The putative phosphate transporter PitB (PP1373) is involved in tellurite uptake in Pseudomonas putida KT2440

Abstract

Tellurium oxyanions are chemical species with great toxicity; their presence in the environment has increased because of mining industries and photovoltaic and electronic waste. Recovery strategies based on microorganisms for this metalloid are of interest, but further studies of the transport systems and enzymes responsible for implementing tellurium transformations are required because many mechanisms remain unknown. Here, we investigated the involvement in tellurite uptake of the putative phosphate transporter PitB (PP1373) in soil bacterium Pseudomonas putida KT2440. For this purpose, through a method based on the CRISPR/Cas9 system, we generated a strain deficient in pitB gene and characterized its phenotype on exposing it to varied concentrations of tellurite. Growth curves and Transmission Electronic Microscopy experiments of wild type and ΔpitB showed that both strains were able to internalize tellurite into the cytoplasm and reduce the oxyanion to black nano-sized and rod-shaped tellurium particles, however, ΔpitB strain showed an increased resistance to the tellurite toxic effects. At a concentration of 100 uM tellurite, where the biomass formation of wild type strain decreased by half, we observed a greater ability of ΔpitB to reduce this oxyanion with respect to wild type strain (~38% vs ~16%), which is related by the greater biomass production of ΔpitB and not by a greater consumption of tellurite per cell. The phenotype of the mutant was restored on over-expressing pitB in trans. In summary, our results indicate that PitB is one of several transporters responsible for tellurite uptake in P. putida KT2440.

The potential of Pseudomonas for bioremediation of oxyanions

“…Furthermore, a previous report by Sanchez-Romero et al (1998) demonstrated that a recombinant strain of P. putida KT2440 transformed with tellurite resistance (Tel R ) plasmids or transposons can grow in potassium tellurite concentrations up to 315 μM, proving that tel resistance genes can be used as selection markers for manipulating Pseudomonas strains. In addition, it was recently reported (Montenegro et al, 2021) that in this bacterium the unspecific putative phosphate transporter (PitB) is involved in tellurite uptake, however, it is suspected that P. putida can use other transporters for this process (Montenegro et al, 2021). The same study confirmed the reduction of tellurite and the formation of black nano-sized and rod-shaped tellurium particles after culturing the bacterium for 24 h with 100 μM of tellurite although the mechanism of the reduction is unknown (Montenegro et al, 2021).…”

“…obtain elemental metals (or even nanoparticles) by the reduction of oxyanions (Avendaño et al, 2016;P aez-Espino et al, 2020;Montenegro et al, 2021). Thus, we propose Pseudomonas as an adequate biotechnological chassis for the recovery of metals and metalloids, which are naturally scarce but have been recently in high demand due to their use in electronic devices.…”

“…Particularly, P. aeruginosa and P. putida strains show a great diversity of plasmids belonging to the P incompatibility group conferring resistance to tellurite (Suzina et al, 1995;Summers and Jacoby, 1997). It has been proposed that tellurite enters the cell through the phosphate transport system (Montenegro et al, 2021). However, recent reports also suggest that the mercury transmembrane transporter (MerC) may be involved in tellurite uptake (Rodríguez-Rojas et al, 2016).…”

“…putida can use other transporters for this process (Montenegro et al ., 2021). The same study confirmed the reduction of tellurite and the formation of black nano‐sized and rod‐shaped tellurium particles after culturing the bacterium for 24 h with 100 μM of tellurite although the mechanism of the reduction is unknown (Montenegro et al ., 2021).…”

“…The ability of Pseudomonas to survive oxidative stress due to the harsh conditions found in its natural niches, in combination with the high quantity of oxidoreductases, makes this bacterium a sturdy microorganism for oxyanion bioremediation and metal/metalloid recovery. Previous studies have demonstrated its intrinsic ability to obtain elemental metals (or even nanoparticles) by the reduction of oxyanions (Avendaño et al ., 2016; Páez‐Espino et al ., 2020; Montenegro et al ., 2021). Thus, we propose Pseudomonas as an adequate biotechnological chassis for the recovery of metals and metalloids, which are naturally scarce but have been recently in high demand due to their use in electronic devices.…”