Three structural classes of (1-->3)-beta-D-glucans are encountered in some important soil-dwelling, plant-associated or human pathogenic bacteria. Linear (1-->3)-beta-glucans and side-chain-branched (1-->3,1-->2)-beta-glucans are major constituents of capsular materials, with roles in bacterial aggregation, virulence and carbohydrate storage. Cyclic (1-->3,1-->6)-beta-glucans are predominantly periplasmic, serving in osmotic adaptation. Curdlan, the linear (1-->3)-beta-glucan from Agrobacterium, has unique rheological and thermal gelling properties, with applications in the food industry and other sectors. This review includes information on the structure, properties and molecular genetics of the bacterial (1-->3)-beta-glucans, together with an overview of the physiology and biotechnology of curdlan production and applications of this biopolymer and its derivatives.

Curdlan and other bacterial (1→3)-β-d-glucans

Background: Oligosaccharides containing a terminal Gal-a1,3-Gal moiety are collectively known as a-Gal epitopes. a-Gal epitopes are integral components of several medical treatments under development, including flu and HIV vaccines as well as cancer treatments. The difficulty associated with synthesizing the a-Gal epitope hinders the development and application of these treatments due to the limited availability and high cost of the a-Gal epitope. This work illustrates the development of a whole-cell biocatalyst for synthesizing the a-Gal epitope, Gala1,3-Lac. Results: Agrobacterium sp. ATCC 31749 was engineered to produce Gal-a1,3-Lac by the introduction of a UDPgalactose 4’-epimerase:a1,3-galactosyltransferase fusion enzyme. The engineered Agrobacterium synthesized 0.4 g/L of the a-Gal epitope. Additional metabolic engineering efforts addressed the factors limiting a-Gal epitope production, namely the availability of the two substrates, lactose and UDP-glucose. Through expression of a lactose permease, the intracellular lactose concentration increased by 60 to 110%, subsequently leading to an improvement in Gal-a1,3-Lac production. Knockout of the curdlan synthase gene increased UDP-glucose availability by eliminating the consumption of UDP-glucose for synthesis of the curdlan polysaccharide. With these additional engineering efforts, the final engineered strain synthesized approximately 1 g/L of Gal-a1,3-Lac. Conclusions: The Agrobacterium biocatalyst developed in this work synthesizes gram-scale quantities of a-Gal epitope and does not require expensive cofactors or permeabilization, making it a useful biocatalyst for industrial production of the a-Gal epitope. Furthermore, the engineered Agrobacterium, with increased lactose uptake and improved UDP-glucose availability, is a promising host for the production of other medically-relevant oligosaccharides.

/pdf/metabolic-engineering-of-agrobacterium-sp-strain-atcc-31749-243616c8ev.pdf

Metabolic engineering of Agrobacterium sp. strain ATCC 31749 for production of an α-Gal epitope

Properties, chemistry, and applications of the bioactive polysaccharide curdlan.

Class I. Alphaproteobacteria class. nov.

β-Glucans are a group of biologically-active fibers or polysaccharides from natural sources with proven medical significance. β-Glucans are known to have antitumor, anti-inflammatory, anti-obesity, anti-allergic, anti-osteoporotic, and immunomodulating activities. β-Glucans are natural bioactive compounds and can be taken orally, as a food supplement, or as part of a daily diet, and are considered safe to use. The medical significance and efficiency of β-glucans are confirmed in vitro, as well as using animal- and human-based clinical studies. However, systematic study on the clinical and physiological significance of β-glucans is scarce. In this review, we not only discuss the clinical and physiological importance of β-glucans, we also compare their biological activities through the existing in vitro and animal-based in vivo studies. This review provides extensive data on the clinical study of β-glucans.

https://www.mdpi.com/1422-0067/18/9/1906/pdf

Clinical and Physiological Perspectives of β-Glucans: The Past, Present, and Future.

Colonies of microorganisms capable of forming curdlan-type polysaccharide in glucose medium were found to stain blue with Aniline Blue, Brilliant Blue, or Trypan Blue, and red with Congo Red. Staining with Aniline Blue was highly specific for colonies forming curdlan-type polysaccharide. With the use of Aniline blue to detect curdlan-type polysaccharide and other β-1, 3-glucans, the distribution of these polysaccharides in microorganisms was investigated. Among 687 strains of bacteria, 5 strains of Bacillus stained with Aniline Blue, in addition to Alcaligenes faecalis var. myxogenes 10C3, some strains derived from it, and some strains of Agrobacterium. Sixteen of 60 strains of yeast also stained with this dye. No positive reaction was detected in 13 strains of fungi tested. This method was also useful for isolation of colonies forming only curdlan-type polysaccharide from organisms with the ability to form other water-soluble polysaccharides.

Takashi Sakane

Papers

DEMONSTRATION OF CURDLAN-TYPE POLYSACCHARIDE AND SOME OTHER β-1, 3-GLUCAN IN MICROORGANISMS WITH ANILINE BLUE