Chromate-tolerant bacteria for enhanced metal uptake by Eichhornia crassipes (MART.)

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 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 from 42% to 95%, (RA1, RA2, RA3, RA5, RA7, and RA8) were genetically diverse according to RAPD analysis using four different primers. 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, compared to uninoculated controls. The highest concentrations of Cr (0.4 g kg-1) and Zn (0.18 g 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-, and 21-fold, respectively, higher Cr concentrations in roots compared to the control. These bacterial isolates are potential candidates in phytoremediation for chromium removal.