Exopolysaccharides produced by Pediococcus acidilactici MT41-11 isolated from camel milk: Structural characteristics and bioactive properties

doi:10.1016/j.ijbiomac.2021.06.152

International Journal of Biological Macromolecules

Volume 185, 31 August 2021, Pages 1036-1049

https://doi.org/10.1016/j.ijbiomac.2021.06.152 Get rights and content

Highlights

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EPS-1 composed of →3)-α-D-Manp-(1→2)-α-D-Manp-(1→, α-d-Manp-(1→
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EPS-2 major composed of →6)-β-d-Glcp-(1→, →4)-α-l-Fucp-(1→, and α-d-Glcp-(1→
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EPS exhibited excellent property to stimulate Lactobacillus growth.
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EPS exhibited good ability to inhibit and to disrupt pathogenic biofilms in vitro.

Abstract

In this study, the chemical structure and bioactive properties of the EPS of Pediococcus acidilactici MT41-11 isolated from camel milk were investigated. Two polysaccharide fractions (EPS-1, EPS-2) with molecular weights about 69.0 kDa were obtained, which were purified using DEAE-Sepharose and Sephadex G-100 chromatography. Based on monosaccharide composition, FT-IR, and 1D, 2D NMR spectra, concluded that EPS-1 had a backbone composed of →2)-α-d-Manp-(1→, →3)-α-d-Manp-(1→ and with branches containing α-d-Manp-(1→, EPS-2 had a backbone composed of →6)-β-d-Glcp-(1→, and with branches containing →2)-α-l-Fucp-(1→, →3)-α-d-Glcp-(1→, →2)-α-d-Glcp-(1→, β-d-Glcp-(1→, and α-d-Glcp-(1→. Remarkably, in vitro assays showed that EPS possessed multiple bioactive properties, including stimulating Lactobacillus growth and a high DPPH free radical scavenging activity. Also, it has a good ability to anti-biofilms. Overall, the analysis of all data showed EPS from P. acidilactici MT41–11 can be used as anti-oxidant, anti-biofilm agent, and also as a potential candidate prebiotic for health food or medicine industry.

Introduction

Exopolysaccharides, as a wide class of biologically synthesized macromolecular carbohydrate polymers, which could be loosely adhered around the bacterial cell or secreted into the surrounding environment during the microorganism growth phase [1]. Attributing to the diversity of chemical composition and biosynthesis mechanisms, exopolysaccharides can be subdivided into different groups: homopolysaccharides (HoPS) and heteropolysaccharides (HePS). The former are composed of repeats of one type of monosaccharide (e.g. glucans, fructans), while the latter are composed of two or more monosaccharide (e.g. glucose, galactose, and rhamnose).

Lactic acid bacteria (LAB) were identified to have a GRAS (Generally Recognized as Safe) status, and LAB EPS are also recognized as safe agents. Recently, many scientific studies reported that LAB-derived EPS from different sources have multiple underlying bioactive activities, such as immunemodulatory properties, anti-cancer, antioxidant activity, anti-biofilm activity, cholesterol lowering properties [2], and prebiotic activities [3]. Additionally, EPS from LAB also exhibited good physicochemical properties, such as coagulation, emulsification, thickening, and heavy metal adsorption activities [4]. EPSs produced by LAB, with its unique health benefits and physicochemical properties make it could be used in wastewater treatment, food additives, pharmaceutical [4], food active edible packaging industrial fields [5] and so on. In fact, the functional properties (bioactive activities and physicochemical properties) of polysaccharides were demonstrated to be closely related to their structural features and complexity (e.g. composition, linkages, molecular weight, and substituent groups) [6]. As yet, understanding of the mechanisms between EPS structure and its functional properties is still obscure. Consequently, an elaborately characterization of the chemical structure of various kinds of well-sourced LAB-EPSs are essential to explore their functional properties. Therefore, a deeply understanding of the functional characteristics of EPS produced by LAB will provide a good foundation for its future application in food and other fields.

Lactic acid bacteria (LAB), including Lactobacillus genus, Pediococcus genus, Weissella genus, and Enterococcus genus is the dominant and advantageous microorganisms of raw camel milk and its derived products [7]. Particularly, many studies have shown that camel milk was also a potential source for obtaining novel probiotic strains. [8], [9], [10]. Previously in our laboratory, abundant Pediococcus species were isolated from raw camel milk, among which P. acidilactici MT41–11 had good exopolysaccharide producing properties. This study, therefore, was aimed to characterize the chemical structure of partial purification EPS fractions from P. acidilactici strain MT41–11 by using a combination of HPLC, HPGPC, FT-IR spectroscopy, NMR spectroscopy, and SEM. Besides, we assessed the bioactive properties (anti-biofilm activity, antioxidant activity and stimulation of Lactobacillus growth) of EPS.

Section snippets

Bacterial strain and growth conditions

In this study, the strain was isolated from camel milk, which was collected from southern Xinjiang, China. It was identified as P. acidilactici (Gene Bank deposited sequence number: MW192048) by its 16S rDNA sequence analysis, and encoded MT41-11. The strain was grown at 37 °C in MRS medium.

Extraction and partial purification of EPS

Strain MT41–11 was incubated in a modified MRS medium (elimination of glucose and added 5% w/v sucrose) for 16 h at 37 °C in a rotary shaker, and the 2% (v/v) inoculation quantity. After incubation,

Partial purification of EPS

The crude EPS was fractionated by a DEAE-FF anion exchange chromatography column. As shown in Fig. 1a, three fractions eluted with 0, 0.1, and 0.3 M NaCl were collected. The eluting components of 0.1 M NaCl and 0.3 M NaCl were collected and named as EPS-1 and EPS-2, respectively. As the water eluting component contains less polysaccharide, it is not collected. The two fractions were further purified by a Sephadex G-100 size exclusion chromatography column. As shown Fig. 1b and c, observed that

Conclusion

In this study, EPS-1 and EPS-2 were purified from the exopolysaccharide produced by P. acidilactici MT41-11. They have similar Mw were about 69.0 KDa. EPS-1 had a backbone composed of →2)-α-d-Manp-(1→, →3)-α-d-Manp-(1→ and with branches containing α-d-Manp-(1→. EPS-2 had a backbone composed of →6)-β-d-Glcp-(1→, and with branches containing →2)-α-l-Fucp-(1→, →3)-α-d-Glcp-(1→, →2)-α-d-Glcp-(1→, α-d-Glcp-(1→, and β-d-Glcp-(1→. The properties of EPS stimulate Lactobacillus growth well. And EPS have

CRediT authorship contribution statement

Yingying Bai: Methodology, Writing-original draft.

Baolong Luo: Investigation, Data curation.

Yan Zhang: Project administration.

Fengwei Tian: Project administration.

Xu Li: Writing- Reviewing and Editing.

Zhen Wang: Software, Visualization.

Yuqing Shan: Software, Visualization.

Min Lu: Software, Visualization.

Yongqing Ni: Writing- Reviewing, Supervision, Resources.

Declaration of competing interest

All the authors confirm that there are no conflicts of interest to declare.

Acknowledgments

This study was supported by the joint key funds of National Natural Science Foundation of China (U1903205) and National Natural Science Foundation of China (31760446).

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Exopolysaccharides produced by Pediococcus acidilactici MT41-11 isolated from camel milk: Structural characteristics and bioactive properties

Highlights

Abstract

Introduction

Section snippets

Bacterial strain and growth conditions

Extraction and partial purification of EPS

Partial purification of EPS

Conclusion

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgments

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