) permafrost soil from which this strain was isolated. Intracellular water likely does not freeze at these in situ temperatures, which allows P. arcticus to live at subzero temperatures.

Expression profiles of genes associated with immune response and oxidative stress in Atlantic cod, Gadus morhua head kidney leukocytes modulated by live and heat-inactivated intestinal bacteria.

The molecular mechanisms of immune response and antioxidant defense in Atlantic cod Gadus morhua head kidney (HK) leukocytes to live and heat-inactivated intestinal bacteria were investigated by transcriptome analyses. The HK leukocytes were incubated with Pseudomonas sp. (GP21) and Psychrobacter sp. (GP12), which are intestinal bacteria of Atlantic cod. The responses of the defense-associated genes at 3 and 24h post-incubation (hpi) were assayed by semi-quantitative RT-PCR. Live and heat-inactivated GP21 caused a significant increase in the transcript levels of bacterial defense genes in the HK leukocytes: BPI/LBP and g-type lysozyme were highest at 24hpi. The levels of BPI/LBP were significantly upregulated at 24hpi by live GP12 but not by the heat-inactivated type. The expression of g-type lysozyme was significantly elevated regardless of the type of GP12. IL-1beta was significantly upregulated by live GP21 and GP12, with maximum expression observed at 3hpi. In contrast, the expression levels of IL-8 in the HK leukocytes were not augmented by both types of GP21 and GP12. A significant upregulation of the non-specific cytotoxic cell receptor protein-1 (NCCRP-1) was observed with live GP12 at 3hpi, whereas in the case of GP21 such a change was noted only with the heat-inactivated type at 24hpi. A definite pattern of granzyme expression was not observed with both the live and heat-inactivated GP21 and GP12. The levels of antioxidant genes (catalase and GSH-Px) remained unchanged except in cells incubated with heat-inactivated GP21, where a significant elevation of GSH-Px was seen at 24hpi. Thus, this in vitro study has revealed that the defense mechanisms in the HK leukocytes can be modulated by the commensal intestinal bacteria of Atlantic cod. The extent of this activation is dependent on the bacterial species and its viability.

Psychrobacter aestuarii sp. nov., isolated from a tidal flat sediment.

A Gram-negative-staining, non-motile, non-spore-forming and strictly aerobic bacterial strain, SC35(T), was isolated from tidal flat sediment collected from the South Sea, Korea, and subjected to a taxonomic study using a polyphasic approach. The organism grew optimally at 20-30 degrees C and with 1-2 % (w/v) NaCl. Strain SC35(T) contained ubiquinone-8 as the predominant respiratory lipoquinone and C(18 : 1)omega9c as the major fatty acid. The DNA G+C content was 48.5 mol%. A phylogenetic tree based on 16S rRNA gene sequences showed that strain SC35(T) formed a lineage within the genus Psychrobacter (94.3-96.5 % sequence similarity), forming a distinct branch in a clade also containing Psychrobacter pacificensis NIBH P2K6(T) and Psychrobacter celer SW-238(T). On the basis of phenotypic and phylogenetic data, strain SC35(T) (=KCTC 22503(T)=JCM 16343(T)) was placed in the genus Psychrobacter as the type strain of a novel species, for which the name Psychrobacter aestuarii sp. nov. is proposed.

Psychrobacter lutiphocae sp. nov., isolated from the faeces of a seal.

The taxonomic status of a Gram-negative-staining bacterium, isolated from the faeces of a seal, was investigated using a polyphasic approach. Comparative 16S rRNA gene sequence analysis showed that the novel isolate formed a distinct phyletic line within the genus Psychrobacter, displaying >3.3% sequence divergence with other known Psychrobacter species. The generic assignment was confirmed by chemotaxonomic data, which revealed a fatty acid profile that included straight-chain saturated, unsaturated and 3-hydroxylated fatty acids, with C18:1omega9c as the major fatty acid. A ubiquinone with eight isoprene units (Q-8) was the predominant respiratory quinone and spermidine was the predominant polyamine. The novel isolate was distinguished from other members of the genus Psychrobacter by using a set of phenotypic properties. On the basis of phenotypic and phylogenetic considerations, it is proposed that the new isolate represents a novel species, for which the name Psychrobacter lutiphocae sp. nov. is proposed. Strain IMMIB L-1110T (=DSM 21542T=CCUG 56590T) is the type strain.

Psychrobacter fulvigenes sp. nov., isolated from a marine crustacean from the Sea of Japan.

Two novel Psychrobacter-like bacteria, strains KC 40(T) and KC 65, were isolated from a marine crustacean specimen collected from the Sea of Japan, and were characterized by using a polyphasic approach. Strains were selected on the basis of their ability to produce black-brown diffusible pigments on commonly used organic media, which appears to be a unique characteristic of recognized members of the genus Psychrobacter. Phylogenetic analyses based on both 16S rRNA and gyrB gene sequences showed that the novel isolates formed a separate cluster within the genus Psychrobacter. Strains KC 40(T) and KC 65 shared highest levels of 16S rRNA gene sequence similarity with Psychrobacter urativorans DSM 14009(T) (98.0 %), Psychrobacter pulmonis CCUG 46240(T) (97.9 %), Psychrobacter cibarius JG-219(T) (97.9 %), Psychrobacter faecalis Iso-46(T) (97.8 %), Psychrobacter aquimaris SW-210(T) (97.6 %), Psychrobacter namhaensis SW-242(T) (97.6 %) and Psychrobacter nivimaris 88/2-7(T) (97.6 %). DNA-DNA hybridization experiments revealed 84 % DNA-DNA relatedness between strains KC 40(T) and KC 65 but much lower levels of relatedness (7-35 %) between the novel strains and the type strains of recognized Psychrobacter species, confirming their assignment to a single novel species of the genus Psychrobacter. The two novel strains could be distinguished from recognized species of the genus Psychrobacter based on a combination of physiological and biochemical characteristics. On the basis of phenotypic and molecular properties, strains KC 40(T) and KC 65 are considered to represent a novel species of the genus Psychrobacter, for which the name Psychrobacter fulvigenes sp. nov. is proposed. The type strain is KC 40(T) (=KMM 3954(T)=NRIC 0746(T)=JCM 15525(T)).

Survivability of Psychrobacter cryohalolentis K5 under simulated martian surface conditions.

Spacecraft launched to Mars can retain viable terrestrial microorganisms on board that may survive the interplanetary transit. Such biota might compromise the search for life beyond Earth if capable of propagating on Mars. The current study explored the survivability of Psychrobacter cryohalolentis K5, a psychrotolerant microorganism obtained from a Siberian permafrost cryopeg, under simulated martian surface conditions of high ultraviolet irradiation, high desiccation, low temperature, and low atmospheric pressure. First, a desiccation experiment compared the survival of P. cryohalolentis cells embedded, or not embedded, within a medium/salt matrix (MSM) maintained at 25 degrees C for 24 h within a laminar flow hood. Results indicate that the presence of the MSM enhanced survival of the bacterial cells by 1 to 3 orders of magnitude. Second, tests were conducted in a Mars Simulation Chamber to determine the UV tolerance of the microorganism. No viable vegetative cells of P. cryohalolentis were detected after 8 h of exposure to Mars-normal conditions of 4.55 W/m(2) UVC irradiation (200-280 nm), -12.5 degrees C, 7.1 mbar, and a Mars gas mix composed of CO(2) (95.3%), N(2) (2.7%), Ar (1.6%), O(2) (0.2%), and H(2)O (0.03%). Third, an experiment was conducted within the Mars chamber in which total atmospheric opacities were simulated at tau = 0.1 (dust-free CO(2) atmosphere at 7.1 mbar), 0.5 (normal clear sky with 0.4 = dust opacity and 0.1 = CO(2)-only opacity), and 3.5 (global dust storm) to determine the survivability of P. cryohalolentis to partially shielded UVC radiation. The survivability of the bacterium increased with the level of UVC attenuation, though population levels still declined several orders of magnitude compared to UVC-absent controls over an 8 h exposure period.