Phenotypic characterization of bacterial isolates from marine waters and plastisphere communities of the Ross Sea (Antarctica)
Authors: Gabriella Caruso , Ombretta Dell’Acqua , Rosalba Caruso , Maurizio Azzaro 
Published: January 2022

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.