Comparative Proteomics Reveals That a Saxitoxin-Producing and a Nontoxic Strain of <i>Anabaena circinalis</i> Are Two Different Ecotypes

In Australia, saxitoxin production
is restricted to the cyanobacterial
species Anabaena circinalis and is strain-dependent.
We aimed to characterize a saxitoxin-producing and nontoxic strain
of A. circinalis at the proteomic level using iTRAQ.
Seven proteins putatively involved in saxitoxin biosynthesis were
identified within our iTRAQ experiment for the first time. The proteomic
profile of the toxic A. circinalis was significantly
different from the nontoxic strain, indicating that each is likely
to inhabit a unique ecological niche. Under control growth conditions,
the saxitoxin-producing A. circinalis displayed a
higher abundance of photosynthetic, carbon fixation and nitrogen metabolic
proteins. Differential abundance of these proteins suggests a higher
intracellular C:N ratio and a higher concentration of intracellular
2-oxoglutarate in our toxic strain compared with the nontoxic strain.
This may be a novel site for posttranslational regulation because
saxitoxin biosynthesis putatively requires a 2-oxoglutarate-dependent
dioxygenase. The nontoxic A. circinalis was more
abundant in proteins, indicating cellular stress. Overall, our study
has provided the first insight into fundamental differences between
a toxic and nontoxic strain of A. circinalis, indicating
that they are distinct ecotypes.