Biology Reference
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genetics (or genomes). They also produce a wide range of secondary metab-
olites that are very diverse in chemical structure: peptides, PKs, peptide and
PK hybrids, alkanes, terpenes, etc. (
Kehr, Gatte Picchi, & Dittmann, 2011
;
Nunnery, Mevers, & Gerwick, 2010
). Again, this chemical diversity prob-
ably reflects the long evolution of cyanobacteria and their adaptation to
diverse ecosystems, growth conditions and competitors or predators. For
instance, at least 800 different secondary metabolites have so far been iden-
tified in marine cyanobacteria and it is believed that this represents only a
small fraction of the natural product repertoire (
Jones et al., 2010
).
The functions of cyanobacterial secondary metabolites, apart from the
sunscreens, are usually unknown but it is expected that the production of a
specific metabolite has given, or gives, some advantage to the producer in a
complex ecosystem. It has also been proposed that these molecules might
be communication molecules although there is no firm experimental data
on this issue. Nevertheless, some of the cyanobacterial secondary metabo-
lites are toxic to higher animals, including humans, and have thus been
called cyanotoxins (
van Apeldoorn, van Egmond, Speijers, & Bakker, 2007
).
Because the presence of these cyanotoxins in the environment poses a
threat to animal and human health, they have been the primary focus of the
research on cyanobacterial secondary metabolites. However, cyanobacteria
also produce secondary metabolites that are potential therapeutic drugs,
such as cryptophycins, and there is a constant interest in discovering new
natural products from cyanobacteria as potential drug candidates (
Nunnery
et al., 2010
).
Another interesting aspect of the research concerning cyanobacterial
secondary metabolites concerns the production of metabolites that can be
used as biofuels. Because these photosynthetic bacteria use carbon dioxide
as carbon source and produce alkanes, alkenes, alcohol, esters or terpenes
and related compounds, there is a growing interest in using these microor-
ganisms as sustainable factories for producing environmentally friendly fuels
(
Wackett, 2011
).
Not all cyanobacteria are prolific producers of secondary metabolites.The
unicellular cyanobacteria, belonging to genera such as
Prochlorococcus
or
Syn-
echococcus
, usually do not produce secondary metabolites while filamentous
(
Anabaena
,
Planktothrix
, or
Lyngbya
) or colonial (
Microcystis
) cyanobacteria
produce diverse secondary metabolites. Interestingly, the genome size of fil-
amentous cyanobacteria is larger by 5-6 Mb than that of unicellular species
as if the genome of unicellular cyanobacteria has only space for primary
metabolism. As noted above, filamentous marine cyanobacteria produce a
