Exploration of an Extracellular Polymeric Substance from Earthworm Gut Bacterium (Bacillus licheniformis) for Bioflocculation and Heavy Metal Removal Potential

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 L−1 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 L−1 metal solution. 94.8% of both the metals at 25 mg L−1 metal solutions were removed by EPS at EPS concentration of 100 mg L−1. From Langmuir isotherm model, the maximum sorption capacities of EPS were calculated to be 58.82 mg g−1 for Cu(II) and 52.45 mg g−1 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 effective agent for environmental remediation of heavy metals and in bioflocculation.

Characterization of novel extracellular polymeric substances produced by Bacillus velezensis P1 for potential biotechnological applications

“…These negatively charged functional groups are responsible for the high-negative zeta potential of this EPS, which was À33.83 mV. 30,37 Busi et al, 9 Shi et al 29 and Biswas et al 38 reported that EPS contained abundant charged functional groups, especially amino and carboxyl groups that might have been mainly responsible for the ability of the studied EPS to bind metal ions and to act as flocculants. EPS could act as biosorbents to efficiently remove heavy metals and as thickening, gelling and emulsifying agents…”

New Exopolysaccharides Produced by Bacillus licheniformis 24 Display Substrate-Dependent Content and Antioxidant Activity

“…B. licheniformis is a Gram-positive, motile, non-pathogenic bacterium ubiquitously spread in natural habitats. As it is associated with plant material, it can be easily isolated from soil, water and the rhizosphere [ 1 , 23 , 24 , 25 , 26 ], but it can also be found on the feathers of terrestrial and aquatic bird species, and in marine water [ 27 ]. B. licheniformis is widely used in industry, horticulture and pharmacy.…”

Articulating the exuberant intricacies of bacterial exopolysaccharides to purge environmental pollutants

“…EPS reported the metal removal potential of 54% and 42% at pH 5, which increases considerably to 86% and 81% at pH 8 for Cu (II) and Zn (II), respectively, at a metal concentration 25 mg/L in solution. The overall metal removal efficiency of 94.8% for both metals are observed at 100 mg/L EPS concentration [ 109 ]. Generally, through electrostatic interactions, the carbohydrate and protein moieties in EPS are furnished with their metal-binding properties and binds with cations.…”