Bioprospecting for Exopolysaccharides from Deep-Sea Hydrothermal Vent Bacteria: Relationship between Bacterial Diversity and Chemical Diversity

Abstract

Many bacteria biosynthesize structurally diverse exopolysaccharides (EPS) and excrete them into their surrounding environment. The EPS functional features have found many applications in industries such as cosmetics and pharmaceutics. In particular, some EPS produced by marine bacteria are composed of uronic acids, neutral sugars, and N-acetylhexosamines, and may also bear some functional sulfate groups. This suggests that they can share common structural features with glycosaminoglycans (GAG) like the two EPS (HE800 and GY785) originating from the deep sea. In an attempt to discover new EPS that may be promising candidates as GAG-mimetics, fifty-one marine bacterial strains originating from deep-sea hydrothermal vents were screened. The analysis of the EPS chemical structure in relation to bacterial species showed that Vibrio, Alteromonas, and Pseudoalteromonas strains were the main producers. Moreover, they produced EPS with distinct structural features, which might be useful for targeting marine bacteria that could possibly produce structurally GAG-mimetic EPS.

Keywords: GAG; exopolysaccharides; glycopolymers; marine bacteria; production; sulfate.

Figure 1

Examples of EPS production visualized by agarose gel electrophoresis (a) MA896B; (b) HE799. Growth medium: (1) glucose, (2) saccharose, (3) mannitol, and (4) ZPHUF alone.

Figure 2

Sulfur content and monomeric composition (% w/w) of EPS for each strain. The EPS were extracted from a 100 mL culture broth.

Figure 3

Phylogenetic relationship of the EPS-producing strains studied.

Figure 4

Box plot representation of the composition of EPS (% w/w) as a function of strain phylogeny: V. stands for Vibrio sp., A. for Alteromonas sp. and P. for Pseudoalteromonas sp. In the boxes, the 25th, 50th, and 75th percentiles are indicated by the bottom, middle and top lines, respectively. Whiskers show the 10th and 90th percentiles. Individual dots are the outliers. EPS were extracted from 100 mL culture broth and analyzed by colorimetric assays (sulfur, proteins, uronic acids, and neutral sugars) and GC (monomers).