VOLATILIZATION MERCURY (II) INTO MERCURY (0) USING CRUDE ENZYME PRODUCED BY A MERCURY–RESISTANT AZOTOBACTERIA

Abstract

Mercury was poisonous and hazardous heavy metal, even one genus bacteria of
Azotobacter was able to grow in a mercury contaminated habitat. This research aim
was to select potential mercury resistant Azotobacter which was able to produce an
extracellular mercury reductase for reducing toxic ion Hg2+ into a volatile less toxic
ion Hg0. The isolates were A1a, A5 and A9 from an urban farming soil in ITS. Their
viability under mercury stress was tested individually in an Azotobacter-selective
agar each containing 0.1; and 5 mg/L HgCl2. The 24-hours bacterial growth was
spectrophotometrically determined at λ600 nm each hour. The crude extracellular
mercury reductase produced under 5mg/L dan 10mg/L HgCl2 stress was then
extracted followed general method. The enzyme activity was spectrophotometrically
measured at 340 nm to detect soluble oxidized NADH in a defined medium for a
mercury reductase assay after 12 hours incubation. The viability test showed that
those 3 isolates had a similar growth curve pattern; all of them were growing under
0.1; and 5 mg/L HgCl2, even after 12 hours incubation time they were start dying.
Anyhow isolate A1a was the slowest growing Azotobacter under particular mercury
stress. Enzyme activity tended to decrease over time; isolates A5 and A9 showed a
greater enzyme activity than isolate A1a. Under 5mg/L HgCl2 stress, after 30, 60 and
120 minutes, isolate A5 and A9 produced 2.50U, 1.15U and 0.60U enzyme
respectively, while under 10mg/L HgCl2 they were 2.70U, 1.44U and 0.7U.