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Microalgae as Second-Generation Energy Plants
Figure 1. Outdoor system for the cultivation of microalgae: ‘open raceway pond’ Seambiotic (Israel)
Figure 2. Indoor system for
the cultivation of microalgae:
Photobioreactor IGV (Germany)
for centuries and were used already by the Mayas. Microalgae, usually cyanobacteria as, e.g., Spirulina spp., were grown in small lakes, ponds and ditches, harvested
and spread nearby for drying and subsequently used as animal food. Modern systems consist of pools of different shapes, in which microalgae are grown in a shallow layer (20–40 cm) that is permanently agitated to guarantee optimal growth
conditions. Most outdoor systems are run today in countries providing optimal
natural conditions concerning temperature and sunshine such as Hawaii, Australia and Japan. The largest outdoor facilities spread on an area of about 440,000
m2 (Spolaore et al., 2006) and produce about 8–12 g dryweight of algal biomass
per m2 and day (Ackermann, 2007).
Indoor systems are closed bioreactors, in which algae are grown under
defined conditions of temperature, light, nutrient supply, etc. (Pulz, 2001). The
largest commercially used indoor system has a volume of about 600 m3 that is
contained in glass tubes 500 km in length (Ackermann, 2007). Production of algal
biomass amounts to 32 g m−2 and day (sunlight only).
THE FUTURE IS GREEN: ON THE BIOTECHNOLOGICAL POTENTIAL
A comparison of pros and cons of both systems shows that open systems are more
cost-efficient than closed systems when optimal and constant climatic conditions
are given, e.g., optimum temperature and sufficient sunshine. However, it is also
obvious that open systems are generally more prone to changes in environmental
conditions, as to the input of spores, germs and particulate matter from the atmosphere and to extreme weather conditions such as thunderstorms, hurricanes, etc.
Continuous production of algal biomass is easier to achieve by closed systems
that, however, require higher financial investments. Various tests have shown that
in closed systems, the maximum cell density that can be obtained under optimum
conditions is about 30 times higher than that in open systems. Taking into account
the economic advantage of a constant and predictable production of high-quality
indoor systems presumably is more cost-efficient than in open systems. Estimates
(Chisti, 2007) calculate the costs for the production of 1 kg of algal biomass to
US$2.85 in closed systems, whereas in open systems it is about US$3.89. When
algae are used for the production of biodiesel (30% of algal biomass is processable), costs of 1 L of biodiesel obtained from open systems would amount to
US$1.81, from closed systems to US$1.40. The same author calculates for 1 L
biodiesel made from palm oil US$0.66 and made from petroleum about US$0.49.
However, it should be mentioned that calculations are a matter of discussion
depending not only on the oil content of algal biomass but also on general operating
costs of the facility that in part may be effected by environmental conditions such
as ambient temperature and duration of sunshine. Other authors calculate for
1 L biodiesel made from microalgae costs ranging from about US$5.35 (Dimitov,
2007) to US$0.16 (Günzburg, 1993). At any rate, most calculations show that
costs of biofuels made from microalgae are still higher than costs of petrofuels.
However, in recent times, the market price of petrofuel is steadily pointing upwards
and the break-even point may be reached sooner than anticipated.
3.3. HIGH-VALUE PRODUCTS
It is not astonishing at all that up to now any economic success of indoor and
outdoor systems was achieved by the production of high-value products such as
pharmaceuticals, cosmetics, products for healthcare, natural colours, unsaturated
fatty acids, essential amino acids, etc. Those high-value substances allow a realistic competition of microalgal cultures with classical production methods such as
isolation of linolic acids from herbs, etc. They allow microalgae cultures to bring
in their specific advantages such as production under reliable sterile conditions, no
risk of contamination with human viruses, prions, etc. Thus, it is conceivable to use
microalgal cultures also for genetic engineering techniques to obtain, for example,
specially designed antibodies, recombinant proteins, etc. Appropriate techniques
are available for microalgae, e.g., in Chlamydomonas sp. (green algae) genetic
manipulation has been successful (Patel-Predd, 2007). An interesting advantage of
microalgae over crop plants concerning genetic manipulation might be that there
should be no public concern about bringing ‘manipulated’ organisms into the ecosystem, because algal systems are not in contact with the environment.
4.1. INCREASE IN EFFICIENCY
As to the future role of microalgae as an alternative energy source, the key question
is whether the production of biofuels by microalgal cultures will ever be able to
compete on a large scale with petrofuels. The answer to this question is not easy.
It depends on how its economical, ecological and political aspects are measured.
There are good reasons to assume that petrofuel will remain the most important
energy source for transportation in the near future and that its price will keep going
up. Therefore, it is a realistic goal to raise the efficiency of microalgal culture systems,
mainly of indoor systems, in order to be able to compete with the price of petrofuels.
Efficiency may be augmented by a lot of measures. The exploitation of light energy
has to be made more efficient, e.g., by keeping algae in small layers as are tested in
new types of bioreactors and by constructing fibre-optic devices that might increase
the capacity of daylight. It is also important to avoid clumping of algae, adhesion to
reactor walls, for example, by special coating techniques of inner tube surfaces and to
establish an automatic control and harvesting system that guarantees a continuous
operating. It will also be desirable to have nearby a cheap source of CO2, such as
power and cement plants, although it should also be made clear that by algal cultures
their output of CO2 never can be reduced to zero.
From the viewpoint of biology, it will be certainly promising to screen for
further microalgal candidates since until now only a rather small part of natures
fundus of about 30,000–40,000 algal species is used, mainly cyanobacteria (e.g.
Spirulina) and green (chlorophycean) algae, such as coccoid (Chlorella, Scenedemus)
and flagellate specimen (Dunaliella, Chlamydomonas). Other microalgal taxa are
represented by a few xanthophycean ( e.g., Botryococcus), eustigmatophycean
(e.g., Nannochloropsis), prasinophycean (e.g., Tetraselmis) and bacillariophycean
(diatom) taxa such as Nitzschia and Phaeodactylum.
Efforts should be aimed at finding species that do not clump, show a lower
photosynthetic compensation point to increase yield at less input of light energy and
perform optimum growth at elevated temperatures to reduce costs of cooling. It will
also be desirable to obtain a higher output of ‘interesting substances’ under standard
conditions. If, for example, the content of processable oil in the algal biomass could
be raised from 30% to 50% of the dryweight, the price of biodiesel would become
competitive. However, this requires much better understanding of the physiological
mechanisms in microalgae responsible for the synthesis of value products such as
lipids and oil. Most algae produce substantial amounts of triacylglycerols such as the
THE FUTURE IS GREEN: ON THE BIOTECHNOLOGICAL POTENTIAL
production of components of storage lipids only under stress conditions, e.g., nutrient
limitation and photooxidative stress (Hu et al., 2008). Thus, the challenge will be to
find culture conditions that combine both optimum growth of microalgae, i.e., high
yield of biomass and high lipid content in cells.
As to the production of bioethanol from algal biomass, it will be recommendable to look by screening or by genetic engineering for algae producing
carbohydrates that are more suitable to fermentation than the standard starch
basis is. The same consideration holds also for other cell parts, such as the cell
wall. Ideally, it consists of material that can also be easily fermented or alternatively used, for example by the BTE-technique, to produce energy.
It could also be promising to think about the problem whether the end product
of fermentation has to be ethanol. Ethanol shows a high solubility in water and therefore is not easy to separate from it; it is poisonous to cells and has relatively relatively
low energy content. Butanol could be a good candidate for ersatz.
A further yet speculative energy source produced by microalgae is H2. The
photoproduction of H2 is mainly studied in Chlamydomonas sp. and represents a
rather promising field of microalgal technology (Patel-Predd, 2007). One of the
current problems to tackle is that H2 production is inhibited by oxygen. Various
strategies to meet this obstacle are under study, for example, the insertion of
leghemoglobin genes into algae. It still requires a lot of basic research and is far
from being exploitable in practice.
In general, the leitmotiv should be to raise the efficiency of biomass processing.
This means to increase the output of energy from algal biomass, either as biofuels
(biodiesel, bioethanol, biogas) or directly in the form of heat energy that may be
used in power plants. Each form of energy has to deal with a different and already
successful competitor in the market. Therefore, it will be important to increase
the current revenue from biomass by combining energy yield with the production
of additional high-value products. Every component of the biomass should be
exploited to add value (‘biorefinery’, Chisti, 2007).
An economic advantage of biomass production by microalgae in closed systems
in comparison with other energy plants is doubtless the fact that production is
constant, predictable and not dependent on such hazards as drought, diseases, and
Under ecological aspects, advantages of microalgal cultures in closed systems are
obvious and have been already discussed here. They neither take up arable land
nor potable water resources; they can be located on marginal land as well as in
buildings downtown used for vertical farming. This means an additional unforeseen
advantage of closed systems since they help avoiding the ‘palmoil-paradoxon’, i.e.,
tropical deforestation in the name of climate protection.
As second-generation energy plants, microalgae represent an alternative
energy source not producing netto CO2. However, this is not a unique qualification. The culture of other second-generation energy plants such as Miscanthus
also does not produce netto CO2 provided that cultivation is done without fertilisers and mechanical processing is limited. Nonetheless, assessment of hazards of
continuous culture such as plant diseases and exhaustion of nutrients in soil is
On the political level, a decision has to be made to what extent we want to
stay dependent on petrofuels that are neither available at a constant price nor
accessible to everyone. For some countries, the return to mining coal could be an
alternative. As to experts, coal reservoirs exceed by far oil and gas supplies, but it
will need a lot of money to (re)activate mining industry and also to establish
effective methods not only to catch the CO2 but also to store it away from the
Another problem that has to be decided by politics is how long we want to
keep on using combustion engines for transportation. Is there a realistic chance
to replace them by motors driven by electric power, for example? Power plants do
not necessarily need petrofuels or biofuels. They can also be driven by biomass.
In the context of microalgal cultures, this could mean that production of combustible biomass becomes more important and more demanded by the market than
special components in algae. It is also conceivable that microalgal cultures will
become part of the trade of CO2 certificates.
The amount of public funding often depends on the number of jobs created
and on the influence of pressure groups. Since in most countries, farmers associations are much more influential than the lobby of people growing microalgae, currently public money is primarily spent to support farmers who grow energy plants
such as rapeseed or Miscanthus. This has also psychological reasons, because most
people are more familiar with flowering plants than with ‘slimy’ algae. As to the
acquisition of venture capital, the situation may be somewhat different.
The plain fact remains that microalgae culture facilities will become a success
story only when they deliver their products – be it energy or chemicals – at a competitive price. However, it should also be kept in mind that current major players in
alternative energy production such as solar and wind energy are still not competitive
and supported by public money. Microalgal technology merits the same chance.
Microalgae provide a lot of value products for human nutrition and health care.
In recent times, they have been propagated as second-generation energy plants
producing biofuels, such as ethanol, biogas and hydrogen, in particular, biodiesel
THE FUTURE IS GREEN: ON THE BIOTECHNOLOGICAL POTENTIAL
of oil-containing specimen. Cultivation of algae under controlled conditions in
photobioreactors guarantees a high and constant yield of biomass independent
from ambient climatic conditions, quality of soil and water supply. For producing
a given amount of biomass, microalgal cultures need about 1,000 times less water
than crops and produce on the same area about 15 times more oil for biodiesel
than, for example, rapeseed. Costs of biodiesel from microalgal cultures mainly
depend on oil content of algae and on algal by-products such as cellulose that can
also be exploited. A breakthrough of algal biodiesel on the market will depend on
both the price of petrodiesel and the political will to support a promising source
of alternative energy.
Ackermann, U. (2007) Konzeptpapier: Zukunftsworkshop Mikrotechniken für eine effizientere
Chisti, Y. (2007) Biodiesel from microalgae. Biotechnol. Adv. 25: 294–306.
Dimitov, K. (2007) Greenfuel technologies: a case study for industrial photosynthetic energy capture.
Gantar, M. and Svircev, Z. (2008) Microalgae and cyanobacteria: food for thought. J. Phycol. 44:
Günzburg, B.Z. (1993) Liquid fuel (oil) from halophilic algae: a renewable source of non-polluting
energy. Renew. Energ. 3: 249–252.
Hu, Q., Sommerfeld, M., Jarvis, E., Ghirardi, M., Posewitz, M., Seibert, M. and Darzins, A. (2008)
Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances. Plant
J. 54: 621–639.
Patel-Predd, P. (2007) Hydrogen from algae. http://www.technologyreview.com
Pulz, O. (2001) Photobioreactors: production systems for phototrophic biosystems. Appl. Microbiol.
Biotechnol. 57: 287–293.
Schiermeier, Q., Tollefson, J., Scully, T., Witze, A. and Morton, O. (2008) Electricity without carbon.
Nature 454: 816–823.
Solarbiofuels (2008) http://www.solarbiofuels.org
Spolaore, P., Joannis-Cassan, C., Duran, E. and Isambert, A. (2006) Commercial applications of
microalgae. J. Biosci. Bioeng. 101: 87–96.
Biodata of Levent Cavas and Georg Pohnert, authors of “The Potential of
Caulerpa spp. for Biotechnological and Pharmacological Applications”
Associate Professor Dr. Levent Cavas is currently the member of the Faculty of Arts
and Sciences, Department of Chemistry–Biochemistry in the University of Dokuz
Eylül, Turkey. He obtained his Ph.D. from the University of Dokuz Eylül in 2005
and continued his studies and research at the University of Dokuz Eylül. Dr. Cavas’s
scientific interests are in the areas of biochemistry of invasive Caulerpa spp. in the
Mediterranean Sea, specifically secondary metabolites from marine algae, antioxidants and lipid peroxidation.
Professor Dr. Georg Pohnert pursued his doctoral studies in the group of Professor
W. Boland. After receiving his Ph.D. in 1997, he moved to the Cornell University
for a postdoc on the biochemical and biophysical characterisation of the E. coli
P-protein with a focus on the phenylalanine receptor site. He moved in 1998 to the
Max–Planck-Institute for Chemical Ecology, where he worked as group leader
on chemical defence mechanisms of algae. In 2005, he was appointed as assistant professor at the Institute of Chemical Sciences and Engineering of the Ecole
Polytechnique Fédérale de Lausanne, Switzerland. He moved to the Friedrich–
Schiller University in Jena, Germany, in 2007, where he was appointed as chair in
Instrumental Analytics. Professor Dr. Pohnert’s research interests are in the field
of plankton chemical ecology and in the elucidation of induced and activated
defence mechanisms of macroalgae.
A. Israel et al. (eds.), Seaweeds and their Role in Globally Changing Environments,
Cellular Origin, Life in Extreme Habitats and Astrobiology 15, 385–397
DOI 10.1007/978-90-481-8569-6_22, © Springer Science+Business Media B.V. 2010
THE POTENTIAL OF CAULERPA SPP. FOR BIOTECHNOLOGICAL
AND PHARMACOLOGICAL APPLICATIONS
LEVENT CAVAS1 AND GEORG POHNERT2
Division of Biochemistry, Department of Chemistry, Faculty of Arts
and Sciences, Dokuz Eylül University, 35160, İzmir, Turkey
Institute for Inorganic and Analytical Chemistry, Friedrich Schiller
University Jena, D-07743, Jena, Germany
The genus Caulerpa belonging to the Bryopsidophyceae consists of about 75 species,
which are distributed worldwide in tropical and temperate regions (Fama et al., 2002).
Caulerpa spp. are siphonous green algae with a unique cellular organisation. Despite
the fact that members of this genus can reach several meters in length, the organisms
are unicellular with giant differentiated cells (Menzel, 1988).
In recent years, this genus has attracted much attention because of Caulerpa
taxifolia, which was termed ‘killer alga’ because of its invasive potential (Meinesz
and Simberloff, 1999; Meinesz et al., 1995). C. taxifolia was introduced into the
Mediterranean Sea in the late 1980s and, within a few years, it spread rapidly and
started to affect coasts of at least six Mediterranean countries (Thibaut et al., 2001;
Jousson et al., 1998). In the invaded areas, dense patches of C. taxifolia cover the sea
floors, which affects massively the local flora and fauna. Invasive specimens from the
same clone were also reported from California and Australia (Jousson et al., 2000;
Anderson, 2005). Many eradication methods such as covering C. taxifolia meadows
with dark-coloured plastic foils, treatment with algicides, heavy metals, dry ice or chlorine bleach have been applied so far (Williams and Schroeder, 2004; Uchimura et al.,
2000). But these methods were only successful if small local patches of C. taxifolia
were treated. However, large-scale applications of any technical solution in the
Mediterranean Sea seem not to be feasible owing to the massive coverage of
C. taxifolia. The specialised sea slug, Lobiger serradifalci, was considered to be
used in the biological war against C. taxifolia. However, it was understood from
laboratory experiments that L. serradifalci can divide C. taxifolia into small viable
fragments that can re-grow, thereby even supporting the rapid proliferation of the
alga (Zuljevic et al., 2001).
Another widely recognised member of the genus Caulerpa is Caulerpa racemosa var. cylindracea. This species was first observed in 1926 in the Mediterranean
Sea at Sousse harbour of Tunisia (Hamel, 1926). At that time, it was considered as
LEVENT CAVAS AND GEORG POHNERT
a lessepsien migrant. C. racemosa did not show any invasive properties up to 1991.
However, thereafter this species spread with massive growth rates and now it has
been observed at the coastlines of 13 Mediterranean countries (Albania, Algeria,
Croatia, Cyprus, France, Greece, Italy, Libya, Malta, Monaco, Spain, Tunisia,
Turkey) (Verlaque et al., 2003, M. Verlaque, 2003).
It is evident that an eradication of invasive Caulerpa spp. in the Mediterranean
Sea or Australia is impossible, since large areas all along the coasts are affected.
Nevertheless, Caulerpa spp. contain unique natural products and are sources for
crude algal preparations, extracts and secondary metabolites with interesting
activities. We believe that a commercially motivated harvesting paired with political management of this new resource might offer a chance to control these algae.
In this chapter, we introduce the dominant secondary metabolites from the algae
and highlight potential biotechnological and pharmaceutical applications of
products derived from Caulerpa spp., thereby providing an outline of potential
commercially interesting applications.
2. The Dominant Secondary Metabolite of Caulerpa Genus: Caulerpenyne (CYN)
Caulerpa spp. contain several linear terpenoid secondary metabolites and especially
caulerpenyne (CYN, Fig. 1) has been associated with anti-cancer, anti-proliferative,
anti-microbial, anti-herpetic and anti-viral properties in many reports. Both invasive
Caulerpa spp. contain the dominant sesquiterpenoid metabolite CYN, which can
be found in high concentrations up to 1.3% of the dry weight of the alga (Amade
and Lemée, 1998; Dumay et al., 2002). CYN contents of invasive and non-invasive
Caulerpa species of the Mediterranean are similar, suggesting that this molecule is
not the key for the success of rapidly spreading species but rather a wider distributed
metabolite of Caulerpa spp. in general (Jung et al., 2002).
Purified CYN is a feeding inhibitor against sea urchins (Erickson et al.,
2006). But in the natural context, this compound might be considered to be
rather a storage form for more reactive metabolites, which are formed enzymatically after wounding the giant algal cells (Weissflog et al., 2008). CYN contains an unusual bis-enoyl acetoxy functionalisation that is transformed rapidly
by esterases once the algal cells are disrupted. This enzymatic transformation
results in the formation of the highly reactive 1,4-bis-aldehyde oxytoxin-2 (Jung
and Pohnert, 2001). The transformation is relevant for the activated chemical
Figure 1. Caulerpenyne, the major terpenoid
metabolite produced by C. taxifolia and C.