Exopolysaccharides from Marine and Marine Extremophilic Bacteria: Structures, Properties, Ecological Roles and Applications

Abstract

The marine environment is the largest aquatic ecosystem on Earth and it harbours microorganisms responsible for more than 50% of total biomass of prokaryotes in the world. All these microorganisms produce extracellular polymers that constitute a substantial part of the dissolved organic carbon, often in the form of exopolysaccharides (EPS). In addition, the production of these polymers is often correlated to the establishment of the biofilm growth mode, during which they are important matrix components. Their functions include adhesion and colonization of surfaces, protection of the bacterial cells and support for biochemical interactions between the bacteria and the surrounding environment. The aim of this review is to present a summary of the status of the research about the structures of exopolysaccharides from marine bacteria, including capsular, medium released and biofilm embedded polysaccharides. Moreover, ecological roles of these polymers, especially for those isolated from extreme ecological niches (deep-sea hydrothermal vents, polar regions, hypersaline ponds, etc.), are reported. Finally, relationships between the structure and the function of the exopolysaccharides are discussed.

Keywords: EPS; GC-MS; NMR; capsular polysaccharide; chemical characterization; exopolysaccharides; extremophile; marine; purification; structure/activity relationship.

Figure 1

Schematic picture illustrating the typology of exopolysaccharides (EPSs): medium released exopolysaccharides (MRPs) and capsular polysaccharides (CPSs).

Figure 2

General scheme illustrating detection, extraction and purification of exopolysaccharides from microorganism’s planktonic and sessile growth.

Figure 3

General flow diagram for the characterization of polysaccharide primary and secondary structures performed during each step of purification.

Figure 4

Repeating units of EPS and CPS structures from marine bacteria and archaebacteria. (a) Alteromonas macleodii subsp. fijiensis strain ST716; (b) Alteromonas strain Jl2810; (c) Alteromonas infernus GY 785; (d) Cobetia marina DSMZ 4741; (e) Colwellia psychrerythraea 34H CPS (4 °C); (f) Colwellia psychrerythraea 34H EPS (4 °C); (g) Colwellia psychrerythraea 34H CPS (8 °C); (h) Haloferax mediterranei; (i) Haloferax gibbonsi ATCC 33959; (l) Haloferax denitrificans ATCC 35960; (m) Rhodococcus erythropolis PR4 and Rhodococcus sp. 33; (n) Pseudoalteromonas strain HYD 721; (o) Shewanella oneidensis MR-4; (p) Vibrio diabolicus (m); (q) Vibrio alginolyticus CNCM I-4994.

Figure 5

Schematic illustration of some EPS functions.

Figure 6

Molecular modelling of Colwellia psychrerythraea 34H CPS (a) and EPS (b).