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and excision of the 11 kb DNA fragment required for its activation take
place in iron-starved Anabaena , even though cells grew in the presence of
combined nitrogen ( Razquin, Schmitz, Fillat, Peleato, & Bohme, 1994 ).
Besides, several iron-responsive genes in cyanobacteria, such as nblA , petH ,
pkn41 and pkn42 , among others, are also modulated by NtcA ( Cheng et al.,
2006 ; Luque, Zabulon, Contreras, & Houmard, 2001 ; Napolitano et al.,
2012 ; Valladares, Muro-Pastor, Fillat, Herrero, & Flores, 1999 ), the global
regulator of nitrogen control. Cross-talk between FurA and NtcA produces
a significant overlapping between the regulatory networks controlled by
those regulators, involving genes that belong to different functional catego-
ries ( López-Gomollón, Hernández, Pellicer et al., 2007 ). All these results
provide strong evidence for the link between iron and nitrogen metabolism
in cyanobacteria that will also be affected by the redox status of the cell.
3.1.5.3. FurA and carbon metabolism
Carbon fixation in cyanobacteria relies on a proper assembly of holopro-
teins associated with photosystems, essential for the production of enough
reducing power and ATP needed for a good photosynthetic performance.
In E. coli , the cyclic AMP receptor protein (CRP) regulates expression of
the carbon regulon in response to carbon availability ( Zhang et al., 2005 ).
In cyanobacteria, the CRP regulons are highly diversified and CRPs have
been lost in some lineages ( Xu & Su, 2009 ). However, in the strains where
this regulator has been preserved, though CRPs seem to regulate different
sets of genes, they are always involved in the modulation of photosyn-
thetic pathways. Several genes encoding components of PSI and PSII
from Anabaena PCC 7120, as well as ccmK , coding for a CO 2 concen-
trating mechanism protein, belong to the FurA regulon ( González et al.,
2010 , 2011 ). As has been reported for E. coli , defining a potential func-
tional interaction between FurA and Crp remains an interesting problem
that will lead to a better understanding of how cyanobacteria allow integra-
tion of signals for iron and carbon availability.
3.1.5.4. Modulation of cyanotoxicity
Certain cyanobacterial species can produce a broad range of bioactive sec-
ondary metabolites potentially toxic to eukaryotic organisms, called cya-
notoxins ( Carmichael et al., 2001 ). Similar to many bacterial toxins, some
cyanotoxins are products of modular peptide synthetases and polyketide
synthases, as is the case of microcystins, nodularins, cylindrospermopsins
or anatoxins-a. The cyclic heptapeptide microcystin is the most commonly
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