Degradation of chlorinated benzoic acid mixtures by plant–bacteria associations

Abstract

Abstract-Phytoremediation technologies must tolerate and degrade mixtures of contaminants, as most contaminated sites contain mixtures of compounds. This study assessed the ability of plant-bacteria associations to degrade mixtures of mono-and dichlorinated benzoic acids. Sixteen forage grasses and combinations of these grasses with several bacterial inoculants were screened for growth in soil contaminated with various concentrations of mono-or dichlorinated benzoic acids. Dahurian wild rye (Elymus dauricus) inoculated with a combination of Pseudomonas aeruginosa strain R75 and Pseudomonas savastanoi strain CB35 reduced 3-chlorobenzoic acid (3CBA) levels in soil by 74% (i.e., 583 to 149 mg/kg). Meadow brome (Bromus biebersteinii) inoculated with Alcaligenes sp. strain BR60 reduced 2,3-dichlorobenzoic acid (23diCBA) levels in soil by 56% (i.e., 125 to 55 mg/kg). Altai wild rye (Elymus angitus) inoculated with strains R75 and CB35 reduced 2,5-dichlorobenzoic acid (25diCBA) levels in soil by 46% (i.e., 211 to 113 mg/kg). Two plant-bacteria associations and uninoculated Dahurian wild rye also degraded mixtures of 3CBA, 23diCBA, or 25diCBA. When 25diCBA was mixed with 23diCBA, uninoculated Dahurian wild rye reduced levels of 25diCBA in soil by 31% and reduced the levels of both 25diCBA and 3CBA by up to 64% when these two contaminants were present in a mixture. Similarly, meadow brome inoculated with BR60 reduced 23diCBA and 3CBA levels by up to 50%. Levels of all three chlorinated benzoic acids were reduced by 53 to 63% by Altai wild rye inoculated with strains R75 and CB35. Our results indicate that plant-bacteria associations can tolerate and degrade mixtures of contaminants in soil but that predictions about phytoremediation of mixed contaminants may not be straightforward.

Selection of Specific Endophytic Bacterial Genotypes by Plants in Response to Soil Contamination

“…Phytoremediation systems that use microbial inoculants are typically more effective than noninoculated plant systems (2,8,11,33). This work examined one of the mechanisms, i.e., root interior colonization, that may be occurring to explain the increased success of plant-bacterial associations in degrading contaminants.…”

“…Plants can stimulate contaminant disappearance by accumulation and transformation (30), by extracellular transformation (13,37) and by stimulating microbial degradative activity in the rhizosphere (3,35). Several authors have investigated the role of microorganisms in phytoremediation, and they have found that certain plant-bacterial associations can increase degradation (1,8,11,33). This suggests that, under certain circumstances, such as in microbially inoculated plants, microorganisms play an important role in phytoremediation systems, but it is not clear what role they play in phytoremediation systems having only indigenous microbial populations.…”

Bioremediation of Chlorobenzoic Acids

“…BR60 remove 56% of 2,3-CBA from the soil and the same consortium was able to metabolize 61% of 2,3-CBA and 50% of 3-CBA if both CBAs were added together. A consortium consisting of Elymus angitus and strains Pseudomonas aeruginosa R75 and Pseudomonas savastanoi CB35 eliminate 46% of 2,5-CBA from soil and from the mixture of 3-CBA, 2,3-CBA and 2,5-CBA this consortium has removed around 40% of all three CBAs from soil [99]. These results were obtained by testing a large number of combinations of grasses with bacterial inoculants.…”

Phytoremediation of Organic Contaminants in Soil and Groundwater

“…phenols, l-carvone, pcymene) in root exudates and dead roots can induce dioxygenase enzymes in microorganisms that degrade polychlorinated biphenyls (PCBs) [58] and other chlorinated organic compounds. [59,60] Salicylic acid (2-hydroxybenzoic acid), which is an intermediate of the naphthalene degradation pathway [61] but also is exuded by plants roots, [62] was shown to be used as a carbon source by Pseudomonas putida [63] and to sustain the density of naphthalene-degrading Pseudomonas strains. [64] Salicylic acid enhanced the initial rates of removal of fluoranthene, pyrene, benz[a]anthracene, chrysene, and benz[a]pyrene in a strain of Pseudomonas saccharophila P15 by inducing PAH dioxygenase activity.…”