Efficacy of soil-borne Enterobacter sp. for carbofuran degradation: HPLC quantitation of degradation rate.

Excessive use of pesticides in agricultural fields is a matter of great concern for living beings as well as the environment across the world, in particular, the third world countries. Therefore, there is an urgent need to find out an effective way to degrade these hazardous chemicals from the soil in an environment-friendly way. In the current project, a bacterial species were isolated through enrichment culture from carbofuran-supplemented rice-field soil and identified as a carbofuran degrader. The rate of carbofuran degradation by this bacterial species was evaluated using reverse-phase high-performance liquid chromatography (RP-HPLC), which confirmed the ability to utilize as a carbon source up to 4 µg/ml of 99% technical grade carbofuran. The morphological, physiological, biochemical characteristics and phylogenetic analysis of the 16S rRNA sequence showed that this strain belongs to the genus of Enterobacter sp. (sequence accession number LC368285 in DDBJ), and the optimum growth condition for the isolated strain was 37°C at pH 7.0. Moreover, an antibiotic sensitivity test showed that it was susceptible to azithromycin, penicillin, ceftazidime, ciprofloxacin, and gentamycin, and the minimal inhibitory concentration value of gentamycin was 400 µg/ml against the bacteria. It shows beyond doubt from the RP-HPLC quantification that the isolated bacterium has the ability to detoxify carbofuran (99% pure). Finally, the obtained results imply that the isolated strain of Enterobacter can be used as a potential and effective carbofuran degrader for bioremediation of contaminated sites through bioaugmentation.

Bioremediation of hexavalent chromium (VI) by a soil-borne bacterium, Enterobacter cloacae B2-DHA.

Chromium and chromium containing compounds are discharged into the nature as waste from anthropogenic activities, such as industries, agriculture, forest farming, mining and metallurgy. Continued disposal of these compounds to the environment leads to development of various lethal diseases in both humans and animals. In this paper, we report a soil borne bacterium, B2-DHA that can be used as a vehicle to effectively remove chromium from the contaminated sources. B2-DHA is resistant to chromium with a MIC value of 1000 µg mL(-1) potassium chromate. The bacterium has been identified as a Gram negative, Enterobacter cloacae based on biochemical characteristics and 16S rRNA gene analysis. TOF-SIMS and ICP-MS analyses confirmed intracellular accumulation of chromium and thus its removal from the contaminated liquid medium. Chromium accumulation in cells was 320 µg/g of cells dry biomass after 120-h exposure, and thus it reduced the chromium concentration in the liquid medium by as much as 81%. Environmental scanning electron micrograph revealed the effect of metals on cellular morphology of the isolates. Altogether, our results indicate that B2-DHA has the potential to reduce chromium significantly to safe levels from the contaminated environments and suggest the potential use of this bacterium in reducing human exposure to chromium, hence avoiding poisoning.

Isolation and characterization of a Lysinibacillus strain B1-CDA showing potential for bioremediation of arsenics from contaminated water.

The main objective of this study was to identify and isolate arsenic resistant bacteria that can be used for removing arsenic from the contaminated environment. Here we report a soil borne bacterium, B1-CDA that can serve this purpose. B1-CDA was isolated from the soil of a cultivated land in Chuadanga district located in the southwest region of Bangladesh. The morphological, biochemical and 16S rRNA analysis suggested that the isolate belongs to Lysinibacillus sphaericus. The minimum inhibitory concentration (MIC) value of the isolate is 500 mM (As) as arsenate. TOF-SIMS and ICP-MS analysis confirmed intracellular accumulation and removal of arsenics. Arsenic accumulation in cells amounted to 5.0 mg g(-1) of the cells dry biomass and thus reduced the arsenic concentration in the contaminated liquid medium by as much as 50%. These results indicate that B1-CDA has the potential for remediation of arsenic from the contaminated water. We believe the benefits of implementing this bacterium to efficiently reduce arsenic exposure will not only help to remove one aspect of human arsenic poisoning but will also benefit livestock and native animal species. Therefore, the outcome of this research will be highly significant for people in the affected area and also for human populations in other countries that have credible health concerns as a consequence of arsenic-contaminated water.