The Biodegradation of Azo Dyes by Actinobacteria - Microbial Degradation of Synthetic Dyes in Wastewaters - page 301

The presence of metals in the medium may also affect the performance of the
microbial enzyme system. For example, the presence of Cu 2+ in the medium
increased the activity of laccase of Streptomyces sp. (Lu et al. 2013 ). Enhanced
activity can be due to

lling of the type-2 copper binding sites with copper ions
(Bao et al. 1993 ). Similarly, the presence of some metalions Co 2+ ,Ba 2+ ,Mn 2+ and
Fe 3+ at low concentrations also stimulate the activity of the enzyme from Strep-
tomyces species (Nagai et al. 2002 ; Baldrian and Gabriel 2006 ). However, high
concentration of these ions decreases the performance of the microbial enzyme
systems. This decrease can be attributed to interference of these metals with pro-
teins or enzymes, which ultimately form complexes with molecules of protein
which may render it inactive or even completely inactivate the enzyme (Mills and
Colwell 1977 ; Jadhav et al. 2012 ).
Carbon source is required by the microorganism as a source of energy and the
electron donor for the removal of color of azo dyes (Moosvi et al. 2007 ; Perumal
et al. 2007 ; Yemendzhiev et al. 2009 ). Among the various carbon sources, such as
glucose, lactose, maltose, xylose, fructose, galactose, mannitol and sucrose, Kho-
bragade and Deshmukh ( 2013 ) found lactose as a carbon source for the strongest
decolorization of Reactive Blue 160. They also tested the ef

cacy of different
nitrogen sources such as urea, peptone, yeast extract, ammonium nitrate, ammo-
nium chloride and potassium nitrate, for color decolorization. Among all, urea was
found to be the best source of nitrogen for the decolorization of dye. Sahasrabudhe
and Pathade ( 2013 ) found yeast extract and sucrose as the best carbon sources for
Georgenia sp. CC-NMPT-T3 to degrade Reactive orange 16 dye. However, con-
trary to the ndings of Khobragade and Deshmukh ( 2013 ), they observed a very

low degradation of the dye in the medium containing urea as a nitrogen source.

6 Conclusions

Actinobacteria are new options for the treatment of azo dye wastewater for safe
disposal into the environment. These bacteria are widely distributed in the eco-
system and can operate in a broad range of environmental conditions. In particular,
under extreme environmental conditions, they can have a better survival due to the
presence of different adaptation mechanisms. These bacteria typically have poly-
phosphate reserves, which not only act as reserves of phosphorus, but also space for
metal chelation, which can reduce the toxicity of the metal ions present in the
industrial wastewater. Presence of superoxide dismutase genes in Actinobacteria
may also play an important role in their resistance against environmental stresses.
This can result in the production of biosurfactant comprising haemolytic, drop
collapsing and activity of lipase production. Biosurfactant increases the surface area
of hydrophobic substances, which enhance the bioavailability of these substances
and modify the properties of the surface of the bacterial cell. Spore formation is
another very important feature in actinomycetes which can be exploited in a
stressed environment for its long-term application in the treatment system.