Antarctic Strains Research Articles

The Psychrotolerant Antarctic Fungus Lecanicillium muscarium CCFEE 5003: A Powerful Producer of Cold-Tolerant Chitinolytic Enzymes.

Lecanicillium muscarium CCFEE 5003, isolated in Continental Antarctica, is a powerful producer of extracellular cold-tolerant enzymes. Chitin-hydrolyzing enzymes seems to be the principal extracellular catalytic activities of this psychrotolerant fungus. The production of chitinolytic activities is induced by chitin and other polysaccharides and is submitted to catabolite repression. The chitinolytic system of L. muscarium consists of a number of different proteins having various molecular weights and diverse biochemical characteristics, but their most significant trait is the marked cold-tolerance. L. muscarium and selected strains of the biocontrol agent of pathogenic fungi Trichoderma harzianum, have been compared for their ability to produce chitinolytic enzymes at different temperatures. At low temperatures the Antarctic strain was definitely much more efficient. Moreover, the fungus was able to exert a strong mycoparasitic action against various other fungi and oomycetes at low temperatures. The parasitic role of this organism appeared related to the production of cell wall degrading enzymes being the release of extracellular chitinolytic enzymes a key event in the mycoparasitic process. Due to the mentioned characteristics, L. muscarium could have an important role for potential applications such as the degradation of chitin-rich materials at low temperature and the biocontrol of pathogenic organisms in cold environments. For these reasons and in view of future industrial application, the production of chitinolytic enzymes by the Antarctic fungus has been up-scaled and optimised in bench-top bioreactor.

Production, purification, and characterization of a novel cold-active superoxide dismutase from the Antarctic strain Aspergillus glaucus 363

The Antarctic fungal strain Aspergillus glaucus 363 produces cold-active (CA) Cu/Zn-superoxide dismutase (SOD). The strain contains at least one gene encoding Cu/Zn-SOD that exhibited high homology with the corresponding gene of other Aspergillus species. To our knowledge, this is the first nucleotide sequence of a CA Cu/Zn-SOD gene in fungi. An effective laboratory technology for A. glaucus SOD production in 3 L bioreactors was developed on the basis of transient cold-shock treatment. The temperature downshift to 10 °C caused 1.4-fold increase of specific SOD activity compared to unstressed culture. Maximum enzyme productivity was 64 × 103 U kg−1 h−1. Two SOD isoenzymes (Cu/Zn-SODI and Cu/Zn-SODII) were purified to electrophoretic homogeneity. The specific activity of the major isoenzyme, Cu/Zn-SODII, after Q-Sepharose chromatography was 4000 U mg−1. The molecular mass of SODI (38 159 Da) and of SODII (15 835 Da) was determined by electrospray quadropole time-of-flight (ESI-Q-TOF) mass spectrometry and dynamic light scattering (DLS). The presence of Cu and Zn were confirmed by inductively coupled plasma mass spectrometry (ICP-MS). The N-terminal amino acid sequence of Cu/Zn-SODII revealed a high degree of structural homology with Cu/Zn-SOD from other fungi, including Aspergillus species.

Diversity and dispersal capacities of a terrestrial algal genus Klebsormidium (Streptophyta) in polar regions.

The distribution of microbial eukaryotes (protists) has been frequently discussed during the last two decades. The ubiquity hypothesis assumes the lack of latitudinal gradients in protist diversity due to their unlimited global dispersal. In this study, we examined the diversity and distribution of the very common, globally distributed green algal genus Klebsormidium across climatic zones, focusing on the polar regions. We tested whether (i) there is comparable diversity among the polar and temperate regions, and (ii) whether a spatial genetic differentiation occurs at the global scale. We collected a total of 58 Arctic, Antarctic and temperate strains, and genetically characterized them by sequencing the rbcL gene and two highly variable chloroplast markers. Our analyses revealed the presence of two different distribution patterns which are supposed to characterize both macroorganisms and protists. On the one hand, we demonstrated unlimited dispersal and intensive gene flow within one of the inferred lineages (superclade B). On the other hand, the majority of Klebsormidium clades showed rather a limited distribution. In addition, we detected a significant decrease of species richness towards the poles i.e. the macroecological pattern typical for macroorganisms. Species within a single protist genus may thus exhibit highly contrasting distribution patterns, based on their dispersal capabilities, which are usually shaped by both intrinsic and extrinsic factors.

Effects of controlled oxidative stress and uncouplers on primary photosynthetic processes in vegetative cells of Antarctic alga Zygnema sp.

In our study, we present responses of Antarctic strain of filamentous alga Zygnema sp. collected at James Ross Island (Antarctica) to application of variuos uncouplers of pri-mary photosynthetic processes. We exposed the alga to different concentrations of nigericin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), dithiothreitol (DTT), methyl viologen (MV) and hydrogen peroxide (H2O2) in order to test stability of photosystem II, involvement of non-photochemical quenching, and PS II functioning under combination of moderate light with particular uncoupler. Oxidative stress tolerance was tested by the combination of hydrogen peroxide (H2O2) and moderate light. Time courses of FV/FM, FPSII, NPQ and qF0 were investigated and particular effects of the above-specified chem-icals discussed. Moderate doses of uncouplers allowing partial recovery, and the doses causing full inhibition of PS II were specified.

Interactive Effects of Temperature and UV Radiation on Photosynthesis of Chlorella Strains from Polar, Temperate and Tropical Environments: Differential Impacts on Damage and Repair.

Global warming and ozone depletion, and the resulting increase of ultraviolet radiation (UVR), have far-reaching impacts on biota, especially affecting the algae that form the basis of the food webs in aquatic ecosystems. The aim of the present study was to investigate the interactive effects of temperature and UVR by comparing the photosynthetic responses of similar taxa of Chlorella from Antarctic (Chlorella UMACC 237), temperate (Chlorella vulgaris UMACC 248) and tropical (Chlorella vulgaris UMACC 001) environments. The cultures were exposed to three different treatments: photosynthetically active radiation (PAR; 400–700 nm), PAR plus ultraviolet-A (320–400 nm) radiation (PAR + UV-A) and PAR plus UV-A and ultraviolet-B (280–320 nm) radiation (PAR + UV-A + UV-B) for one hour in incubators set at different temperatures. The Antarctic Chlorella was exposed to 4, 14 and 20°C. The temperate Chlorella was exposed to 11, 18 and 25°C while the tropical Chlorella was exposed to 24, 28 and 30°C. A pulse-amplitude modulated (PAM) fluorometer was used to assess the photosynthetic response of microalgae. Parameters such as the photoadaptive index (Ek) and light harvesting efficiency (α) were determined from rapid light curves. The damage (k) and repair (r) rates were calculated from the decrease in ΦPSIIeff over time during exposure response curves where cells were exposed to the various combinations of PAR and UVR, and fitting the data to the Kok model. The results showed that UV-A caused much lower inhibition than UV-B in photosynthesis in all Chlorella isolates. The three isolates of Chlorella from different regions showed different trends in their photosynthesis responses under the combined effects of UVR (PAR + UV-A + UV-B) and temperature. In accordance with the noted strain-specific characteristics, we can conclude that the repair (r) mechanisms at higher temperatures were not sufficient to overcome damage caused by UVR in the Antarctic Chlorella strain, suggesting negative effects of global climate change on microalgae inhabiting (circum-) polar regions. For temperate and tropical strains of Chlorella, damage from UVR was independent of temperature but the repair constant increased with increasing temperature, implying an improved ability of these strains to recover from UVR stress under global warming.

Screening of microorganisms from Antarctic surface water and cytotoxicity metabolites from Antarctic microorganisms.

The Antarctic is a potentially important library of microbial resources and new bioactive substances. In this study, microorganisms were isolated from surface water samples collected from different sites of the Antarctic. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay-based cytotoxicity-tracking method was used to identify Antarctic marine microorganism resources for antitumor lead compounds. The results showed that a total of 129 Antarctic microorganism strains were isolated. Twelve strains showed potent cytotoxic activities, among which a Gram-negative, rod-shaped bacterium, designated as N11-8 was further studied. Phylogenetic analysis based on 16S rRNA gene sequence showed that N11-8 belongs to the genus Bacillus. Fermented active products of N11-8 with molecular weights of 1-30 kDa had higher inhibitory effects on different cancaer cells, such as BEL-7402 human hepatocellular carcinoma cells, U251 human glioma cells, RKO human colon carcinoma cells, A549 human lung carcinoma cells, and MCF-7 human breast carcinoma cells. However, they displayed lower cytotoxicity against HFL1 human normal fibroblast lung cells. However, they displayed lower cytotoxicity against HFL1 human normal fibroblast lung cells. Microscopic observations showed that the fermented active products have inhibitory activity on BEL-7402 cells similar to that of mitomycin C. Further studies indicated that the fermented active products have high pH and high thermal stability. In conclusion, most strains isolated in this study may be developed as promising sources for the discovery of antitumor bioactive substances. The fermented active products of Antarctic marine Bacillus sp. N11- 8 are expected to be applied in the prevention and treatment of cancer.

Purification and characterization of cold-adapted beta-agarase from an Antarctic psychrophilic strain.

An extracellular β-agarase was purified from Pseudoalteromonas sp. NJ21, a Psychrophilic agar-degrading bacterium isolated from Antarctic Prydz Bay sediments. The purified agarase (Aga21) revealed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with an apparent molecular weight of 80 kDa. The optimum pH and temperature of the agarase were 8.0 and 30 °C, respectively. However, it maintained as much as 85% of the maximum activities at 10 °C. Significant activation of the agarase was observed in the presence of Mg2+, Mn2+, K+; Ca2+, Na+, Ba2+, Zn2+, Cu2+, Co2+, Fe2+, Sr2+ and EDTA inhibited the enzyme activity. The enzymatic hydrolyzed product of agar was characterized as neoagarobiose. Furthermore, this work is the first evidence of cold-adapted agarase in Antarctic psychrophilic bacteria and these results indicate the potential for the Antarctic agarase as a catalyst in medicine, food and cosmetic industries.

Actividad inhibitoria del sobrenadante de la bacteria Antártica Pseudomonas sp. M19B en la formación de biopelículas de Flavobacterium psychrophilum 19749

Flavobacterium psyhrophilum affects farmed salmon and trout worldwide and is the etiological agent of bacterial cold water disease. The treatment of this disease is made with antibiotics. The emergence of resistant strains and its ability to form biofilms have increased the resistance to antibiotics. Considering the diverse bioactivity of Antarctic bacteria, we evaluated the inhibitory effect of compounds secreted by Antarctic bacterial strains on the biofilm formation of F. psychrophilum 19749. 26.9% of the Antarctic bacterial isolates inhibited strongly the biofilm, the greatest effect was shown by M19B. Proteins (48-56 kDa) secreted by M19B may be related to the inhibition of the biofilm formation of F. psychrophilum 19749.

Antarctic strain of green filamentous alga Zygnema sp. shows a high resistance to photoinhibition under simulated polar conditions

This study deals with treatment-dependent differences in sensitivity of Antarctic filamentous alga Zygnema sp. to photoinhibition. Zygnema sp. (strain EEL201) was collected at the James Ross Island, Antarctica (57° 52´ 57´´ W, 63° 48´ 02´´ S). In a laboratory, the alga was cultivated on agar first and then innoculated to liquid medium. They were exposed to a short-term (30 min.) high light (HL) treatments. Particular treatments comprised 600, 1 400 and 2 100 and 3 500 μmol m-2 s-1 of photosynthetically active radiation (PAR). Photosynthetic efficiency of Zygnema sp. in individual HL treatments was monitored by chlorophyll fluorescence parameters, potential (FV/FM) and actual (FPSII) quantum yield of photochemical processes in photosystem II in particular. Zygnema sp. showed a high resistance to HL since it both chlorophyll fluorescence parameters recovered to about 70% of initial values after 4 h in dark. Chlorophyll fluorescence measured immediately after particular treatment, showed HL-dependent decrease in absolute values of chlorophyll fluorescence signal and consequent uncompleted recovery as well. Quenching of F0, an indicator of changes in light-harvesting complexes of photosystem II, did not show dose-dependent response, however, general trend was a decrease found immediately HL treatment with consequent uncompleated recovery. In general, Zygnema sp. exhibited high resistance to PAR doses that the species can whitness in the field during austral summer. Thus the species could be considered highly adapted for high light and has effective mechanisms to cope with photoinhibition. Involvement of particular photoprotective mechanism, their activation and share in natural environment is a topic for future studies.

Genetic relationships in bipolar species of the protist ciliate, Euplotes

Protists thrive in polar oceans, where they represent a major driving force for globally important biogeochemical cycles and a key food-web component. Their biogeography is frequently associated to bipolar patterns of distribution. Although conceptually well supported by apparently unrestricted migration rates, the experimental certification of these patterns copes with the protist paucity of morphological characters with taxonomic value and difficulties in applying conventional species concepts. We studied three marine species of the ciliate Euplotes, E. euryhalinus, E. nobilii, and E. petzi, for their bipolar distribution by comparing the SSU-rRNA gene sequences and mating interactions of Antarctic, Patagonian, and Arctic strains. Each species was analogously found not to carry significantly varied SSU-rRNA gene sequences, implying a common occurrence of trans-equatorial genetic mixing. However, mating analyses revealed significant inter-species differences. Scarce Antarctic × Arctic strain mating compatibility distinguished E. petzi from E. euryhalinus and E. nobilii, in which mating pairs between Antarctic and Arctic strains were successfully induced. Yet, E. nobilii was the only one of the two species to show cross-fertilizing and fertile mating pairs. Taking the biological concept of species as discriminatory, it was thus concluded that only E. nobilii warrants the definition of genuine bipolar species.

Genomic and phenotypic insights into the ecology of Arthrobacter from Antarctic soils.

BackgroundMembers of the bacterial genus Arthrobacter are both readily cultured and commonly identified in Antarctic soil communities. Currently, relatively little is known about the physiological traits that allow these bacteria to survive in the harsh Antarctic soil environment. The aim of this study is to investigate if Antarctic strains of Arthrobacter owe their resilience to substantial genomic changes compared to Arthrobacter spp. isolated from temperate soil environments.ResultsQuantitative PCR-based analysis revealed that up to 4% of the soil bacterial communities were comprised of Arthrobacter spp. at four locations in the Ross Sea Region. Genome analysis of the seven Antarctic Arthrobacter isolates revealed several features that are commonly observed in psychrophilic/psychrotolerant bacteria. These include genes primarily associated with sigma factors, signal transduction pathways, the carotenoid biosynthesis pathway and genes induced by cold-shock, oxidative and osmotic stresses. However, these genes were also identified in genomes of seven temperate Arthrobacter spp., suggesting that these mechanisms are beneficial for growth and survival in a range of soil environments. Phenotypic characterisation revealed that Antarctic Arthrobacter isolates demonstrate significantly lower metabolic versatility and a narrower salinity tolerance range compared to temperate Arthrobacter species. Comparative analyses also revealed fewer protein-coding sequences and a significant decrease in genes associated with transcription and carbohydrate transport and metabolism in four of the seven Antarctic Arthrobacter isolates. Notwithstanding genome incompleteness, these differences together with the decreased metabolic versatility are indicative of genome content scaling.ConclusionsThe genomes of the seven Antarctic Arthrobacter isolates contained several features that may be beneficial for growth and survival in the Antarctic soil environment, although these features were not unique to the Antarctic isolates. These genome sequences allow further investigations into the expression of physiological traits that enable survival under extreme conditions and, more importantly, into the ability of these bacteria to respond to future perturbations including climate change and human impacts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1220-2) contains supplementary material, which is available to authorized users.

Genome-scale metabolic reconstruction and constraint-based modelling of the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125.

The Antarctic strain Pseudoalteromonas haloplanktis TAC125 is one of the model organisms of cold-adapted bacteria and is currently exploited as a new alternative expression host for numerous biotechnological applications. Here, we investigated several metabolic features of this strain through in silico modelling and functional integration of -omics data. A genome-scale metabolic model of P. haloplanktis TAC125 was reconstructed, encompassing information on 721 genes, 1133 metabolites and 1322 reactions. The predictive potential of this model was validated against a set of experimentally determined growth rates and a large dataset of growth phenotypic data. Furthermore, evidence synthesis from proteomics, phenomics, physiology and metabolic modelling data revealed possible drawbacks of cold-dependent changes in gene expression on the overall metabolic network of P. haloplanktis TAC125. These included, for example, variations in its central metabolism, amino acid degradation and fatty acid biosynthesis. The genome-scale metabolic model described here is the first one reconstructed so far for an Antarctic microbial strain. It allowed a system-level investigation of variations in cellular metabolic fluxes following a temperature downshift. It represents a valuable platform for further investigations on P. haloplanktis TAC125 cellular functional states and for the design of more focused strategies for its possible biotechnological exploitation.

Effect of UV-B radiation on photosystem II functions in Antarctic and mesophilic strains of a green alga Chlorella vulgaris and a cyanobacterium Synechocystis salina

The green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina cells isolated from Antarctic and mesophilic environments, grown in batch cultures under continuous visible light, were used to assess the effect of the UV-B radiation on the photosystem II (PSII). UV-induced changes in its functional activity were estimated by Pulse Amplitude Modulated chlorophyll fluorescence and oxygen evolution (measured with oxygen rate electrode). The data reveal a relatively stronger UV-B-induced inhibition of oxygen evolution in comparison to that of the primary photochemistry of the PSII in both green algae and cyanobacteria. The inhibition of oxygen evolution was a result of the decrease in the number of functionally active PSII centers. The modification of active reaction centers was also recorded through the relatively more effect on fast operating PSII centers than that of the slow operating PSII centers. On the other hand, the PSII activity of cyanobacteria was more vulnerable to UV-B radiation than that of green algae. Likewise, the mesophilic strain of S. salina was more susceptible to UV-B radiation than the Antarctic isolates.

Improved description of the bipolar ciliate, Euplotes petzi, and definition of its basal position in the Euplotes phylogenetic tree

Data improving the characterization of the marine Euplotes species, E. petziWilbert and Song, 2008, were obtained from morphological, ecological and genetic analyses of Antarctic and Arctic wild-type strains. This species is identified by a minute (mean size, 46μm×32μm) and ellipsoidal cell body which is dorsally decorated with an argyrome of the double-patella type, five dorsal kineties (of which the median one contains 8–10 dikinetids), five sharp-edged longitudinal ridges, and a right anterior spur. Ventrally, it bears 10 fronto-ventral, five transverse, two caudal and two marginal cirri, 30–35 adoral membranelles, and three inconspicuous ridges. Euplotes petzi grows well at 4°C on green algae, does not produce cysts, undergoes mating under the genetic control of a multiple mating-type system, constitutively secretes water-borne pheromones, and behaves as a psychrophilic microorganism unable to survive at >15°C. While the α-tubulin gene sequence determination did not provide useful information on the E. petzi molecular phylogeny, the small subunit rRNA (SSU rRNA) gene sequence determination provided solid evidence that E. petzi clusters with E. sinicusJiang et al., 2010a, into a clade which represents the deepest branch at the base of the Euplotes phylogentic tree.

Aerobic endospore-forming bacteria isolated from Antarctic soils as producers of bioactive compounds of industrial interest

Spore-forming bacteria are known to produce various enzymes and bioproducts valuable to different industries and to bear the harsh conditions found in the Antarctic environment. However, aerobic or facultative spore-forming bacterial communities found in maritime Antarctic soils yet remain poorly studied. In this study, 80 spore-forming and cold-adapted bacterial strains were isolated from nine different soil samples of King George Island, in maritime Antarctica, and further clustered into amplified ribosomal DNA restriction analysis groups within each soil. Representative strains were then identified as belonging to Bacillus, Rummeliibacillus, Paenibacillus and Sporosarcina by 16S rRNA gene sequencing. The ability to produce extracellular enzymes, antimicrobial substances and biosurfactants was determined in all isolates. The enzymatic activities most frequently found among the isolates were as follows: esterase (45 %), caseinase (30 %), amylase (16.2 %) and gelatinase (15 %). Biosurfactant production was detected in 25 % of the isolates. The growth inhibition of methicillin-resistant Staphylococcus aureus was observed in 13.7 % of the strains tested, but only two strains inhibited the growth of Candida albicans. The isolated spore-forming bacterial species were also compared with the characteristics of the different Antarctic soils sampled based on their physicochemical properties, showing that pH, C and P were the main factors correlated with the distribution of this group of bacteria in the Antarctic soils studied. These Antarctic endospore-forming bacterial strains may have a potential for industrial processes occurring at low temperatures.

Lysis of Antarctic algal strains by bacterial pathogen

The present paper describes the isolation, physiological and genetic characteristic of a bacterial agent which inhibits the growth of algae and causes death of laboratory cultures of Antarctic microalgal strains: prokaryotic cyanobacteria Synechocystis salina and green eukaryotic microalga Choricistis minor. The bacterial strain LB1 was isolated from algal damaged laboratory cultures of S. salina. It was established that this bacterium is obligate aerobic, Gram-positive, non-spore-forming, immotile, irregular rods with dimensions 0.3-2μm. Our results showed that LB1 has algicidal effect to S. salina as well as to C. minor. Transmission electron microscopy observations confirmed the destruction of S. salina by the bacterium. Biochemical analysis of LB1 revealed positive reaction to D-glucose, catalase, hydrolysis of gelatin, acid production from: lactose, L-arabinose, L-ramnose, esculin and β-galactosidase. The partial sequence (1,404bp) of the 16S rRNA gene of LB1 showed 99% similarity with type strains of the genus Microbacterium. The results of the biochemical, antimicrobial and of 16S rRNA analysis of LB1 allowed us to identify LB1 as Microbacterium sp. Studying expression of pathogenicity of the bacteria to algal cultures will help to solve the problem of algal production for biotechnological purposes.

Draft genomes of three Antarctic Psychrobacter strains producing antimicrobial compounds against Burkholderia cepacia complex, opportunistic human pathogens

Herein we present the draft genomes of three Psychrobacter strains isolated from Antarctic sponges and able to inhibit the growth of bacteria belonging to the Burkholderia cepacia complex, responsible for infections of the respiratory system in patients affected by Cystic Fibrosis. The comparative analysis of the annotated genomes of these Psychrobacter strains highlighted their differences in terms of overall genomic content (e.g. shared gene sets) and allowed the identification of gene clusters hypothetically involved in the biosynthesis of antimicrobial compounds.

Ecophysiological properties of cultivable heterotrophic bacteria and yeasts dominating in phytocenoses of Galindez Island, maritime Antarctica

Antarctic plants are stable specific microenvironments for microbial colonization that are still less explored. In this study, we investigated cultivable heterotrophic bacteria and yeasts dominating in plant samples collected from different terrestrial biotopes near Ukrainian Antarctic Base on Galindez Island, maritime Antarctica. Phylogenetic analysis revealed affiliation of the bacterial isolates to genera Pseudomonas, Stenotrophomonas, Brevundimonas, Sporosarcina, Dermacoccus, Microbacterium, Rothia and Frondihabitans, and the yeast isolates to genera Rhodosporidium, Cryptococcus, Leucosporidiella, Candida and Exophiala. Some ecophysiological properties of isolated strains were determined that are important in response to different stresses such as psychro- and halotolerance, UV-resistance and production of hydrolytic enzymes. The majority of isolates (88 %) was found to be psychrotolerant; all are halotolerant. Significant differences in survival subsequent to UV-C radiation were observed among the isolates, as measured by culturable counts. For the bacterial isolates, lethal doses in the range 80-600 J m⁻² were determined, and for the yeast isolates--in the range 300-1,000 J m⁻². Dermacoccus profundi U9 and Candida davisiana U6 were found as most UV resistant among the bacterial and yeast isolates, respectively. Producers of caseinase, gelatinase, β-glucosidase, and cellulase were detected. To the best of our knowledge, this is the first report on isolation of UV resistant strain D. profundi, and Frondihabitans strain from Antarctica, and on detection of cellulase activity in Antarctic yeast strain C. davisiana. The results obtained contribute to clarifying adaptation strategies of Antarctic microbiota and its possible role in functional stability of Antarctic biocenoses. Stress tolerant strains were detected that are valuable for ecological and applied studies.

DNA barcoding species in Alexandrium tamarense complex using ITS and proposing designation of five species

Alexandrium species can be very difficult to identify, with A. catenella, A. tamarense, and A. fundyense that compose “Alexandrium tamarense species complex” (Atama complex) as a distinct example. DNA barcoding is promising to offer a solution but remains to be established. In this study, we examined the utility of ITS in resolving the Atama species complex, by analyzing previously studied strains plus unstudied Chinese strains within the LSU- and SSU-rDNA based group/clade frameworks recently established. We further investigated the presence of intragenomic polymorphism and its implications in species delimitation. Similar to the previous SSU and LSU results, our ITS-based phylogenies divided the complex to five clusters, but with longer and evener branch lengths between the clusters. Based on the ITS region, the inter-cluster genetic distances (p=0.134–0.216) were consistently and substantially greater than intra-cluster genetic distances (p=0.000–0.066), with an average inter-cluster (species) distance (p=0.167) 7.6-fold of the average intraspecific difference (p=0.022), qualifying the approximately 510–520bp ITS as a DNA barcode for Atama complex. We detected varying levels of intragenomic polymorphism in ITS but found that this did not impact the taxon-resolving power of this gene. With this DNA barcode, the new East and South China Sea strains and one Antarctic strain were placed in Clade IIC/Group IV, even though there were 7–10 polymorphic sites in their ITS, in contrast to none in SSU. Furthermore, our results suggest that the five clusters are recognizable as distinct species according to the phylogenetic species concept. Based on the phylogenetic placements of the type-locality strains of the existing three morphospecies and the dominant localities of other strains, we propose that Group I/Clade I be designated as A. fundyense, Group III/Clade IIB as A. tamarense, Group IV/Clade IIC as A. catenella, Group II/Clade IIA as A. mediterranis, and Group V/Clade IID as A. australis.

Genomic analysis of three sponge-associated Arthrobacter Antarctic strains, inhibiting the growth of Burkholderia cepacia complex bacteria by synthesizing volatile organic compounds

In this work we analyzed the ability of three Arthrobacter strains (namely TB23, TB26 and CAL618), which were isolated from the Antarctic sponges Haliclonissa verrucosa and Lyssodendrix nobilis, to specifically inhibit the growth of a panel of 40 Burkholderia cepacia complex strains, representing a major cause of infections in patients that are affected by Cystic Fibrosis. The inhibitory activity was due to the synthesis of antimicrobial compounds, very likely volatile organic compounds (VOCs), and was partially dependent on the growth media that were used for Antarctic strains growth. The phylogenetic analysis revealed that two of them (i.e. CAL 618 and TB23) were very close and very likely belonged to the same Arthrobacter species, whereas the strain TB26 was placed in a distant branch. The genome of the strains TB26 and CAL618 was also sequenced and compared with that of the strain TB23. The analysis revealed that TB23 and CAL618 shared more genomic properties (GC content, genome size, number of genes) than with TB26. Since the three strains exhibited very similar inhibition pattern vs Bcc strains, it is quite possible that genes involved in the biosynthesis of antimicrobial compounds very likely belong to the core genome.