Bioaccumulation of fluoride from aqueous system and genotoxicity study on Allium cepa using Bacillus licheniformis.

Removal of fluoride (F-) was performed using a novel bacterium isolated from F- contaminated soil collected from Pappireddipatti block of Dharmapuri District in Tamil Nadu, India. Impact of changing variables for the removal of F- from synthetic medium at different concentrations of carbon and nitrogen sources (0.5, 1.0 and 1.5 g) was studied with bio inoculants of the bacterial strain (PPR8). The effects of different environmental parameters viz., pH (5.0-9.0) and temperature (25-45 °C) on the biosorption of F- biosorption were also evaluated. The strain PPR8 was identified as Bacillus licheniformis through 16S rRNA sequencing and phylogenetic analysis. Bioaccumulation of F- in the bacterial cells was confirmed by FTIR, SEM and TEM-EDAX and almost 97% of F- removal was established. To test the potential applicability of the bacterium, the bioreactor study was carried out with F- contaminated groundwater collected from the contaminated area. Furthermore, the treated and untreated F- contaminated waters were used to evaluate the genotoxicity on the root cells of onion (Allium cepa) by root tip assay. The experimental results proved that the significant removal of F- by Bacillus licheniformis PPR8 (KX646393) and it could be used as a potential adsorbent in removing F- from contaminated ground waters.

Microbial degradation, spectral analysis and toxicological assessment of malachite green by Streptomyces chrestomyceticus S20.

Malachite green (MG), a triphenylmethane dye is extensively used for coloring silk, aquaculture and textile industries, it has also has been reported toxic to life forms. This study aimed to investigate the biodegradation potential of MG by actinobacteria. The potent actinobacterial strain S20 used in this study was isolated from forest soil (Sabarimala, Kerala, India) and identified as Streptomyces chrestomyceticus based on phenotype and molecular features. Strain S20 degraded MG up to 59.65 ± 0.68% was studied in MSM medium and MG (300 mg l-1) and degradation was increased (90-99%) by additions of 1% glucose and yeast extract into the medium at pH 7. The treated metabolites from MG by S20 characterized by FT-IR and GC-MS. The results showed MG has been degraded into nontoxic compounds evaluated by (1) phytotoxic assay on Vigna radiata, (2) microbial toxicity on Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Streptococcus sp. and Escherichia coli, (3) cytotoxicity assay in a human cell line (MCF 7). The toxicity studies demonstrated that the byproducts from MG degradation by S. chrestomyceticus S20 were no toxic to plants and microbes and less toxic to human cells as compared to the parent MG. Perhaps this is the first work reported on biodegradation of MG by S. chrestomyceticus which could be a potential candidate for the removal of MG from various environments.

Redox transformation and biogeochemical interaction of heavy metals in Korean soil using different treatment columns in the presence of Shewanella sp.

The redox transformation and biogeochemical interactions of heavy metals in soil was examined using facultative anaerobic bacterium Shewanella sp. (HN-41) in batch mode and with small scale columns. A preliminary study was carried out to determine the influence of various glucose concentrations (10, 20 and 30 mM) on the bacterial growth and releasing of heavy metals from soil using a defined medium. The results showed that the heavy metals were released tremendously in the medium supplemented with 30 mM glucose. Therefore, 30 mM glucose was used as the sole carbon source for further studies. Then, the dissolution and redox transformation of heavy metals were studied using small scale columns. Bacterially enriched synthetic water with and without glucose and soil organic matter, such as humic acid (HA) and anthraquinone-2,6-disulphonate (ADQS), were supplied to each column. Among the treatments in the column, the dissolution and redox transformation of heavy metals was highest in the synthetic water supplemented with glucose and ADQS. The efficiency was relatively low without the organic substrates and bacterial inoculum. These results clearly show that the addition of electron donor (glucose) and electron shuttles (ADQS) assists a maximum transformation of heavy metals from soil/sediment.

Desorption and dissolution of heavy metals from contaminated soil using Shewanella sp. (HN-41) amended with various carbon sources and synthetic soil organic matters.

Heavy metals in soil are considered a major environmental problem facing many countries around the world. Contamination of heavy metals occurs in soil due to both anthropogenic and natural causes. During the last two decades, extensive attention has been paid to the management and control of soil contamination. Decontamination of heavy metals in the soil has been a challenge for a long time. Microbial solubilization is one of promising process for remediation of heavy metals from contaminated sites. In this study, we attempted to treat soil contaminated with heavy metals using a facultative anaerobic bacterium Shewanella sp. (HN-41). The effect of carbon sources on the dissolution and conversion of heavy metals was first investigated using a defined medium containing 1 g of highly contaminated soil to select the most effective carbon source. Among three carbon sources, namely glucose, acetic acid and lactic acid, glucose at 10 mM was found to be the most effective. Therefore, glucose was used as a representative carbon source for the second part of the biological treatment in the defined medium, amended with humic acid (HA) and anthraquinone-2,6-disulfonate (ADQS), respectively. Among the heavy metals, iron and manganese exhibited the highest dissolution efficiency in the medium supplemented with glucose at 10mM. The rates of dissolution and removal of heavy metals were little bit higher in the medium amended with humic acid and ADQS. Per these results outlined above, a combined system of humic acid and ADQS incorporated with glucose was found to be effective for the removal of heavy metals from soil.

Nitrate removal efficiency of bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) in synthetic nitrate-rich water.

The efficiency of bacterial isolates to reduce nitrate from synthetic nitrate-rich water was tested using a batch scale process. Two efficient nitrate reducing bacterial species were isolated from water samples collected from Kodaikanal and Yercaud lakes. Bacterial analysis of the samples revealed the presence of nitrate reducing bacteria belonging to the genera Pseudomonas, Bacillus, Micrococcus and Alcaligenes. Among the isolates, the consortium of Pseudomonas sp. KW1 and Bacillus sp. YW4 was found to be efficient in nitrate reduction. Influences of various carbon sources, incubation temperature and pH on nitrate reduction from synthetic wastewater were also studied. The results showed a rapid and efficient process of nitrate removal (99.4%) from synthetic wastewater supplemented with starch (1%), inoculated by bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) at incubation temperature of 30 degrees C at pH 7. This observation has led to the conclusion that the bacterial consortium was responsible for nitrate removal from synthetic nitrate-rich wastewater.

Two-stage removal of nitrate from groundwater using biological and chemical treatments.

In this study, we attempted to treat groundwater contaminated with nitrate using a two-stage removal system: one is biological treatment using the nitrate-degrading bacteria Pseudomonas sp. RS-7 and the other is chemical treatment using a coagulant. For the biological system, the effect of carbon sources on nitrate removal was first investigated using mineral salt medium (MSM) containing 500 mg l(-1) nitrate to select the most effective carbon source. Among three carbon sources, namely, glucose, starch and cellulose, starch at 1% was found to be the most effective. Thus, starch was used as a representative carbon source for the remaining part of the biological treatment where nitrate removal was carried out for MSM solution and groundwater samples containing 500 mg l(-1) and 460 mg l(-1) nitrate, respectively. About 86% and 89% of nitrate were removed from the MSM solution and groundwater samples, respectively at 72 h. Chemical coagulants such as alum, lime and poly aluminium chloride were tested for the removal of nitrate remaining in the samples. Among the coagulants, lime at 150 mg l(-1) exhibited the highest nitrate removal efficiency with complete disappearance for the MSM solutions. Thus, a combined system of biological and chemical treatments was found to be more effective for the complete removal of nitrate from groundwater.