nongrowth, known as photoinhibition. Selection of a light resistant strain will
provide generally higher yields or production microalgae cultures. To prevent high
irradiance in the upper layers of the microalgae culture mixing is an important
culture parameter. Good mixing can prevent photo inhibition due to lower average
light intensities per cell.
Dark respiration It is known that dark respiration can be responsible for more
than 35 % of biomass loss produced during luminous daytime (Vonshak and
Richmond 1988). It is desirable to use low dark respiration rate strains for largescale cultures (Vonshak 1987; Becker 1994; Abalde et al. 1995).
High O 2 concentration High oxygen concentration can be deleterious for the
photosynthesis process. The carbon intake decreases when oxygen is highly
concentrated in a culture, sometimes leading to cell death and total collapse of the
culture (Becker 1994; Albalde et al. 1995). It is interesting to note that even in this
area research is needed since heated debates are ongoing on how microalgae die,
either by apoptosis or necrosis, or some other mechanism(s) (Jiménez et al. 2009).
A good solution for maintaining the culture alive and healthy is by mixing thus
homogenizing nutrients and reducing high oxygen gradients. It is also generally
desirable to choose a high oxygen-tolerant strain.
Osmotic stress In open pond large-scale cultures (See Chap. 4 for further
explanation) high evaporation rates occur (more than 10 L m
-2 d
-1 ) (Albalde
et al. 1995). Addition of new nutritive medium can cause an increase in salts in the
system and microalgae can undergo osmotic stress with deleterious results. It is
recommendable to select salt-resistant strains. Some microalgae species prosper in
a natural way in mixohaline environments; these are a good alternative since they
are already adapted to these conditions.
Culture media It is desirable that the selected strain is not a highly selective
organism in relation to its metabolic necessities, so it can possibly be fed by a wide
variety of alternative media like plant fertilizers, agricultural fertilizers, worm
slurry, or modified commercial media in order to get an economic system.
Competitiveness The selected strain preferably should be highly competitive if
an open production system is used in order to avoid contamination. Ecological
displacement is a common problem in outdoor cultures at large scale.
Indigenous strains An indigenous strain is an alga population occurring naturally near the place of the culture installation. Indigenous strains are already
adapted to the particular local environmental and fluctuations. This provides a
serendipitous ecological benefit since the species is adapted to survive in its niche.
Co-products Although one of the most important goals is to obtain biomass, a
good strategy is also to obtain high-value biological co-products like polyunsaturated fatty acids, steroids, pigments, carotenoids, antioxidants, antibiotics, antifouling substances, among several others. The production of these substances,
besides bulk production of proteins, can make the culture system that is economically feasible or more profitable.
A good strain selection is a key process for microalgae culture success. The
strains that have been collected and isolated from extreme natural environments
are the ones that will give us better results to isolate and grow them in mass
264
M. Vanthoor-Koopmans et al.
provide generally higher yields or production microalgae cultures. To prevent high
irradiance in the upper layers of the microalgae culture mixing is an important
culture parameter. Good mixing can prevent photo inhibition due to lower average
light intensities per cell.
Dark respiration It is known that dark respiration can be responsible for more
than 35 % of biomass loss produced during luminous daytime (Vonshak and
Richmond 1988). It is desirable to use low dark respiration rate strains for largescale cultures (Vonshak 1987; Becker 1994; Abalde et al. 1995).
High O 2 concentration High oxygen concentration can be deleterious for the
photosynthesis process. The carbon intake decreases when oxygen is highly
concentrated in a culture, sometimes leading to cell death and total collapse of the
culture (Becker 1994; Albalde et al. 1995). It is interesting to note that even in this
area research is needed since heated debates are ongoing on how microalgae die,
either by apoptosis or necrosis, or some other mechanism(s) (Jiménez et al. 2009).
A good solution for maintaining the culture alive and healthy is by mixing thus
homogenizing nutrients and reducing high oxygen gradients. It is also generally
desirable to choose a high oxygen-tolerant strain.
Osmotic stress In open pond large-scale cultures (See Chap. 4 for further
explanation) high evaporation rates occur (more than 10 L m
-2 d
-1 ) (Albalde
et al. 1995). Addition of new nutritive medium can cause an increase in salts in the
system and microalgae can undergo osmotic stress with deleterious results. It is
recommendable to select salt-resistant strains. Some microalgae species prosper in
a natural way in mixohaline environments; these are a good alternative since they
are already adapted to these conditions.
Culture media It is desirable that the selected strain is not a highly selective
organism in relation to its metabolic necessities, so it can possibly be fed by a wide
variety of alternative media like plant fertilizers, agricultural fertilizers, worm
slurry, or modified commercial media in order to get an economic system.
Competitiveness The selected strain preferably should be highly competitive if
an open production system is used in order to avoid contamination. Ecological
displacement is a common problem in outdoor cultures at large scale.
Indigenous strains An indigenous strain is an alga population occurring naturally near the place of the culture installation. Indigenous strains are already
adapted to the particular local environmental and fluctuations. This provides a
serendipitous ecological benefit since the species is adapted to survive in its niche.
Co-products Although one of the most important goals is to obtain biomass, a
good strategy is also to obtain high-value biological co-products like polyunsaturated fatty acids, steroids, pigments, carotenoids, antioxidants, antibiotics, antifouling substances, among several others. The production of these substances,
besides bulk production of proteins, can make the culture system that is economically feasible or more profitable.
A good strain selection is a key process for microalgae culture success. The
strains that have been collected and isolated from extreme natural environments
are the ones that will give us better results to isolate and grow them in mass
264
M. Vanthoor-Koopmans et al.