Biosorption of cadmium by a Cd2+-hyperresistant Bacillus cereus strain HQ-1 newly isolated from a lead and zinc mine

Recent advances in bacterial biosensing and bioremediation of cadmium pollution: a mini-review

Cadmium (Cd) pollution has become a global environmental issue because Cd gets easily accumulated and translocated in the food chain, threatening human health. Considering the detrimental effects and non-biodegradability of environmental Cd, this is an urgent issue that needs to be addressed through the development of robust, cost-effective, and eco-friendly green routes for monitoring and remediating toxic levels of Cd. This article attempts to review various bacterial approaches toward biosensing and bioremediation of Cd in the environment. This review focuses on the recent development of bacterial cell-based biosensors for the detection of bioavailable Cd and the bioremediation of toxic Cd by natural or genetically-engineered bacteria. The present limitations and future perspectives of these available bacterial approaches are outlined. New trends for integrating synthetic biology and metabolic engineering into the design of bacterial biosensors and bioadsorbers are additionally highlighted.

Remediation of Cd, Pb and as Co-contaminated Paddy Soil by Applying Different Amendments

The current study investigated the efficiency of sepiolite (SE), sodium humate (HS), microbial fertilizer (JF) and SE combined with JF/HS in a ratio of 2:1 (w/w) (JF-2SE and HS-2SE) on Cd, Pb and As bioavailability in field trials with rice (Oryza sativa L.). The results showed that all the amendments remarkably decreased (p < 0.05) the contents of available Cd and available Pb in soil. Only JF-2SE treatment reduced available As concentration in soil. All the amendments were found to effectively reduce (p < 0.05) the contents of As in brown rice. Both JF-2SE and HS-2SE co-applications reduced the concentrations of Cd in brown rice to 0.108 and 0.135 mg kg^-1, and that of Pb reduced to 0.2 and 0.175 mg kg^-1, which met the national standard limit of China. Thus, the co-application of JF/HS-2SE can be a promising remediation strategy in Cd, Pb and As co-contaminated paddy soil.

Bioadsorption and biostabilization of cadmium by Enterobacter cloacae TU

Biostabilization of cadmium, a hazardous chemical found widely in China, was attempted using Enterobacter cloacae TU (E.cloacae TU). A cadmium (Cd)-tolerant E.cloacae TU was obtained by mutagenesis using an atmosphere pressure glow discharge plasma system, and it displayed regular growth behavior in the presence of 250 mg/L Cd in solution. The maximum stabilization capacity of E.cloacae TU toward Cd reached 67.0 ± 3.5 mg/g dry cell weight at an initial Cd concentration of 200 mg/L. The percentage of Cd removal by E.cloacae TU reached 97.4± 0.3% at an initial Cd concentration of 20 mg/L. A desorption experiment confirmed both extracellular adsorption and intracellular uptake contribute to biostabilization, although Cd was mainly distributed on the surface of E.cloacae TU cells due to over-secretion of extracellular polysaccharides under Cd stimulus. The changes in morphology and functional groups of the E.cloacae TU cell surface in the presence of Cd were analyzed using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Fourier Transform Infrared Spectoscopy (FT-IR). The feasibility of using E.cloacae TU for this purpose was further confirmed by on site remediation, in which the application of E.cloacae TU reduced the bioavailability and moreover the accumulation of Cd in tobacco plants without affecting the quality of flue-cured tobacco.

Biosorption of nickel by Lysinibacillus sp. BA2 native to bauxite mine

The current scenario of environmental pollution urges the need for an effective solution for toxic heavy metal removal from industrial wastewater. Bioremediation is the most cost effective process employed by the use of microbes especially bacteria resistant to toxic metals. In this study, Lysinibacillus sp. BA2, a nickel tolerant strain isolated from bauxite mine was used for the biosorption of Ni(II). Lysinibacillus sp. BA2 biomass had isoelectric point (pI) of 3.3. The maximum negative zeta potential value (-39.45) was obtained at pH 6.0 which was highly favourable for Ni(II) biosorption. 238.04mg of Ni(II) adsorbed on one gram of dead biomass and 196.32mg adsorbed on one gram of live biomass. The adsorption of Ni(II) on biomass increased with time and attained saturation after 180min with rapid biosorption in initial 30min. The Langmuir and Freundlich isotherms could fit well for biosorption of Ni(II) by dead biomass while Langmuir isotherm provided a better fit for live biomass based on correlation coefficient values. The kinetic studies of Ni(II) removal, using dead and live biomass was well explained by second-order kinetic model. Ni(II) adsorption on live biomass was confirmed by SEM-EDX where cell aggregation and increasing irregularity of cell morphology was observed even though cells were in non-growing state. The FTIR analysis of biomass revealed the presence of carboxyl, hydroxyl and amino groups, which seem responsible for biosorption of Ni(II). The beads made using dead biomass of Lysinibacillus sp. BA2 could efficiently remove Ni(II) from effluent solutions. These microbial cells can substitute expensive methods for treating nickel contaminated industrial wastewaters.

Bioaccumulation characterization of zinc and cadmium by Streptomyces zinciresistens, a novel actinomycete

The bioaccumulation characteristics of Zn(2+) and Cd(2+) by a novel species, Streptomyces zinciresistens CCNWNQ0016(T), were investigated. S. zinciresistens accumulated Zn(2+) and Cd(2+) mainly on the cell wall followed by intracellular accumulation. The mycelium was deformed, aggregated and formed precipitate of zinc and cadmium on the cell surface. Electron dense granules were detected on the cell wall as well as within the cytoplasm. The amino, carboxyl, hydroxyl and carbonyl groups were responsible for the biosorption of Zn(2+) and Cd(2+). The Langmuir isotherm model fitted the experimental data of metals adsorption processes better than Freundlich isotherm model. Cu(2+) and Cr(3+) competed for adsorption sites on the cell surface with Zn(2+) and Cd(2+). 87.33% and 98.11% recovery of Zn(2+) and Cd(2+), respectively, could be obtained at pH≤2 from metal-loaded biomass of S. zinciresistens desorption.

Biosorption of nickel(II) from aqueous solution by Aspergillus niger: response surface methodology and isotherm study

In the present study, the effects of biosorbent Aspergillus niger dosage, initial solution pH and initial Ni(II) concentration on the uptake of Ni(II) by NaOH pretreated biomass of A. niger from aqueous solution were investigated. Batch experiments were carried out in order to model and optimize the biosorption process. The influence of three parameters on the uptake of Ni(II) was described using a response surface methodology (RSM) as well as Langmuir and Freundlich isotherm models. Optimum Ni(II) uptake of 4.82 mg Ni(II)g(-1) biomass (70.30%) was achieved at pH 6.25, biomass dosage of 2.98 gL(-1) and initial Ni(II) concentration of 30.00 mgL(-1) Ni(II). Langmuir and Freundlich were able to describe the biosorption isotherm fairly well. However, prediction of Ni(II) biosorption using Langmuir and Freundlich isotherms was relatively poor in comparison with RSM approaches. The biosorption mechanism was also investigated by using Fourier transfer infrared (FT-IR) analysis of untreated, NaOH pretreated, and Ni(II) loaded A. niger biomass.

Bioremediation of diesel oil in a co-contaminated soil by bioaugmentation with a microbial formula tailored with native strains selected for heavy metals resistance

The aim of the work is to assess the feasibility of bioremediation of a soil, containing heavy metals and spiked with diesel oil (DO), through a bioaugmentation strategy based on the use of a microbial formula tailored with selected native strains. The soil originated from the metallurgic area of Bagnoli (Naples, Italy). The formula, named ENEA-LAM, combines ten bacterial strains selected for multiple resistance to heavy metals among the native microbial community. The biodegradation process of diesel oil was assessed in biometer flasks by monitoring the following parameters: DO composition by GC-MS, CO2 evolution rate, microbial load and composition of the community by T-RFLP, physiological profile in Biolog ECOplates and ecotoxicity of the system. The application of this microbial formula allowed to obtain, in the presence of heavy metals, the complete degradation of n-C(12-20), the total disappearance of phenantrene, a 60% reduction of isoprenoids and an overall reduction of about 75% of the total diesel hydrocarbons in 42 days. Concurrently with the increase of metabolic activity at community level and the microbial load, the gradual abatement of the ecotoxicity was observed. The T-RFLP analysis highlighted that most of the ENEA-LAM strains survived and some minor native strains, undetectable in the soil at the beginning of the experiment, developed. Such a bioaugmentation approach allows the newly established microbial community to strike a balance between the introduced and the naturally present microorganisms. The results indicate that the use of a tailored microbial formula may efficiently facilitate and speed up the bioremediation of matrices co-contaminated with hydrocarbons and heavy metals. The study represents the first step for the scale up of the system and should be verified at a larger scale. In this view, this bioaugmentation strategy may contribute to overcome a critical bottleneck of the bioremediation technology.