Microalgae: A Renewable Source of Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 215

9 Microalgae: A Renewable Source
of Bioproducts
Susan I. Blackburn and John K. Volkman
9.1 INTRODUCTION
Microalgae are single-celled plants that are found in aquatic environments globally. With a
vast biodiversity they are an essential part of the aquatic food web and produce a range of
bioproducts, including bioactive compounds, lipids of nutritional and energy importance,
pigments, proteins, polysaccharides, vitamins, and antioxidants. This, combined with their
capacity to be cultured, means they are a renewable resource of considerable economic
potential. Used historically as human foods and in recent decades developed for aquaculture
feeds, microalgae are still a relatively untapped source for bioproducts. The intense interest
in biofuels for renewable energy has given a new focus on microalgae not only for biofuels
but also for the relatively untapped potential for algae for a range of products as part of a
biorefinery concept. New, more efficient growth technologies and genetic engineering pave
the way for microalgae to be a significant future source of renewable bioproducts.
9.2 MICROALGAE AND THEIR GLOBAL IMPORTANCE
Microalgae are found in all aquatic environments - oceans, lakes, rivers, even small ponds -
as well as some extreme terrestrial environments, such as deserts and polar environments.
With sizes (length or breadth) ranging from 10 -6 of a metre (1 μm) to less than a millimetre
they are mostly invisible to the naked eye, except when they form natural proliferations
called algal blooms. Microalgae have many varied and often beautiful morphologies that
may only be revealed at high magnification. Examples of microalgae viewed with the
scanning electron microscope are shown in Figure 9.1.
Microalgae are the world's fastest-growing plants. Typically they reproduce vegetatively,
dividing by binary fission, that is, one cell divides to form two cells, two to four cells, and
so on. Doubling times range from more than once per day for some species (e.g. the
cyanobacterium (blue green alga) Synechococcus ), to doubling times of two or more days
for some dinoflagellates. Some microalgae can also reproduce sexually with consequent
genetic exchange, thus maintaining genetic variation within a population. Some species
form resting stages that can survive long periods in aquatic environments. These are often
associated with sexual reproduction, thus combining the survival strategies of resistance to