Polyhydroxyalkanoate involvement in stress-survival of two psychrophilic bacterial strains from the High Arctic.

An ever-growing body of literature evidences the protective role of polyhydroxyalkanoates (PHAs) against a plethora of mostly physical stressors in prokaryotic cells. To date, most of the research done involved bacterial strains isolated from habitats not considered to be life-challenging or extremely impacted by abiotic environmental factors. Polar region microorganisms experience a multitude of damaging factors in combinations rarely seen in other of Earth's environments. Therefore, the main objective of this investigation was to examine the role of PHAs in the adaptation of psychrophilic, Arctic-derived bacteria to stress conditions. Arctic PHA producers: Acidovorax sp. A1169 and Collimonas sp. A2191, were chosen and their genes involved in PHB metabolism were deactivated making them unable to accumulate PHAs (ΔphaC) or to utilize them (Δi-phaZ) as a carbon source. Varying stressors were applied to the wild-type and the prepared mutant strains and their survival rates were assessed based on CFU count. Wild-type strains with a functional PHA metabolism were best suited to survive the freeze-thaw cycle - a common feature of polar region habitats. However, the majority of stresses were best survived by the ΔphaC mutants, suggesting that the biochemical imbalance caused by the lack of PHAs induced a permanent cell-wide stress response thus causing them to better withstand the stressor application. Δi-phaZ mutants were superior in surviving UV irradiation, hinting that PHA granule presence in bacterial cells is beneficial despite it being biologically inaccessible. Obtained data suggests that the ability to metabolize PHA although important for survival, probably is not the most crucial mechanism in the stress-resistance strategies arsenal of cold-loving bacteria. KEY POINTS: • PHA metabolism helps psychrophiles survive freezing • PHA-lacking psychrophile mutants cope better with oxidative and heat stresses • PHA granule presence enhances the UV resistance of psychrophiles.

Polar-Region Soils as Novel Reservoir of Lactic Acid Bacteria from the Genus Carnobacterium.

Polar habitats offer excellent sites to isolate unique bacterial strains due to their diverse physical, geochemical, and biological factors. We hypothesize that the unique environmental conditions of polar regions select for distinct strains of lactic acid bacteria (LAB) with novel biochemical properties. In this study, we characterized ten strains of psychrotrophic LAB isolated from hitherto poorly described sources-High Arctic and maritime Antarctic soils and soil-like materials, including ornithogenic soils, cryoconites, elephant seal colonies, and postglacial moraines. We evaluated the physiological and biochemical properties of the isolates. Based on 16S rRNA and housekeeping genes, the four LAB strains were assigned to three Carnobacterium species: C. alterfunditum, C. maltaromaticum, and C. jeotgali. The remaining strains may represent three new species of the Carnobacterium genus. All isolates were neutrophilic and halophilic psychrotrophs capable of fermenting various carbohydrates, organic acids, and alcohols. The identified metabolic properties of the isolated Carnobacterium strains suggest possible syntrophic interactions with other microorganisms in polar habitats. Some showed antimicrobial activity against food pathogens such as Listeria monocytogenes and human pathogens like Staphylococcus spp. Several isolates exhibited unique metabolic traits with potential biotechnological applications that could be more effectively exploited under less stringent technological conditions compared to thermophilic LAB strains, such as lower temperatures and reduced nutrient concentrations. Analysis of extrachromosomal genetic elements revealed 13 plasmids ranging from 4.5 to 79.5 kb in five isolates, featuring unique genetic structures and high levels of previously uncharacterized genes. This work is the first comprehensive study of the biochemical properties of both known and new Carnobacterium species and enhances our understanding of bacterial communities in harsh and highly selective polar soil ecosystems.

Native and Alien Antarctic Grasses as a Habitat for Fungi.

Biological invasions are now seen as one of the main threats to the Antarctic ecosystem. An example of such an invasion is the recent colonization of the H. Arctowski Polish Antarctic Station area by the non-native grass Poa annua. This site was previously occupied only by native plants like the Antarctic hair grass Deschampsia antarctica. To adapt successfully to new conditions, plants interact with soil microorganisms, including fungi. The aim of this study was to determine how the newly introduced grass P. annua established an interaction with fungi compared to resident grass D. antarctica. We found that fungal diversity in D. antarctica roots was significantly higher compared with P. annua roots. D. antarctica managed a biodiverse microbiome because of its ability to recruit fungal biocontrol agents from the soil, thus maintaining a beneficial nature of the endophyte community. P. annua relied on a set of specific fungal taxa, which likely modulated its cold response, increasing its competitiveness in Antarctic conditions. Cultivated endophytic fungi displayed strong chitinolysis, pointing towards their role as phytopathogenic fungi, nematode, and insect antagonists. This is the first study to compare the root mycobiomes of both grass species by direct culture-independent techniques as well as culture-based methods.

Genetic engineering of low-temperature polyhydroxyalkanoate production by Acidovorax sp. A1169, a psychrophile isolated from a subglacial outflow.

In recent years, extremophilic microorganisms have been employed as producers of the microbial bioplastics polyhydroxyalkanoates (PHA), which are of great biotechnological value. Nevertheless, cold-loving or psychrophilic (cryophilic) bacteria have been neglected in this regard. Here, we present an investigation of the Arctic glacier-derived PHA producer Acidovorax sp. A1169. Biolog GEN III Microplates were used as a screening tool to identify the most suitable carbon substrate concerning PHA synthesis. The strain produced homopolymer poly(3-hydroxybutyrate) (PHB) most efficiently (2 g/L) at a temperature of 15 °C when supplied with fructose or mannitol as carbon sources with a substantial decrease of PHB biosynthesis at 17.5 °C. The PHB yield did not increase considerably or even decreased when carbon source concentration exceeded 10 g/L hinting that the strain is oligotrophic in nature. The strain was also capable of introducing 3-hydroxyvalerate (3HV) into the polymer structure, which is known to improve PHA thermoplastic properties. This is the first investigation providing insight into a PHA biosynthesis process by means of a true psychrophile, offering guidelines on polar-region bacteria cultivation, production of PHA and also on the methodology for genetic engineering of psychrophiles.

Pedobacter fastidiosus sp. nov., isolated from glacial habitats of maritime Antarctica.

Strains P8930T and 478 were isolated from Antarctic glaciers located on James Ross Island and King George Island, respectively. They comprised Gram-stain-negative short rod-shaped cells forming pink pigmented colonies and exhibited identical 16S rRNA gene sequences and highly similar MALDI TOF mass spectra, and hence were assigned as representatives of the same species. Phylogenetic analysis based on 16S rRNA gene sequences assigned both isolates to the genus Pedobacter and showed Pedobacter frigidisoli and Pedobacter terrae to be their closest phylogenetic neighbours, with 97.4 and 97.2 % 16S rRNA gene sequence similarities, respectively. These low similarity values were below the threshold similarity value of 98.7%, confirming the delineation of a new bacterial species. Further genomic characterization included whole-genome sequencing accompanied by average nucleotide identity (ANI) and digital DNA-DNA hybridization calculations, and characterization of the genome features. The ANI values between P8930T and P. frigidisoli RP-3-11T and P. terrae DSM 17933T were 79.7 and 77.6 %, respectively, and the value between P. frigidisoli RP-3-11T and P. terrae DSM 17933T was 77.7 %, clearly demonstrating the phylogenetic distance and the novelty of strain P8930T. Further characterization included analysis of cellular fatty acids, quinones and polar lipids, and comprehensive biotyping. All the obtained results proved the separation of strains P8930T and 478 from the other validly named Pedobacter species, and confirmed that they represent a new species for which the name Pedobacter fastidiosus sp. nov. is proposed. The type strain is P8930T (=CCM 8938T=LMG 32098T).

Root-Associated Bacteria Community Characteristics of Antarctic Plants: Deschampsia antarctica and Colobanthus quitensis-a Comparison.

Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. are the only Magnoliophyta to naturally colonize the Antarctic region. The reason for their sole presence in Antarctica is still debated as there is no definitive consensus on how only two unrelated flowering plants managed to establish breeding populations in this part of the world. In this study, we have explored and compared the rhizosphere and root-endosphere dwelling microbial community of C. quitensis and D. antarctica specimens sampled in maritime Antarctica from sites displaying contrasting edaphic characteristics. Bacterial phylogenetic diversity (high-throughput 16S rRNA gene fragment targeted sequencing) and microbial metabolic activity (Biolog EcoPlates) with a geochemical soil background were assessed. Gathered data showed that the microbiome of C. quitensis root system was mostly site-dependent, displaying different characteristics in each of the examined locations. This plant tolerated an active bacterial community only in severe conditions (salt stress and nutrient deprivation), while in other more favorable circumstances, it restricted microbial activity, with a possibility of microbivory-based nutrient acquisition. The microbial communities of D. antarctica showed a high degree of similarity between samples within a particular rhizocompartment. The grass' endosphere was significantly enriched in plant beneficial taxa of the family Rhizobiaceae, which displayed obligatory endophyte characteristics, suggesting that at least part of this community is transmitted vertically. Ultimately, the ecological success of C. quitensis and D. antarctica in Antarctica might be largely attributed to their associations and management of root-associated microbiota.

Metabolic fingerprinting of the Antarctic cyanolichen Leptogium puberulum-associated bacterial community (Western Shore of Admiralty Bay, King George Island, Maritime Antarctica).

Lichens are presently regarded as stable biotopes, small ecosystems providing a safe haven for the development of a diverse and numerous microbiome. In this study, we conducted a functional diversity assessment of the microbial community residing on the surface and within the thalli of Leptogium puberulum, a eurytopic cyanolichen endemic to Antarctica, employing the widely used Biolog EcoPlates which test the catabolism of 31 carbon compounds in a colorimetric respiration assay. Lichen thalli occupying moraine ridges of differing age within a proglacial chronosequence, as well as those growing in sites of contrasting nutrient concentrations, were procured from the diverse landscape of the western shore of Admiralty Bay in Maritime Antarctica. The L. puberulum bacterial community catabolized photobiont- (glucose-containing carbohydrates) and mycobiont-specific carbon compounds (D-Mannitol). The bacteria also had the ability to process degradation products of lichen thalli components (D-cellobiose and N-acetyl-D-glucosamine). Lichen thalli growth site characteristics had an impact on metabolic diversity and respiration intensity of the bacterial communities. While high nutrient contents in lichen specimens from "young" proglacial locations and in those from nitrogen enriched sites stimulated bacterial catabolic activity, in old proglacial locations and in nutrient-lacking sites, a metabolic activity restriction was apparent, presumably due to lichen-specific microbial control mechanisms.

Biogenic synthesis of silica nanoparticles from corn cobs husks. Dependence of the productivity on the method of raw material processing.

Corn processing generates thousands of tons of cob husks, which still contains many valuable elements. To make the most of these wastes, they are applied as substrates for biotransformation's procedures. This approach allowed converting or releasing, the elements deposited in the plant material and obtaining valuable products. Thus bioconversion of corn cob husks (CCH) using a fungus of the Fusarium culmorum genus resulted in obtaining silica nanoparticles of defined size and morphology. SEM analysis excluded their presence on the surface of the substrate. FTIR confirmed the presence of siloxane bonds and O-Si-O bonds in post-biotransformation fluid. Using the Heteropoly Blue Method, it was checked that the highest concentration of silica during 16-day biotransformation falls on the 7th day of the process, in which both the substrate sterilization and the process of the biocatalyst starvation were of key importance. Using the STEM and EDX analysis, it was proved that the obtained nanoparticles with a spherical form are structured and their dimensions are ~40 and ~70 nm. ICP-OES proved that the overall process efficiency was 47%. Such nanoparticles can be successfully used in the medical industry.

Modification of Bacterial Cellulose with Quaternary Ammonium Compounds Based on Fatty Acids and Amino Acids and the Effect on Antimicrobial Activity.

In the present work, bacterial cellulose (BC) membranes have been modified with bioactive compounds based on long chain dimer of C18 linoleic acid, referred to as the dilinoleic acid (DLA) and tyrosine (Tyr), a natural amino acid capable of forming noncovalent cation-π interactions with positively charged ethylene diamine (EDA). This new compound, [EDA][DLA-Tyr], has been synthesized by simple coupling reaction, and its chemical structure was characterized by 1H NMR and Fourier transform infrared spectroscopy. The antimicrobial activity of a new compound against S. aureus and S. epidermidis, two cocci associated with skin and wound infections, was assessed. The [EDA][DLA-Tyr] impregnated BC exhibited strong and long-term antimicrobial activity against both staphylococcal species. The results showed a 57-66% and 56-60% reduction in S. aureus and S. epidermidis viability, respectively, depending on [EDA][DLA-Tyr] concentration used. Importantly, [EDA][DLA-Tyr] molecules were released gradually from the BC pellicle, while a reference antibiotic, erythromycine (ER), did not show any antibacterial activity against S. aureus and S. epidermidis after 48 h of soaking in deionized water. Thus, a combination of [EDA][DLA-Tyr] and BC could be a promising new class of wound dressing displaying both biocompatibility and antimicrobial activity.

The Impact of Oxidative Stress Factors on the Viability, Senescence, and Methylation Status of Olfactory Bulb-Derived Glial Cells Isolated from Human Cadaver Donors.

The olfactory bulb (OB) is a unique structure in the central nervous system that retains the ability to create new neuronal connections. Glial cells isolated from the OB have been recently considered as a novel and promising tool to establish an effective therapy for central nervous system injuries. Due to the hindered access to autologous tissue for cell isolation, an allogeneic source of tissues obtained postmortem has been proposed. In this study, we focused on the morphological and molecular characteristics of human OB-derived glial cells isolated postmortem, at different time points after a donor's death. We evaluated the proliferative activity of the isolated cells, and investigated the ultrastructure of the mitochondria, the accumulation of intracellular reactive oxygen species, and the activity of superoxide dismutase. The data obtained clearly indicate that the duration of ischemia is crucial for the viability/senescence rate of OB-derived glial cells. The OB can be isolated during autopsy and still stand as a source of viable glial cells, but ischemia duration is a major factor limiting its potential usefulness in therapies.

Enrichment of Cryoconite Hole Anaerobes: Implications for the Subglacial Microbiome.

Glaciers have recently been recognized as ecosystems comprised of several distinct habitats: a sunlit and oxygenated glacial surface, glacial ice, and a dark, mostly anoxic glacial bed. Surface meltwaters annually flood the subglacial sediments by means of drainage channels. Glacial surfaces host aquatic microhabitats called cryoconite holes, regarded as "hot spots" of microbial abundance and activity, largely contributing to the meltwaters' bacterial diversity. This study presents an investigation of cryoconite hole anaerobes and discusses their possible impact on subglacial microbial communities, combining 16S rRNA gene fragment amplicon sequencing and the traditional enrichment culture technique. Cryoconite hole sediment harbored bacteria belonging mainly to the Proteobacteria (21%), Bacteroidetes (16%), Actinobacteria (14%), and Planctomycetes (6%) phyla. An 8-week incubation of those sediments in Postgate C medium for sulfate reducers in airtight bottles, emulating subglacial conditions, eliminated a great majority of dominant taxa, leading to enrichment of the Firmicutes (62%), Proteobacteria (14%), and Bacteroidetes (13%), which consisted of anaerobic genera like Clostridium, Psychrosinus, Paludibacter, and Acetobacterium. Enrichment of Pseudomonas spp. also occurred, suggesting it played a role as a dominant oxygen scavenger, providing a possible scenario for anaerobic niche establishment in subglacial habitats. To our knowledge, this is the first paper to provide insight into the diversity of the anaerobic part of the cryoconite hole microbial community and its potential to contribute to matter turnover in anoxic, subglacial sites.

Antioxidant and Anti-Senescence Effect of Metformin on Mouse Olfactory Ensheathing Cells (mOECs) May Be Associated with Increased Brain-Derived Neurotrophic Factor Levels-An Ex Vivo Study.

Metformin, the popular anti-diabetic drug was shown to exert multiple biological effects. The most recent metformin gained attention as an agent that mobilizes endogenous progenitor cells and enhances regenerative potential of organisms, for example by promoting neurogenesis. In the present study, we examined the role of metformin on mouse olfactory ensheathing cells (mOECs) derived from animals receiving metformin for eight weeks at a concentration equal to 2.8 mg/day. The mOECs expanded ex vivo were characterized in terms of their cellular phenotype, morphology, proliferative activity, viability and accumulation of oxidative stress factors. Moreover, we determined the mRNA and protein levels of brain-derived neurotrophic factor (BDNF), distinguishing the secretion of BDNF by mOECs in cultures and circulating serum levels of BDNF. The mOECs used in the experiment were glial fibrillary acidic protein (GFAP) and p75 neurotrophin receptor (p75NTR) positive and exhibited both astrocyte-like and non-myelin Schwann cell-like morphologies. Our results revealed that the proliferation of OECs derived from mice treated with metformin was lowered, when compared to control group. Simultaneously, we noted increased cell viability, reduced expression of markers associated with cellular senescence and a decreased amount of reactive oxygen species. We observed increased mRNA expression of BDNF and its down-stream genes. Obtained results indicate that metformin may exert antioxidant, anti-apoptotic and senolytic action on OECs expanded ex vivo.

Evidence of adaptation, niche separation and microevolution within the genus Polaromonas on Arctic and Antarctic glacial surfaces.

Polaromonas is one of the most abundant genera found on glacier surfaces, yet its ecology remains poorly described. Investigations made to date point towards a uniform distribution of Polaromonas phylotypes across the globe. We compared 43 Polaromonas isolates obtained from surfaces of Arctic and Antarctic glaciers to address this issue. 16S rRNA gene sequences, intergenic transcribed spacers (ITS) and metabolic fingerprinting showed great differences between hemispheres but also between neighboring glaciers. Phylogenetic distance between Arctic and Antarctic isolates indicated separate species. The Arctic group clustered similarly, when constructing dendrograms based on 16S rRNA gene and ITS sequences, as well as metabolic traits. The Antarctic strains, although almost identical considering 16S rRNA genes, diverged into 2 groups based on the ITS sequences and metabolic traits, suggesting recent niche separation. Certain phenotypic traits pointed towards cell adaptation to specific conditions on a particular glacier, like varying pH levels. Collected data suggest, that seeding of glacial surfaces with Polaromonas cells transported by various means, is of greater efficiency on local than global scales. Selection mechanisms present of glacial surfaces reduce the deposited Polaromonas diversity, causing subsequent adaptation to prevailing environmental conditions. Furthermore, interactions with other supraglacial microbiota, like algae cells may drive postselectional niche separation and microevolution within the Polaromonas genus.

Microbial community development on the surface of Hans and Werenskiold Glaciers (Svalbard, Arctic): a comparison.

Surface ice and cryoconite holes of two types of polythermal Svalbard Glaciers (Hans Glacier--grounded tidewater glacier and Werenskiold Glacier-land-based valley glacier) were investigated in terms of chemical composition, microbial abundance and diversity. Gathered data served to describe supraglacial habitats and to compare microbe-environment interactions on those different type glaciers. Hans Glacier samples displayed elevated nutrient levels (DOC, nitrogen and seston) compared to Werenskiold Glacier. Adjacent tundra formations, bird nesting sites and marine aerosol were candidates for allochtonic enrichment sources. Microbial numbers were comparable on both glaciers, with surface ice containing cells in the range of 10(4) mL(-1) and cryoconite sediment 10(8) g(-1) dry weight. Denaturating gradient gel electrophoresis band-based clustering revealed differences between glaciers in terms of dominant bacterial taxa structure. Microbial community on Werenskiold Glacier benefited from the snow-released substances. On Hans Glacier, this effect was not as pronounced, affecting mainly the photoautotrophs. Over-fertilization of Hans Glacier surface was proposed as the major factor, desensitizing the microbial community to the snow melt event. Nitrogen emerged as a limiting factor in surface ice habitats, especially to Eukaryotic algae.

The effect of the bioactive sphingolipids S1P and C1P on multipotent stromal cells--new opportunities in regenerative medicine.

Sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) belong to a family of bioactive sphingolipids that act as important extracellular signaling molecules and chemoattractants. This study investigated the influence of S1P and C1P on the morphology, proliferation activity and osteogenic properties of rat multipotent stromal cells derived from bone marrow (BMSCs) and subcutaneous adipose tissue (ASCs). We show that S1P and C1P can influence mesenchymal stem cells (MSCs), each in a different manner. S1P stimulation promoted the formation of cellular aggregates of BMSCs and ASCs, while C1P had an effect on the regular growth pattern and expanded intercellular connections, thereby increasing the proliferative activity. Although osteogenic differentiation of MSCs was enhanced by the addition of S1P, the effectiveness of osteoblast differentiation was more evident in BMSCs, particularly when biochemical and molecular marker levels were considered. The results of the functional osteogenic differentiation assay, which includes an evaluation of the efficiency of extracellular matrix mineralization (SEM-EDX), revealed the formation of numerous mineral aggregates in BMSC cultures stimulated with S1P. Our data demonstrated that in an appropriate combination, the bioactive sphingolipids S1P and C1P may find wide application in regenerative medicine, particularly in bone regeneration with the use of MSCs.

The diversity of bacteria isolated from antarctic freshwater reservoirs possessing the ability to produce polyhydroxyalkanoates.

The diversity of polyhydroxyalkanoates-producing bacteria in freshwater reservoirs in the Ecology Glacier foreland, Antarctica, was examined by a cultivation-dependent method. Isolated strains were analyzed phylogenetically by 16S rRNA gene sequencing, and classified as members of Alpha-, Beta-, or Gammaproteobacteria classes. Polymerase chain reaction was used to detect PHA synthase genes. Potential polyhydroxyalkanoates (PHAs) producers belonging mainly to Pseudomonas sp., and Janthinobacterium sp. were isolated from all five sampling sites, suggesting that PHA synthesis is a common bacterial feature at pioneer sites. All Pseudomonas strains had the genetic potential to synthesize medium-chain-length PHAs, whereas some isolated Janthinobacterium strains might produce short-chain-length PHAs or medium-chain-length PHAs. It is the first report revealing that Janthinobacterium species could have the potential to produce medium-chain-length PHAs.

Sulphate reducing activity detected in soil samples from Antarctica, Ecology Glacier Forefield, King George Island.

We determined sulphate-reducing activities in media inoculated with soils and with kettle lake sediments in order to investigate their potential in geomicrobiological processes in low-temperature, terrestrial maritime Antarctic habitats. Soil and sediment samples were collected in a glacier valley abandoned by Ecology Glacier during the last 30 years: from a new formed kettle lake sediment and forefield soil derived from ground moraine. Inoculated with these samples, liquid Postgate C and minimal media supplemented with various carbon sources as electron donors were incubated for 8 weeks at 4°C. High rates of sulphate reduction were observed only in media inoculated with soil. No sulphate reduction was detected in media inoculated with kettle lake sediments. In soil samples culture media calcite and elemental sulphur deposits were observed, demonstrating that sulphate-reducing activity is associated with a potential to mineral formation in cold environments. Cells observed on scanning microscopy (SEM) micrographs of post-culture-soil deposits could be responsible for sulphate-reducing activity.

Effects of steroids on the morphology and proliferation of canine and equine mesenchymal stem cells of adipose origin - in vitro research.

Disorders of the locomotive system, especially those occurring due to degenerative changes of the joints, are serious problems in daily veterinary medical practice. Steroid injections are the main way of treating these disorders. However, this approach brings usually only temporary effects of pain relief, and may cause many side effects. Alternative therapies focus on regeneration of damaged tissue using adult mesenchymal stem cells (MSCs). Since 2002, the great plasticity and immunomodulatory properties of MSCs isolated from adipose tissue (AdMSCs) have been used successfully in the treatment of degenerative joint diseases (DJD) of both dogs and horses. Possible simultaneous application of steroid therapy and stem cell transplantation could improve the commonly used clinical procedure. In this paper, the influence of the two steroid drugs (betamethasone and methylprednisolone) on AdMSCs was evaluated on the basis of morphology and proliferation rate. Both steroids positively influenced the viability and proliferation state of cells in a concentration of 0.01 mg/ml and 0.1 mg/ml, respectively. However, the concentration of 1 mg/ml had a cytotoxic effect. Moreover, the lower dosage of steroid drugs used in the experiment did not affect the morphology of cells and significantly increased cellular activity. In conclusion, our data demonstrate the stimulating effect of steroid drugs on cell morphology, proliferation rate and cytophysiological activity. These findings may influence the use of stem cells and steroids in applied regenerative veterinary medical practice in the future.

Sequence determination and analysis of three plasmids of Pseudomonas sp. GLE121, a psychrophile isolated from surface ice of Ecology Glacier (Antarctica).

Pseudomonas sp. GLE121 (a psychrophilic Antarctic strain) carries three plasmids: pGLE121P1 (6899 bp), pGLE121P2 (8330 bp) and pGLE121P3 (39,583 bp). Plasmids pGLE121P1 and pGLE121P2 show significant sequence similarity to members of the IncP-9 and IncP-7 incompatibility groups, respectively, while the largest replicon, pGLE121P3, is highly related to plasmid pNCPPB880-40 of Pseudomonas syringae pathovar tomato NCPPB880. All three plasmids have a narrow host range, limited to members of the genus Pseudomonas. Plasmid pGLE121P3 encodes a conjugal transfer system, while pGLE121P1 carries only a putative MOB module, conserved in many mobilizable plasmids. Plasmid pGLE121P3 contains an additional load of genetic information, including a pair of genes with homology to the rulAB operon, responsible for ultraviolet radiation (UVR) tolerance. Given the increasing UV exposure in Antarctic regions, the expression of these genes is likely to be an important adaptive response.

Bacterial communities of Antarctic lichens explored by gDNA and cDNA 16S rRNA gene amplicon sequencing.

Recently, lichens came once more into the scientific spotlight due to their unique relations with prokaryotes. Several temperate region lichen species have been thoroughly explored in this regard yet, the information on Antarctic lichens and their associated bacteriobiomes is somewhat lacking. In this paper, we assessed the phylogenetic structure of the whole and active fractions of bacterial communities housed by Antarctic lichens growing in different environmental conditions by targeted 16S rRNA gene amplicon sequencing. Bacterial communities associated with lichens procured from a nitrogen enriched site were very distinct from the communities isolated from lichens of a nitrogen depleted site. The former were characterized by substantial contributions of Bacteroidetes phylum members and the elusive Armatimonadetes. At the nutrient-poor site the lichen-associated bacteriobiome structure was unique for each lichen species, with chlorolichens being occupied largely by Proteobacteria. Lichen species with a pronounced discrepancy in diversity between the whole and active fractions of their bacterial communities had the widest ecological amplitude, hinting that the nonactive part of the community is a reservoir of latent stress coping mechanisms. This is the first investigation to make use of targeted metatranscriptomics to infer the bacterial biodiversity in Antarctic lichens.