Microbial communities inhabiting the Antarctic Ocean show psychrophilic and halophilic adaptations conferring interesting properties to the enzymes they produce, which could be exploited in biotechnology and bioremediation processes. Use of cold- and salt-tolerant enzymes allows to limit costs, reduce contaminations, and minimize pretreatment steps. Here, we report on the screening of 186 morphologically diverse microorganisms isolated from marine biofilms and water samples collected in Terra Nova Bay (Ross Sea, Antarctica) for the identification of new laccase activities. After primary screening, 13.4 and 10.8% of the isolates were identified for the ability to oxidize 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the dye azure B, respectively. Amongst them, the marine Halomonas sp. strain M68 showed the highest activity. Production of its laccase-like activity increased six-fold when copper was added to culture medium. Enzymatic activity-guided separation coupled with mass spectrometry identified this intracellular laccase-like protein (named Ant laccase) as belonging to the copper resistance system multicopper oxidase family. Ant laccase oxidized ABTS and 2,6-dimethoxy phenol, working better at acidic pHs The enzyme showed a good thermostability, with optimal temperature in the 40–50°C range and maintaining more than 40% of its maximal activity even at 10°C. Furthermore, Ant laccase was salt- and organic solvent-tolerant, paving the way for its use in harsh conditions. To our knowledge, this is the first report concerning the characterization of a thermo- and halo-tolerant laccase isolated from a marine Antarctic bacterium.
Atmospheric pCO2 has increased since the industrial revolution leading to a lowering of the ocean surface water pH, a phenomenon called ocean acidification (OA). OA is claimed to be a major threat for marine organisms and ecosystems and, particularly, for Polar regions. We 2 explored the impact of OA on the shell mechanical properties of the Antarctic scallop Adamussium colbecki exposed for one month to acidified (pH 7.6) and natural conditions (unmanipulated littoral water), by performing Scanning Electron Microscopy, nanoindentation and Vickers indentation on the scallop shell. No effect of pH could be detected either in crystal deposition or in the mechanical properties. A. colbecki shell was found to be resistant to OA, which suggests this species to be able to face a climate change scenario that may threat the persistence of the endemic Antarctic species. Further investigation should be carried out in order to elucidate the destiny of this key species in light of global change.
Background: In aquatic environments, microbial biofilms are hot spots of microbial diversity, as well as a substrate for larval settlement of many invertebrate species. Examining the functional diversity of microorganisms in polar regions is a new and still unknown field of aquatic microbiology, that is attracting increasing interest for its significance in both scientific research and resources exploitation. The context and purpose of the study: In the framework of research aimed at studying microbial colonization occurring at Terra Nova Bay, culturable heterotrophic bacteria were quantified and characterized phenotypically at two study areas (Road Bay and Tethys Bay) with different environmental characteristics: the first one was close to Mario Zucchelli research station and impacted by anthropogenic pressure due to sewage wastes, while the second was exposed to salinity gradients due to glacier melting. In this context, artificial structures hosting plastic (polyvinyl chloride, PVC and polyethylene, PE) panels were deployed at -5 and -20m depths at each of the stations (one Impact and one Control) chosen per each study area. Water samples were contextually collected at the time of recovery of the plastic panels, namely after 12 months of deployment; at Road Bay, at the -5 m depth, a short-term experiment was also performed, with the recovery of the panels after 2.5 and 9 months of deployment. Bacterial strains were isolated in axenic culture both from water and biofilm matrices, and examined for their main phenotypical traits and functional diversity, through Gram staining, oxidase production, glucose fermentation and screened for enzymatic activity profiles (proteolytic, glycolytic and phosphatasic activities) using specific fluorogenic substrates. Results: Most of the bacterial isolates were Gram-negative, oxidase-positive and glucose-fermenting strains. Higher enzyme diversification was found in Road Bay at the site impacted by the sewage wastes from the research station, compared to the control site. A higher abundance of heterotrophic bacteria was detected on PVC compared to PE. Several pigmented strains, ascribable to Flavobacterium sp., were isolated from biofilm with respect to the ones isolated from the pelagic environment. Main findings: The screening of bacterial isolates for the production of hydrolytic enzymes revealed that proteolytic and phosphatase activities were a common metabolic trait of both water and biofilm-derived isolated. Microbes inhabiting Antarctica represent a very important and not completely known source of bioactive molecules with possibly multiple applications, from biomedicine to pharmaceutical, cosmetics, biodegradation, and so on. Conclusions: This is the first contribution to characterize phenotypically the bacteria colonizing the Ross Sea seabed in comparison with pelagic heterotrophic bacteria and to explore their metabolic abilities and the biotechnological potential of these microorganisms. The preliminary data regarding the metabolic profiles and composition of the microbial community have highlighted the plasticity of the microbial community, whose metabolism is modulated by the organic matter supplies found near the Mario Zucchelli Station. Brief summary: Heterotrophic bacteria in the waters and in the biofilm covering the surface of settlement panels in plastics deployed at sea for different time periods were studied in two bays of the Ross Sea, Road Bay and Tethys Bay. The main phenotypical characteristics of the bacterial isolates were examined. The production of hydrolytic enzymes makes microbial biofilms interesting sources of molecules with a potential applicative interest. Any potential implications: Bioprospecting research on polar microorganisms represents an attractive field of microbiology that is supported by increasing attention towards the discovery of hydrolytic enzymes as new active compounds having unexplored properties and applications.
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