Abstract:
The present study shows the potential of an extracellular polymeric substance (EPS)
produced by Bacillus licheniformis strain KX657843 isolated from earthworm (Metaphire posthuma) gut
in the sorption of Cu(II) and Zn(II) and in flocculation. After harvesting bacterial cells from sucrose
supplemented denitrifying culture medium, the EPS was extracted following ethanolic extraction
method. The Fourier Transform Infrared Spectroscopy (FTIR) and 1H and 13C Nuclear Magnetic
Resonance (NMR) of EPS revealed its functional groups, electronegative constituents, unsaturated
carbon, and carbonyl groups. The negatively charged functional groups of carbohydrates and protein
moiety of the EPS endowed it with heavy metal binding capacity through electrostatic interactions.
The highest flocculation activity (83%) of EPS was observed at 4 mg L1 and pH 11. The metal
sorption by EPS increased with increasing pH. At pH 8, the EPS was able to remove 86 and 81%
Cu(II) and Zn(II), respectively, from a 25 mg L1 metal solution. 94.8% of both the metals at 25 mg
L1 metal solutions were removed by EPS at EPS concentration of 100 mg L1. From Langmuir
isotherm model, the maximum sorption capacities of EPS were calculated to be 58.82 mg g1 for
Cu(II) and 52.45 mg g1 for Zn(II). The bacterial EPS showed encouraging flocculating and metal
sorption properties. The potential to remove Cu(II) and Zn(II) implies that the EPS obtained from the
earthworm gut bacteria can be used as an e ective agent for environmental remediation of heavy
metals and in bioflocculation.