New Arctic Pseudomonas sp. able to produce a cell-bound Levan type polysaccharide: hyperproduction, fermentation strategies and biotechnological applications

Microbial survival strategies in cold niches include the synthesis of extracellular polymeric substances (EPSs), adopted by a number of psychrophilic bacteria to cope with extremely low temperatures by protecting microbial cells from the direct contact with the surrounding environments (Poli et al. 2017). The ecological roles played by bacterial EPSs in natural habitats could ?nd applications in many biotechnological ?elds. The EPS production by psychrophilic microorganisms has been investigated during recent years, due to the wide versatility, the considerable application possibilities in several industrial sectors, and the ecological and protective roles that play for microbial cells (Finore et al., 2019, 2020). Nevertheless, cold-adapted bacteria from Arctic and Antarctic matrices (e.g. sediment, sea-ice and sponges, lakes) have seldom been explored as a source of EPSs. Ongoing research focusing on polysaccharides produced by extremophiles, isolated from Arctic region, will be reported including chemical structures, fermentation technology and biotechnological application. Pseudomonas strain 2ASCA, an EPS producing microorganism, was isolated from sediment sample of permafrost thaw pond (thermokarst lake) in the Sasapimakwananisikw River valley near Kuujjuarapik-Whapmagoostui, in subarctic Québec (Canada). P. strain 2ASCA, grows optimally at temperature of 15°C and is able to produce an exopolymer (yield: 1.17g/l), located in the loosely bound cell membrane fraction, in presence of sucrose 6% (w/v) as sole carbon source, after 96 hours of incubation. Higher Levan yields were reached by setting-up microbial fermentation conditions based on the use of cheaper broth medium composed by end-products belonging to the food production chains. Spectroscopy studies revealed the levan type nature of exopolymer released by strain 2ASCA with a repeating unit consisting of ?-(2,6)-linked fructose. Experiments aiming to define a molecular weight of Levan through the Gel Permeation Chromatography showed that the polymer possessed a molecular mass higher than 2,000,000 Da. Scanning Electron Microscope -energy dispersive X-ray spectroscopy (SEM-EDS) showed the levan capability to sequester different heavy metals, such as Cu (II), Zn (II), Pb (II), Fe (III) and Cd (II). Moreover, the SEM analyses of EPS control sample, without any heavy metals, showed a matrix texture revealing a tendency of polymer to develop nano-particles (Figure 1).Preliminary results revealed that Levan from Pseudomonas strain 2ASCA plays a cryo-protective role towards the microbial cells of strain, suggesting an ecological role in the natural cold environment. There are still many opportunities for the improvement of strain 2ASCA system as a microbial cell factory, since its molecular toolbox is still relatively unexplored: an expansion would open to further potential applications, especially in terms of genetic and metabolic engineering thanks to genome sequence recently obtained.