Assessment of plant growth promoting rhizobacteria (PGPR) on potential biodegradation of glyphosate in contaminated soil and aquifers

Abstract

Glyphosate [N-(phosphonomethyl)-glycine] is a broad-spectrum non-selective herbicide that is commonly used to control perennial weeds in agriculture. Glyphosate losses to the environment are undesirable because of possible environmental hazards – e.g. soil and water contamination. It is important to develop methods for enhancing glyphosate degradation and elimination in soil and water. Microbes play a crucial role in degrading organic contaminants. Hence, the capabilities of glyphosate degrading microorganisms in soil and water could effectively be used as a sustainable solution for glyphosate contamination. Two bacterial isolates, Pseudomonas sp., Bacillus sp. and mixed culture of Pseudomonas sp. and Bacillus sp. were isolated by using constituted basal medium from the long-term glyphosate exposed rice field. Following the same isolation technique mixed culture of native forest soil bacteria was also isolated. Isolated microorganisms capable of degrading glyphosate were used in four treatments and tested for their abilities to utilize glyphosate at different concentrations of 50, 100, and 150 mg/ml. The utilization of glyphosate by the isolates was studied by monitoring their biomass production in a basal medium containing glyphosate by spectrophotometry at 660 nm wavelength. The rate of glyphosate degradation in the medium by these isolates was also studied by assessing the remaining glyphosate concentration in the medium at 265 nm wavelength. The results revealed that Pseudomonas sp., Bacillus sp., and the mix of both organisms showed significant growth at low concentrations and degrade glyphosate efficiently. Further, it was emphasized that the Pseudomonas sp. and Bacillus sp. mix of approximately 1.5 × 108 (CFU/ml), which was isolated soil from a glyphosate contaminated field, capable of degrading glyphosate even at high concentrations (150 mg/ml) of glyphosate additions. It was evident that the bacterial isolates tested can be used as effective bioremediating agents for treating glyphosate contaminated soils and aquifers.