Glyphosate is an agricultural herbicide with usage in the amounts of thousands of tonnes per year
in Malaysia. In certain soils, glyphosate can persist for months and its removal through
bioremediation is the most economical and practical. A previously isolated glyphosate-degrading
bacterium showed substrate inhibition to the degradation rate. Important degradation inhibition
constants can be reliably obtained through nonlinear regression modelling of the degradation rate
profile using substrate inhibition models such as Luong, Yano, Teissier-Edward, Aiba, Haldane,
Monod and Han and Levenspiel models. The Aiba model was chosen as the best model based on
statistical tests such as root-mean-square error (RMSE), adjusted coefficient of determination
(adjR2), bias factor (BF) and accuracy factor (AF). The calculated values for the Aiba-Edwards
constants qmax (the maximum specific substrate degradation rate (h−1), Ks (concentration of
substrate at the half maximal degradation rate (mg/L) and Ki (inhibition constant (mg/L)) were
131±34, 4446±2073, and 24323±5094, respectively. Novel constants obtained from the
modelling exercise would be useful for further secondary modelling implicating the effect of
media conditions and other factors on the degradation of glyphosate by this bacterium.
Commercialisation of glyphosate [N-(phosphonomethyl)glycine] in the early 1970s has left a big leap in the agriculture sector. This is due to its effectiveness in controlling a wide range of weeds. Glyphosate translocates well in plants. In addition, with added surfactant in its formulae, it can also be used in wet conditions. Its ability to kill weeds by targeting the 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS) makes no competing herbicide analogs in its class. Considering its cost effectiveness, only small amount is needed to cover a large sector in agricultural land. The most important aspect in the success of glyphosate is the introduction of transgenic, glyphosate-resistant crops in 1996. However, glyphosate is not an environmental friendly herbicide. This systematic herbicide has raised environmental concern due to its excessive use in agriculture. Studies have shown traces of glyphosate found in drinking water. Meanwhile, it's rapid binding on soil particles possesses adverse effect to soil organisms. Glyphosate degradation in soil usually carried out by microbial activity. Microbes’ capable utilising glyphosate mainly as phosphate source. However, the activity of C-P lyase in breaking down glyphosate have not clearly understood. This review presents a collective summary on the understanding on how glyphosate works and its environmental fate.
Isolate JR1 was isolated from the polluted textile industry activities site in the Juru Penang area.
This bacterium was characterized as a gram-positive Bacillus bacterium and also gave a
positive biochemical test for catalase test and oxidase test. The isolate JR1 gave a maximum
decolourization of Amaranth dye under static conditions with the rate of decolorization of
98.82%. Seven variables which are pH, temperature (°C), ammonium acetate (g/L), glucose
(g/L), sodium chloride (g/L), yeast (g/L) and dye concentration (ppm) was run by using
Plackett-Burman design for the effective parameter of the decolourization of Amaranth. From
the seven variables, three effective variables which were ammonium acetate, glucose, and dye
concentration were further optimized by using a central composite design. The optimum value
of ammonium acetate concentration at 0.74 g/L, glucose concentration at 3.0 g/L and a dye
concentration at 58.1 ppm gave the highest percentage of decolourization. Thus, this isolate
could provide an alternate solution in removing toxic dyes from environments.
The issue of heavy metal contamination and toxic xenobiotics has become a rapid global
concern. This has ensured that the bioremediation of these toxicants, which are being carried out
using novel microbes. A bacterium with the ability to reduce molybdenum has been isolated
from contaminated soils and identified as Serratia marcescens strain DR.Y10. The bacterium
reduced molybdenum (sodium molybdate) to molybdenum blue (Mo-blue) optimally at pHs of
between 6.0 and 6.5 and temperatures between 30°C and 37°C. Glucose was the best electron
donor for supporting molybdate reduction followed by sucrose, adonitol, mannose, maltose,
mannitol glycerol, salicin, myo-inositol, sorbitol and trehalose in descending order. Other
requirements include a phosphate concentration of 5 mM and a molybdate concentration of
between 10 and 30 mM. The absorption spectrum of the Mo-blue produced was similar to the
previously isolated Mo-reducing bacterium and closely resembles a reduced phosphomolybdate.
Molybdenum reduction was inhibited by Hg (ii), Ag (i), Cu (ii), and Cr (vi) at 78.9, 69.2, 59.5
and 40.1%, respectively. We also screen for the ability of the bacterium to use various organic
xenobiotics such as phenol, acrylamide, nicotinamide, acetamide, iodoacetamide, propionamide,
acetamide, sodium dodecyl sulfate (SDS) and diesel as electron donor sources for aiding
reduction. The bacterium was also able to grow using amides such as acrylamide, propionamide
and acetamide without molybdenum reduction. The unique ability of the bacterium to detoxify
many toxicants is much in demand, making this bacterium a vital means of bioremediation.