Biosurfactants from Marine Microorganisms

The marine biosphere represents a yet underexploited natural source of bioactive compounds, mainly of microbial origin. Among them, biosurfactants (BSs) are functional molecules, which are attracting a great interest due to their biocompatibility, versatility, and applications in several biotechnological fields. BSs are surface active amphipathic compounds, containing both a hydrophilic and a hydrophobic moiety, which are grouped in low (glycolipids and lipopeptides) or high molecular weight (polymeric complexes) compounds. A number of environmental factors such as pH, salinity, temperature, and nutrient availability can affect microbial BS production. Marine microorganisms with different phylogenetic affiliations and isolated from several marine habitats (e.g., seawater, sediments, and higher organisms) worldwide (spanning from the Mediterranean Sea to Antarctica) have been reported as surfactant producers. However, most of the marine microbial world remains still unexplored. The present chapter aims at giving a general overview on the recent advances about BSs of marine origin, in order to enhance the knowledge inherent their production, chemical characterization and identification, interesting biological properties, and potential biotechnological applications

Incidence of plasmid and antibiotic resistance in psychrotrophic bacteria isolated from Antarctic sponges

A total of 297 bacterial strains were isolated from five Antarctic sponge species and tested by agarose gel electrophoresis for the presence of plasmid molecules. At least one kind of plasmid was carried by 69 isolates (about 23%). The disc diffusion susceptibility test was used to assay the resistance of plasmid-harbouring bacteria towards 11 antibiotics. A multiple resistance was observed for the 72% of strains, among which the 33% were resistant to only two antibiotics. Bacteria showed a high degree of resistance towards O/129 (71%), tetracycline (42%) and nalidixic acid (25%), whereas any isolate showed resistance to gentamicin. The 16S rDNA sequencing revealed that plasmid-harbouring strains were mainly affiliated to the Gammaproteobacteria (81%), whereas the other detected phylogenetic groups (i.e. Firmicutes, Alphaproteobacteria, Actinobacteria and CFB group of Bacteroidetes) were less abundant, each representing between 1% and 6% of the total isolates. The present study will contribute to the poor and fragmentary knowledge on plasmid incidence in natural microbial populations. In addition, monitoring antibiotic resistance in bacteria from remote areas, such as Antarctica, could also be a useful tool to evaluate the impact of anthropic pressure

Ecophysiological characterization of cultivable Antarctic psychrotolerant marine bacteria able to degrade hydrocarbons

The basic understanding of both the physiology and ecology of psychrotolerant Antarctic bacteria is a crucial step for the optimization of their biodegradative activity in cold environments. The detection of cold-adapted hydrocarbon-degrading bacteria in Antarctic seawaters is certainly of great interest for bioremediative purpose in oil polluted marine Antarctic systems, where the introduction of non native species is not allowed. This study focused on psychrotolerant marine bacteria inhabiting an Antarctic coastal area directly influenced by the human activity at the Italian Research Station (Terra Nova Bay). Fifty bacterial strains were isolated from hydrocarbon-degrading enrichment cultures obtained from seawater samples collected in the inlet Road Bay (Ross Sea). A preliminary Restriction Fragment Length Polymorphism (RFLP) analysis, carried out on 16S rDNA amplified via PCR using RSAI and AluI restriction enzymes, was applied to cluster the isolates according to the restriction profile they showed. One representative isolate per cluster was selected for further characterization; to elucidate their taxonomic position, conventional phenotypic and phylogenetic analyses were performed. Results led to the identification of the isolates as members of ten genera belonging to four phylogenetic groups: the alfa- and gamma-proteobacteria subdivisions, the gram-positive branch and the Cytophaga-Flexibacter-Bacteroides (CFB) phylum. Results indicate a high degree of biodiversity within the peculiar ecophysiological group of the hydrocarbon-degrading marine bacteria

Intestinal bacterial flora of Mediterranean gilthead sea bream (Sparus aurata Linnaeus) as a novel source of natural surface active compounds

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Ricerche sulla biodiversità delle comunità batteriche in tre laghi antartici

The bacterial diversity in three Antarctic lakes located at Crater Cirque (CC), Inexpressible Island (INI) and Luther Peak (LH) in the Victoria Land was investigated by a combination of culture-dependent and culture-independent techniques. The in situ abundance of different bacterial groups was determined by fluorescent in situ hybridization (FISH), while bacterial diversity among the cultivable microflora was investigated by culturing and genetic fingerprinting. Differences in the composition of bacterial assemblages were observed among the lakes investigated, when using the two approaches reported above. Overall, the detection rate by FISH of DAPI-stained cells varied from 48.4% to 68.9% with the general bacterial probe EUB338. Bacteria hybridizing with the group-specific probe CF319a were found to be abundant in the three lakes. A total of 478 strains were isolated from R2A agar plates and grouped by restriction analysis technique; sequencing of representative 16S rDNAs was performed to elucidate the taxonomic positions of isolates. Overall, isolates were placed within five different taxa: ?-Proteobacteria (39%), Bacteroidetes (35%), ?-Proteobacteria (8%), Actinobacteria (7%) and ?-Proteobacteria (5%). Finally, the 5.8% of total isolates shared the highest degree of sequence identity with unclassified bacteria. Members of the ?-Proteobacteria predominated at INI, whereas isolates from CC and LH mainly belonged to the Bacteroidetes. Among the ?-Proteobacteria, the genus Pseudomonas was predominant, whereas Flavobacterium spp. were very common among the Bacteroidetes. Finally, several Actinobacteria were closely related to unknown Antarctic bacteria

Bacterial Diversity in a Dynamic and Extreme Sub-Arctic Watercourse (Pasvik River, Norwegian Arctic)

Microbial communities promptly respond to the environmental perturbations, especially in the Arctic and sub-Arctic systems that are highly impacted by climate change, and fluctuations in the diversity level of microbial assemblages could give insights on their expected response. 16S rRNA gene amplicon sequencing was applied to describe the bacterial community composition in water and sediment through the sub-Arctic Pasvik River. Our results showed that river water and sediment harbored distinct communities in terms of diversity and composition at genus level. The distribution of the bacterial communities was mainly affected by both salinity and temperature in sediment samples, and by oxygen in water samples. Glacial meltwaters and runoff waters from melting ice probably influenced the composition of the bacterial community at upper and middle river sites. Interestingly, marine-derived bacteria consistently accounted for a small proportion of the total sequences and were also more prominent in the inner part of the river. Results evidenced that particular conditions occurring at sampling sites (such as algal blooms, heavy metal contamination and anaerobiosis) may select species at local scale from a shared bacterial pool, thus favoring certain bacterial taxa. Conversely, the few phylotypes specifically detected in some sites are probably due to localized external inputs introducing allochthonous microbial groups

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 27.69 pg l− 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%)

Benthic Microbial Communities in a Seasonally Ice-Covered Sub-Arctic River (Pasvik River, Norway) Are Shaped by Site-Specific Environmental Conditions

The Pasvik River experiences chemical, physical, and biological stressors due to the direct discharges of domestic sewage from settlements located within the catchment and runoff from smelter and mine wastes. Sediments, as a natural repository of organic matter and associated contaminants, are of global concern for the possible release of pollutants in the water column, with detrimental effects on aquatic organisms. The present study was aimed at characterizing the riverine benthic microbial community and evaluating its ecological role in relation to the contamination level. Sediments were sampled along the river during two contrasting environmental periods (i.e., beginning and ongoing phases of ice melting). Microbial enzymatic activities, cell abundance, and morphological traits were evaluated, along with the phylogenetic community composition. Amplified 16S rRNA genes from bacteria were sequenced using a next-generation approach. Sediments were also analyzed for a variety of chemical features, namely particulate material characteristics and concentration of polychlorobiphenyls, polycyclic aromatic hydrocarbons, and pesticides. Riverine and brackish sites did not affect the microbial community in terms of main phylogenetic diversity (at phylum level), morphometry, enzymatic activities, and abundance. Instead, bacterial diversity in the river sediments appeared to be influenced by the micro-niche conditions, with differences in the relative abundance of selected taxa. In particular, our results highlighted the occurrence of bacterial taxa directly involved in the C, Fe, and N cycles, as well as in the degradation of organic pollutants and toxic compounds.Benthic Microbial Communities in a Seasonally Ice-Covered Sub-Arctic River (Pasvik River, Norway) Are Shaped by Site-Specific Environmental ConditionspublishedVersio

Trophic and Microbial Patterns in the Ross Sea Area (Antarctica): Spatial Variability during the Summer Season

In open regions of the Ross Sea, the role of the microbial community in the turnover of organic matter has scarcely been investigated; indeed, very little is known on how microbial distribution and functional diversity respond to environmental conditions and hydrographic structures. During the austral summer of 2017, two pelagic areas of the Ross Sea [the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya (A area), and the continental Shelf Break area near Cape Adare (C area)] were studied at selected depths [surface, Deep Chlorophyll Maximum (DCM), Circumpolar Deep Water (CDW), deep waters]. Trophic properties [nutrient concentrations, particulate (POC), dissolved organic carbon (DOC) and its optically significant fraction (CDOM) were measured, together with the main hydrological variables. Microbial community abundance [total prokaryotes, living, dead, and actively respiring fraction, high- and low nucleic acid cells (HNA and LNA), picoand nano-eukaryotes, culturable heterotrophic bacteria], composition, and metabolism (as whole community and as isolated bacteria) were also assessed. Through a multidisciplinary dataset, this study highlighted the variable response of microbial abundance, diversity, and metabolism of the microbial community to the changing local environmental conditions of the Ross Sea. Different forces, such as organic matter inputs (mostly of detrital nature) released from the Drygalski glacier in the A area, and a coastal-to-offshore gradient in the C area, coexisted within this extreme ecosystem. This resulted in a significant spatial segregation of the edaphic parameters, and of the microbial community distribution and metabolic activity patterns