Bioprospecting for novel marine polysaccharides for the life sciences

  • Guy Trimby

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by UHI)


[the full thesis is embargoed until 14/4/2025 due to commercial agreements]
Polysaccharides have a staggering diversity of structural and chemical properties that affect the biological activity, with some used for cryopreservation and others to degrade oil as a carbon source. In some cases, polysaccharides display biocompatibility, scalability and rheological properties such as hyaluronic acid (HA), which is the primary exopolysaccharide (EPS) used within medical device formulations to conduct several ophthalmic surgeries, such as cataract removal. Despite this biocompatibility, the use of HA has considerable drawbacks including swelling, pain, injection site necrosis and the formation of cystic legions. Furthermore, a residual toxicity is present in HA extracted from the pathogenic Streptoccocus zooepidemicus, the current standard bacterium for HA production, where other fermentation products such as different proteins, are also present in the final HA product and causes immune responses in patients. Therefore, a solution to these drawbacks is required to improve safety. Marine EPS-producing bacteria are generally considered as having low or no toxicity to humans, with relatively low levels of protein contamination, where the ocean represents an untapped resource for the discovery of novel polysaccharides. Several deep-sea marine bacterial EPS have been found to confer beneficial effects in the medical industry, with some having bone healing abilities and others as an anticoagulant. As the deep-sea requires considerable amounts of time, specialist equipment and money to sample from, coastal niches that require extremophilic adaptations offer an alternative opportunity for biodiscovery.
Marine EPS-producing bacteria were isolated from a range of samples taken from coastal niches on the Scottish West Coast during winter to improve the chances of isolating a diversity of bacteria with extremophilic adaptations. Several methods were used to increase the cultivable bacterial diversity and provide the biological library required for this thesis including the use of a homogenate and agar overlays to better replicate the natural environment of the bacteria. Of all the samples taken, sugar kelp cultivated with a homogenate had the greatest cultivable diversity as found by alpha-diversity analysis. Compared to previous work on the cultivable microbiome of sugar kelp, the method in this thesis yielded a greater cultivable diversity, however only 3 bacterial genera were found in common, suggesting that the method, sample, location and season may have affected the bacteria present.
Sugar kelp was also found to have the highest number of EPS-producers of 110 compared to 49 EPS producers from a sand sample with the second highest number of EPS producers. Several bacteria, all later identified as members of the Paraglaciecola genus using 16s rRNA analysis, showed unusual EPS-producing properties where the EPS appeared dry and leathery. The fermentative abilities of these strains of Paraglaciecola, as well as several other genera, were identified resulting in the identification of four Paraglaciecola strains producing above 1 g/L in 50 mL cultures, with a maximum production of 5.48 g/L. Three of these Paraglaciecola strains were scaled-up to 1 L to better understand the fermentative abilities, with the highest producing 2.5 g/L. Though all the Paragalciecola strains produced above 1 g/L in a 1 L fermentation, a general reduction in EPS yield was observed for all strains and this is likely a cause of the extraction process post-fermentation. EPS from these strains was viscous and their extraction required an evolving process of increasingly invasive methods to separate the EPS from the cellular biomass. The use of hot trichloroacetic acid (TCA) at 80°C was found to be the best method for their extraction.
Monosaccharide analysis found that the EPS from selected Paraglaciecola strains were not considerably different, as such it was hypothesised that the side chains and decorations may be the cause of their different behaviours observed during extraction. The extensive range of monosaccharides found in the Paraglaciecola strains incorporates the monosaccharides found in glycosaminoglycan (GAG)-like or sphingan EPS, however they do not conform to the strict and limited definition of GAG-like or sphingan-like EPS due to the number of different monosaccharides present. Instead, the monosaccharides observed in the Paraglaciecola EPS are comparable to deep-sea Alteromonas species, though some differences still exist. These Paraglaciecola EPS appear to be highly novel, which I propose to call Paraglaciecans.
Date of Award14 Apr 2023
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SponsorsHyaltech Ltd & ESF PRA
SupervisorDavid Green (Supervisor), Arlene Ditchfield (Supervisor) & Brian Boag (Supervisor)

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