Use of plant growth-promoting bacteria to enhance chromium phytoremediation by Salvinia biloba

Heavy metals, such as chromium (Cr), are toxic even at low concentrations and are a significant environmental concern. Phytoremediation is an emerging biotechnological method to clean contaminated environments, using plant biomass to absorb and accumulate contaminants. To enhance the phytoremediation capacity, plant growth-promoting bacteria (PGPB) have been proposed as a strategy. This study aimed to evaluate the effect of PGPB isolated from sediment samples of the Paraná River Delta (Argentina) on the phytoremediation of Cr by Salvinia biloba , a floating macrophyte native to the region.The plants were exposed to 1, 3, and 5 ppm of Cr, exhibiting phytotoxicity characterized by turgor loss, which resulted in an increased vegetation cover; however, the photosynthetic pigment content remained unaffected at these concentrations. The total Cr concentration decreased by 32%, 26%, and 21% in the 1, 3, and 5 ppm treatments, respectively, while hexavalent chromium (Cr(VI)) was reduced by 82%, 45%, and 33%.Three microorganisms exhibiting the highest plant growth-promoting activity were selected, as they positively impacted plant growth and tolerated different Cr(VI) concentrations. To assess the effect of PGPB on the phytoremediation process, inoculated S. biloba plants were exposed to 5 ppm of Cr(VI). Notably, inoculation with microorganism ER-Y, identified as Serratia nematodiphila , a previously reported PGPB, enhanced plant growth in contaminated systems. Furthermore, inoculation significantly increased vegetation cover compared to the uninoculated control; however, unlike the increase observed in uninoculated plants, this expansion was not due to turgor loss but rather to actual plant growth stimulated by the PGPB under Cr(VI) exposure. Additionally, ER-Y contributed to an almost 9% greater Cr(VI) reduction compared to the uninoculated group, highlighting its potential role in improving both plant resilience and remediation efficiency.