285
ated antagonistic interactions with microbes, such as grazers, viruses and bacteria
(Wolfe et al. 1997; Seyedsayamdost et al. 2011b; Vardi et al. 2012; Bidle 2015).
However, it produces one key metabolite that promotes beneficial relationships:
dimethylsulphoniopropionate (DMSP). This sulphurous compound is used as an
antioxidant, osmoregulator and cryoprotector (Stefels 2000; Burkill et al. 2002;
Sunda et al. 2002). Roseobacters, which are numerically dominant in E. huxleyi
blooms (Green et al. 2015), play a critical role in converting DMSP into dimethyl
sulphide (DMS), an important source of carbon and sulphur for the bacteria
(González et al. 2000; Kiene et al. 2000; Moran et al. 2003; Malmstrom et al. 2004;
Miller and Belas 2004; Geng and Belas 2010; Seymour et al. 2010). DMS forms the
basis of cloud condensation nuclei, thereby affecting weather and having global
relevance in affecting Earth’s climate (Howard et al. 2006; Dickschat et al. 2010).
DMSP may be supplemented with polyhydroxyalkanoate (PHA) as a carbon
source, as shown for the bacterium Dinoroseobacter shibae when in coculture with
the dinoflagellate Prorocentrum minimum, with differential usage during light and
dark periods observed (Wang et al. 2014b). One roseobacter, Ruegeria pomeroyi
DSS-3, was shown to have upregulated catabolism of another sulphur compound
produced by its algal host Thalassiosira pseudonana, 2,3-dihydroxypropane-1sulphonate (DHPS). The algal host did not upregulate the production of DHPS in
the presence of the bacterium, so the molecule is not released in response to the
coculture, but rather the bacteria seems to take advantage of the presence of this
molecule (Durham et al. 2015). In both examples, the bacteria provided the vitamin
B 12 to the auxotrophic algae (Wang et al. 2014b; Durham et al. 2015).
Some bacteria can also control the community composition of other bacteria in
the phycosphere through their production of antibiotics. In the most extreme case,
this can give the bacteria exclusive access to the alga’s secreted nutrients while providing the alga with a defence mechanism against fouling agents (other bacteria)
that might otherwise be harmful (Rao et al. 2007). Bacteria in the roseobacter clade
are thought to produce several antibiotics of interest (Cude et al. 2012; BentzonTilia and Gram 2017). One such antibiotic that is controlled by quorum sensing
(QS) is tropodithietic acid (TDA), a potent antibiotic produced by several roseobacters such as Phaeobacter and Ruegeria (Brinkhoff et al. 2004; Bruhn et al. 2005). In
Phaeobacter gallaeciensis, TDA production is controlled by AHLs, and the TDA
can itself act as an autoinducer for TDA production (Berger et al. 2011). However,
QS is only one of the regulatory systems involved in TDA synthesis, as P. gallaeciensis QS mutants show delayed TDA production, not complete lack of TDA
synthesis (Prol García et al. 2013).
Some algae have evolved mechanisms to turn this bacterial antimicrobial biosynthesis to their advantage by manipulating their bacterial symbionts. For example,
some algae secrete compounds that mimic QS signalling molecules naturally produced by bacteria. QS molecules are autoinducers released by bacteria as a function
of their population, and when they reach the minimum concentration (quorum),
expression of specific genes is induced (Waters and Bassler 2005). Algae are known
to manipulate this process by producing analogues to block QS-regulated virulence
in algal pathogens (Rao et al. 2007; Case et al. 2011; Harder et al. 2012), and they
14 Bioactive Small Molecules Mediate Microalgal-Bacterial Interactions
ated antagonistic interactions with microbes, such as grazers, viruses and bacteria
(Wolfe et al. 1997; Seyedsayamdost et al. 2011b; Vardi et al. 2012; Bidle 2015).
However, it produces one key metabolite that promotes beneficial relationships:
dimethylsulphoniopropionate (DMSP). This sulphurous compound is used as an
antioxidant, osmoregulator and cryoprotector (Stefels 2000; Burkill et al. 2002;
Sunda et al. 2002). Roseobacters, which are numerically dominant in E. huxleyi
blooms (Green et al. 2015), play a critical role in converting DMSP into dimethyl
sulphide (DMS), an important source of carbon and sulphur for the bacteria
(González et al. 2000; Kiene et al. 2000; Moran et al. 2003; Malmstrom et al. 2004;
Miller and Belas 2004; Geng and Belas 2010; Seymour et al. 2010). DMS forms the
basis of cloud condensation nuclei, thereby affecting weather and having global
relevance in affecting Earth’s climate (Howard et al. 2006; Dickschat et al. 2010).
DMSP may be supplemented with polyhydroxyalkanoate (PHA) as a carbon
source, as shown for the bacterium Dinoroseobacter shibae when in coculture with
the dinoflagellate Prorocentrum minimum, with differential usage during light and
dark periods observed (Wang et al. 2014b). One roseobacter, Ruegeria pomeroyi
DSS-3, was shown to have upregulated catabolism of another sulphur compound
produced by its algal host Thalassiosira pseudonana, 2,3-dihydroxypropane-1sulphonate (DHPS). The algal host did not upregulate the production of DHPS in
the presence of the bacterium, so the molecule is not released in response to the
coculture, but rather the bacteria seems to take advantage of the presence of this
molecule (Durham et al. 2015). In both examples, the bacteria provided the vitamin
B 12 to the auxotrophic algae (Wang et al. 2014b; Durham et al. 2015).
Some bacteria can also control the community composition of other bacteria in
the phycosphere through their production of antibiotics. In the most extreme case,
this can give the bacteria exclusive access to the alga’s secreted nutrients while providing the alga with a defence mechanism against fouling agents (other bacteria)
that might otherwise be harmful (Rao et al. 2007). Bacteria in the roseobacter clade
are thought to produce several antibiotics of interest (Cude et al. 2012; BentzonTilia and Gram 2017). One such antibiotic that is controlled by quorum sensing
(QS) is tropodithietic acid (TDA), a potent antibiotic produced by several roseobacters such as Phaeobacter and Ruegeria (Brinkhoff et al. 2004; Bruhn et al. 2005). In
Phaeobacter gallaeciensis, TDA production is controlled by AHLs, and the TDA
can itself act as an autoinducer for TDA production (Berger et al. 2011). However,
QS is only one of the regulatory systems involved in TDA synthesis, as P. gallaeciensis QS mutants show delayed TDA production, not complete lack of TDA
synthesis (Prol García et al. 2013).
Some algae have evolved mechanisms to turn this bacterial antimicrobial biosynthesis to their advantage by manipulating their bacterial symbionts. For example,
some algae secrete compounds that mimic QS signalling molecules naturally produced by bacteria. QS molecules are autoinducers released by bacteria as a function
of their population, and when they reach the minimum concentration (quorum),
expression of specific genes is induced (Waters and Bassler 2005). Algae are known
to manipulate this process by producing analogues to block QS-regulated virulence
in algal pathogens (Rao et al. 2007; Case et al. 2011; Harder et al. 2012), and they
14 Bioactive Small Molecules Mediate Microalgal-Bacterial Interactions