Rhizosphere metagenome analysis and wet-lab approach to derive optimal strategy for lead remediation in situ

The Environmental Protection Agency (EPA) reports a significant number of heavy metal-contaminated sites across the United States. To address this public health concern, rhizoremediation using microbes has emerged as a promising solution, considering the limitations and inefficiencies of current approaches. We hypothesized that if Pseudomonas fluorescens, Burkholderia vietnamiensis, and Rhizobium leguminosarum are cultivated in the rhizospheres (area around the plant roots) of Brassica juncea, Oryza sativa, or Pisum sativum in lead-contaminated soil, then a significant reduction in soil-lead content should be observed. To determine the most effective soil microbe, we obtained raw sequences of 16s rRNA from 96 soil samples from the National Center for Biotechnology Information and processed the sequences through Qiime2 to examine bacterial taxonomy in lead-contaminated and uncontaminated rhizospheres. A combination of soil microbes – P. fluorescens, B. vietnamiensis, and R. leguminosarum – were inoculated in the rhizosphere of B. juncea, O. sativa, and P. sativum in soil contaminated with 500 parts per million (ppm) of lead. Soil lead content was measured at various stages of plant growth. After four weeks, we noticed a 70% decline in the lead content with P. fluorescens-B. juncea combination and a 90% decline with P. fluorescens-R. leguminosarum-B. vietnamiensis triple combination with B. juncea. Chlorophyll content analysis of the dried leaves of plant groups showed similar optical density to control leaves, indicating that lead decontamination in the soil did not negatively affect plant health. Therefore, rhizoremediation is an effective bioremediation strategy and may increase crop productivity by converting nonarable lands into arable lands.