228 Marine Macro- and Microalgae: An Overview
light, circadian cycle) and the role of bacteria may be critical issues to fully understand the inter- and
intraspecific variability in toxin composition and content.
The ability of dinoflagellates to produce several toxins with a wide spectrum of bioactivities has
provided the impetus for potential drug development therefrom. Most said toxins may have noteworthy
application in treatment human or animal treatment diseases, for example, cancer, respiratory,
neurological, or immunologic degenerative pathologies; and they can also play the role of antibiotic,
analgesic, anticholesterol, and/or citotoxic agents. However, several difficulties remain in attempts to
implement and commercialize the aforementioned substances, namely sufficient amounts for clinical
trials. Only small quantities of such compounds are indeed available, with extra limitations arising from
their outrageous prices and frequent discontinued distribution by the supplier. The limited availability of
natural sources, along with main complications for de novo synthesis, genetic and metabolic engineering
have been a restraining dinoflagellate biotechnology development. In addition, the difficulties in growing
them in the laboratory, have been humpering bulk uses of their unique metabolites for pharmacalogical
pursposes. Although chemical synthesis may be possible, this is not probable to succeed in short run. In
praticte, it will entail laborious and hard-demanding steps with low cost-effectiveness. Despite several
efforts, the peculiar DNA of dinoflagellates, and their complex and specific metabolism have greatly
constrained applicability of genetic and metabolic tools already available for other organisms. Lack of
a general transformation system, and scarce information about gene-mapping have severely hampered
the improvement of the synthetic pathways regarding toxin production. Menwhile, high throughput
technologies are evolving rather fast, and may constitute a useful tool in a near future. As for now, the
only realistic approach to improve toxin production is resorting to autotrophic growth of dinoflagellates
in photobioreactors. However, shear stress, cell damage and growth inhibition remain an issue during
such cultivations, due to turbulence arising from stirring or bubbling. Dinoflagellate cells are extremely
sensitive to external mechanical forces with obvious consequences upon morphology, growth, and toxin
production. These phenomena are not well understood at molecular level—yet it has been claimed that
their cytoskeleton is involved in stimuli transduction, which may lead to alterations in DNA conformation.
The range of outcomes (i.e., growth inhibition, cell damage) is apparently species- and strain-dependent.
Obviously, the duration and magnitude of forces also have an effect on shear consequences. Even species
with theca—once thought to possess additional protection against shear, are themselves sensitive to
turbulent liquid motion.
Despite the above difficulties, dinoflagellate cultivation has undergone considerable advances, even at
large scale. It should be noted that such cultures must be confined to closed reactors, since open systems may
raise an environmental contamination issue. Additionally, toxins—for pharmaceutical application—have
to be obtained with good and consistent quality, and this may be uncompatible with growth under somewhat
unpredictable conditions. Advances to date encompass development of several types of photobioreactors
(carboys, chemostats, airlift, bubble column, flat-plate, biofilm PBRs), from bench to large scale
(700 L); however, further improvements are still a must to maximize biomass production. In this regard, it
is crucial to improve design and operation of photobioreactors along with better knowledge of mechanism
of synthesis in vivo of a given toxin—in terms of morphology and/or metabolic requirements. It is
expected that such efforts will eventually overcome the aforementioned limitations upon dinoflagellate
cultivation, by achieving higher volumetric titers and toxin productivities suitable for performance of
clinical experimentation and thus, pharmacological development afterwards.
Acknowledgments
This research was partially supported by project DINOSSAUR—PTDC/BBB-EBB/1374/2014 - POCI01-0145-FEDER-016640, funded by FEDER funds through COMPETE2020—Programa Operacional
Competitividade e Internacionalização (POCI), and by national funds through FCT—Fundação para
a Ciência e a Tecnologia, I.P., coordinated by author F.X.M.; and also partially supported by project
POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and
Energy—UID/EQU/00511/2013), funded by the European Regional Development Fund (ERDF), through
COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI) and by national
light, circadian cycle) and the role of bacteria may be critical issues to fully understand the inter- and
intraspecific variability in toxin composition and content.
The ability of dinoflagellates to produce several toxins with a wide spectrum of bioactivities has
provided the impetus for potential drug development therefrom. Most said toxins may have noteworthy
application in treatment human or animal treatment diseases, for example, cancer, respiratory,
neurological, or immunologic degenerative pathologies; and they can also play the role of antibiotic,
analgesic, anticholesterol, and/or citotoxic agents. However, several difficulties remain in attempts to
implement and commercialize the aforementioned substances, namely sufficient amounts for clinical
trials. Only small quantities of such compounds are indeed available, with extra limitations arising from
their outrageous prices and frequent discontinued distribution by the supplier. The limited availability of
natural sources, along with main complications for de novo synthesis, genetic and metabolic engineering
have been a restraining dinoflagellate biotechnology development. In addition, the difficulties in growing
them in the laboratory, have been humpering bulk uses of their unique metabolites for pharmacalogical
pursposes. Although chemical synthesis may be possible, this is not probable to succeed in short run. In
praticte, it will entail laborious and hard-demanding steps with low cost-effectiveness. Despite several
efforts, the peculiar DNA of dinoflagellates, and their complex and specific metabolism have greatly
constrained applicability of genetic and metabolic tools already available for other organisms. Lack of
a general transformation system, and scarce information about gene-mapping have severely hampered
the improvement of the synthetic pathways regarding toxin production. Menwhile, high throughput
technologies are evolving rather fast, and may constitute a useful tool in a near future. As for now, the
only realistic approach to improve toxin production is resorting to autotrophic growth of dinoflagellates
in photobioreactors. However, shear stress, cell damage and growth inhibition remain an issue during
such cultivations, due to turbulence arising from stirring or bubbling. Dinoflagellate cells are extremely
sensitive to external mechanical forces with obvious consequences upon morphology, growth, and toxin
production. These phenomena are not well understood at molecular level—yet it has been claimed that
their cytoskeleton is involved in stimuli transduction, which may lead to alterations in DNA conformation.
The range of outcomes (i.e., growth inhibition, cell damage) is apparently species- and strain-dependent.
Obviously, the duration and magnitude of forces also have an effect on shear consequences. Even species
with theca—once thought to possess additional protection against shear, are themselves sensitive to
turbulent liquid motion.
Despite the above difficulties, dinoflagellate cultivation has undergone considerable advances, even at
large scale. It should be noted that such cultures must be confined to closed reactors, since open systems may
raise an environmental contamination issue. Additionally, toxins—for pharmaceutical application—have
to be obtained with good and consistent quality, and this may be uncompatible with growth under somewhat
unpredictable conditions. Advances to date encompass development of several types of photobioreactors
(carboys, chemostats, airlift, bubble column, flat-plate, biofilm PBRs), from bench to large scale
(700 L); however, further improvements are still a must to maximize biomass production. In this regard, it
is crucial to improve design and operation of photobioreactors along with better knowledge of mechanism
of synthesis in vivo of a given toxin—in terms of morphology and/or metabolic requirements. It is
expected that such efforts will eventually overcome the aforementioned limitations upon dinoflagellate
cultivation, by achieving higher volumetric titers and toxin productivities suitable for performance of
clinical experimentation and thus, pharmacological development afterwards.
Acknowledgments
This research was partially supported by project DINOSSAUR—PTDC/BBB-EBB/1374/2014 - POCI01-0145-FEDER-016640, funded by FEDER funds through COMPETE2020—Programa Operacional
Competitividade e Internacionalização (POCI), and by national funds through FCT—Fundação para
a Ciência e a Tecnologia, I.P., coordinated by author F.X.M.; and also partially supported by project
POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and
Energy—UID/EQU/00511/2013), funded by the European Regional Development Fund (ERDF), through
COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI) and by national