Optimisation of culture composition for glyphosate degradation by Burkholderia vietnamiensis strain AQ5-12

Abstract

The herbicide glyphosate is often used to control weeds in agricultural lands. However, despite its ability to effectively kill weeds at low cost, health problems are still reported due to its toxicity level. The removal of glyphosate from the environment is usually done by microbiological process since chemical process of degradation is ineffective due to the presence of highly stable bonds. Therefore, finding glyphosate-degrading microorganisms in the soil of interest is crucial to remediate this glyphosate. Burkholderia vietnamiensis strain AQ5-12 was found to have glyphosate-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time (OFAT) and response surface methodology (RSM). Five parameters including carbon and nitrogen source, pH, temperature and glyphosate concentration were optimised. Based on OFAT result, glyphosate degradation was observed to be optimum at fructose concentration of 6, 0.5 g/L ammonia sulphate, pH 6.5, temperature of 32 °C and glyphosate concentration at 100 ppm. Meanwhile, RSM resulted in a better degradation with 92.32% of 100 ppm glyphosate compared to OFAT. The bacterium was seen to tolerate up to 500 ppm glyphosate while increasing concentration results in reduced degradation and bacterial growth rate.

Keywords: Bioremediation; Burkholderia vietnamiensis; Glyphosate; One-factor-at-time (OFAT); Response surface methodology (RSM).

Fig. 1

Effects of different carbon source on biodegradation of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis isolate AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 2

Effects of different fructose concentration on biodegradation of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 3

Effects of nitrogen source on biodegradation of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 4

Effects of different ammonia sulphate concentrations on biodegradation of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 5

Effects of pH on bacteria growth (filled blue circle, red square, black diamond) and biodegradation (open blue circle, red square, black diamond) of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Acetate buffer (filled blue circle, open blue circle), Tris (filled red square, open red square), Tris–HCl (filled black diamond, open black diamond). Error bars represent mean ± standard deviation (n = 3)

Fig. 6

Effects of temperature on biodegradation of 50 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 7

Effects of glyphosate concentration on biodegradation of glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 8

Similarity plot between predicted and actual value for free cells of Burkholderia vietnamiensis strain AQ5-12

Fig. 9

Response surface 3D plot showing the effect of pH and carbon concentration on glyphosate degradation. Value variable temperature, nitrogen and glyphosate concentration remained constant

Fig. 10

Effects of higher fructose concentration on biodegradation of 100 ppm glyphosate by resting cells of Burkholderia vietnamiensis strain AQ5-12. Error bars represent mean ± standard deviation (n = 3)

Fig. 11

Validation of experiment (RSM) conducted to ascertain the optimum solution obtained through the conduct of the experiment. Error bars represent mean ± standard deviation (n = 3)