Search

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. [ABSTRACT FROM AUTHOR]

Porifera are one of the dominant components of the marine benthic communities in the Antarctic Sea (44% of the total species are endemic). Despite these data and the various studies on marine biodiversity, the abundance and diversity of sponges on shallow Antarctic reefs and in the deep sea are likely significantly underestimated. In this context, our work deals with the description of Antarctic sponges inhabiting Tethys Bay (Ross Sea). A total of 46 sponge specimens were collected at different depths during three separate Italian Antarctic Expeditions and identified into 15 species within the Demospongiae and Hexactinellida classes. More importantly, we report on finding two species, i.e. Haliclona scotti and Mycale (Aegogropila) denticulata, for the first time after 114 and 16 years, respectively, from their original description. More details are also given on their taxonomic re-description and molecular characterization. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Here, we present the results related to a new unique terrestrial ecosystem found in an englacial hypersaline brine found in Northern Victoria Land (Antarctica). Both the geochemistry and microbial (prokaryotic and fungal) diversity revealed an unicity with respect to all the other known Antarctic brines and suggested a probable ancient origin mainly due a progressive cryoconcentration of seawater. The prokaryotic community presented some peculiarities, such as the occurrence of sequences of Patescibacteria (which can thrive in nutrient-limited water environments) or few Spirochaeta, and the presence of archaeal sequences of Methanomicrobia closely related to Methanoculleus, a methanogen commonly detected in marine and estuarine environments. The high percentage (35%) of unassigned fungal taxa suggested the presence of a high degree of undiscovered diversity within a structured fungal community (including both yeast and filamentous life forms) and reinforce the hypothesis of a high degree of biological uniqueness of the habitat under study. [ABSTRACT FROM AUTHOR]

The Antarctic environment offers a unique opportunity to study the interactions between Porifera and their microbial symbionts. Reports on the association between prokaryotes and Antarctic sponges are increasing. However, a comparison of the bacterial communities associated to the same sponge species but inhabiting different Antarctic areas has seldom been addressed. This study explored the prokaryotes associated with the sponge species Mycale (Oxymycale) acerata (Kirkpatrick, 1907) and Dendrilla antarctica (Topsent, 1905) collected from South Cove at Rothera Point (Antarctic Peninsula) and Thetys Bay (Ross Sea). In D. antarctica , some groups were equally represented at both sites (e.g., Amylibacter , Cutibacterium , Yoonia-Loktanella), whereas members in the genera Polaribacter and Kistimonas were more abundant in Rothera. Similarly, M. acerata individuals collected from Rothera showed a higher relative abundance of some bacterial genera, such as Polaribacter , Sulfitobacter , and Ulvibacter. The results allowed us to identify some taxa common to sponges belonging to the same species and highlighted the possible influence of site-specific environmental conditions in shaping symbionts. • The prokaryotic communities associated with two common Antarctic sponge species is reported. • Mycale acerata and Dendrilla antarctica specimens were collected from two distant Antarctic sectors. • Site-specific environmental conditions prevailed in shaping the sponge-associated prokaryotic communities. • Some distinct microbial features characterized the two sponge species. [ABSTRACT FROM AUTHOR]

Marine Porifera (sponges) are known to produce several bioactive metabolites having a biotechnological potential, mostly derived from their bacterial symbionts; however, current knowledge on the production of metabolites such as enzymes and antibacterial molecules in sponges living in Antarctic environments is not fully exhaustive and needs further deepened investigation. The interest in discovering the broad spectrum of natural products potentially derived from species adapted to colonize extreme environments stimulates the research toward Antarctic sponge bioprospection. In this study, whole homogenates of Antarctic Demospongiae, belonging to five different species [Haliclona (Rhizoniera) sp., Haliclona (Rhizoniera) dancoi, Microxina sarai, Dendrilla antarctica, and Mycale acerata] were collected from Terra Nova Bay (Ross Sea) and examined for presence and activity of enzymes, including lysozyme, and antibacterial substances. Enzyme activities (leucine aminopeptidase, beta-glucosidase, and alkaline phosphatase) were measured using fluorogenic substrates; lysozyme content was determined on plates containing lyophilized Micrococcus lysodeikticus cell walls as a substrate. Homogenates were screened in microtiter plates for their antibacterial activity against Antarctic bacterial isolates, and the absorbance reduction was measured with a microplate reader. All homogenates exhibited proteolytic, glycolytic, and phosphatasic activities, lysozyme and antibacterial activities at near "in situ" temperature (5 °C), with some differences among the examined species. Results confirmed that Antarctic sponge homogenates are interesting sources of different bioactive substances, likely produced from associated bacterial symbionts, and that could have great potential to be used in medicine or industrial applications. [ABSTRACT FROM AUTHOR]

The potentially metabolically active components within the prokaryotic assemblages inhabiting the Antarctic Lake Limnopolar (Byers Peninsula, Maritime Antarctica) were investigated by a polyphasic approach which included culture-dependent and culture-independent methods (based on RNA molecules). Results support previous observations on the Proteobacteria and Bacteroidetes dominance, followed by Actinobacteria, in Antarctic lakes. In particular, Alpha-, Betaproteobacteria and Bacteroidetes were mainly detected by CARD-FISH and cDNA cloning, whereas Gammaproteobacteria and Actinobacteria dominated within the cultivable fraction. Overall, this study demonstrates the survival potential and physiological heterogeneity of the prokaryotic community in the Lake Limnopolar. The microbial community composition in the lake is affected by external influences (such as marine environment by sea spray and seabird dropping, and microbial mats and mosses of the catchment). However, most external bacteria would be inactive, whereas typical polar taxa dominate the potentially active fraction and are subsidized by external nutrient sources, thus assuming the main biogeochemical roles within the lake. [ABSTRACT FROM AUTHOR]

Bacteria belonging to the Pseudoalteromonas genus have important ecological implications in marine environments, playing a role in the control of microbial community as producers of bioactive molecules endowed with antifouling activity and able to antagonize larvae, fungi and bacteria, including important human pathogens. For these reasons, representatives of this genus are very promising for biotechnological and biomedical applications. In this work, we used different genome-scale approaches to infer the taxonomy of 38 Pseudoalteromonas representatives (most of which isolated from Antarctica) and whose complete genome has been sequenced. We show that an accurate re-evaluation of the real taxonomic relationships of Pseudoalteromonas representatives is needed since many inconsistencies with the current taxonomic annotation were observed. Moreover, data obtained with different genome-scale methods are consistent, confirming the reliability of the genomic approaches. On the basis of these data, we propose a re-annotation for some Pseudoalteromonas species. This proposal should be validated in the future by comparing the phenotypes of these strains. [ABSTRACT FROM AUTHOR]

The risk of hydrocarbon contamination in marine polar areas is constantly increasing. Autochthonous bacteria, due to their ability to cope and survive under extreme environmental conditions, can play a fundamental role in the hydrocarbon degradation. The degradation process is often enhanced by the production of biosurfactant molecules. The present study reports for the first time on the isolation of biosurfactant-producing bacteria from Arctic and Antarctic shoreline sediments. A total of 199 psychrotolerant bacterial isolates were obtained from hydrocarbon-amended (with crude or diesel oil) microcosms. A total of 18 isolates were selected for their ability to grow in the presence of crude oil and produce biosurfactants, as it was revealed by the production of good E values (≥50 %) and/or reduction in the surface tension (under 30 mN/m). The positive response of the isolates to both tests suggests a possible production of biosurfactants with emulsifying and interfacial activities. Biosurfactant-producing isolates were mainly affiliated to the genera Rhodococcus (14 isolates), followed by Pseudomonas (two isolates), Pseudoalteromonas (one isolate) and Idiomarina (one isolate). Thin-layer chromatography of biosurfactant crude extracts revealed that the majority of the selected isolates were able to produce glycolipidic surfactants. Our results enlarge the knowledge, which is still poor and fragmentary, on biosurfactant producers from polar areas and indicate marine polar sediments as a source of bacteria with potential applications in the remediation of hydrocarbon-contaminated cold environments. [ABSTRACT FROM AUTHOR]

Antarctic freshwater ecosystems are especially vulnerable to human impacts. Polychlorobiphenyls (PCBs) are persistent organic pollutants that have a long lifetime in the environment. Despite their use having either been phased out or restricted, they are still found in nature, also in remote areas. Once in the environment, the fate of PCBs is strictly linked to bacteria which represent the first step in the transfer of toxic compounds to higher trophic levels. Data on PCB-oxidizing bacteria from polar areas are still scarce and fragmented. In this study, the occurrence of PCB-oxidizing cold-adapted bacteria was evaluated in water and sediment of four coastal lakes at Edmonson Point (Northern Victoria Land, Antarctica). After enrichment with biphenyl, 192 isolates were obtained with 57 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, as a proxy for PCB degradation potential, was harbored by 37 isolates (out of 57), mainly affiliated to the genera Salinibacterium, Arthrobacter (among Actinobacteria) and Pusillimonas (among Betaproteobacteria). Obtained results enlarge our current knowledge on cold-adapted PCB-oxidizing bacteria and pose the basis for their potential application as a valuable eco-friendly tool for the recovery of PCB-contaminated cold sites. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The bacterial community inhabiting the water column at Terra Nova Bay (Ross Sea, Antarctica) was examined by the fluorescent in situ hybridization (FISH) technique and the genotypic and phenotypic characterization of 606 bacterial isolates. Overall, the FISH analysis revealed a bacterioplankton composition that was typical of Antarctic marine environments with the Cytophaga/Flavobacter (CF) group of Bacteroidetes that was equally dominant with the Actinobacteria and Gammaproteobacteria. As sampling was performed during the decay of sea-ice, it is plausible to assume the origin of Bacteroidetes from the sea-ice compartment where they probably thrive in high concentration of DOM which is efficiently remineralized to inorganic nutrients. This finding was supported by the isolation of Gelidibacter, Polaribacter, and Psychroflexus members (generally well represented in Antarctic sea-ice) which showed the ability to hydrolyze macromolecules, probably through the production of extracellular enzymes. A consistently pronounced abundance of the Gammaproteobacteria (67.8%) was also detected within the cultivable fraction. Altogether, the genera Psychromonas and Pseudoalteromonas accounted for 65.4% of total isolates and were ubiquitous, thus suggesting that they may play a key role within the analyzed bacterioplankton community. In particular, Pseudoalteromonas isolates possessed nitrate reductase and were able to hydrolyze substrates for protease, esterase, and β-galactosidase, thus indicating their involvement in the carbon and nitrogen cycling. Finally, the obtained results highlight the ability of the Actinobacteria to survive and proliferate in the Terra Nova Bay seawater as they generally showed a wide range of salt tolerance and appeared to be particularly competitive with strictly marine bacteria by better utilizing supplied carbon sources. [ABSTRACT FROM AUTHOR]

mong sub-Antarctic ecosystems, the microbiology of the Straits of Magellan has been poorly documented due to the scarcity of observations. In this context, the spatial distribution of microbiological parameters, both in terms of abundance (total picoplankton and picophytoplankton, cultivable heterotrophic bacteria) and biochemical assays (adenosine triphosphate and lipolysaccharide estimations, as well as electron transport system activity), was investigated in the epipelagic layer along the Straits during late summer 1991 and early autumn 1995. The microbial dynamics showed significant variations along the Straits, with increasing values generally determined eastward both in 1991 and 1995. Microbiological results were additionally correlated with available data on the physico-chemical and biological properties of the analyzed water masses. Taking into consideration the whole dataset, the principal component analysis led to the identification of three main macro-areas along the Straits of Magellan (Paso Largo, Paso Ancho and Angostura/Isla Isabel) with different trophic features. This held true when the two cruises were individually considered, as well as when comparing each macro-area between the two cruises. Additionally, a first attempt to quantify the carbon flux through the microbial compartment within the main identified macro-areas was made. The present work will allow the gaining of further understanding of the microbiology of this under-investigated sub-Antarctic marine ecosystem. [ABSTRACT FROM AUTHOR]

A total of 253 hydrocarbon-oxidizing bacterial isolates were achieved from eight Antarctic surface seawater samples enriched on diesel oil at 4°C. Isolates were screened by amplified ribosomal DNA restriction analysis prior to 16S rRNA gene sequencing. Sequences were compared to those in available databases using the Basic Local Alignment Search Tool network service to determine their approximate phylogenetic affiliations. The majority of the isolates were affiliated to the Actinobacteria (75.9%) and the Gamma-Proteobacteria (22.9%). The Alpha- and Beta-Proteobacteria represented 0.8 and 0.4% of total isolates, respectively. The Actinobacteria were predominantly allocated to the genera Arthrobacter, Cryobacterium and Rhodococcus. The Gamma-Proteobacteria were mainly found to be related to the genus Pseudomonas. Conversely, the Alpha- and Beta-Proteobacterial isolates shared the highest degree of sequence identity with unclassified bacteria. Differences in the distribution of the detected phylotypes were observed among the analyzed samples. Isolates representing each phylotype were selected for further characterization, including phenotypic assays and screening for the growth ability in the presence of individual hydrocarburic substrates as the sole supplied carbon and energy source. Isolates possessed different patterns of substrate utilization. Aliphatic hydrocarbons supported the growth of a higher number of isolates than aromatics. Results confirm the ability of our Antarctic marine bacteria to utilize hydrocarbons at low temperature and therefore suggesting that isolates with different substrate specificities can act in nature as a consortium in the utilization of complex hydrocarburic mixtures. [ABSTRACT FROM AUTHOR]

Antarctic marine bacteria were screened for their ability to degrade polychlorinated biphenyls (PCB) as the sole carbon and energy source at both 4°C and 15°C. PCB-degrading isolates (7.1%) were identified by sequencing their 16S rDNA as Pseudoalteromonas, Psychrobacter and Arthrobacter members. One representative isolate per genera was selected for evaluating the biodegradative potential under laboratory scale and phenotypically characterized. Removal of individual PCB congeners was between 35.6% and 79.8% at 4°C and between 0.4% and 82.8% at 15°C. Differences in the removal patterns of PCB congeners were observed in relation to the phylogenetic affiliation: Arthrobacter isolate showed similar biodegradation efficiencies when growing at 4°C and 15°C, while Pseudoalteromonas better degraded PCBs at 15°C. No biodegradation was detected for Psychrobacter isolate at 4°C. Results obtained highlight the occurrence of PCB-degrading bacteria in Antarctic seawater and suggest the potential exploitation of autochthonous bacteria for PCB bioremediation in cold marine environments. [Copyright &y& Elsevier]

One hundred and forty bacteria isolated from Antarctic seawater samples were examined for their ability to inhibit the growth of indigenous isolates and their sensitivity to antibacterial activity expressed by one another. On the basis of 16S rRNA gene sequencing and analysis, bacterial isolates were assigned to five phylogenetically different taxa, Actinobacteria, alpha and gamma subclasses of Proteobacteria, Bacillaceae, and Bacteroidetes. Twenty-one isolates (15%), predominantly Actinobacteria, exhibited antagonistic properties against marine bacteria of Antarctic origin. Members of Bacteroidetes and Firmicutes did not show any inhibitory activity. Differences were observed among inhibition patterns of single isolates, suggesting that their activity was more likely strain-specific rather than dependent on phylogenetic affiliation. A novel analysis based on network theory confirmed these results, showing that the structure of this population is probably robust to perturbations, but also that it depends strongly on the most active strains. The determination of plasmid incidence in the bacterial strains investigated revealed that there was no correlation between their presence and the antagonistic activity. The data presented here provide evidence for the antagonistic interactions within bacterial strains inhabiting Antarctic seawater and suggest the potential exploitation of Antarctic bacteria as a novel source of antibiotics. [ABSTRACT FROM AUTHOR]

Different polar environments (lakes and glaciers), also in Antarctica, encapsulate brine pools characterized by a unique combination of extreme conditions, mainly in terms of high salinity and low temperature. Since 2014, we have been focusing our attention on the microbiology of brine pockets from three lakes in the Northern Victoria Land (NVL), lying in the Tarn Flat (TF) and Boulder Clay (BC) areas. The microbial communities have been analyzed for community structure by next generation sequencing, extracellular enzyme activities, metabolic potentials, and microbial abundances. In this study, we aim at reconsidering all available data to analyze the influence exerted by environmental parameters on the community composition and activities. Additionally, the prediction of metabolic functions was attempted by the phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) tool, highlighting that prokaryotic communities were presumably involved in methane metabolism, aromatic compound biodegradation, and organic compound (proteins, polysaccharides, and phosphates) decomposition. The analyzed cryoenvironments were different in terms of prokaryotic diversity, abundance, and retrieved metabolic pathways. By the analysis of DNA sequences, common operational taxonomic units ranged from 2.2% to 22.0%. The bacterial community was dominated by Bacteroidetes. In both BC and TF brines, sequences of the most thermally tolerant and methanogenic Archaea were detected, some of them related to hyperthermophiles. [ABSTRACT FROM AUTHOR]

It has been demonstrated that the englacial ecosystem in volcanic environments is inhabited by active bacteria. To know whether this result could be extrapolated to other Antarctic glaciers and to study the populations of microeukaryotes in addition to those of bacteria, a study was performed using ice samples from eight glaciers in the South Shetland archipelago. The identification of microbial communities of bacteria and microeukaryotes using 16S rRNA and 18S rRNA high throughput sequencing showed a great diversity when compared with microbiomes of other Antarctic glaciers or frozen deserts. Even the composition of the microbial communities identified in the glaciers from the same island was different, which may be due to the isolation of microbial clusters within the ice. A gradient in the abundance and diversity of the microbial communities from the volcano (west to the east) was observed. Additionally, a significant correlation was found between the chemical conditions of the ice samples and the composition of the prokaryotic populations inhabiting them along the volcanic gradient. The bacteria that participate in the sulfur cycle were those that best fit this trend. Furthermore, on the eastern island, a clear influence of human contamination was observed on the glacier microbiome. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A special issue (SI) titled "Microbial Diversity in Extreme Environments: Implications for Ecological and Applicative Perspectives" has been launched with the aim of showcasing the diversity and biotechnological potential of extremophilic microorganisms. The issue includes 10 research papers and four reviews that mainly address prokaryotes inhabiting hyperarid, hypercold, hyperalkaline and hypersaline (or polyextreme) environments, spanning from deserts to meromictic and glacier lakes around the globe. Thermophilic prokaryotes from shallow hydrothermal vents and Antarctic geothermal soils are also treated. The ecology and biotechnological perspectives of eukaryotes are discussed in two review papers and one research paper. This special issue serves as a memorial to Dr. Luigi Michaud (1974–2014), who dramatically passed away in Antarctica during underwater sampling activities. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Shallow marine sediments were collected from seven stations (three of which located at Gerlache Inlet, two at Tethys Bay, one at Adelie Cove and one just beneath the Italian Research Base) along the Terra Nova Bay coast (Ross Sea, Antarctica). Their chemical, biochemical and microbiological properties were studied in order to provide further insights in the knowledge of this Antarctic benthic ecosystem. Overall, the organic carbon (OC) represented the major fraction of total carbon (TC) and displayed concentrations similar to or slightly lower than those previously measured in Antarctic bottom sediments. The biopolymeric carbon within OC ranged from 4.1% to 19.9% and showed a wide trophic range (65–834μgg−1 d.w.). Proteins (PRT) represented on average the main biochemical class contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). The activity of aminopeptidase, β-d-glucosidase, alkaline phosphatase and esterase was checked, giving the highest values at Tethys Bay and at the deepest water sediments. The principal component analysis, which was computed considering physical, chemical (elemental and biochemical sedimentary composition) and microbiological parameters (including bacterial abundance, ectoenzymatic activities, T-RFs richness and diversity indices), allowed to obtain two main clusters (“Tethys Bay” and “other stations”). Based on data obtained, two representative 16S rRNA clone libraries using samples from Tethys Bay and Gerlache Inlet were constructed. The sequences of 171 clones were compared to those available in public databases to determine their approximate phylogenetic affiliations. Both aerobic and anaerobic bacteria were disclosed, with the majority of them affiliated with the Gamma- and Deltaproteobacteria, Bacteroidetes and Acidobacteria. The occurrence of strictly anaerobic bacteria suggests that sediments might also undergo anoxic conditions that, in turn, could favor the accumulation of PRT in respect to CHO, assuming that fermentation of amino acids is slower than that of sugars from decomposing polysaccharides. [Copyright &y& Elsevier]