Microalgal Biomass Production 65
Maintenance of axenic culture
Marine microalgae isolated from coastal environments are unlikely to be optimally adapted to the new
pond environment. Therefore, genetic selection may significantly improve productivities of the algal
mass cultures. For example, when a single limiting factor exists such as the nutrient source, genetic
selection will offer a greater advantage for growth. If two organisms differ through a hereditable genetic
difference to utilize the same limiting substance, then the one that is better in capturing the limiting
nutrient will prevail in that environment. Eventually competition for one limiting factor will result in a
single type of dominant organism. There are many factors that determine the species dominance which
include: (i) resource-growth rate relationships for different algae, (ii) variable environmental conditions,
(iii) inhibition of one organism by another through excreted allelopathic substances, and (iv) loss of
growth due to predation or sinking. Free fatty acids, cell wall degradation products, exo-metabolites
produced by algae and cyanobacteria, such as cyanobacterin (Gleason and Paulson 1984; Gleason and
Baxa 1986) and fischerellin (Gross et al. 1991; Hagmann and Jüttner 1996) could also have allelopathic
potential. Simple mathematical competition models can be designed for two organisms that compete in
the pond. The above factors can be included as terms in the model.
The effect of single or specific variables or combination variables on the growth of organisms in a
laboratory scale can be made. The key issue is difficulty in simulation of the outdoor environment in the
laboratory conditions or extrapolation of data from lab to mass culture condition. Maintaining a specific,
genetically selected mono-algal culture of a specific inoculated strain in outdoor ponds is necessary to
exhibit the high lipid productivities. The problem of species dominance and competition in outdoor mass
cultures can be controlled by variations of biota, light, temperature, pH, and oxygen and nutrient supplies.
For example, high ammonia or pH will inhibit most zooplankton infestations, or selecting a growth
environment for specific microalgae species such as a very high alkalinity for Spirulina and high salinity
for Dunaliella. These techniques are expensive and result in severe reduction of algal productivities.
Severe contamination in Chlorella production could be solved by high density inoculations and semi-batch
operations, but this resulted in reduced overall productivity. Both Dunaliella and Chlorella are dominant
in their optimal environments. Contamination can be better managed in closed photobioreactors, but
upon continuous cultivation, both open and closed systems become more susceptible to contaminations.
Careful strain isolation and characterization, cultivation parameters of individual microalgal candidates,
and the expected contaminants in the region can reduce the contamination issues.
Strain development and domestication
Increase in the production of valuable compounds of microalgae requires optimum strain development and
domestication. Due to the absence of cell differentiation in microalgae represent a much simpler system
for genetic manipulations compared with higher plants. Techniques to introduce DNA into algal cells
with suitable promoters, new selectable marker genes, and expression vectors have to be standardized for
each ideal species. Currently, all these requirements have been fulfilled for the diatom Phaeodactylum,
the green alga, Chlamydomonas and the blue green algae, Synechococcus and Synechocystis. Successful
genetic engineering has been achieved in the expression of mosquito larvicidal properties in blue green
algae (Boussiba et al. 2000). The development of a functional transformation system can be expected in
the near future for other diatoms, blue green algae, and the red alga, Porphyridium. The success of genetic
engineering lies in the improvement of nutritional value and product yield with optimal production
parameters (Raja et al. 2008). However, the following factors are to be considered to achieve the above
features:
1. The accumulation of valuable substances in algae via genetic transformation can only increase up to
a point where cellular metabolism starts negatively affecting the production.
2. Transgenic algae potentially pose a considerable threat to the ecosystem and will most likely to be
banned from the outdoor cultivations or otherwise be under strict regulation.
3. Usually the transgenic cells exhibit less fitness than the wild type and therefore cells that lose the
newly introduced gene quickly outgrow the transformants.
Maintenance of axenic culture
Marine microalgae isolated from coastal environments are unlikely to be optimally adapted to the new
pond environment. Therefore, genetic selection may significantly improve productivities of the algal
mass cultures. For example, when a single limiting factor exists such as the nutrient source, genetic
selection will offer a greater advantage for growth. If two organisms differ through a hereditable genetic
difference to utilize the same limiting substance, then the one that is better in capturing the limiting
nutrient will prevail in that environment. Eventually competition for one limiting factor will result in a
single type of dominant organism. There are many factors that determine the species dominance which
include: (i) resource-growth rate relationships for different algae, (ii) variable environmental conditions,
(iii) inhibition of one organism by another through excreted allelopathic substances, and (iv) loss of
growth due to predation or sinking. Free fatty acids, cell wall degradation products, exo-metabolites
produced by algae and cyanobacteria, such as cyanobacterin (Gleason and Paulson 1984; Gleason and
Baxa 1986) and fischerellin (Gross et al. 1991; Hagmann and Jüttner 1996) could also have allelopathic
potential. Simple mathematical competition models can be designed for two organisms that compete in
the pond. The above factors can be included as terms in the model.
The effect of single or specific variables or combination variables on the growth of organisms in a
laboratory scale can be made. The key issue is difficulty in simulation of the outdoor environment in the
laboratory conditions or extrapolation of data from lab to mass culture condition. Maintaining a specific,
genetically selected mono-algal culture of a specific inoculated strain in outdoor ponds is necessary to
exhibit the high lipid productivities. The problem of species dominance and competition in outdoor mass
cultures can be controlled by variations of biota, light, temperature, pH, and oxygen and nutrient supplies.
For example, high ammonia or pH will inhibit most zooplankton infestations, or selecting a growth
environment for specific microalgae species such as a very high alkalinity for Spirulina and high salinity
for Dunaliella. These techniques are expensive and result in severe reduction of algal productivities.
Severe contamination in Chlorella production could be solved by high density inoculations and semi-batch
operations, but this resulted in reduced overall productivity. Both Dunaliella and Chlorella are dominant
in their optimal environments. Contamination can be better managed in closed photobioreactors, but
upon continuous cultivation, both open and closed systems become more susceptible to contaminations.
Careful strain isolation and characterization, cultivation parameters of individual microalgal candidates,
and the expected contaminants in the region can reduce the contamination issues.
Strain development and domestication
Increase in the production of valuable compounds of microalgae requires optimum strain development and
domestication. Due to the absence of cell differentiation in microalgae represent a much simpler system
for genetic manipulations compared with higher plants. Techniques to introduce DNA into algal cells
with suitable promoters, new selectable marker genes, and expression vectors have to be standardized for
each ideal species. Currently, all these requirements have been fulfilled for the diatom Phaeodactylum,
the green alga, Chlamydomonas and the blue green algae, Synechococcus and Synechocystis. Successful
genetic engineering has been achieved in the expression of mosquito larvicidal properties in blue green
algae (Boussiba et al. 2000). The development of a functional transformation system can be expected in
the near future for other diatoms, blue green algae, and the red alga, Porphyridium. The success of genetic
engineering lies in the improvement of nutritional value and product yield with optimal production
parameters (Raja et al. 2008). However, the following factors are to be considered to achieve the above
features:
1. The accumulation of valuable substances in algae via genetic transformation can only increase up to
a point where cellular metabolism starts negatively affecting the production.
2. Transgenic algae potentially pose a considerable threat to the ecosystem and will most likely to be
banned from the outdoor cultivations or otherwise be under strict regulation.
3. Usually the transgenic cells exhibit less fitness than the wild type and therefore cells that lose the
newly introduced gene quickly outgrow the transformants.