Screen Of Pb-resistant Psychrotrophic Bacteria And Its Characterization Of Pb²⁺ Biosorption

With the rapid development of industrialization,a massive amount of industrial wastes containing heavy metals are discharged,resulting in a serious environmental problem.Among all the existing remediation approaches for dealing with heavy metal contamination,microbial remediation technology has been aroused widespread concern due to a low energy consumption,high effiency and environment friendliness.Nevertheless,wastewater containing lead?Pb?is treated inefficiently by microbial remediation method using mesophilic microorganism under cold condition.It is of great importance to find a way to treat Pb contaminated water under low temperature condition.In the current study,several Pb-resistant psychrotrophic bacteria were isolated from soil of Mohe wetland.The strain that possesses the best selectivity on the adsorption for Pb among all the isolated Pb-resistant bactetial strains was selected as the research target.The different performances of Pb²⁺ biosorption between living and nonliving biosorbents were analyzed and the coresponding mechanisms of Pb²⁺ adsorption were also investigated.To further improve the adsorption ability of bacterial strain for Pb²⁺,an effective salt was selected to modify the cell wall by affecting the functional groups on the cell wall during its growth period,thus enhancing the biosorption of Pb²⁺.The experimental results are as follows:Four Pb-resistant psychrotrophic bacteria screened from the soil of Mohe wetland are termed as I3,I4,I9 and I10.Preliminary study indicated that strain I3 had the best selectivity on the adsorption for Pb among those four isolates.Therefore,bacterial strain I3 was selected for further investigations.Morphological and molecular identification results showed that strain I3 was phylogenetically close to the members of the genus Pseudomonas with a 99% 16 S rRNA gene sequence identity.The minimum inhibitory concentration?MIC?of strain I3 for Pb²⁺ was 7.5 mM,which was 5-fold higher than the reference strain Escherichia coli DH5?,indicating that Pseudomonas sp.I3 was well tolerant to Pb²⁺.Acid digestion results proved that intracellular Pb accumulation was mainly contributed to the distinct performance between living and non-living biosorbents,which was further confirmed by the analyses of TEM-EDS.The results of MIC and acid digestion also showed that there was no direct relationship between biosorption ability of bacteria and their metal-resistance.Results of FTIR revealed that functional groups including –CH2,C=O,C–N,N–H,–COO and –SO3 were participated in the biosorption process of the tested biosorbents no matter whether bacteria were living or not.The optimum adsorption conditions were as follows: pH 5.0,temperature 15 ?,biomass concentration 0.5 g/L,initial concentration of Pb²⁺ 50 mg/L,The equilibrium time of living and nonliving biosorbents were 120 and 30 min.The equilibrium data for living and non-living biosorbents were well fitted to Langmuir model,which represented monolayer adsorption.The kinetic data for each biosorbent were well described by pseudo-second order kinetic model,indicating that the rate control step in Pb²⁺ biosorption mechanism of the living and non-living biomass was the chemical interactions between functional groups on the surface of biosorbent and Pb²⁺ ion.Pseudomonas sp.I3 seemed to be an effective biosorbent for cleansing Pb²⁺ from contaminated wastewater at low temperature.The reagent K₂SO₄ was successfully screened to improve the adsorption capacity of strain I3 for Pb²⁺.Bacterial biomass collected from salt modified LB medium with supplementation of 30 g/L K₂SO₄ was assigned as KSI3-30.The adsorption capacity of KSI3-30 to Pb²⁺ was 62.89 mg/g at 15 ?,and the adsorption capacity increased by 42.35% compared with the control group.This stimulation effect was ascribed to the increase of potassium and sulfur containing groups on KSI3-30 surface via metabolic dependent ways,which was confirmed by the analyses of SEM-EDS.Results of FTIR and XPS revealed that functional groups including N–H/N–C,C?N,C?O,O?C–O,C–O/–OH and –SO3 were participated in the biosorption of Pb²⁺.The probable mechanisms for Pb²⁺ adsorption were ion-exchange and chemical complexation.The optimum adsorption conditions were as follows: pH 5.0,initial concentration of Pb²⁺ 50 mg/L,the equilibrium time was 30 min.Good recyclability and effectively dealing with real wastewater under low temperature suggested KSI3-30 was a promising biosorbent for Pb-contaminated wastewater treatment.