International Microbiology

, Volume 22, Issue 1, pp 91–101 | Cite as

Flocculating, emulsification and metal sorption properties of a partial characterized novel exopolysaccharide produced by Rhizobium tropici SRA1 isolated from Psophocarpus tetragonolobus (L) D.C.

  • Sandip Das
  • Ipsita Kumar Sen
  • Ahmet Kati
  • Sudip Some
  • Amit Kumar MandalEmail author
  • Syed Sirajul Islam
  • Rabindranath Bhattacharyya
  • Aparna Mukhopadhyay
Original Article


A novel exopolysaccharide (EPS) was produced by a bacterium which was isolated from Psophocarpus tetragonolobus (L) D.C. and identified as 99% Rhizobium tropici SRA1 by 16S rDNA sequencing. The flocculating performances along with emulsifying activity began simultaneously with the growth and the production of EPS and reached its utmost at 28 h. EPS was purified via chilled ethanol precipitation followed by dialysis and lyophilization. The existence of hydroxyl, methoxyl, and carboxylic functional groups were confirmed by Fourier transform infrared (FT-IR) spectrum. EPS was found to be compose of 82.44% neutral sugar and 15.93% uronic acid. The average molecular weight of the exopolysaccharide was estimated as ~ 1.8 × 105. Gas–liquid chromatography indicated the presence of glucose and galactose at a molar ratio of 3:1 in EPS. In the pH range of 3–5 with EPS dosage of 15 mg/l at 30 °C, cation-independent flocculation greater than 90% was observed. Emulsification indices (E24) of EPS were observed as 86.66%, 83.33%, 76.66%, and 73.33% with olive oil, kerosene, toluene, and n-hexane respectively. Biosorption of Cu K [45.69 wt%], Cu L [05.67 wt%], Co K [15.58 wt%], and Co L [11.72 wt%] by EPS was confirmed by energy-dispersive X-ray spectroscopy (EDS). This report on the flocculating, emulsifying, and metal sorption properties of EPS produced by R. tropici SRA1 is unique in the literature.


Exopolysaccharide Rhizobium tropici SRA1 Psophocarpus tetragonolobus Flocculation Emulsification Energy-dispersive X-ray spectroscopy 



The authors are thankful to Anupam Roy, Indian Institute of Technology, Kharagpur, for conducting SEM-EDS study.


SD was provided with independent RGNF (RGNF-2015-17-SC-WES-22946) from UGC, New Delhi, India.

Compliance with ethical standards

This article does not contain any studies with human participants or animals performed by any of the authors.

Conflict of interest

The authors declare that they have no competing interests.

Supplementary material

10123_2018_31_MOESM1_ESM.png (2.1 mb)
Supplementary Fig. 1 A) Isolation of microsymbionts from the root nodule of Psophocarpus tetragonolobus (L.) Congo red containing YEMA plates. B) Scanning Electron Microscopy image of R. tropici strain SRA1 (PNG 2135 kb)
10123_2018_31_MOESM2_ESM.png (839 kb)
Supplementary Fig. 2 16S rRNA gene sequence based neighbor-joining tree, showing the position of Rhizobium tropici SRA1 (blue color) among the members of genus Rhizobium. Bootstrap percentages are given at the branching nodes. Bartonella japonica Fuji 18-1T (NR112790) was used as outgroup. Bar 0.01 changes per nucleotide position (PNG 838 kb)
10123_2018_31_MOESM3_ESM.png (884 kb)
Supplementary Fig. 3 A) Flow diagram showing the steps involved in purification of EPS from R. tropici SRA1. B) Gel permeation chromatography of crude EPS using Sepharose-6B column (PNG 884 kb)
10123_2018_31_MOESM4_ESM.png (931 kb)
Supplementary Fig. 4 A) Effect of different CaCl2 concentration on flocculating rate. B) Flocculating rate of EPS in different pH values in the presence and absence of CaCl2. C) Effect of temperature on flocculating rate (PNG 930 kb)


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Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  • Sandip Das
    • 1
    • 2
  • Ipsita Kumar Sen
    • 3
    • 4
  • Ahmet Kati
    • 5
    • 6
  • Sudip Some
    • 7
  • Amit Kumar Mandal
    • 7
    Email author
  • Syed Sirajul Islam
    • 3
  • Rabindranath Bhattacharyya
    • 1
  • Aparna Mukhopadhyay
    • 1
  1. 1.Department of Life SciencesPresidency UniversityKolkataIndia
  2. 2.School of Sciences (Botany)Netaji Subhas Open UniversityDurgapur, West BurdwanIndia
  3. 3.Department of Chemistry and Chemical TechnologyVidyasagar UniversityMidnaporeIndia
  4. 4.Department of Science and HumanitiesSidhu Kanhu Birsa PolytechnicKeshiaryIndia
  5. 5.Hayat Chemicals Inc.Research and Development CenterKocaeliTurkey
  6. 6.Department of Medical Microbiology, School of MedicineAcıbadem Mehmet Ali Aydınlar UniversityAtasehir, IstanbulTurkey
  7. 7.Chemical Biology Laboratory, Department of SericultureRaiganj UniversityRaiganj, Uttar DinajpurIndia

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