The copper-resistant bacterium ACU isolated from the rhizosphere of Eichhornia crassipes (Mart.) increased the endurance of Potamogeton crispus L. to copper toxicity.

Aims: This study aimed to develop endurance to copper stress in Potamogeton crispus L. by inoculation with the anti-copper strain ACU - a novel Enterobacteriaceae bacterium isolated from the rhizosphere of Eichhornia crassipes with high copper-removal ability. Methods and Results: A spherical copper-resistant bacterium, namely ACU, was isolated from the rhizosphere of E. crassipes. It was demonstrated to have substantial copper-removing capability, even at copper concentrations as high as 69 mg l(-1). The 16S rRNA gene sequence of ACU suggested it to be a novel Enterobacteriaceae bacterium most closely related to Providencia sp. With increasing copper concentrations, the growth rate of ACU gradually decreased with a delay in the logarithmic growth phase. ACU demonstrated high copper-removal ability at the lag phase when cultivated in media with high copper concentrations. A 48-kDa extracellular copper-binding protein was detected in ACU. When P. crispus was inoculated with ACU, the growth ability of P. crispus significantly improved at all the tested copper concentrations, and the lethal time for 10 mg l(-1) was delayed. Further study revealed that while ACU cells were rarely detected in the culture solution, they were associated with the surface of P. crispus. These findings indicated that ACU grew by anchoring itself on the surface of P. crispus and could increase the ability of P. crispus to resist copper toxicity. Conclusion: To the best of our knowledge, the Enterobacteriaceae bacterium ACU is a novel nonpathogenic bacterium with high copper-removing ability from water. Significance and Impact of the Study: This study demonstrated that the Enterobacteriaceae bacterium ACU has potential applicability for use in copper removal and in the protection of aquatic plants in copper-polluted water.