Dinoflagellates and Toxin Production 223
capacity apparently results from multiple independent evolutionary origins (Lin 2011)—what may turn
out hampering the identification of toxin-related genes.
The identification of genes and enzymes involved in the biosynthesis of toxins by dinoflagellates
has been limited so far, in spite of considerable efforts (Kellmann et al. 2010). Gene-function mapping
would be essential for engineering improved production of dinoflagellate derived-bioactives (GallardoRodríguez et al. 2012a). To date, all data regarding gene regulation mechanisms in dinoflagellates has
emerged inconsistently, from studies of specific genes that are of interest for a particular function (Hackett
et al. 2004). The molecular genetics underlying biosynthesis of dinoflagellate able to produce toxins is
scarcely understood. However, it is known that the genes responsible for toxin synthesis are in their
chromosomes, with some exceptions. For instance, polyketide synthase (PKS) genes—a sequence closely
related to the toxigenic cyanobacteria PKS genes, has been found in Karenia brevis chloroplast (LópezLegentil et al. 2010). This clearly suggests multiple independent origins regarding toxin competence of
some dinoflagellates (Lin 2011).
The majority of dinoflagellates apparently produce their toxins via the polyketide pathway, which
involves a polyketide synthase that may be combined with some functional segments—such as nonribosomal peptide synthase (Kellmann et al. 2010). The enzymes carrying out polyketide synthesis,
PKSs, have been classified into three types, depending on their domain organization. According to
chemical structure, it is suggested that type I PKS are the enzymes involved in its production (Kathleen
and Snyder 2006). In addition, the PSP toxins are believed to be synthesize via a pathway involving
arginine, S-adenosylmethionine (SAM), and acetate. Interestingly, homologs of SAM synthetase gene
have been identified in both toxic and non-toxic dinoflagellates (Harlow et al. 2007).
Despite many difficulties, new high-throughput omic tools are moving towards exploring toxin
genes and proteins related to dinoflagellate-mediated toxin production, and may provide some insights
about their biosyntheses (Wang et al. 2016).
Bioreactor culture and shear-stress
Despite their remarkable ecological importance and productivity in nature, dinoflagellates are of limited
biotechnological importance due mainly to the difficulty in establishing such groups in conventional
reactors (i.e., closed fermentors) or even in adequate synthetic media (Not et al. 2012). Nevertheless,
general attempts have focused on photoautotrophic dinoflagellate cultures (e.g., Gallardo-Rodríguez et
al. 2010; Fuentes-Grünewald et al. 2016; López-rosales et al. 2016). As dinoflagellates exhibit an intricate
metabolism, and exhibit substantially lower growth rates than common microalgae (Wong and Kwok
2005), toxin concentrations have rarely gone over the microgram/liter threshold (Gallardo-Rodríguez et
al. 2012a).
The sensitivity of dinoflagellates to shear stress and turbulence when in suspension apperar to be
a critical issue (García-Camacho et al. 2007). Dinoflagellates obey a strict circadian cycle, where cells
divide at the end of the dark period and grow during the light phase (corresponding to the G1 phase
of the cell cycle), precisely when production of many toxins occurs (Pan et al. 1999). This can also
be problematic when they are cultivated in conventional photobioreactor configurations and operating
conditions. As an example, several simplistic modes of light supply (i.e., continuous illumination)
combined with the typical uniform levels of nutrients may break down natural rhythms, and metabolic
behavior may accordingly depart from the original one. Any type of agitation, shaking, aeration and
stirring imposed in laboratory cultures by typical photobioreactor configurations are largely reported to
affect dinoflagellate cells (Sullivan et al. 2003; Berdalet et al. 2007). Even in natural settings, turbulent
conditions may discourage bloom formation—because of physical dispersion and lower time-integrated
light exposure of individual cells (Juhl et al. 2001).
High levels of turbulence translate to high hydrodynamic shear forces, especially very small eddies
(Chisti 2000; Berdalet et al. 2007) that lead to inhibition of cell growth or cell damage—and, consequently,
low biotoxin-associated productivities (Gallardo-Rodríguez et al. 2009).
High liquid motions (turbulent regimes) inside photobioreactors are needed to potentiate gas
exchanges into media to sufficiently high transfer rate so as to promote photosynthetic growth (Carvalho
capacity apparently results from multiple independent evolutionary origins (Lin 2011)—what may turn
out hampering the identification of toxin-related genes.
The identification of genes and enzymes involved in the biosynthesis of toxins by dinoflagellates
has been limited so far, in spite of considerable efforts (Kellmann et al. 2010). Gene-function mapping
would be essential for engineering improved production of dinoflagellate derived-bioactives (GallardoRodríguez et al. 2012a). To date, all data regarding gene regulation mechanisms in dinoflagellates has
emerged inconsistently, from studies of specific genes that are of interest for a particular function (Hackett
et al. 2004). The molecular genetics underlying biosynthesis of dinoflagellate able to produce toxins is
scarcely understood. However, it is known that the genes responsible for toxin synthesis are in their
chromosomes, with some exceptions. For instance, polyketide synthase (PKS) genes—a sequence closely
related to the toxigenic cyanobacteria PKS genes, has been found in Karenia brevis chloroplast (LópezLegentil et al. 2010). This clearly suggests multiple independent origins regarding toxin competence of
some dinoflagellates (Lin 2011).
The majority of dinoflagellates apparently produce their toxins via the polyketide pathway, which
involves a polyketide synthase that may be combined with some functional segments—such as nonribosomal peptide synthase (Kellmann et al. 2010). The enzymes carrying out polyketide synthesis,
PKSs, have been classified into three types, depending on their domain organization. According to
chemical structure, it is suggested that type I PKS are the enzymes involved in its production (Kathleen
and Snyder 2006). In addition, the PSP toxins are believed to be synthesize via a pathway involving
arginine, S-adenosylmethionine (SAM), and acetate. Interestingly, homologs of SAM synthetase gene
have been identified in both toxic and non-toxic dinoflagellates (Harlow et al. 2007).
Despite many difficulties, new high-throughput omic tools are moving towards exploring toxin
genes and proteins related to dinoflagellate-mediated toxin production, and may provide some insights
about their biosyntheses (Wang et al. 2016).
Bioreactor culture and shear-stress
Despite their remarkable ecological importance and productivity in nature, dinoflagellates are of limited
biotechnological importance due mainly to the difficulty in establishing such groups in conventional
reactors (i.e., closed fermentors) or even in adequate synthetic media (Not et al. 2012). Nevertheless,
general attempts have focused on photoautotrophic dinoflagellate cultures (e.g., Gallardo-Rodríguez et
al. 2010; Fuentes-Grünewald et al. 2016; López-rosales et al. 2016). As dinoflagellates exhibit an intricate
metabolism, and exhibit substantially lower growth rates than common microalgae (Wong and Kwok
2005), toxin concentrations have rarely gone over the microgram/liter threshold (Gallardo-Rodríguez et
al. 2012a).
The sensitivity of dinoflagellates to shear stress and turbulence when in suspension apperar to be
a critical issue (García-Camacho et al. 2007). Dinoflagellates obey a strict circadian cycle, where cells
divide at the end of the dark period and grow during the light phase (corresponding to the G1 phase
of the cell cycle), precisely when production of many toxins occurs (Pan et al. 1999). This can also
be problematic when they are cultivated in conventional photobioreactor configurations and operating
conditions. As an example, several simplistic modes of light supply (i.e., continuous illumination)
combined with the typical uniform levels of nutrients may break down natural rhythms, and metabolic
behavior may accordingly depart from the original one. Any type of agitation, shaking, aeration and
stirring imposed in laboratory cultures by typical photobioreactor configurations are largely reported to
affect dinoflagellate cells (Sullivan et al. 2003; Berdalet et al. 2007). Even in natural settings, turbulent
conditions may discourage bloom formation—because of physical dispersion and lower time-integrated
light exposure of individual cells (Juhl et al. 2001).
High levels of turbulence translate to high hydrodynamic shear forces, especially very small eddies
(Chisti 2000; Berdalet et al. 2007) that lead to inhibition of cell growth or cell damage—and, consequently,
low biotoxin-associated productivities (Gallardo-Rodríguez et al. 2009).
High liquid motions (turbulent regimes) inside photobioreactors are needed to potentiate gas
exchanges into media to sufficiently high transfer rate so as to promote photosynthetic growth (Carvalho