|Van Berkum, Peter|
Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2006
Publication Date: 4/22/2007
Citation: Van Berkum, P.B., Abou-Shanab, R.I., Angle, J.S. 2007. Chromate-tolerant bacteria for enhanced metal uptake by eichhornia crassipes (mart.). International Journal of Phytoremediation. v. 9. p.91-105. Interpretive Summary: Soil close to plant roots is referred to as the rhizosphere, and is especially suited for bacteria because it is rich in nutrients. The problem is that very little is known about plant-microbe interactions in the rhizosphere. This interaction was investigated by determining genomic variation of bacteria in the rhizosphere of water hyacinth and by measuring bacterial effects on chromium uptake by the plant. Although the precise identity of the rhizosphere bacteria was not possible they were shown to be genetically diverse. Variation also was found in resistance to the metal chromium in the form of chromate salts. Growing plants in the presence of the bacteria that were resistant to the metal was shown to lead to enhanced levels of chromate in the roots compared to plants growing without bacteria. This result would imply an importance of these bacteria in bioremediation, which is cleaning the environment of toxic metal pollutants. This information will be used further to identify these bacteria in order to learn whether they are related to other important bacteria found in the rhizosphere such as rhizobia. Also, the results may be used in the development of approaches to remove toxic metals from polluted environments. Therefore, this information is useful for scientists working to decontaminate soils, bacterial population geneticists and bacterial taxonomists.
Technical Abstract: A total of 85 chromate-resistant bacteria were isolated from the rhizosphere of water hyacinth grown in Mariout Lake, Egypt, as well as the sediment and water of this habitat. Only 4(11%), 2(8%), and 2(8%) of isolates from each of the environments, respectively, were able to tolerate 200 mg Cr(VI) L-1. When tested for their ability to tolerate other metals or to reduce chromate, six isolates (RA1, RA2, RA3, RA5, RA7 and RA8) were resistant to Zn, Mn, and Pb, and displayed different degrees of chromate reduction (42% to 95%) under aerobic conditions. These 6 isolates were genetically diverse as demonstrated by RAPD analysis using four different primers. Water hyacinth inoculated with RA5 and RA8 increased Mn accumulation in roots by 2.4- and 1.2- fold, compared to uninoculated controls. The highest concentrations of Cr (0.4g kg-1) and Zn (0.18g kg-1) were accumulated in aerial portions of water hyacinth inoculated with RA3. Plants inoculated with RA1, RA2, RA3, RA5, RA7 and RA8 had 7, 11, 24, 29, 35, 21-fold, higher Cr concentrations in roots compared to the control, respectively. These bacterial isolates are potential candidates in phytoremediation for chromium removal.