Behaviour of bacterial populations isolated from rhizosphere of Diplachne fusca dominant in industrial sites

A total of 107 bacterial strains were isolated from rhizosphere soil of Diplachne fusca naturally grown in industrial metal-contaminated soils. All the isolates were examined for their ability to tolerate Cd²⁺, Cr ³⁺, Co²⁺, Cu²⁺, Pb²⁺, Ni ²⁺ and Zn²⁺ in their growth medium, in addition, three related phenotypic characters, the ability to produce acids and siderophores and/or calcium phosphate solubilization, were tested. The resistance patterns, expressed as MICs, for all bacterial isolates to seven different metal ions were surveyed by using the agar dilution method. A great proportion of the isolates were resistant to Cr (99%), Pb (93%), Cu (87%) and Zn (86%). On the other hand, 77, 49 and 45% were sensitive to Co, Ni and Cd, respectively. The majority of the strains tested (98%) were multiple metal-resistant, with hexametal resistance as the major pattern (24.2%). The increase in metal ion uptake (especially Cr, Pb, Zn and Ni) by D. fusca was correlated with higher numbers of siderophore-producing, phosphate-solubilizing and acid-producing bacteria 95, 81 and 64%, respectively.