Phytotoxicity alleviation by bacterial species isolated from polycyclic aromatic hydrocarbons (PAHs) contaminated sites

The increasing industrialization has led to a high accumulation of xenobiotic contaminants in the natural environments. Most frequently, such pollutants include petroleum hydrocarbons (PHCs), polycyclic aromatic hydrocarbons (PAHs), halogenated hydrocarbons, agrochemicals, solvents, heavy metals and salts; among all of them, PAHs are particularly hazardous for their toxicity, mutagenic and carcinogenic potential, since they also feature a very high potential of accumulation in several food chains. Although several remediation techniques based on physical and chemical processes have been developed, the biological approach seems to be the most promising, since it very often allows the complete removal of the xenobiotics from the environment. In this work, the cultivable microbial community has been isolated from PAHs polluted soils and each individual strain has been tested for its ability to grow on both naphthalene and phenanthrene. Out of forty-seven isolates, two bacterial strains able of growing on the xenobiotics were found (T1 and W1) and the 16S rDNA was sequenced. The potential ability of both T1 and W1 to alleviate phytotoxicity symptoms was assessed by running an ecotoxicity test, using Lepidium sativum as indicator plant. Interestingly, both T1 and W1 alleviated the naphthalene-induced phytotoxicity in cress plants, whilst their contributions were not effective when plants were exposed to the highest concentrations of phenanthrene. In conclusion, our data highlighted that both the plants sensitivity to PAHs and the microbial ability to degrade xenobiotics are strongly dependent on either plant or bacterial species and on the xenobiotic molecule. In addition, considering the plant growth promotion traits displayed by T1 and W1, the isolated bacterial strains might represent a promising tool to possibly enhance the plant fitness, even in xenobiotic contaminated soils.