Optimisation on biodegradation of glyphosate by locally isolated bacteria
N-Phosphonomethylglycine (glyphosate) is often used to control weeds in agriculture land. In Malaysia alone, thousands of tonnes of glyphosate formulation is used annually. Although this low-cost herbicide is able to effectively in killing weeds, its extensive use has been negatively linked to...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Online Access: | http://psasir.upm.edu.my/id/eprint/75631/1/FBSB%202018%2034%20IR.pdf http://psasir.upm.edu.my/id/eprint/75631/ |
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| Summary: | N-Phosphonomethylglycine (glyphosate) is often used to control weeds in agriculture
land. In Malaysia alone, thousands of tonnes of glyphosate formulation is used annually.
Although this low-cost herbicide is able to effectively in killing weeds, its extensive use
has been negatively linked to the human health due to its toxicity. Moreover, many past
studies have reported its negative effects on aquatic animals and vertebrates. Thus, there
is a need for an eco-friendly method to manage this environmental contaminant.
Furthermore, it is crucial to find glyphosate-degrading microorganisms in the soil of
interest for local applications. The objective of this study is to isolate local glyphosatedegrading
bacteria and optimisation of culture medium condition to improve the
degradation rate. Two bacteria isolated from agriculture site located in Kedah, Malaysia
were identified by physical, biochemical and 16S rRNA sequencing techniques as
Burkholderia vietnamiensis strain AQ5-12 and Burkholderia sp. strain AQ5-13. These
strains were found with the ability to tolerate up to 12 mL/L Roundup concentration and
were successfully used to degrade glyphosate. Factors affecting glyphosate
biodegradation such as carbon and nitrogen sources, pH of the medium, glyphosate
concentration and temperature were optimised using one factor at time (OFAT) and
response surface method (RSM) using free cells. Initial free cells of strain AQ5-12 and
AQ5-13 were able to degrade 79.7% and 40.67% of 50 ppm glyphosate, respectively,
within 24 h incubation. Using these optimisation processes, free cells of AQ5-12 were
able to degrade 94% of 100 ppm glyphosate, whereas strain AQ5-13 degraded 94% of
50 ppm glyphosate under optimal condition. The results illustrated fructose at 8.62 g/L,
ammonium sulphate at 0.5 g/L, pH 5.41, 100 ppm of glyphosate concentration and 32ºC
as the optimum biodegradation conditions required by Burkholderia vietnamiensis strain
AQ5-12, whereas the optimum biodegradation conditions for Burkholderia sp. strain
AQ5-13 were sucrose at 8.0 g/L, ammonium sulphate at 0.5 g/L, pH 6.0, 50 ppm of
glyphosate concentration and temperature at 32ºC. The optimised condition for free cells
resulted in significant improvement in degradation rate. The bacteria were immobilised
in gellan gum gelling agent with its conditions optimised. The results presented a
degradation rate of 87.2% 100 ppm glyphosate with gellan gum concentration of 0.55 g,
285 number of beads and bead size of 0.48 cm for immobilised cells of AQ5-12.Meanwhile, immobilised cells of AQ5-13 illustrated a degradation rate of 96.68% 50
ppm glyphosate with gellan gum concentration of 0.55 g, 280 number of beads and bead
size of 0.45 cm. It was seen that immobilised form of bacteria showed better
biodegradation in terms of duration as it degrades the glyphosate within 12 h compared
to free cells that require 24 h degradation process in optimised media. In conclusion,
these strains possess the potential of being used in the management of glyphosate
contamination. Furthermore, the success of isolating bacteria from local soils in Malaysia
has shown prominent ability in glyphosate degradation rate, which can be applied for
glyphosate treatment in agricultural land. |
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