Bacterially Induced Weathering of Ultramafic Rock and Its Implications for Phytoextraction

Abstract

The bioavailability of metals in soil is often cited as a limiting factor of phytoextraction (or phytomining). Bacterial metabolites, such as organic acids, siderophores, or biosurfactants, have been shown to mobilize metals, and their use to improve metal extraction has been proposed. In this study, the weathering capacities of, and Ni mobilization by, bacterial strains were evaluated. Minimal medium containing ground ultramafic rock was inoculated with either of two Arthrobacter strains: LA44 (indole acetic acid [IAA] producer) or SBA82 (siderophore producer, PO 4 solubilizer, and IAA producer). Trace elements and organic compounds were determined in aliquots taken at different time intervals after inoculation. Trace metal fractionation was carried out on the remaining rock at the end of the experiment. The results suggest that the strains act upon different mineral phases. LA44 is a more efficient Ni mobilizer, apparently solubilizing Ni associated with Mn oxides, and this appeared to be related to oxalate production. SBA82 also leads to release of Ni and Mn, albeit to a much lower extent. In this case, the concurrent mobilization of Fe and Si indicates preferential weathering of Fe oxides and serpentine minerals, possibly related to the siderophore production capacity of the strain. The same bacterial strains were tested in a soil-plant system: the Ni hyperaccumulator Alyssum serpyllifolium subsp. malacitanum was grown in ultramafic soil in a rhizobox system and inoculated with each bacterial strain. At harvest, biomass production and shoot Ni concentrations were higher in plants from inoculated pots than from noninoculated pots. Ni yield was significantly enhanced in plants inoculated with LA44. These results suggest that Ni-mobilizing inoculants could be useful for improving Ni uptake by hyperaccumulator plants.

Determining soil enzyme activities for the assessment of fungi and citric acid-assisted phytoextraction under cadmium and lead contamination

“…Microorganisms can produce organic acids such as fumaric acid, succinic acid, lactic acid, malic acid, and citric acid in their metabolic processes (Tsao et al 1999). These microbial metabolites have the potential to alleviate the heavy metal stress on many soil enzyme activities by mobilizing heavy metals that can then be easily removed by plants (Becerra-Castro et al 2013;Braud et al 2009). Addition of citric acid can also enhance heavy metal availability by chelation, and high heavy metal availability is one of the key factors to increase the uptake of metals in the hyperaccumulator.…”

The Characteristics of Phytoremediation of Soil and Leachate Polluted by Landfills

“…Soil metal bioavailability is often cited as a limiting factor in phytoextraction (or phytomining). Bacterial metabolites such as organic acids, siderophores, and bio surfactants have been shown to mobilize metals, and the use of microbial inoculants to improve metal extraction has been proposed by several authors [20].…”

Phytoremediation of Heavy Metals: The Use of Green Approaches to Clean the Environment

“…Similarly, the biomass production and shoot Ni concentrations in Alyssum serpyllifolium subsp. malacitanum was found to be higher when inoculated with two bacterial strains LA44 and SBA82 of Arthrobacter than non-inoculated plants (Becerra-Castro et al 2013 ). The phytoextraction effi ciency can also be affected by fungicidal sprays, soil pH, planting density, and cropping period Simmons et al 2014 ).…”