Environmental Engineering Reference
In-Depth Information
literature. From about 1960 to 1990, most studies reported that dealkylation of
the N-alkyl substituents on the s-triazine ring of atrazine was the major route
for bacterial metabolism (Shapir et al. 2007 ), whereas more recent reports
indicated that atrazine degradation by bacteria proceeds via dechlorination
to hydroxyatrazine, and not dealkylation. Despite this hopeful outlook, for the
first approximately 35 years of its use, there were no reports of the isolation of
a pure culture of a micro-organism that had the ability to completely minera-
lise atrazine to CO 2 and NH 4 . A large number of studies carried out from
the 1960s through the 1970s described the s-triazine herbicides in terms of
their biological properties, chemistry and herbicidal properties (Knusli & Gysin
1960 ; Knusli et al. 1969 ; Kaufman & Kearney 1970 ; Esser et al. 1975 ). In 1980,
Geller reported that the physical and chemical decomposition of atrazine was
likely more important than microbial degradation, even though microbes with
the ability to degrade atrazine are likely present in soils. This idea was widely
held for some time, and the formation of hydroxyl-s-triazine derivatives in
soils were thought to be due to abiotic processes. In the late 1980s, both Cook
( 1987 ) and Erickson and Lee ( 1989 ) each reported the identification of micro-
organisms that degraded the side chains of chlorinated triazines. Since these
microbes failed to dechlorinate atrazine before the molecule was dealkylated,
it was hypothesised that the presence of both alkyl side chains inhibited
dechlorination reaction. Fungi have also been reported to degrade s-triazine
compounds. Sporothrix schenckii has been shown to utilise cyanuric acid, biuret
and urea as sole nitrogen sources for growth (Zeyer et al. 1981 ), and the white
rot fungi Pleurotus pulmonarius and Phanerochaete chrysosporium have been
reported to degrade atrazine via N-dealkylation to deethylatrazine, deispropy-
latrazine and deethyldeisopropylatrazine (Masaphy et al. 1993 ) and hydroxya-
trazine (Lucas et al. 1993 ), respectively.
In 1995, Mandelbaum and co-workers reported the isolation of a pure bacterial
culture, Pseudomonas sp. strain ADP, with the ability to rapidly degrade atrazine
under aerobic, anoxic and non-growth conditions. Moreover, Pseudomonas ADP
used atrazine as a sole source of N for growth, and the organism completely
and very rapidly mineralized the s-triazine ring of atrazine. Interestingly, and
within a relatively short time, several other laboratories across the United States
and the world reported the isolation of pure bacterial cultures that could mine-
ralise atrazine (Mandelbaum et al. 1995 ; Radosevich et al. 1995 ; Yanze-Kontchou &
Gschwind 1995 ; Bouquard et al. 1997 ;Strutherset al. 1998 ). Since this time, other
taxonomically unique, gram-positive and gram-negative atrazine-degrading
bacteria ( Table 10.1 ) have been isolated worldwide (Topp et al. 2000a , b ;Rousseaux
et al. 2001 ;Stronget al. 2002 ;Caiet al. 2003 ; Piutti et al. 2003 ; Rousseaux et al.
2003 ; Devers et al. 2007 ). These results suggest that atrazine degradation ability
rapidly spread to a large number of genetically and geographically disparate
soil micro-organisms in a relatively short time frame.
Search WWH ::




Custom Search