Role of microbes in phytoremediation

Environmental remediation can be accomplished using various types of microbes, whether bacteria, algae or fungus.

Use of bacteria to remediate selenium-contaminated wastewater: The salt-tolerant bacteria we identified in a solar evaporation pond in the San Joaquin Valley, CA had several important applications. The bacteria could be used to: 1) bioaugment evaporation ponds to increase selenium (Se) removal, 2) remediate agricultural drainage water in a bioreactor, and 3) provide a reservoir of genes (for potential incorporation into plants) encoding enzymes facilitating tolerance to extremely high concentrations of Se and salt.

Use of microalgae to remediate Se-contaminated wastewater: In our pursuit of microbes capable of Se phytoremediation, we found a microalga (Chlorella sp.) that was able to volatilize Se at rates that were orders of magnitude higher than those previously obtained with higher plants. The Chlorella cultures reduced 87% of accumulated selenate to organic forms within 24 hours, dramatically better than higher plants which reduce selenate at much slower rates.

Use of root-associated bacteria to cleanup zinc/cadmium contaminated soil: Bacteria associated with plant roots can play important roles in the accumulation of toxic metals or metalloids by plants. Because of the considerable amount of interest in hyperaccumulator plants (discussed above), we investigated the possibility that root-associated microbes might be involved in the hyperaccumulation process of the well-known zinc and cadmium hyperaccumulator, Thlaspi caerulescens. This plant species accumulates zinc to concentrations greater than 10 mg Zn g-1 shoot dry weight without any symptoms of toxicity. The physiological and biochemical basis of this enhanced capacity to accumulate heavy metals was thought to reside strictly within the plant. However, researchers from our laboratory showed that bacteria were necessary to facilitate the solubilization of zinc from non-labile soils.