Analysis of the Extracellular Polysaccharide-based Structures Produced by a Halophylic Archaeon

Abstract

This paper investigates the components distribution and structure of an extracellular polysaccharide (EPS) produced by the halophilic archaeon Haloferax mediterranei in the presence or absence of the archaeon by using optical microscopy. The results show that EPS at the end of cultivation is arranged as a discontinuous biofilm and the cells are embedded in this biofilm. EPS and cells cannot be separated through centrifugation, cells remaining attached to the polysaccharide; the biofilm in the supernatant has a similar aspect as in the cultivation broth. The biofilm formed from the supernatant by drying at room temperature is very rich in salts from the cultivation broth (around 200 g/l from which 125 g/l NaCl) and consists on salt crystals which incorporate or are embedded by a film of EPS, distributed discontinuously and having some globular components. In the absence of salts (removed through dialysis), the biofilm formed in the aqueous environment is discontinuous and consists on globular polysaccharides connected by linear EPS which entraps cells remained after centrifugation.