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Tellurite (TeO3(2-)) is the most toxic and soluble oxyanion among tellurium (Te) compounds. The effects of the metalloid anion on the oxidative stress response of the obligate aerobe Pseudomonas pseudoalcaligenes KF707 were investigated. Cells treated with sub-lethal concentrations of TeO3(2-) showed neither adaptation to it nor cross-protection against oxidants such as 1,1'-4,4'-bipyridinium dichloride (paraquat, PQ2+), diazenedicarboxylic acid bis-N,N-dimethylamide (diamide), tert-butyl hydroperoxide (tBH) and hydrogen peroxide (H2O2). Notably, TeO3(2-) exerted a synergic effect on the toxicity of these latter oxidants. Tellurite was shown to decrease the cellular content of reduced thiols (RSH) with a consequent increase in the production of reactive oxygen species (ROS) and stimulation of the superoxide dismutase (SOD) activity. However, since the time course of ROS production by TeO3(2) (t1/2 > 30 min) was much slower than that with PQ2+ and/or diamide (t1/2

The susceptibility to various biocides was examined in planktonic cells and biofilms of the obligate aerobe, PCBs degrader, Pseudomonas pseudoalcaligenes KF707. The toxicity of two antibiotics, amikacin and rifampicin, three metalloid oxyanions (AsO2 −, SeO3 2−, TeO3 2−) and three metal cations (Cd2+, Ni2+, Al3+) was tested at two stages of the biofilm-development (4 and 24 h) and compared to planktonic cells susceptibility. Mature biofilms formed in rich (LB, Luria–Bertani) medium were thicker (23 μm) than biofilms grown in minimal (SA saccarose-arginine) medium (13 μm). Early grown (4 h) SA-biofilms, which consisted of a few sparse/attached cells, were 50–100 times more resistant to antibiotics than planktonic cells. Conversely, minor changes in tolerance to metal(loid)s were seen in both SA- and LB-grown biofilms. In contrast to planktonic cells, no reduction of TeO3 2− to elemental Te(0) or SeO3 2− to elemental Se(0) was seen in KF707 biofilms. The data indicate that: (a) metal tolerance in KF707 biofilms, under the growth and exposure conditions described here, is different than antibiotic tolerance; (b) KF707 planktonic cells and biofilms, are almost equally susceptible to killing by metal cations and oxyanions, and (c) biofilm-tolerance to TeO3 2− and SeO3 2− is not linked to metalloid reduction; this means that KF707 planktonic cells and biofilms differ in their physiology and strategy to counteract metalloid toxicity.