Bacterial swimming, swarming and chemotactic response to heavy metal presence: which could be the influence on wastewater biotreatment efficiency?

Fixed-bed reactors are usually designed for wastewater biotreatments, where the biofilm establishment and maintenance play the most important roles. Biofilm development strictly relies on different types of bacterial motility: swimming, swarming, and chemotaxis, which can be altered by the microenvironment conditions. The aim of this work is to do an integrated study on the effects of Cu(II), Cd(II), Zn(II) and Cr(VI) on swimming, swarming and chemotaxis of Pseudomonas veronii 2E, Delftia acidovorans AR and Ralstonia taiwanensis M2 to improve biofilm development and maintenance for metal loaded wastewater biotreatment in fixed-bed bioreactors. Swimming, swarming and chemotactic response evaluation experiments were carried out at different metal concentrations. P. veronii 2E motility was not affected by metal presence, being this strain optimal for fixed-bed reactors. D. acidovorans AR swarming was inhibited by Cd and Zn. Although R. taiwanensis M2 showed high resistance to Cu, Cd, Cr and Zn, motility was definitively altered, so further studies on R. taiwanensis M2 resistance mechanisms would be particularly interesting.