Removal of heavy metals by exopolymeric substances produced by resistant purple nonsulfur bacteria isolated from contaminated shrimp ponds

Abstract

Two purple nonsulfur bacteria (PNSB) strains, Rhodobium marinum NW16 and Rhodobacter sphaeroides KMS24 were investigated for their potential to remove heavy metals (HMs) from contaminated shrimp pond water. Tolerance of both PNSB strains growing with both microaerobic-light and aerobic-dark conditions, based on their minimum inhibitory concentrations, was in the order of Cu 2+ > Zn 2+ > Cd 2+ (Pb precipitation occurred at 0.34 mM). Results from a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDX) indicated that Cu 2+ and Zn 2+ altered the cellular morphology of both strains and accumulated HMs were found in their cells. The highest amounts of both cations were found in their cell walls followed by the cytoplasm and cell membrane. Using the highest concentrations (mM) of HMs found in shrimp pond of 0.0067 Cd 2+ , 0.54 Cu 2+ , 0.30 Pb 2+ , 0.89 Zn 2+ and 3% NaCl under both incubating conditions exopolymeric substances (EPS) produced by both strains showed a greater removal of all HMs (average percentages; 90.52-97.29) than their cells (average percentages; 14.02-75.03).

Mercury Pollution and Bioremediation—A Case Study on Biosorption by a Mercury-Resistant Marine Bacterium

“…Production of EPS and H 2 S assays followed by mercury removal assay confirms the mercury biosorption capability of the isolate, which is the sole cause of mercury resistance by the isolate. Due to greater potential for EPS secretion and biofilm formation, the Hg 21 could be entrapped in the bacterial exopolymeric substances (Braissant et al, 2007;Panwichian et al, 2011), thus not allowing Hg 21 to enter into the bacterial system and thereby conferring resistance to the bacterial isolate. Furthermore, the bacterial isolates, after their use in the contaminated environments, may be harvested and the adsorbed mercury may be extracted from them to be used as a raw material for further processing.…”

A comparative study of fatty acid profile and formation of biofilm inGeobacillus gargensisexposed to variable abiotic stress

“…The bacterial EPS is also a potential biosorbent for heavy metals from polluted water and environment. The entrapment is through the formation of complexes between EPS and heavy metals such as Cd(II); this leads to environmental bioremediation (Panwhichian et al 2011). Temperature, salinity, pH, and availability of oxygen are also important factors that facilitate the formation of EPS.…”

Removal of Cr (III) from model solutions and a real effluent by Phanerochaete chrysosporium isolated living microorganism: equilibrium and kinetics

“…Firstly, heavy metals can be removed by passive process or independent from cell activity (electrostatic bounding with cell surface). Secondly, heavy metals would be removed by bounding with exopolymeric substances which only occurs in viable body [26,27]. Therefore, maximum biomass concentration would occur at an optimal chromium level or maximum fungal tolerance to chromium toxicity.…”

“…Since in viable systems, the solute sorption rate is affected by the growth rate of microorganisms (leading to the production of exopolymeric substances) [27,32], determination of the optimal pH is needed and have been therefore investigated (Fig. 2).…”

“…In viable systems, adjusting the culture conditions is needed to provide essential nutrients to organism growth, since removal efficiency is related to both production of extracellular products and biomass concentration [27][28][29]. Since tanning effluents are deficient in nitrogen, some nitrogen sources were therefore tested for fungal growth and removal efficiency.…”