Endophytes are microorganisms that colonize living, internal tissues of plants without causing any immediate, overt negative effects. In recent years, both endophytic bacteria and fungi have been demonstrated to be excellent exopolysaccharides (EPS) producers. This review focuses on the recent advances in EPS produced by endophytes, including its production, isolation and purification, structural characterization, physiological role and biological activity. In general, EPS production is influenced by media components and cultivation conditions. The structures of purified EPS range from linear homopolysaccharides to highly branched heteropolysaccharides. These structurally novel EPS not only play important roles in plant-endophyte interactions; but also exhibit several biological functions, such as antioxidant, antitumor, anti-inflammatory, anti-allergic and prebiotic activities. In order to utilize endophytic EPS on an industrial scale, both yield and productivity enhancement strategies are required at several levels. Besides, the exact mechanisms on the physiological roles and biological functions of EPS should be elucidated in future.

exopolysaccharides, biological activity, Structural characterization, endophytes, physiological role

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@H](O[C@H]2[C@@H](CO)O[C@@H](O[C@H]3[C@@H](CO)O[C@@H](O[C@H]4[C@@H](CO)O[C@@H](O[C@H]5[C@@H](CO[C@@H]6O[C@@H](C)[C@H](O)[C@@H](O)[C@H]6O)O[C@@H]([*])[C@H](O)[C@H]5O)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)O[C@@H](C)[C@H](O)[C@H]1O

940.848 g/mol (C₃₆H₆₀R₂O₂₈, R = next and previous repeats, not counted in mol weight)

Although the ability to secrete exopolysaccharides (EPS) is widespread among microorganisms, only a few bacterial (e.g. xanthan, levan, dextran) and fungal (e.g. pullulan) EPS have reached full commercialization. During the last years, other microbial EPS producers have been the subject of extensive research, including endophytes, extremophiles, microalgae and Cyanobacteria, as well as mixed microbial consortia. Those studies have demonstrated the great potential of such microbial systems to generate biopolymers with novel chemical structures and distinctive functional properties. In this work, an overview of the bioprocesses developed for EPS production by the wide diversity of reported microbial producers is presented, including their development and scale-up. Bottlenecks that currently hinder microbial EPS development are identified, along with future prospects for further advancement.

bacteria, Extremophiles, exopolysaccharide (EPS), fungi, mixed microbial consortia

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@H](O[C@H]2[C@@H](CO)O[C@@H](O[C@H]3[C@@H](CO)O[C@@H](O[C@H]4[C@@H](CO)O[C@@H](O[C@H]5[C@@H](CO[C@@H]6O[C@@H](C)[C@H](O)[C@@H](O)[C@H]6O)O[C@@H]([*])[C@H](O)[C@H]5O)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)O[C@@H](C)[C@H](O)[C@H]1O

940.848 g/mol (C₃₆H₆₀R₂O₂₈, R = next and previous repeats, not counted in mol weight)

A bioactive exopolysaccharide [EPS (PS-I)], having Mw ~187000 Da was produced by submerged culture of an endophytic fungus Fusarium solani SD5. Structural elucidation of the EPS (PS-I) was carried out by a series of experiments. Result indicates the presence of terminal α-l-rhamnopyranosyl, (1→2)-α-l-rhamnopyranosyl, (1→4)-β-D-galactopyranosyl, (1→4,6)-β-D-galactopyranosyl moieties in a molar ratio of nearly 1:1:3:1. TEM image showed fibril structure of the EPS with a diameter of approximately 1 nm. Melting point range of the EPS was found 172-178 °C. The isolated PS-I exhibit in vitro anti inflammatory and anti allergic activity. EPS (1000 μg/ml) protects 55% erythrocytes from hypotonic solution induced membrane lysis. Compound 48/80 induced mast cell degranulation was also protected by 56% with 100 μg/ml EPS.

NMR, exopolysaccharide, GLC-MS, anti allergic activity, anti inflammatory activity, endophytic Fusarium solani SD5

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,4,4,4	aLRhap	100.8	78.1	70.3	73.2	69.4	17.4
4,4,4	bDGalp	104.3	71.3	73.2	74.8	76.1	60.9
4,4	bDGalp	104.3	71.3	73.2	74.8	76.1	60.9
4	bDGalp	104.3	71.3	73.2	74.8	76.1	60.9
6	aLRhap	100.3	71.2	71.8	74.3	74.8	16.7
	bDGalp	104.3	71.3	72.7	76.2	75.1	67.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,4,4,4	aLRhap	5.20	4.01	3.78	3.56	3.87	1.29
4,4,4	bDGalp	4.61	3.43	3.57	3.93	3.66	3.67-3.72
4,4	bDGalp	4.61	3.43	3.57	3.93	3.66	3.67-3.72
4	bDGalp	4.61	3.43	3.57	3.93	3.66	3.67-3.72
6	aLRhap	5.10	3.93	3.81	3.54	3.89	1.27
	bDGalp	4.61	3.44	3.51	3.91	3.69	3.76-4.17


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,4,4,4	aLRhap	100.8/5.20	78.1/4.01	70.3/3.78	73.2/3.56	69.4/3.87	17.4/1.29
4,4,4	bDGalp	104.3/4.61	71.3/3.43	73.2/3.57	74.8/3.93	76.1/3.66	60.9/3.67-3.72
4,4	bDGalp	104.3/4.61	71.3/3.43	73.2/3.57	74.8/3.93	76.1/3.66	60.9/3.67-3.72
4	bDGalp	104.3/4.61	71.3/3.43	73.2/3.57	74.8/3.93	76.1/3.66	60.9/3.67-3.72
6	aLRhap	100.3/5.10	71.2/3.93	71.8/3.81	74.3/3.54	74.8/3.89	16.7/1.27
	bDGalp	104.3/4.61	71.3/3.44	72.7/3.51	76.2/3.91	75.1/3.69	67.4/3.76-4.17

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@H](O[C@H]2[C@@H](CO)O[C@@H](O[C@H]3[C@@H](CO)O[C@@H](O[C@H]4[C@@H](CO)O[C@@H](O[C@H]5[C@@H](CO[C@@H]6O[C@@H](C)[C@H](O)[C@@H](O)[C@H]6O)O[C@@H]([*])[C@H](O)[C@H]5O)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)O[C@@H](C)[C@H](O)[C@H]1O

940.848 g/mol (C₃₆H₆₀R₂O₂₈, R = next and previous repeats, not counted in mol weight)