Page 30 - Volume 6, Issue 2, July 2013

Bempelou

et al.

78

yl maleate and piperonyl butoxide (one in a

time), no significant inhibition (<5%) was ob-

served in the development of their cultiva-

tions. Therefore 10 μg/mL of each enzymat-

ic inhibitor was added in the 250 mL flasks

of the biodegradation trials. As it was ob-

served after 10 days of incubation, triphenyl

phosphate did not affect the biodegrada-

tion of diazinon by

Rh. glutinis

and

Rh. rubra

and similar results were produced after the

addition of piperonyl butoxide. On the con-

trary, diethyl maleate substantially inhibit-

ed the biodegradation rate of diazinon. Af-

ter the end of the experiment 92.2% of the

initial concentration of diazinon was recov-

ered. These results enforced the above pre-

liminary statements that GSTs are involved

in the biodegradation of diazinon by the

two epiphytic yeasts.

Biodegradation pathway

The biodegradation of diazinon by the

epiphytic yeasts

Rh. glutinis

and

Rh. rubra

is

attributed to the cleavage of the parent moi-

ety by the action of the enzymes of gluta-

thione- S- transferases and the conjugation

of glutathione with the leaving group. The

conjugate is afterwards hydrolyzed and the

metabolite 2-isopropoyl-6-methyl-4-pyrim-

idinol (IMP) is produced (Figure 6).

Biodegradation of diazinon on tomato

fruits

The biodegradation of diazinon by the

yeasts

Rh. glutinis

and

Rh. rubra

in tomato

fruits is shown in Table 2. Obviously the de-

crease of diazinon in the treated samples is

much higher in comparison with the con-

trol. In control samples diazinon showed a

Figure 4.

Effect of temperature in the biodegradation of diazinon by the yeasts

Rhodotorula glutinis

and

Rhodotorula rubra

,

after the incubation of the microorganisms with 10 μg/mL diazinon in 15°C, 25°C and 35°C, respectively.