The isolation and characterization of arsenic-tolerant endophytes and the potential role of biofilms in arsenic tolerance

Abstract

The prevalence and persistence of arsenic pollution is a health and ecological issue of global concern. Conventional engineering techniques (e.g., excavation and capping) have proven be effective at remediating the most highly contaminated sites, but the high cost has limited their use. Phytoremediation presents an opportunity to expand the reach of conventional remediation in a low-cost, environmentally friendly manner. Improving the phytoremediation of arsenic contaminated soils requires reducing phytotoxicity and increasing uptake and translocation of the arsenic into the harvestable tissues. Endophytes, microorganisms colonizing the internal tissues of plants, could provide an effective way to improve phytoremediation outcomes. Beneficial endophytes reduce phytotoxicity in the host plant through improving nutrient acquisition, producing phytohormones, suppressing pathogens, and reducing the host plant stress response. These benefits are well described in the literature, and their effect on plant tolerance has been demonstrated in a wide range of applications. Additionally, endophytes may improve phytoremediation outcomes by directly interacting with the arsenic through various mechanisms such as adsorption, sequestration, chelation, or precipitation. The endophytes, Pseudomonas PD9R and Rahnella PD12R, were isolated from native plants growing on arsenic-contaminated soils, and both strains showed tolerance to arsenate (AsV) and arsenite (AsIII). It was also observed that both strains produced extracellular polymeric substances (EPS) when exposed to arsenic. Biofilms, consisting of microorganisms embedded in a matrix of extracellular polymeric substances (EPS), are a common defense mechanism against various biotic and abiotic stresses, including toxic metals. This investigation looked at the role of endophytic biofilms in arsenic tolerance as a potential direct mechanism by which endophytes might improve phytoremediation outcomes.