No 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).

In order to remove heavy metals (HMs) from contaminated shrimp pond at the highest concentrations found of; 0.75 mg/l Cd 2? , 62.63 mg/l Pb 2? , 34.60 mg/l Cu 2? and 58.50 mg/l Zn 2? , two strains of purple nonsulfur bacteria isolated from shrimp ponds (NW16 and KMS24) were investigated for their ability to immobilize HMs in 3% NaCl in both microaerobic-light and aerobic-dark conditions. Based on metabolic inhibition and metabolic-dependent studies, it was concluded that both strains removed HMs using biosorption and also bioaccumulation. The efficiency of removal by both strains with both incubating conditions tested was in the order of lead (Pb) [ copper (Cu) [ zinc (Zn) [ cadmium (Cd). Optimal conditions for removal of HMs by strain NW16 were; cells in the log phase at 4.5 mg DCW/ml, pH 6.0, and 30°C for 30 min. With microaerobic-light conditions, the relative percent removal of HMs was: Pb, 83; Cu, 59; Zn, 39; Cd, 23 and slightly more with the aerobic-dark conditions (Pb, 90; Cu, 69; Zn, 46; Cd, 28). Cells in the log phase at 5.0 mg DCW/ml, pH 5.5, and 35°C for 45 min were optimal conditions for strain KMS24 and there were no significant differences for the removal percentages of HMs with either incubating conditions (averages: Pb, 96; Cu, 75; Zn, 46; Cd, 30). The presence of Ca 2? and Mg 2? significantly decreased the removal capacity of HMs for both strains.

The potential of the purple nonsulfur bacteria (PNSB), NW16 and KMS24, to remove heavy metals (HMs) and salts was investigated in a synthetic solution (62.63 Pb 2+ , 34.60 Cu 2+ , 58.5 Zn 2+ and 0.75 Cd 2 mg/L) containing 3% NaCl, sediment, and water collected from contaminated post cultured shrimp ponds and seed germination of 2 plants were used to assay their plant toxicities after bioremediation. Both light metal ions (85 mg/L Ca 2+ and 160 mg/L Mg 2+ to the synthetic HMs solution) significantly decreased the HMs removal efficiency and the mixed culture gave the highest efficiency to remove HMs (removal percentages; 85 Pb 2+ , 74 Cu 2+ , 47 Zn 2+ and 28 Cd 2+). The best set for the treatment of contaminated water from shrimp ponds (Cu 2+ , Zn 2+ ; 0.043, 0.057 mg/L and salinity, 10.23% 0) under the conditions of aerobicdark and microaerobic-light was a set of native with added mixed culture with a decrease of roughly 75, 31 and 77% for Cu 2+ , Zn 2+ and salinity, respectively. For the sediment samples, a set of native with added mixed culture also produced the highest efficiency to remove HMs (initial concentrations in mg/kg dry weight; 23.15 Pb 2+ , 15.05 Cu 2+ , 22.16 Zn 2+ and 0.29 Cd 2+) and salinity (0.84% 0) under aerobicdark conditions with the removal percentages of HMs; 84.29, 62.52, 43.33 and 40.95, and 100% salinity. Consequently, this set produced the most effective treatment as the germination index was 34.50 and 35.29% for rice seed (Oryza sativa) and water spinach (Ipomoea aquatic) respectively in the treated water and 115.70 and 139.33% for rice and water spinach respectively in the treated sediment.