A Glacier Bacterium Produces High Yield of Cryoprotective Exopolysaccharide

Abstract

Pseudomonas sp. BGI-2 is a psychrotrophic bacterium isolated from the ice sample collected from Batura glacier, Pakistan. This strain produces highly viscous colonies on agar media supplemented with glucose. In this study, we have optimized growth and production of exopolysaccharide (EPS) by the cold-adapted Pseudomonas sp. BGI-2 using different nutritional and environmental conditions. Pseudomonas sp. BGI-2 is able to grow in a wide range of temperatures (4-35 • C), pH (5-11), and salt concentrations (1-5%). Carbon utilization for growth and EPS production was extensively studied and we found that glucose, galactose, mannose, mannitol, and glycerol are the preferable carbon sources. The strain is also able to use sugar waste molasses as a growth substrate, an alternative for the relatively expensive sugars for large scale EPS production. Maximum EPS production was observed at 15 • C, pH 6, NaCl (10 g L −1), glucose as carbon source (100 g L −1), yeast extract as nitrogen source (10 g L −1), and glucose/yeast extract ratio (10/1). Under optimized conditions, EPS production was 2.01 g L −1 , which is relatively high for a Pseudomonas species compared to previous studies using the same method for quantification. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) analysis of EPS revealed glucose, galactose, and glucosamine as the main sugar monomers. Membrane protection assay using human RBCs revealed significant reduction in cell lysis (∼50%) in the presence of EPS, suggesting its role in membrane protection. The EPS (5%) also conferred significant cryoprotection for a mesophilic Escherichia coli k12 which was comparable to glycerol (20%). Also, improvement in lipid peroxidation inhibition (in vitro) resulted when lipids from the E. coli was pretreated with EPS. Increased EPS production at low temperatures, freeze thaw tolerance of the EPS producing strain, and increased survivability of E. coli in the presence of EPS as cryoprotective agent supports the hypothesis that EPS production is a strategy for survival in extremely cold environments such as the glacier ice.

Glacier clear ice bands indicate englacial channel microbial distribution

“…Most of these taxa have been described as being exopolysaccharide (EPS), ice-binding protein and antifreeze protein producers (Cid and others, 2016; Kielak and others, 2016; Chrismas and others, 2018). These substances have been shown to facilitate and protect cells from freeze/thaw cycles and to alter ice crystal formation therefore providing cryoprotection to promote their survival in this challenging environment (Casillo and others, 2017; Deming and Young, 2017; Ali and others, 2020). The Cyanobacteria found are also typical of the glacial environment (Lutz and others, 2017) and most of the genera (e.g.…”

Marine Polysaccharides for Wound Dressings Application: An Overview

“…Emulsifier Chelates heavy metals [225] Pseudomonas sp. BGI-2 Glacier ice Antioxidant Low temperature protection [226] Paenibacillus sp. TKU042 Marine chitinous materials Antioxidant Anti-inflammatory Alpha-glucosidase inhibitor [227] Bacillus subtilis SH1 Marine surface sediment Antiviral Antibacterial Antioxidant [228] Bacillus vallismortis WF4 Coast Anti-fungal Anti-itch [229] Even though marine microorganisms EPS could provide various bioactivities, their utilization in wound dressings is still limited [230].…”

Psychrophilic Bacterial Phosphate-Biofertilizers: A Novel Extremophile for Sustainable Crop Production under Cold Environment

“…To thrive well under cold extremes and to protect themselves from cellular injuries or to reduce the destructive effects of ice crystal formation, generally termed "Osmoprotection", microorganisms have developed various structural and functional modifications [51,52]. These adaptations include (i) variation in membrane fluidity [53]; (ii) conformational flexibility; (iii) better enzyme activity associated with essential cellular processes such as transcription and translation [54]; (iv) induction of cold-shock proteins [55]; (v) pro-duction of antifreeze proteins (AFPs) [56,57]; (vi) excretion of high amounts of exopolymeric substances with cryoprotection activity [58][59][60][61]; (vii) synthesis and accumulation of various other compatible solutes such as polyamines, sugars, polyols, amino acids, etc. [62,63].…”