280
14.1 Introduction
Phytoplankton are a diverse group of photosynthetic microorganisms, or primary
producers, including both eukaryotic algae and cyanobacteria, which live planktonically in the water column (Litchman et al. 2015). Phytoplankton are important players in global biogeochemical cycles, accounting for approximately 40–50% of the
world’s carbon fixation and driving the marine carbon pump (Falkowski 1994). In
other words, phytoplankton contribute almost half of the global net primary productivity, despite accounting for less than 1% of the global photosynthetic biomass
(Field et al. 1998; Falkowski 2012). In addition, phytoplankton make up the base of
the marine food web, are major players in driving ecosystem functioning and diversification and act as a habitat-forming species in the open ocean, where they form
massive blooms (Falkowski 2012; Stevenson 2014).
Phytoplankton also represent most of the diversity in algae, a term applied to a
large and diverse group of photosynthetic eukaryotic organisms only distantly related
across the phylogenetic tree of life (Fig. 14.1) (Archibald 2009; Keeling 2010). A billion years ago, the establishment of a cyanobacterium as an endosymbiont in a nonphotosynthetic eukaryote created the chloroplast (Gray 1999; Yoon et al. 2004),
leading to the evolution of the ancestor of all extant archaeplastids (primary endosymbiosis). However, the subsequent understanding of plastid evolution becomes murky
due to successive transfers to other lineages through secondary and tertiary endosymbiotic events, as well as multiple loss events (Keeling 2010). This has led to algae
being present in nearly every one of the major eukaryotic supergroups, namely,
Archaeplastida, Excavata, the SAR (Stramenopiles- Alveolates- Rhizaria) group and
the currently unaffiliated haptophytes and cryptophytes (Fig. 14.1). Although these
groups are clearly distinct phylogenetically, there is a continuing debate on their relationship to each other (Keeling 2013; Burki 2014; Derelle et al. 2015).
In their natural environment, microalgae are surrounded by bacteria. Their interactions can be shaped by the complex exchange of small bioactive molecules. These
bacterial and algal bioactive molecules may be involved in communication, behavioural modification, or as weaponry between bacteria and eukaryotes, with possible
biotechnology applications. For example, algae are a rich source of natural products
(such as antibiotics, lipids, fatty acids, toxins, nutraceuticals and pharmaceuticals)
(Bhatnagar and Kim 2010), with phytoplankton accounting for approximately 15%
Contents
14.1 Introduction .................................................................................................................... 280
14.2 Beneficial Interactions ................................................................................................... 282
14.2.1 Mutualism ......................................................................................................... 282
14.2.2 Commensalism ................................................................................................. 287
14.3 Negative Interactions ..................................................................................................... 287
14.3.1 Parasitism ......................................................................................................... 287
14.3.2 Pathogenicity .................................................................................................... 288
14.4 Possible Applications ..................................................................................................... 291
14.5 Conclusion ..................................................................................................................... 292
References ................................................................................................................................. 292
L. Labeeuw et al.
14.1 Introduction
Phytoplankton are a diverse group of photosynthetic microorganisms, or primary
producers, including both eukaryotic algae and cyanobacteria, which live planktonically in the water column (Litchman et al. 2015). Phytoplankton are important players in global biogeochemical cycles, accounting for approximately 40–50% of the
world’s carbon fixation and driving the marine carbon pump (Falkowski 1994). In
other words, phytoplankton contribute almost half of the global net primary productivity, despite accounting for less than 1% of the global photosynthetic biomass
(Field et al. 1998; Falkowski 2012). In addition, phytoplankton make up the base of
the marine food web, are major players in driving ecosystem functioning and diversification and act as a habitat-forming species in the open ocean, where they form
massive blooms (Falkowski 2012; Stevenson 2014).
Phytoplankton also represent most of the diversity in algae, a term applied to a
large and diverse group of photosynthetic eukaryotic organisms only distantly related
across the phylogenetic tree of life (Fig. 14.1) (Archibald 2009; Keeling 2010). A billion years ago, the establishment of a cyanobacterium as an endosymbiont in a nonphotosynthetic eukaryote created the chloroplast (Gray 1999; Yoon et al. 2004),
leading to the evolution of the ancestor of all extant archaeplastids (primary endosymbiosis). However, the subsequent understanding of plastid evolution becomes murky
due to successive transfers to other lineages through secondary and tertiary endosymbiotic events, as well as multiple loss events (Keeling 2010). This has led to algae
being present in nearly every one of the major eukaryotic supergroups, namely,
Archaeplastida, Excavata, the SAR (Stramenopiles- Alveolates- Rhizaria) group and
the currently unaffiliated haptophytes and cryptophytes (Fig. 14.1). Although these
groups are clearly distinct phylogenetically, there is a continuing debate on their relationship to each other (Keeling 2013; Burki 2014; Derelle et al. 2015).
In their natural environment, microalgae are surrounded by bacteria. Their interactions can be shaped by the complex exchange of small bioactive molecules. These
bacterial and algal bioactive molecules may be involved in communication, behavioural modification, or as weaponry between bacteria and eukaryotes, with possible
biotechnology applications. For example, algae are a rich source of natural products
(such as antibiotics, lipids, fatty acids, toxins, nutraceuticals and pharmaceuticals)
(Bhatnagar and Kim 2010), with phytoplankton accounting for approximately 15%
Contents
14.1 Introduction .................................................................................................................... 280
14.2 Beneficial Interactions ................................................................................................... 282
14.2.1 Mutualism ......................................................................................................... 282
14.2.2 Commensalism ................................................................................................. 287
14.3 Negative Interactions ..................................................................................................... 287
14.3.1 Parasitism ......................................................................................................... 287
14.3.2 Pathogenicity .................................................................................................... 288
14.4 Possible Applications ..................................................................................................... 291
14.5 Conclusion ..................................................................................................................... 292
References ................................................................................................................................. 292
L. Labeeuw et al.