2017). A recent study has characterized the strain FA-HZ1 from waste water. It has
been demonstrated that during DF degradation several biodegradation intermediates
are formed and the conversion of DF to 1,2-dihydroxy-1,2-dihydrodibenzofuran
requires a novel enzyme called HZ6359 dioxygenase (Fawad et al. 2019).
14.8 Biodegradation of Dibenzofuran
Cunninghamella elegans and Beijerinckia (B8/36, a mutant strain) can oxidize DF to
2,3-dihydroxy-2,3-dihydrodibenzofuran (Cerniglia et al. 1979). The bacterial metabolite thus formed was extremely unstable. It can be converted into a mixture of 2and 3-hydroxydibenzofuran in the presence of acid rapidly. Contrary to this, C.
elegans formed a stable 2,3-dihydroxy-2,3-dihydrodibenzofuran intermediate. This
intermediate can yield 2- and 3-hydroxydibenzofuran only under acidic conditions.
The contrary results are due to formation of cis- and trans-isomers of 2,3-dihydroxy2,3-dihydrodibenzofuran by Beijerinckia B8/36 and C. elegans, respectively. Also,
C. elegans oxidizes dibenzofuran to 2-hydroxydibenzofuran and 3hydroxydibenzofuran. During these conditions dehydration of trans-dihydrodiol is
not promoted thus implicating the formation of dibenzofuran- 2,3-epoxide after
oxidation of dibenzofuran by fungus. Cis-1,2-dihydroxy-1,2-dihydrodibenzofuran
is an unstable dihydrodiol produced by Beijerinckia B8/36. Therefore, it is evident
that fungus and bacteria carry out dibenzofuran oxidation by different mechanisms.
There are some studies available about Phlebia lindtneri (white-rot fungus) in which
oxidation of DD and DF to 2-hydroxy-DD, and 3-hydroxy-DF catalysed by cytochrome P-450 monooxygenase introduces hydroxyl group to its substrates; however,
the alkalophilic environment and extreme condition in contaminated site would not
allow the fungus survival (Mori and Kondo 2002). Bacteria are known for its
metabolic diversity and can survive up to extreme condition as well. So bacteria
are better promising options for degradation of DF including dioxins.
In 1989, the microorganisms that can metabolize DF were described by Strubel et
al. and Fortnagel et al. DPO1361 from Terrabacter sp., HH69 from Sphingomonas
sp. and DBF 63 from Staphylococcus auriculans (Schmid et al. 1997; Strubel et al.
1989; Harms et al. 1995; Fortnagel et al. 1990; Kasuga et al. 2001; Schmid et al.
1997) can convert DF to two key intermediates (2,2
0 0.3-trihydroxybiphenyl and
salicylic acid) through a novel angular dioxygenation mechanism. Contrary to the
above-mentioned strains, Sphingomonas sp. RW1 (river Elbe) can degrade DF and
also mineralize DD (Wittich et al. 1992; Harms et al. 1990; Chai et al. 2016). It has
been reported that the compound DD can only be co-metabolized using other strains.
The first step in DF metabolism is formation of phenolic hemiacetals where
stereospecific angular dioxygenation of the aromatic rings is responsible further on
rearomatize to yield trihydroxylated intermediates (2,2
0 ,3-trihydroxybiphenyl and
2,2
0 ,3-trihydroxydiphenyl ether). These intermediates undergo extradiol ring
cleavage same as bacterial metabolism of biphenyl (ring cleavage of 2,3dihydroxybiphenyl) (Eltis et al. 1993). 2,2
0 ,3-trihydroxybiphenyl undergo the ring
298
P. K. Jaiswal and J. Gupta
been demonstrated that during DF degradation several biodegradation intermediates
are formed and the conversion of DF to 1,2-dihydroxy-1,2-dihydrodibenzofuran
requires a novel enzyme called HZ6359 dioxygenase (Fawad et al. 2019).
14.8 Biodegradation of Dibenzofuran
Cunninghamella elegans and Beijerinckia (B8/36, a mutant strain) can oxidize DF to
2,3-dihydroxy-2,3-dihydrodibenzofuran (Cerniglia et al. 1979). The bacterial metabolite thus formed was extremely unstable. It can be converted into a mixture of 2and 3-hydroxydibenzofuran in the presence of acid rapidly. Contrary to this, C.
elegans formed a stable 2,3-dihydroxy-2,3-dihydrodibenzofuran intermediate. This
intermediate can yield 2- and 3-hydroxydibenzofuran only under acidic conditions.
The contrary results are due to formation of cis- and trans-isomers of 2,3-dihydroxy2,3-dihydrodibenzofuran by Beijerinckia B8/36 and C. elegans, respectively. Also,
C. elegans oxidizes dibenzofuran to 2-hydroxydibenzofuran and 3hydroxydibenzofuran. During these conditions dehydration of trans-dihydrodiol is
not promoted thus implicating the formation of dibenzofuran- 2,3-epoxide after
oxidation of dibenzofuran by fungus. Cis-1,2-dihydroxy-1,2-dihydrodibenzofuran
is an unstable dihydrodiol produced by Beijerinckia B8/36. Therefore, it is evident
that fungus and bacteria carry out dibenzofuran oxidation by different mechanisms.
There are some studies available about Phlebia lindtneri (white-rot fungus) in which
oxidation of DD and DF to 2-hydroxy-DD, and 3-hydroxy-DF catalysed by cytochrome P-450 monooxygenase introduces hydroxyl group to its substrates; however,
the alkalophilic environment and extreme condition in contaminated site would not
allow the fungus survival (Mori and Kondo 2002). Bacteria are known for its
metabolic diversity and can survive up to extreme condition as well. So bacteria
are better promising options for degradation of DF including dioxins.
In 1989, the microorganisms that can metabolize DF were described by Strubel et
al. and Fortnagel et al. DPO1361 from Terrabacter sp., HH69 from Sphingomonas
sp. and DBF 63 from Staphylococcus auriculans (Schmid et al. 1997; Strubel et al.
1989; Harms et al. 1995; Fortnagel et al. 1990; Kasuga et al. 2001; Schmid et al.
1997) can convert DF to two key intermediates (2,2
0 0.3-trihydroxybiphenyl and
salicylic acid) through a novel angular dioxygenation mechanism. Contrary to the
above-mentioned strains, Sphingomonas sp. RW1 (river Elbe) can degrade DF and
also mineralize DD (Wittich et al. 1992; Harms et al. 1990; Chai et al. 2016). It has
been reported that the compound DD can only be co-metabolized using other strains.
The first step in DF metabolism is formation of phenolic hemiacetals where
stereospecific angular dioxygenation of the aromatic rings is responsible further on
rearomatize to yield trihydroxylated intermediates (2,2
0 ,3-trihydroxybiphenyl and
2,2
0 ,3-trihydroxydiphenyl ether). These intermediates undergo extradiol ring
cleavage same as bacterial metabolism of biphenyl (ring cleavage of 2,3dihydroxybiphenyl) (Eltis et al. 1993). 2,2
0 ,3-trihydroxybiphenyl undergo the ring
298
P. K. Jaiswal and J. Gupta