Chemical and microbiological insights into two littoral Antarctic demosponge species: Haliclona (Rhizoniera) dancoi (Topsent 1901) and Haliclona (Rhizoniera) scotti (Kirkpatrick 1907)

Introduction

Antarctic Porifera have gained increasing interest as hosts of diversified associated microbial communities that could provide interesting insights on the holobiome system and its relation with environmental parameters.

Methods

The Antarctic demosponge species Haliclona dancoi and Haliclona scotti were targeted for the determination of persistent organic pollutant (i. e., polychlorobiphenyls, PCBs, and polycyclic aromatic hydrocarbons, PAHs) and trace metal concentrations, along with the characterization of the associated prokaryotic communities by the 16S rRNA next generation sequencing, to evaluate possible relationships between pollutant accumulation (e.g., as a stress factor) and prokaryotic community composition in Antarctic sponges. To the best of our knowledge, this approach has been never applied before.

Results

Notably, both chemical and microbiological data on H. scotti (a quite rare species in the Ross Sea) are here reported for the first time, as well as the determination of PAHs in Antarctic Porifera. Both sponge species generally contained higher amounts of pollutants than the surrounding sediment and seawater, thus demonstrating their accumulation capability. The structure of the associated prokaryotic communities, even if differing at order and genus levels between the two sponge species, was dominated by Proteobacteria and Bacteroidota (with Archaea abundances that were negligible) and appeared in sharp contrast to communities inhabiting the bulk environment.

Discussions

Results suggested that some bacterial groups associated with H. dancoi and H. scotti were significantly (positively or negatively) correlated to the occurrence of certain contaminants.

Deciphering the evolvement of microbial communities from hydrothermal vent sediments in a global change perspective

Microbial communities first respond to changes of external environmental conditions. Observing the microbial responses to environmental changes in terms of taxonomic and functional biodiversity is therefore of great interest, particularly in extreme environments, where the already extreme conditions can become even harsher. In this study, sediment samples from three different shallow hydrothermal vents in Levante Bay (Vulcano Island, Aeolian Islands, Italy) were used to set up microcosm experiments with the aim to explore the microbial dynamics under changing conditions of pH and redox potential over a 90-days period. The leading hypothesis was to establish under microcosm conditions whether the starting microbial communities of the sediments evolved differently depending on their origin. To profile the dynamics of microbial populations over time, biodiversity, enzymatic profile, total cell abundance estimations, total/respiring cell ratio were estimated by using different approaches. An evident change in the microbial community structure was observed, mainly in the microcosm containing the sediment from the most acidified site, which was characterized by a highly diversified microbial community (in prevalence composed of Thermotoga, Desulfobacterota, Planctomycetota, Synergistota and Deferribacterota). An increase in microbial resistant forms (e.g., spore-forming species) with anaerobic metabolism was detected in all experimental conditions. Differential physiological responses characterized the sedimentary microbial communities. Proteolytic activity appeared to be stimulated under microcosm conditions, whereas the alkaline phosphatase activity was significantly depressed at low pH values, like those that were measured at the station showing intermediate pH-conditions. The results confirmed a differential response of microbial communities depending on the starting environmental conditions.

Freshwater Sponges as a Neglected Reservoir of Bacterial Biodiversity

Freshwater sponges (Spongillida: Demospongiae), including more than 240 described species, are globally distributed in continental waters (except for Antarctica), where they cover both natural and artificial surfaces. However, fragmentary studies have targeted their microbiome, making it difficult to test hypotheses about sponge-microbe specificity and metabolic relationships, along with the environmental factors playing key roles in structuring the associated microbial communities. To date, particular attention has been paid to sponges (family Lubomirskiidae) that are endemic to Lake Baikal. Few other freshwater sponge species (e.g., Ephydatia spp., Eunapius spp., and Spongilla lacustris), from lakes and rivers spanning from Europe to South and North America, have been targeted for microbiological studies. Representatives of the phyla Proteobacteria, Bacteroidetes, and Actinobacteria largely predominated, and high differences were reported between the microbiome of freshwater and marine sponges. Several bacterial strains isolated from freshwater sponges can produce bioactive compounds, mainly showing antibiotic activities, with potential application in biotechnology. Understanding the roles played by sponge microbiomes in freshwater ecosystems is still in its infancy and has yet to be clarified to disentangle the ecological and evolutionary significance of these largely under-investigated microbial communities. This review was aimed at providing the main available information on the composition and biotechnological potential of prokaryotic communities associated with healthy freshwater sponges, as a neglected component of the global sponge microbiome, to stimulate researchers interested in the field.

Marine sponges as bioindicators of pollution by synthetic microfibers in Antarctica

Different marine sponge species from Tethys Bay, Antarctica, were analyzed for contamination by polyester and polyamide microplastics (MPs). The PISA (Polymer Identification and Specific Analysis) procedure was adopted as it provides, through depolymerization and HPLC analysis, highly sensitive mass-based quantitative data. The study focused on three analytes resulting from the hydrolytic depolymerization of polyesters and polyamides: terephthalic acid (TPA), 6-aminohexanoic acid (AHA), and 1-6-hexanediamine (HMDA). TPA is a comonomer found in the polyesters poly(ethylene terephthalate) (PET) and poly(butylene adipate co terephthalate) (PBAT), and in polyamides such as poly(1,4-p-phenylene terephthalamide) (Kevlar™ and Twaron™ fibers) and poly(hexamethylene terephthalamide) (nylon 6 T). AHA is the monomer of nylon 6. HMDA is a comonomer of the aliphatic nylon 6,6 (HMDA-co-adipic acid) and of semi-aromatic polyamides such as, again, nylon 6 T (HMDA-co-TPA). Except for the biodegradable PBAT, these polymers exhibit high to extreme mechanical, thermal and chemical resistance. Indeed, they are used as technofibers in protective clothing able to withstand extreme conditions as those typical of Antarctica. Of the two amine monomers, only HMDA was found above the limit of quantification, and only in specimens of Haliclona (Rhizoniera) scotti, at a concentration equivalent to 27 μg/kg of nylon 6,6 in the fresh sponge. Comparatively higher concentrations, corresponding to 2.5-4.1 mg/kg of either PBAT or PPTA, were calculated from the concentration of TPA detected in all sponge species. Unexpectedly, TPA did not originate from PET (the most common textile fiber) as it was detected in the acid hydrolysate, whereas the PISA procedure results in effective PET depolymerization only under alkaline conditions. The obtained results showed that sponges, by capturing and concentrating MPs from large volumes of filtered marine waters, may be considered as effective indicators of the level and type of pollution by MPs and provide early warnings of increasing levels of pollution even in remote areas.

A Deep Insight into the Diversity of Microfungal Communities in Arctic and Antarctic Lakes

We assessed fungal diversity in water and sediment samples obtained from five Arctic lakes in Ny-Ålesund (Svalbard Islands, High Arctic) and five Antarctic lakes on Livingston and Deception Islands (South Shetland Islands), using DNA metabarcoding. A total of 1,639,074 fungal DNA reads were detected and assigned to 5980 ASVs amplicon sequence variants (ASVs), with only 102 (1.7%) that were shared between the two Polar regions. For Arctic lakes, unknown fungal taxa dominated the sequence assemblages, suggesting the dominance of possibly undescribed fungi. The phylum Chytridiomycota was the most represented in the majority of Arctic and Antarctic samples, followed by Rozellomycota, Ascomycota, Basidiomycota, and the less frequent Monoblepharomycota, Aphelidiomycota, Mortierellomycota, Mucoromycota, and Neocallimastigomycota. At the genus level, the most abundant genera included psychrotolerant and cosmopolitan cold-adapted fungi including Alternaria, Cladosporium, Cadophora, Ulvella (Ascomycota), Leucosporidium, Vishniacozyma (Basidiomycota), and Betamyces (Chytridiomycota). The assemblages displayed high diversity and richness. The assigned diversity was composed mainly of taxa recognized as saprophytic fungi, followed by pathogenic and symbiotic fungi.

Low-Temperature Microbiology Meets the Global Challenges of Our Time

Low-temperature microbiology is intimately associated with the exploration of the polar regions, and research in recent decades has focused on characterizing the microbial biodiversity of the cryosphere [...].

A plastic world: A review of microplastic pollution in the freshwaters of the Earth's poles

Microplastic (MP) pollution is of great environmental concern. MPs have been found all over the Earth, including in the poles, which is indicative for the important threat they constitute. Yet, while the ocean is object of major interest, the data available in the literature about MP pollution in the freshwaters of the Earth's poles are still limited. Here, we review the current knowledge of MP pollution in the freshwaters of the Arctic, Antarctica and Third Pole, and we assess its ecological implications. This review highlights the presence of MPs in the lakes, rivers, snow, and glaciers of the investigated sites, questions the transport patterns through which MPs reach these remote areas, and illustrates that MP pollution is a real problem not only in marine systems, but also in the freshwater environments of the Earth's poles. MPs can indeed be ingested by animals and can physically damage their digestive tracts, as well as escalate the trophic levels. MPs can also alter microbial communities by serving as surfaces onto which microbes can grow and develop, and can enhance ice melting when trapped in glaciers. Hence, considered the limited data available, we encourage more research on the theme.

How much biodiversity is concealed in the word 'biodiversity'?

Amidst a global biodiversity crisis¹, the word 'biodiversity' has become indispensable for conservation and management². Yet, biodiversity is often used as a buzzword in scientific literature. Resonant titles of papers claiming to have studied 'global biodiversity' may be used to promote research focused on a few taxonomic groups, habitats, or facets of biodiversity - taxonomic, (phylo)genetic, or functional. This usage may lead to extrapolating results outside the target systems of these studies with direct consequences for our understanding of life on Earth and its practical conservation. Here, we used a random sample of papers with the word 'biodiversity' in their title to take a long view of the use of this term. Despite improvements in analytical tools, monitoring technologies, and data availability^3,4, we found that the taxonomic scope of research articles has not increased in recent years. We also show that studies with a wider taxonomic scope attract more citations and online attention. Our results have broad ramifications for understanding how extrapolating from studies with narrow taxonomic scope affects our view of global biodiversity and conservation.

Characterization of the exopolymer-producing Pseudoalteromonas sp. S8-8 from Antarctic sediment

Abstract

A synergistic approach using cultivation methods, chemical, and bioinformatic analyses was applied to explore the potential of Pseudoalteromonas sp. S8-8 in the production of extracellular polymeric substances (EPSs) and the possible physiological traits related to heavy metal and/or antibiotic resistance. The effects of different parameters (carbon source, carbon source concentration, temperature, pH and NaCl supplement) were tested to ensure the optimization of growth conditions for EPS production by the strain S8-8. The highest yield of EPS was obtained during growth in culture medium supplemented with glucose (final concentration 2%) and NaCl (final concentration 3%), at 15 °C and pH 7. The EPS was mainly composed of carbohydrates (35%), followed by proteins and uronic acids (2.5 and 2.77%, respectively) and showed a monosaccharidic composition of glucose: mannose: galactosamine: galactose in the relative molar proportions of 1:0.7:0.5:0.4, as showed by the HPAE-PAD analysis. The detection of specific molecular groups (sulfates and uronic acid content) supported the interesting properties of EPSs, i.e. the emulsifying and cryoprotective action, heavy metal chelation, with interesting implication in bioremediation and biomedical fields. The analysis of the genome allowed to identify a cluster of genes involved in cellulose biosynthesis, and two additional gene clusters putatively involved in EPS biosynthesis.

Key points

• A cold-adapted Pseudoalteromonas strain was investigated for EPS production.

• The EPS showed emulsifying, cryoprotective, and heavy metal chelation functions.

• Three gene clusters putatively involved in EPS biosynthesis were evidenced by genomic insights.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12180-x.

Isolation and Identification of Bacteria with Surface and Antibacterial Activity from the Gut of Mediterranean Grey Mullets

Fish gut represents a peculiar ecological niche where bacteria can transit and reside to play vital roles by producing bio-compounds with nutritional, immunomodulatory and other functions. This complex microbial ecosystem reflects several factors (environment, feeding regimen, fish species, etc.). The objective of the present study was the identification of intestinal microbial strains able to produce molecules called biosurfactants (BSs), which were tested for surface and antibacterial activity in order to select a group of probiotic bacteria for aquaculture use. Forty-two bacterial isolates from the digestive tracts of twenty Mediterranean grey mullets were screened for testing emulsifying (E-24), surface and antibiotic activities. Fifty percent of bacteria, ascribed to Pseudomonas aeruginosa, Pseudomonas sp., P. putida and P. anguilliseptica, P. stutzeri, P. protegens and Enterobacter ludwigii were found to be surfactant producers. Of the tested strains, 26.6% exhibited an antibacterial activity against Staphylococcus aureus (10.0 ± 0.0–14.5 ± 0.7 mm inhibition zone), and among them, 23.3% of isolates also showed inhibitory activity vs. Proteus mirabilis (10.0 ± 0.0–18.5 ± 0.7 mm inhibition zone) and 6.6% vs. Klebsiella pneumoniae (11.5 ± 0.7–17.5 ± 0.7 mm inhibition zone). According to preliminary chemical analysis, the bioactive compounds are suggested to be ascribed to the class of glycolipids. This works indicated that fish gut is a source of bioactive compounds which deserves to be explored.

Prokaryotic Diversity and Metabolically Active Communities in Brines from Two Perennially Ice-Covered Antarctic Lakes

The genomic diversity of bacteria and archaea in brines (BC1, BC2, and BC3) from two adjacent and perennially frozen Antarctic lakes (L16 and L-2) in the Boulder Clay (BC) area was investigated together with the metabolically active fraction of both communities, by analyzing the bulk rRNA as a general marker of metabolic activity. Although similar bacterial and archaeal assemblages were observed at phylum level, differences were encountered when considering the distribution in species. Overall, the total bacterial communities were dominated by Bacteroidetes. A massive occurrence of flavobacterial sequences was observed within the metabolically active bacterial communities of the BC1 brine, whereas the active fractions in BC2 and BC3 strongly differed from the bulk communities being dominated by Betaproteobacteria (mainly Hydrogenophaga members). The BC lakes also hosted sequences of the most thermally tolerant archaea, also related to well-known hyperthermophiles. Interestingly, RNA sequences of the hyperthermophilic genus Ferroglobus were retrieved in all brine samples. Finally, a high abundance of the strictly anaerobic methanogens (such as Methanosarcina members) within the active community suggests that anoxic conditions might occur in the lake brines. Our findings indicate perennially ice-covered Antarctic lakes as plausible terrestrial candidates for the study of the potential for extant life on different bodies of our solar system.

Prokaryotic Diversity of the Composting Thermophilic Phase: The Case of Ground Coffee Compost

Waste biomass coming from a local coffee company, which supplied burnt ground coffee after an incorrect roasting process, was employed as a starting material in the composting plant of the Experimental Station of the University of Naples Federico II at Castel Volturno (CE). The direct molecular characterization of compost using ¹³C-NMR spectra, which was acquired through cross-polarization magic-angle spinning, showed a hydrophobicity index of 2.7% and an alkyl/hydroxyalkyl index of 0.7%. Compost samples that were collected during the early "active thermophilic phase" (when the composting temperature was 63 °C) were analyzed for the prokaryotic community composition and activities. Two complementary approaches, i.e., genomic and predictive metabolic analysis of the 16S rRNA V3-V4 amplicon and culture-dependent analysis, were combined to identify the main microbial factors that characterized the composting process. The whole microbial community was dominated by Firmicutes. The predictive analysis of the metabolic functionality of the community highlighted the potential degradation of peptidoglycan and the ability of metal chelation, with both functions being extremely useful for the revitalization and fertilization of agricultural soils. Finally, three biotechnologically relevant Firmicutes members, i.e., Geobacillus thermodenitrificans subsp. calidus, Aeribacillus pallidus, and Ureibacillus terrenus (strains CAF1, CAF2, and CAF5, respectively) were isolated from the "active thermophilic phase" of the coffee composting. All strains were thermophiles growing at the optimal temperature of 60 °C. Our findings contribute to the current knowledge on thermophilic composting microbiology and valorize burnt ground coffee as waste material with biotechnological potentialities.

The Variety and Inscrutability of Polar Environments as a Resource of Biotechnologically Relevant Molecules

The application of an ever-increasing number of methodological approaches and tools is positively contributing to the development and yield of bioprospecting procedures. In this context, cold-adapted bacteria from polar environments are becoming more and more intriguing as valuable sources of novel biomolecules, with peculiar properties to be exploited in a number of biotechnological fields. This review aims at highlighting the biotechnological potentialities of bacteria from Arctic and Antarctic habitats, both biotic and abiotic. In addition to cold-enzymes, which have been intensively analysed, relevance is given to recent advances in the search for less investigated biomolecules, such as biosurfactants, exopolysaccharides and antibiotics.

Cultivable Bacterial Communities in Brines from Perennially Ice-Covered and Pristine Antarctic Lakes: Ecological and Biotechnological Implications

The diversity and biotechnological potentialities of bacterial isolates from brines of three Antarctic lakes of the Northern Victoria Land (namely Boulder Clay and Tarn Flat areas) were first explored. Cultivable bacterial communities were analysed mainly in terms of bacterial response to contaminants (i.e., antibiotics and heavy metals) and oxidation of contaminants (i.e., aliphatic and aromatic hydrocarbons and polychlorobiphenyls). Moreover, the biosynthesis of biomolecules (antibiotics, extracellular polymeric substances and enzymes) with applications for human health and environmental protection was assayed. A total of 74 and 141 isolates were retrieved from Boulder Clay and Tarn Flat brines, respectively. Based on 16S rRNA gene sequence similarities, bacterial isolates represented three phyla, namely Proteobacteria (i.e., Gamma- and Alphaproteobacteria), Bacteroidetes and Actinobacteria, with differences encountered among brines. At genus level, Rhodobacter, Pseudomonas, Psychrobacter and Leifsonia members were dominant. Results obtained from this study on the physiological and enzymatic features of cold-adapted isolates from Antarctic lake brines provide interesting prospects for possible applications in the biotechnological field through future targeted surveys. Finally, findings on contaminant occurrence and bacterial response suggest that bacteria might be used as bioindicators for tracking human footprints in these remote polar areas.

Peculiarities of extracellular polymeric substances produced by Antarctic bacteria and their possible applications

Extracellular polymeric substances (EPSs) possess diversified ecological role, including the cell adhesion to surfaces and cell protection, and are highly involved in the interactions between the bacterial cells and the bulk environments. Interestingly, EPSs find valuable applications in the industrial field, due to their chemical versatility. In this context, Antarctic bacteria have not been given the attention they deserve as producers of EPS molecules and a very limited insight into their EPS production capabilities and biotechnological potential is available in literature to date. Antarctic EPS-producing bacteria are mainly psychrophiles deriving from the marine environments (generally sea ice and seawater) around the continent, whereas a unique thermophilic bacterium, namely Parageobacillus thermantarcticus strain M1, was isolated from geothermal soil of the crater of Mount Melbourne. This mini-review is aimed at showcasing the current knowledge on EPS-producing Antarctic bacteria and the chemical peculiarities of produced EPSs, highlighting their biotechnological potential and the yet unexplored treasure they represent for biodiscovery.

Effects of a Simulated Acute Oil Spillage on Bacterial Communities from Arctic and Antarctic Marine Sediments

Background: The bacterial community responses to oil spill events are key elements to predict the fate of hydrocarbon pollution in receiving aquatic environments. In polar systems, cold temperatures and low irradiance levels can limit the effectiveness of contamination removal processes. In this study, the effects of a simulated acute oil spillage on bacterial communities from polar sediments were investigated, by assessing the role of hydrocarbon mixture, incubation time and source bacterial community in selecting oil-degrading bacterial phylotypes. Methods: The bacterial hydrocarbon degradation was evaluated by gas chromatography. Flow cytometric and fingerprinting profiles were used to assess the bacterial community dynamics over the experimental incubation time. Results: Direct responses to the simulated oil spill event were found from both Arctic and Antarctic settings, with recurrent bacterial community traits and diversity profiles, especially in crude oil enrichment. Along with the dominance of Pseudomonas spp., members of the well-known hydrocarbon degraders Granulosicoccus spp. and Cycloclasticus spp. were retrieved from both sediments. Conclusions: Our findings indicated that polar bacterial populations are able to respond to the detrimental effects of simulated hydrocarbon pollution, by developing into a more specialized active oil degrading community.

Antarctic sponges from the Terra Nova Bay (Ross Sea) host a diversified bacterial community

Sponges represent important habitats for a community of associated (micro)organisms. Even if sponges dominate vast areas of the Antarctic shelves, few investigations have been performed on Antarctic sponge-associated bacteria. Using a culture-dependent approach, the composition of the bacterial communities associated with 14 Antarctic sponge species from different sites within the Terra Nova Bay (Ross Sea) area was analyzed. Overall, isolates were mainly affiliated to Gammaproteobacteria, followed by Actinobacteria and CF group of Bacteroidetes, being the genera Pseudoalteromonas, Arthrobacter and Gillisia predominant, respectively. Alphaproteobacteria and Firmicutes were less represented. Cluster analyses highlighted similarities/differences among the sponge-associated bacterial communities, also in relation to the sampling site. The gammaproteobacterial Pseudoalteromonas sp. SER45, Psychrobacter sp. SER48, and Shewanella sp. SER50, and the actinobacterial Arthrobacter sp. SER44 phylotypes occurred in association with almost all the analyzed sponge species. However, except for SER50, these phylotypes were retrieved also in seawater, indicating that they may be transient within the sponge body. The differences encountered within the bacterial communities may depend on the different sites of origin, highlighting the importance of the habitat in structuring the composition of the associated bacterial assemblages. Our data support the hypothesis of specific ecological interactions between bacteria and Porifera.

Microbial Assemblages in Pressurized Antarctic Brine Pockets (Tarn Flat, Northern Victoria Land): A Hotspot of Biodiversity and Activity

Two distinct pressurized hypersaline brine pockets (named TF4 and TF5), separated by a thin ice layer, were detected below an ice-sealed Antarctic lake. Prokaryotic (bacterial and archaeal) diversity, abundances (including virus-like particles) and metabolic profiles were investigated by an integrated approach, including traditional and new-generation methods. Although similar diversity indices were computed for both Bacteria and Archaea, distinct bacterial and archaeal assemblages were observed. Bacteroidetes and Gammaproteobacteria were more abundant in the shallowest brine pocket, TF4, and Deltaproteobacteria, mainly represented by versatile sulphate-reducing bacteria, dominated in the deepest, TF5. The detection of sulphate-reducing bacteria and methanogenic Archaea likely reflects the presence of a distinct synthrophic consortium in TF5. Surprisingly, members assigned to hyperthermophilic Crenarchaeota and Euryarchaeota were common to both brines, indicating that these cold habitats host the most thermally tolerant Archaea. The patterns of microbial communities were different, coherently with the observed microbiological diversity between TF4 and TF5 brines. Both the influence exerted by upward movement of saline brines from a sub-surface anoxic system and the possible occurrence of an ancient ice remnant from the Ross Ice Shelf were the likely main factors shaping the microbial communities.

Metal Resistance in Bacteria from Contaminated Arctic Sediment is Driven by Metal Local Inputs

Anthropogenic impact over the Pasvik River (Arctic Norway) is mainly caused by emissions from runoff from smelter and mine wastes, as well as by domestic sewage from the Russian, Norwegian, and Finnish settlements situated on its catchment area. In this study, sediment samples from sites within the Pasvik River area with different histories of metal input were analyzed for metal contamination and occurrence of metal-resistant bacteria in late spring and summer of 2014. The major differences in microbial and chemical parameters were mostly dependent on local inputs than seasonality. Higher concentrations of metals were generally detected in July rather than May, with inner stations that became particularly enriched in Cr, Ni, Cu, and Zn, but without significant differences. Bacterial resistance to metals, which resulted from viable counts on amended agar plates, was in the order Ni²⁺>Pb²⁺>Co²⁺>Zn²⁺>Cu²⁺>Cd²⁺>Hg²⁺, with higher values that were generally determined at inner stations. Among a total of 286 bacterial isolates (mainly achieved from Ni- and Pb-amended plates), the 7.2% showed multiresistance at increasing metal concentration (up to 10,000 ppm). Selected multiresistant isolates belonged to the genera Stenotrophomonas, Arthrobacter, and Serratia. Results highlighted that bacteria, rapidly responding to changing conditions, could be considered as true indicators of the harmful effect caused by contaminants on human health and environment and suggested their potential application in bioremediation processes of metal-polluted cold sites.

The art of adapting to extreme environments: The model system Pseudoalteromonas

Extremophilic microbes have adapted to thrive in ecological niches characterized by harsh chemical/physical conditions such as, for example, very low/high temperature. Living organisms inhabiting these environments have developed peculiar mechanisms to cope with extreme conditions, in such a way that they mark the chemical-physical boundaries of life on Earth. Studying such mechanisms is stimulating from a basic research viewpoint and because of biotechnological applications. Pseudoalteromonas species are a group of marine gamma-proteobacteria frequently isolated from a range of extreme environments, including cold habitats and deep-sea sediments. Since deep-sea floors constitute almost 60% of the Earth's surface and cold temperatures represent the most common of the extreme conditions, the genus Pseudoalteromonas can be considered one of the most important model systems for studying microbial adaptation. Particularly, among all Pseudoalteromonas representatives, P. haloplanktis TAC125 has recently gained a central role. This bacterium was isolated from seawater sampled along the Antarctic ice-shell and is considered one of the model organisms of cold-adapted bacteria. It is capable of thriving in a wide temperature range and it has been suggested as an alternative host for the soluble overproduction of heterologous proteins, given its ability to rapidly multiply at low temperatures. In this review, we will present an overview of the recent advances in the characterization of Pseudoalteromonas strains and, more importantly, in the understanding of their evolutionary and chemical-physical strategies to face such a broad array of extreme conditions. A particular attention will be given to systems-biology approaches in the study of the above-mentioned topics, as genome-scale datasets (e.g. genomics, proteomics, phenomics) are beginning to expand for this group of organisms. In this context, a specific section dedicated to P. haloplanktis TAC125 will be presented to address the recent efforts in the elucidation of the metabolic rewiring of the organisms in its natural environment (Antarctica).

Heavy metal tolerance and polychlorinated biphenyl oxidation in bacterial communities inhabiting the Pasvik River and the Varanger Fjord area (Arctic Norway)

Heavy metals (HMs) and polychlorobiphenyls (PCBs) enter the Arctic environment through a variety of anthropogenic sources with deleterious effects towards biota and public health. Bacteria first transfer toxic compounds to higher trophic levels and, due to the tight link existing between prokaryotic community functions and the type and concentration of contaminants, they may be useful indicator of pollution events and potential toxicity to other forms of life. The occurrence and abundance of HM-tolerant and PCB-oxidizing bacteria in the sub-Arctic Pasvik river area, heavily impacted by anthropogenic modifications, was related to HM and PCB contamination. This latter more likely derived from local inputs rather than a global contamination with higher PCB and HM amounts (and higher bacterial viable counts) that were determined in inner and middle sections of the River. Finally, a panel of bacteria with potential applications in the bioremediation of cold environments were selected and phylogenetically identified.

New Insights into the Culture Method and Antibacterial Potential of Gracilaria gracilis

Enormous marine biodiversity offers an endless reservoir of chemicals for many applications. In this scenario, the extraction of seaweeds represents an interesting source of compounds displaying antimicrobial activity. In particular, among the different red algae, Gracilaria gracilis plays an important role due to the presence of important bioactives in its composition. In spite of these features, an efficient culture system is still absent. In the present study, a novel algal culture method was developed and compared to another more common cultural practice, widely reported in literature. A higher efficiency of the new method, both for daily growth rate and biomass, was assessed. Furthermore, the growth inhibitory activity of five extracts, obtained using ethanol, methanol, acetone, chloroform or diethyl ether as a solvent, from the cultured G. gracilis was tested against Gram-positive and Gram-negative pathogens. Algal extracts exhibited a considerable inhibitory activity against B. subtilis strains, while a slight inhibition was observed against V. fischeri. The different extracts showed significant differences in bacterial growth inhibition, with the highest activity that was recorded for the ethanol extract, followed by that of methanol. Based on the chemical characterization, these findings could be related to the antimicrobial activity played by the combination of total carbohydrates and polyphenols, which were determined at high levels in ethanol and methanol extracts, as well as by the highest number and levels of single polyphenols. Conversely, the lower growth inhibitory activities found in chloroform and diethyl ether extracts could be related to the isolation of minor lipid classes (e.g., neutral and medium polar lipids) composed by fatty acids, such as stearic, oleic and arachidonic acids, typically characterized by antimicrobial activity. In consideration of the results obtained, the present study has a double implication, involving both the field of cultural practices and the exploitation of natural sources for the isolation of antimicrobial agents useful both in pharmaceutical and food applications.

Effects of microplastics on trophic parameters, abundance and metabolic activities of seawater and fish gut bacteria in mesocosm conditions

Plastic pollution is an emerging threat with severe implications on animals' and environmental health. Nevertheless, interactions of plastic particles with both microbial structure and metabolism are a new research challenge that needs to be elucidated yet. To improve knowledge on the effects played by microplastics on free-living and fish gut-associated microbial community in aquatic environments, a 90-day study was performed in three replicated mesocosms (control-CTRL, native polyvinyl chloride-MPV and weathered polyvinyl chloride-MPI), where sea bass specimens were hosted. In CTRL mesocosm, fish was fed with no-plastic-added food, whilst in MPV and MPI food was supplemented with native or exposed to polluted waters polyvinylchloride pellets, respectively. Particulate organic carbon (POC) and nitrogen, total and culturable bacteria, extracellular enzymatic activities, and microbial community substrate utilization profiles were analyzed. POC values were lower in MPI than MPV and CRTL mesocosms. Microplastics did not affect severely bacterial metabolism, although enzymatic activities decreased and microbes utilized a lower number of carbon substrates in MPI than MPV and CTRL. No shifts in the bacterial community composition of fish gut microflora were observed by denaturing gradient gel electrophoresis fingerprinting analysis.

Effect of the natural arsenic gradient on the diversity and arsenic resistance of bacterial communities of the sediments of Camarones River (Atacama Desert, Chile)

Arsenic (As), a highly toxic metalloid, naturally present in Camarones River (Atacama Desert, Chile) is a great health concern for the local population and authorities. In this study, the taxonomic and functional characterization of bacterial communities associated to metal-rich sediments from three sites of the river (sites M1, M2 and M3), showing different arsenic concentrations, were evaluated using a combination of approaches. Diversity of bacterial communities was evaluated by Illumina sequencing. Strains resistant to arsenic concentrations varying from 0.5 to 100 mM arsenite or arsenate were isolated and the presence of genes coding for enzymes involved in arsenic oxidation (aio) or reduction (arsC) investigated. Bacterial communities showed a moderate diversity which increased as arsenic concentrations decreased along the river. Sequences of the dominant taxonomic groups (abundances ≥1%) present in all three sites were affiliated to Proteobacteria (range 40.3–47.2%), Firmicutes (8.4–24.8%), Acidobacteria (10.4–17.1%), Actinobacteria (5.4–8.1%), Chloroflexi (3.9–7.5%), Planctomycetes (1.2–5.3%), Gemmatimonadetes (1.2–1.5%), and Nitrospirae (1.1–1.2%). Bacterial communities from sites M2 and M3 showed no significant differences in diversity between each other (p = 0.9753) but they were significantly more diverse than M1 (p<0.001 and p<0.001, respectively). Sequences affiliated with Proteobacteria, Firmicutes, Acidobacteria, Chloroflexi and Actinobacteria at M1 accounted for more than 89% of the total classified bacterial sequences present but these phyla were present in lesser proportions in M2 and M3 sites. Strains isolated from the sediment of sample M1, having the greatest arsenic concentration (498 mg kg^-1), showed the largest percentages of arsenic oxidation and reduction. Genes aio were more frequently detected in isolates from M1 (54%), whereas arsC genes were present in almost all isolates from all three sediments, suggesting that bacterial communities play an important role in the arsenic biogeochemical cycle and detoxification of arsenical compounds. Overall, results provide further knowledge on the microbial diversity of arsenic contaminated fresh-water sediments.

Efficiency in hydrocarbon degradation and biosurfactant production by Joostella sp. A8 when grown in pure culture and consortia

Joostella strains are emerging candidates for biosurfactant production. Here such ability was analyzed for Joostella strain A8 in comparison with Alcanivorax strain A53 and Pseudomonas strain A6, all previously isolated from hydrocarbon enrichment cultures made of polychaete homogenates. In pure cultures Joostella sp. A8 showed the highest stable emulsion percentage (78.33%), hydrophobicity rate (62.67%), and an optimal surface tension reduction during growth in mineral medium supplemented with diesel oil (reduction of about 12mN/m), thus proving to be highly competitive with Alcanivorax and Pseudomonas strains. During growth in pure culture different level of biodegradation were detected for Alcanivorax strain A53 (52.7%), Pseudomonas strain A6 (38.2%) and Joostella strain A8 (26.8%). When growing in consortia, isolates achieved similar abundance values, with the best efficiency that was observed for the Joostella-Pseudomonas co-culture. Gas-chromatographic analysis revealed an increase in the biodegradation efficiency in co-cultures (about 90%), suggesting that the contemporary action of different bacterial species could improve the process. Results were useful to compare the efficiencies of well-known biosurfactant producers (i.e. Pseudomonas and Alcanivorax representatives) with a still unknown biosurfactant producer, i.e. Joostella, and to confirm them as optimal biosurfactant-producing candidates.

Bacterial community structure along the subtidal sandy sediment belt of a high Arctic fjord (Kongsfjorden, Svalbard Islands)

Open fjords are subject to contrasting environmental conditions, owing to meltwater glacial inputs, terrestrial runoff, and marine water mass exchanges, which are exacerbated by anthropogenic and climate perturbations. Following a slope-dependent water circulation, the subtidal sandy sediment belt regulates the convergent transport of nutrients downward the fjord depths, and the effective entrapment of suspended particles and microorganisms. In this study, we aimed at testing how glacial and seawater inputs may influence the bacterial community structure of subtidal sand deposits in the Kongsfjorden. Through total and viable cell counting and an amplicon sequencing approach, we found relevant differences in bacterial community structure along the glacio-marine sampling transect. Viable and high nucleic acid content (HNA) cells represented an important fraction of the total community, generally decreasing toward the glacier front. Besides the predominance of Alpha- and Gammaproteobacteria, Bacteroidetes, Firmicutes and Parcubacteria, the bacterial community structure was likely affected by the glacial activity in the inner fjord, with the occurrence of distinctive phylotypes belonging to Gemmatimonadates, Nitrospirae, Acidobacteria, and Chloroflexi. Overall, our outcomes highlighted that exploring the bacterial community distribution and structure can provide new insights into the active role of sand deposits in coastal cold environments.

Extracellular polymeric substances with metal adsorption capacity produced by Pseudoalteromonas sp. MER144 from Antarctic seawater

The EPS-producing Pseudoalteromonas sp. MER144 was selected among 606 isolates from Antarctic seawater due to its evident slimy appearance on agar plates. The production of EPSs was enhanced by a step-by-step approach varying the carbon source, substrate and NaCl concentrations, temperature, and pH. Optimal conditions for the EPS production resulted at temperature of 4 °C and pH 7, with addition of 2% sucrose (w/v) and 3% NaCl (w/v). EPSs produced under optimal conditions were chemically characterized, resulting in a moderate carbohydrate content (35%), uronic acids (14%), and proteins (12%). Monosaccharide composition was estimated to be Glu:Man:GluN:Ara:GluA:GalA:Gal (1:0.36:0.26:0.06:0.06:0.05:0.03), while the estimated molecular weight was about 250 kDa. The addition of sucrose in the culture medium, by stimulating the EPS production, allowed MER144 to tolerate higher concentrations of mercury and cadmium. This finding was probably dependent on the presence of uronic acids and sulfate groups, which can bind cations, in the extracted EPSs. Monitoring EPS production under optimal conditions at different concentrations of mercury and cadmium revealed that EPS amounts increased at increasing heavy metal concentrations, indicating an adaptation to the stress conditions tested.

Bacterial isolates from the Arctic region (Pasvik River, Norway): assessment of biofilm production and antibiotic susceptibility profiles

Bacterial biofilm production is recognized as a strategy that helps aquatic bacteria in resisting to the presence of several kinds of pollutants, including antibiotics, in the bulk environment. The Pasvik River, located between Norway, Russia and Finland, is a sub-Arctic site polluted by wastes from metallurgic and mining activities. In order to study whether and to what extent bacteria are able to produce biofilms, and to assess whether this physiological characteristic influences their resistance to antibiotics, an investigation was performed on bacteria isolated from water and sediment collected along the Pasvik River course during two surveys (May and July). Bacterial strains were screened for their biofilm production and profiles of susceptibility to antibiotics. Results showed that biofilm formation was a widespread characteristic of the isolates. Most of them were also resistant to several antibiotics, such as ampicillin (100% of the isolates) as well as cefazolin, cefoxitin, ceftriaxone, mezlocillin, nitrofurantoin and sisomicin (90% of the total strains). This study shows a significant association between biofilm formation and antibiotic resistance at inner stations both in water and in sediments in May only. This suggests that in Pasvik River colder temperature may stimulate bacterial aggregation into biofilm and simultaneously decrease bacterial susceptibility to antibiotics; since the occurrence of antibiotic resistance has frequently been linked to the presence of pollutants, this result could represent a strategy of bacterial survival under altered environmental conditions.

Prokaryotic Abundance and Activity in Permafrost of the Northern Victoria Land and Upper Victoria Valley (Antarctica)

Victoria Land permafrost harbours a potentially large pool of cold-affected microorganisms whose metabolic potential still remains underestimated. Three cores (BC-1, BC-2 and BC-3) drilled at different depths in Boulder Clay (Northern Victoria Land) and one sample (DY) collected from a core in the Dry Valleys (Upper Victoria Valley) were analysed to assess the prokaryotic abundance, viability, physiological profiles and potential metabolic rates. The cores drilled at Boulder Clay were a template of different ecological conditions (different temperature regime, ice content, exchanges with atmosphere and with liquid water) in the same small basin while the Dry Valleys site was very similar to BC-2 conditions but with a complete different geological history and ground ice type. Image analysis was adopted to determine cell abundance, size and shape as well as to quantify the potential viable and respiring cells by live/dead and 5-cyano-2,3-ditolyl-tetrazolium chloride staining, respectively. Subpopulation recognition by apparent nucleic acid contents was obtained by flow cytometry. Moreover, the physiological profiles at community level by Biolog-Ecoplate™ as well as the ectoenzymatic potential rates on proteinaceous (leucine-aminopeptidase) and glucidic (ß-glucosidase) organic matter and on organic phosphates (alkaline-phosphatase) by fluorogenic substrates were tested. The adopted methodological approach gave useful information regarding viability and metabolic performances of microbial community in permafrost. The occurrence of a multifaceted prokaryotic community in the Victoria Land permafrost and a large number of potentially viable and respiring cells (in the order of 10⁴-10⁵) were recognised. Subpopulations with a different apparent DNA content within the different samples were observed. The physiological profiles stressed various potential metabolic pathways among the samples and intense utilisation rates of polymeric carbon compounds and carbohydrates, mainly in deep samples. The measured enzymatic activity rates suggested the potential capability of the microbial community to decompose proteins and polysaccharides. The microbial community seems to be appropriate to contribute to biogeochemical cycling in this extreme environment.

Ecology of cold environments: new insights of bacterial metabolic adaptation through an integrated genomic-phenomic approach

Cold environments dominate Earth's biosphere, hosting complex microbial communities with the ability to thrive at low temperatures. However, the underlying molecular mechanisms and the metabolic pathways involved in bacterial cold-adaptation mechanisms are still not fully understood. Herein, we assessed the metabolic features of the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 (PhTAC125), a model organism for cold-adaptation, at both 4 °C and 15 °C, by integrating genomic and phenomic (high-throughput phenotyping) data and comparing the obtained results to the taxonomically related Antarctic bacterium Pseudoalteromonas sp. TB41 (PspTB41). Although the genome size of PspTB41 is considerably larger than PhTAC125, the higher number of genes did not reflect any higher metabolic versatility at 4 °C as compared to PhTAC125. Remarkably, protein S-thiolation regulated by glutathione and glutathionylspermidine appeared to be a new possible mechanism for cold adaptation in PhTAC125. More in general, this study represents an example of how 'multi-omic' information might potentially contribute in filling the gap between genotypic and phenotypic features related to cold-adaptation mechanisms in bacteria.

Enrichment, isolation and biodegradation potential of psychrotolerant polychlorinated-biphenyl degrading bacteria from the Kongsfjorden (Svalbard Islands, High Arctic Norway)

Persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), have been detected in abiotic Arctic matrices: surface sediments and seawater from coastal areas in the Kongsfjorden were collected and analyzed. Levels of PCBs varied depending on the sampling site. Total PCB concentrations were between 11.63 (site C2W) and 27.69pgl^-1 (site AW). These levels were comparable to those reported previously in lake sediments from the northern Svalbard. The occurrence and biodegradation potential of cold-adapted PCB-oxidizing bacteria in seawater and sediment along the fjord was also evaluated. After enrichment with biphenyl, 246 isolates were obtained with 45 of them that were able to grow in the presence of the PCB mixture Aroclor 1242, as the sole carbon source. The catabolic gene bphA was harbored by 17 isolates with affiliates to the genera Algoriphagus, Devosia and Salinibacterium that have been never reported as able to utilize PCBs, thus deserving further investigation. The total removal of Aroclor 1242 and selected PCB congeners was evaluated at 4 and 15°C for eight bphA-harboring isolates and Gelidibacter sp. DS-10. With few exceptions, tested strains showed greater efficiency at 15 than at 4°C. Isolates were able to reduce most chromatographic peaks by >50%, with some di- and trichlorobiphenyls that were quite totally removed (>90%).

The pangenome of (Antarctic) Pseudoalteromonas bacteria: evolutionary and functional insights

BACKGROUND

Pseudoalteromonas is a genus of ubiquitous marine bacteria used as model organisms to study the biological mechanisms involved in the adaptation to cold conditions. A remarkable feature shared by these bacteria is their ability to produce secondary metabolites with a strong antimicrobial and antitumor activity. Despite their biotechnological relevance, representatives of this genus are still lacking (with few exceptions) an extensive genomic characterization, including features involved in the evolution of secondary metabolites production. Indeed, biotechnological applications would greatly benefit from such analysis.

RESULTS

Here, we analyzed the genomes of 38 strains belonging to different Pseudoalteromonas species and isolated from diverse ecological niches, including extreme ones (i.e. Antarctica). These sequences were used to reconstruct the largest Pseudoalteromonas pangenome computed so far, including also the two main groups of Pseudoalteromonas strains (pigmented and not pigmented strains). The downstream analyses were conducted to describe the genomic diversity, both at genus and group levels. This allowed highlighting a remarkable genomic heterogeneity, even for closely related strains. We drafted all the main evolutionary steps that led to the current structure and gene content of Pseudoalteromonas representatives. These, most likely, included an extensive genome reduction and a strong contribution of Horizontal Gene Transfer (HGT), which affected biotechnologically relevant gene sets and occurred in a strain-specific fashion. Furthermore, this study also identified the genomic determinants related to some of the most interesting features of the Pseudoalteromonas representatives, such as the production of secondary metabolites, the adaptation to cold temperatures and the resistance to abiotic compounds.

CONCLUSIONS

This study poses the bases for a comprehensive understanding of the evolutionary trajectories followed in time by this peculiar bacterial genus and for a focused exploitation of their biotechnological potential.

Prokaryotic Community in Lacustrine Sediments of Byers Peninsula (Livingston Island, Maritime Antarctica)

Byers Peninsula (Livingston Island, Antarctica), the largest seasonally ice-free region of the Maritime Antarctica, holds a large number of lakes, ponds, and streams. The prokaryotic structure and bacterial diversity in sediment samples collected during the 2008-2009 austral summer from five inland lakes, two coastal lakes, and an estuarine site were analyzed by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) and 16S rRNA 454 tag pyrosequencing techniques, respectively. Differently from inland lakes, which range around the oligotrophic status, coastal lakes are eutrophic environments, enriched by nutrient inputs from marine animals. Although the prokaryotic abundances (estimated as DAPI stained cells) in sediment samples were quite similar among inland and coastal lakes, Bacteria always far dominated over Archaea. Despite the phylogenetic analysis indicated that most of sequences were affiliated to a few taxonomic groups, mainly referred to Proteobacteria, Bacteroidetes, and Actinobacteria, their relative abundances greatly differed from each site. Differences in bacterial composition showed that lacustrine sediments were more phyla rich than the estuarine sediment. Proteobacterial classes in lacustrine samples were dominated by Betaproteobacteria (followed by Alphaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria), while in the estuarine sample, they were mainly related to Gammaproteobacteria (followed by Deltaproteobacteria, Epsilonproteobacteria, Alphaproteobacteria, and Betaproteobacteria). Higher number of sequences of Alphaproteobacteria, Cyanobacteria, Verrucomicrobia, and Planctomycetes were observed in sediments of inland lakes compared to those of coastal lakes, whereas Chloroflexi were relatively more abundant in the sediments of coastal eutrophic lakes. As demonstrated by the great number of dominant bacterial genera, bacterial diversity was higher in the sediments of inland lakes than that in coastal lakes. Ilumatobacter (Actinobacteria), Gp16 (Acidobacteria), and Gemmatimonas (Gemmatimonadetes) were recovered as dominant genera in both inland and coastal lakes, but not in the estuarine sample, indicating that they may be useful markers of Antarctic lakes. The proximity to the sea, the different lake depths and the external or internal origin of the nutrient sources shape the bacterial communities composition in lacustrine sediments of Byers Peninsula.

Biosurfactant activity, heavy metal tolerance and characterization of Joostella strain A8 from the Mediterranean polychaete Megalomma claparedei (Gravier, 1906)

The effect of heavy metals on the activity of biosurfactants produced by Joostella strain A8 from the polychaete Megalomma claparedei was investigated. Biosurfactant activity was first improved by evaluating the influence of abiotic parameters. Higher E(24) indices were achieved at 25 °C in mineral salt medium supplemented with 2 % glucose, 3 % sodium chloride (w/v) and 0.1 % ammonium chloride (w/v). Considerable surface tension reduction was never recorded. Heavy metal tolerance was preliminarily assayed by plate diffusion method resulting in the order of toxicity Cd > Cu > Zn. The activity of biosurfactants was then evaluated in the presence of heavy metals at different concentrations in liquid cultures that were incubated under optimal conditions for biosurfactant activity. The production of stable emulsions resulted generally higher in the presence of metals. These findings suggest that biosurfactant production could represent a bacterial adaptive strategy to defend cells from a stress condition derived from heavy metals in the bulk environment.

Influence of salinity and temperature on the activity of biosurfactants by polychaete-associated isolates

Influence of different parameters on biosurfactant (BS) activity was carried out on strains that were isolated from the polychaetes Megalomma claparedei, Sabella spallanzanii and Branchiomma luctuosum and additional 30 strains that were previously identified as potential BS producers from crude oil enrichments of the same polychaete specimens. The selection of BS-producing strains from polychaete natural samples was carried out by using standard screening tests. The BS activity by each isolate was evaluated for the effect of salinity and temperature on emulsion production and surface tension reduction, during incubation in mineral medium supplemented with tetradecane or diesel oil. All isolates showed a similar time course of BS activity, and the latter was more influenced by salinity rather than temperature. Some of the BS producers belonged to genera that have not (i.e. Citricoccus, Cellulophaga, Tenacibaculum and Maribacter) or have poorly been (Psychrobacter, Vibrio, and Pseudoalteromonas) reported as able to produce BSs. This is remarkable as some of them have previously been detected in hydrocarbon-enriched samples. Results confirm that filter-feeding polychaetes are an efficient source for the isolation of BS producers.

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.

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.

Bacteria associated with sabellids (Polychaeta: Annelida) as a novel source of surface active compounds

A total of 69 bacteria were isolated from crude oil enrichments of the polychaetes Megalomma claparedei, Sabella spallanzanii and Branchiomma luctuosum, and screened for biosurfactant (BS) production by conventional methods. Potential BS-producers (30 isolates) were primarily selected due to the production of both interesting spots on thin layer chromatography (TLC) plates and highly stable emulsions (E₂₄ ≥ 50%). Only few strains grew on cetyltrimethylammonium bromide and blood agar plates, indicating the probable production of anionic surfactants. The 16S rRNA gene sequencing revealed that selected isolates mainly belonged to the CFB group of Bacteroidetes, followed by Gammaproteobacteria and Alphaproteobacteria. A number of BS-producers belonged to genera (i.e., Cellulophaga, Cobetia, Cohaesibacter, Idiomarina, Pseudovibrio and Thalassospira) that have been never reported as able to produce BSs, even if they have been previously detected in hydrocarbon-enriched samples. Our results suggest that filter-feeding Polychaetes could represent a novel and yet unexplored source of biosurfactant-producing bacteria.

Response of bacterial isolates from Antarctic shallow sediments towards heavy metals, antibiotics and polychlorinated biphenyls

The response of bacterial isolates from Antarctic sediments to polychlorinated biphenyls (Aroclor 1242 mixture), heavy metal salts (cadmium, copper, mercury and zinc) and antibiotics (ampicillin, chloramphenicol, kanamycin and streptomycin) was investigated. Overall, the ability to growth in the presence of Aroclor 1242 as a sole carbon source was observed for 22 isolates that mainly belonged to Psychrobacter spp. Tolerance to the heavy metals assayed in this study was in the order of Cd > Cu > Zn > Hg and appeared to be strictly related to the metal concentrations, as determined during previous chemical surveys in the same area. With regards to antibiotic assays, the response of the isolates to the tested antibiotics ranged from complete resistance to total susceptibility. In particular, resistances to ampicillin and chloramphenicol were very pronounced in the majority of isolates. Our isolates differently responded to the presence of toxic compounds primarily based on their phylogenetic affiliation and secondarily at strain level. Moreover, the high incidence of resistance either to metal or antibiotics, in addition to the capability to grow on PCBs, confirm that bacteria are able to cope and/or adapt to the occurrence pollutants even in low human-impacted environments.