International Journal of Phytoremediatioll, 9:91-105, 2007 Copyright © Taylor & Francis Group, LLC ISSN: 1522-6514 print/ 1549-7879 online 001: 10.1080/15226510701232708 '0 Taylor & Francis ToIyk>r&FrancisGroup CHROMATE-TOLERANT BACTERIA FOR ENHANCED METAL UPTAKE BY E/CHHORN/A CRASS/PES (MART.) R. A. I. Abou-Shanab Environmental Biotechnology Department, Genetic Engineering and Biotechnology Research Institute, Mubarak City for Scientific Research, Borg El-Arab, Alexandria, Egypt J. S. Angle College of Agricultural and Environmental Sciences, University of Georgia, Athens, Georgia, USA P. van Berkum USDA-ARS, Beltsville, Maryland, USA A total of85 chromate-resistantbacteria were isolatedfrom the rhizosphere of waterhyacinth 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 these eight isolates were tested for their ability to tolerate other metals or to reduce chromate, they were shown to also be resistant to Zn, Mn, and Pb, and to display different degrees of chromate reduction (28% to 95%) under aerobic conditions. The isolates with the higher chromate reduction rates jrom42% to 95%, (RA1, RA2, RA3, RA5, RA7, and RA8) were genetically diverse according to RAPD analysisysing four differentprimers. Bacterial isolates RA1, RA2, RA3, RA5, and RA8 had 16 S rRNA gene sequences that were most similar to Pseudomonas diminuta, Brevundimonas diminuta, Nitrobacteria irancium, Ochrobactrum anthropi, and Bacillus cereus, respectively. Water hyacinth inoculated with RA5 and RA8 increased Mn accumulation in roots by 2.4- and 1.2- fold, respectively, comparedto uninoculatedcontrols. The highestconcentrations ofCr (0.4 g kg- 1 ) and Zn (0.18 g kg- 1 ) were accumulated in aerial POrtiOllS of waterhyacinth inoculated with RA3. Plants inoculated with RAJ, RA2, RA3, RA5, RA7, and RA8 had 7-, 11-,24-,29-, 35-, and 21-fold, respectively, higher Cr concentrations in roots compared to the control. These bacterial isolates are potential candidates in phytoremediationfor chromium removal. KEY WORDS: rhizofiltration, chromate reduction, rhizosphere, bacteria, metal tolerance, water hyacinth INTRODUCTION Contamination of aquatic environments by toxic metal ions is a serious pollution problem. Metals cannot be easily degraded and cleanup usually requires chemical or Address correspondence to R. A. 1. Abou-Shanab, Environmental Biotechnology Department, Genetic Engineering and Biotechnology Research Institute, Mubarak City for Scientific Research, Borg El-Arab, Alexandria, Egypt. E-mail: redaabushanab@yahoo.com 91