Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 39

1

N OH

N

HO

SOG

NADPH

NADP +

HN OH

NH

HO

NADPH

2 NADP +

+

NH 2 H 2 N OH

HO

( 2 )

( 1 )

0 5 10 15 20 25 30

Retention time (min)

Fig. 10 Proposed mechanisms for the biotransformation of the azo dye Sudan orange G by
PpAzoR and HPLC chromatograms of the reaction mixture after 24 h of reaction with (thin line)or
without (thick line) PpAzoR. Products of the reaction were identi ed, in comparison to the
standards: (1) aniline, (2) 4-aminoresorcinol

Fig. 11 Inhibitory effects of
intact dyes over
Saccharomyces cerevisiae
(dark bars) and
Caenorhabditis elegans
(dashed bars) (adapted from
Mendes et al. 2011a )

120

100

80

60

40

20

0

DB1 AB194 DB38 RB5 RY145 DR80

Azo dyes

However, for the majority of the other dyes tested, the enzymatic products
present a higher toxicity than intact dyes themselves, as assessed by the S. cere-
visiae system, exhibiting 2 to 4-fold higher toxicity than intact dyes (Fig. 12 )
(Mendes et al. 2011a ).

3.3 Engineering of PpAzoR for Improved Thermal Stability

PpAzoR broad substrate speci city makes it attractive for bioremediation processes,

but its low thermal stability (half life of 13 min at 50 C) impairs its full potential

for environmental related applications. Thermal stability is a critical property, as it

°