282
et al. 2012; Philippot et al. 2013). While the existence of associations between macroalgae and their bacterial assemblages has also been recognized for a long time
(Provasoli 1958), research has primarily focused on macroalgae rather than microalgae (De Nys et al. 1995; Matsuo et al. 2005; Rao et al. 2007; Fernandes et al.
2011; Egan et al. 2013). Microalgae have been largely overlooked due to their small
size (μm scale) and low concentrations (<10
3
cells/mL) in normal conditions
(Li 2002), making them an unlikely habitat-forming species. However, the expansiveness of the oceans and their ability to form dense communities during bloom
conditions (>10
6
cells/mL) (Tyrrell and Merico 2004) allow them to host a diverse
bacterial consortium throughout the illuminated ocean. Bacteria inhabit the immediate phytoplankton surface, and its ‘phycosphere’—the space immediately surrounding the microalgal cell (Bell and Mitchell 1972)—is a favourable habitat due
to the nutrients leaked from the algal cell, leading to a high diversity of bacteria
(Ramanan et al. 2016).
Researchers are beginning to eavesdrop on the chemical cross talk occurring
between algae and bacteria, which may have a vast potential for new knowledge,
relating to understanding bacterial-algal relationships, evolution and possibly
hijacking this communication to better control microbes in commercial systems
(Demuez et al. 2015). For instance, bacteria have been shown to affect microalgal aggregation and sinking, which has important implications for better understanding of algal bloom dynamics in both natural and industrial systems (Grossart
et al. 2006).
These algal-bacterial interactions can be classified into several categories
(Fig. 14.2), including mutualistic, where both parties benefit; commensal, where
one party benefits; parasitic, where the bacteria negatively affect the health and
fecundity of algae; or pathogenic, which causes disease and/or death of the host
(Joint et al. 2002; Mayali and Azam 2004; Grossart et al. 2005; Azam and Malfatti
2007; Seyedsayamdost et al. 2011b; Amin et al. 2012). Bioactive molecules are
important mediators in these interactions; but in many cases, they are not well
understood or have yet to be identified. This review will look at the small molecules
involved in both the beneficial and negative interactions between microalgae and
their consortia of bacteria.
14.2 Beneficial Interactions
14.2.1 Mutualism
There are many potential advantages for bacteria in living near or attaching to an
algal host. Many bacteria can rapidly sense and respond to chemical gradients using
chemotaxis, allowing them to navigate towards the algal host (Miller et al. 2004;
Stocker and Seymour 2012). Attachment to the host gives the bacteria a ready supply of organic compounds and an environment to interact closely with other bacteria
(Geng and Belas 2010). Bacteria have been shown to chemotax to small diffusible
L. Labeeuw et al.
et al. 2012; Philippot et al. 2013). While the existence of associations between macroalgae and their bacterial assemblages has also been recognized for a long time
(Provasoli 1958), research has primarily focused on macroalgae rather than microalgae (De Nys et al. 1995; Matsuo et al. 2005; Rao et al. 2007; Fernandes et al.
2011; Egan et al. 2013). Microalgae have been largely overlooked due to their small
size (μm scale) and low concentrations (<10
3
cells/mL) in normal conditions
(Li 2002), making them an unlikely habitat-forming species. However, the expansiveness of the oceans and their ability to form dense communities during bloom
conditions (>10
6
cells/mL) (Tyrrell and Merico 2004) allow them to host a diverse
bacterial consortium throughout the illuminated ocean. Bacteria inhabit the immediate phytoplankton surface, and its ‘phycosphere’—the space immediately surrounding the microalgal cell (Bell and Mitchell 1972)—is a favourable habitat due
to the nutrients leaked from the algal cell, leading to a high diversity of bacteria
(Ramanan et al. 2016).
Researchers are beginning to eavesdrop on the chemical cross talk occurring
between algae and bacteria, which may have a vast potential for new knowledge,
relating to understanding bacterial-algal relationships, evolution and possibly
hijacking this communication to better control microbes in commercial systems
(Demuez et al. 2015). For instance, bacteria have been shown to affect microalgal aggregation and sinking, which has important implications for better understanding of algal bloom dynamics in both natural and industrial systems (Grossart
et al. 2006).
These algal-bacterial interactions can be classified into several categories
(Fig. 14.2), including mutualistic, where both parties benefit; commensal, where
one party benefits; parasitic, where the bacteria negatively affect the health and
fecundity of algae; or pathogenic, which causes disease and/or death of the host
(Joint et al. 2002; Mayali and Azam 2004; Grossart et al. 2005; Azam and Malfatti
2007; Seyedsayamdost et al. 2011b; Amin et al. 2012). Bioactive molecules are
important mediators in these interactions; but in many cases, they are not well
understood or have yet to be identified. This review will look at the small molecules
involved in both the beneficial and negative interactions between microalgae and
their consortia of bacteria.
14.2 Beneficial Interactions
14.2.1 Mutualism
There are many potential advantages for bacteria in living near or attaching to an
algal host. Many bacteria can rapidly sense and respond to chemical gradients using
chemotaxis, allowing them to navigate towards the algal host (Miller et al. 2004;
Stocker and Seymour 2012). Attachment to the host gives the bacteria a ready supply of organic compounds and an environment to interact closely with other bacteria
(Geng and Belas 2010). Bacteria have been shown to chemotax to small diffusible
L. Labeeuw et al.