Factors affecting immobilization of heavy metals by purple nonsulfur bacteria isolated from contaminated shrimp ponds

Abstract

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 use of selected purple nonsulfur bacteria to remove heavy metals and salts from sediment and water collected from contaminated areas to decrease their phytotoxicity

“…A ten percent inoculum of each active isolate was grown in Glutamate-Malate medium (GM medium) as previously described by Panwichian et al (2010a) under microaerobic-light conditions (3000 lux). Culture broths were harvested in the log phase of growth because previously it had been established that this was the most effective time for them to remove HMs (Panwichian et al, 2010b). After centrifugation (Sorvall RC 5C Plus, Du-pont, Delaware, USA) at 9,300 x g for 15 min, the cell pellets were washed twice with 0.1% peptone water.…”

“…The sets of HMs solution without inoculating with bacterial cells were used as abiotic controls. The optimum conditions for removing HMs by each culture was adopted from one of our previous studies (Panwichian et al, 2010b) as follows; 4.5 mg DCW/ml, pH 6.0, 30°C, 30 min for strain NW16 and 5.0 mg DCW/ml, pH 5.5, 35°C, 45 min for strain KMS24. The mixed culture consisted of 2.5 mg DCW/ml of each culture and it was tested at both the optimal conditions for removal of HMs by strains NW16 and KMS24.…”

“…Cell suspensions were shaken in an incubator at a speed of 150 rpm for 30 to 45 min under aerobic-dark conditions. Aerobic-dark conditions were also used because they provided a higher efficiency for removal of HMs when compared to microaerobic-light conditions (Panwichian et al, 2010b). Cell suspensions were centrifuged, and the remaining HMs in each supernatant was analyzed using ICP-OES.…”

“…The uptakes of HMs and salts by biomass of both PNSB strains were conducted under both microaerobic-light and aerobic-dark conditions due to both incubating conditions having an effect on the efficiency of HMs removal by PNSB (Panwichian et al, 2010b). The cells of NW16 and KMS24 present as a suspension of either a pure or mixed culture were added into the collected water samples that had been sterilized (autoclaving at 121°C, 15 min) and not sterilized (native set).…”

“…The exposure time for binding between HMs and cells was short between 30 and 45 min, so biosorption was likely to be the main mechanism for removing HMs (no energy requirement). This biosorption may require many passive processes such as adsorption, covalent bond formation, complexation, chelation, ion exchange and microprecipitation (Panwichian et al, 2010b;Ahluwalia and Goyal, 2007). However, some bioaccumulation (requiring energy) of HMs by PNSB cells was possible (Panwichian et al, 2010b).…”