that only about 10% of the total number of natural products that can be synthesized
by these organisms have been discovered. Surprisingly, most of the antibioticproducing bacteria were isolated from non-polluted environments, for instance,
Amycolatopsis balhimycina, Amycolatopsis orientalis, Streptomyces mediterranei,
and Streptomyces erythreus among others. As an interesting hypothesis,
actinobacteria isolated from contaminated areas may harbor in their genomes clusters linked to the production of specialized metabolites that allowed them to survive
in those extreme environments. Over the last few years, Amycolatopsis and Streptomyces strains were isolated from highly contaminated areas in the province of
Tucumán, Argentina. Resistance to elevated concentrations of heavy metals such as
Cu, Cr, and Cd was widely demonstrated in Streptomyces sp. MC1 and
Amycolatopsis tucumanensis (Polti et al. 2007; Dávila Costa et al. 2011a, 2012).
These strains, together with Streptomyces sp. M7 and Streptomyces sp. A5, were also
able to degrade toxic organic compounds such as hexachlorocyclohexane, methoxychlor, and phenanthrene among others. Given the potential of these strains for being
used in bioremediation processes, their genomes were recently sequenced. As
expected, genetic elements involved in mechanisms of resistance to heavy metals
and genes related to the degradation of xenobiotics were identified. In addition,
genomic bioinformatics analysis of the strains with the software antiSMASH
revealed the presence of several genes that may participate in the biosynthesis of
specialized metabolites. These clusters include biosynthetic genes for siderophores,
terpenes, bacteriocins, butyrolactones, and polyketides (Table 6.1). Certainly, outstanding advances in the field of specialized metabolites produced by actinobacteria
were achieved in the last few years. However, as we mentioned above, only about
10% of the total number of natural products synthesized by these bacteria are known.
Even more, antimicrobial produced by actinobacteria growing in the presence of
toxic compounds were not reported yet.
Although Streptomyces and Amycolatopsis are well known for producing
specialized metabolites, we could postulate that the second one is a rarer genus.
Currently, exist 823 species described for the genus Streptomyces, while only 71 were
described for Amycolatopsis so far (http://www.bacterio.net/amycolatopsis.html) (last
access October 2017). The genus Amycolatopsis was proposed in 1986. These
bacteria are characterized to have a type IV cell wall (meso-diaminopimelic acid,
arabinose, and galactose in the cell wall); muramic acid in an N-acetyl form; absence
of mycolic acids; phosphatidylethanolamine as a diagnostic phospholipid; and a
complex mixture of saturated and branched chain fatty acids. Besides, members of
this genus are able to metabolize (+)-L-arabinose, (+)-D-cellobiose, (+)-D-fructose,
(+)-D-galactose, (+)-D-lactose, (+)-D-mannose, (+)-D-trehalose, and (+)-D-xylose
(see Dávila Costa and Amoroso 2014 for a comprehensive review). Amycolatopsis
tucumanensis was recognized as new species in 2010 (Albarracín et al. 2010), and it
is the only heavy metal-resistant member into the genus. Particularly, copper resistance was demonstrated in this bacterium. Copper homeostasis mechanisms include
antioxidant molecules and enzymes, production of exopolysaccharide, and cupric
reductase activity (Dávila Costa et al. 2011a; b, 2012). The variety of carbon source
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
207
by these organisms have been discovered. Surprisingly, most of the antibioticproducing bacteria were isolated from non-polluted environments, for instance,
Amycolatopsis balhimycina, Amycolatopsis orientalis, Streptomyces mediterranei,
and Streptomyces erythreus among others. As an interesting hypothesis,
actinobacteria isolated from contaminated areas may harbor in their genomes clusters linked to the production of specialized metabolites that allowed them to survive
in those extreme environments. Over the last few years, Amycolatopsis and Streptomyces strains were isolated from highly contaminated areas in the province of
Tucumán, Argentina. Resistance to elevated concentrations of heavy metals such as
Cu, Cr, and Cd was widely demonstrated in Streptomyces sp. MC1 and
Amycolatopsis tucumanensis (Polti et al. 2007; Dávila Costa et al. 2011a, 2012).
These strains, together with Streptomyces sp. M7 and Streptomyces sp. A5, were also
able to degrade toxic organic compounds such as hexachlorocyclohexane, methoxychlor, and phenanthrene among others. Given the potential of these strains for being
used in bioremediation processes, their genomes were recently sequenced. As
expected, genetic elements involved in mechanisms of resistance to heavy metals
and genes related to the degradation of xenobiotics were identified. In addition,
genomic bioinformatics analysis of the strains with the software antiSMASH
revealed the presence of several genes that may participate in the biosynthesis of
specialized metabolites. These clusters include biosynthetic genes for siderophores,
terpenes, bacteriocins, butyrolactones, and polyketides (Table 6.1). Certainly, outstanding advances in the field of specialized metabolites produced by actinobacteria
were achieved in the last few years. However, as we mentioned above, only about
10% of the total number of natural products synthesized by these bacteria are known.
Even more, antimicrobial produced by actinobacteria growing in the presence of
toxic compounds were not reported yet.
Although Streptomyces and Amycolatopsis are well known for producing
specialized metabolites, we could postulate that the second one is a rarer genus.
Currently, exist 823 species described for the genus Streptomyces, while only 71 were
described for Amycolatopsis so far (http://www.bacterio.net/amycolatopsis.html) (last
access October 2017). The genus Amycolatopsis was proposed in 1986. These
bacteria are characterized to have a type IV cell wall (meso-diaminopimelic acid,
arabinose, and galactose in the cell wall); muramic acid in an N-acetyl form; absence
of mycolic acids; phosphatidylethanolamine as a diagnostic phospholipid; and a
complex mixture of saturated and branched chain fatty acids. Besides, members of
this genus are able to metabolize (+)-L-arabinose, (+)-D-cellobiose, (+)-D-fructose,
(+)-D-galactose, (+)-D-lactose, (+)-D-mannose, (+)-D-trehalose, and (+)-D-xylose
(see Dávila Costa and Amoroso 2014 for a comprehensive review). Amycolatopsis
tucumanensis was recognized as new species in 2010 (Albarracín et al. 2010), and it
is the only heavy metal-resistant member into the genus. Particularly, copper resistance was demonstrated in this bacterium. Copper homeostasis mechanisms include
antioxidant molecules and enzymes, production of exopolysaccharide, and cupric
reductase activity (Dávila Costa et al. 2011a; b, 2012). The variety of carbon source
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
207