321
endosymbiotic dinoflagellates, bacterial and viral associates of polyp, and dinoflagellates (Rohwer et al. 2002). Coral polyps are composed of two layers of cells, the epidermis and gastrodermis, covered by a surface mucus layer and connected to a large,
porous calcium carbonate skeleton (Rosenberg et al. 2007). The symbiotic dinoflagellate from the genus Symbiodinium is a photosynthetic associate that resides inside the
membrane-bound vacuoles within specialized cells of the polyp. They are the main
source of carbon nutrition as they translocate approximately 60–80% of their photosynthate to the coral host, allowing the holobiont to thrive in nutrient-poor waters
(Tremblay et al. 2012). These dinoflagellate endosymbionts contribute significantly to
the physiological attributes of the coral holobiont as these associations are dynamic
and flexible. Corals can expel their dinoflagellate symbionts and acquire new strains
(or even clades) of Symbiodinium that may be more effective in aiding holobiont to
respond under environmental stress conditions (Little et al. 2004). The flexible associations of the dinoflagellates with coral encouraged researchers to investigate flexibility of the interactions between corals and the bacteria. With the incorporation of
new high-throughput techniques like metagenomics, DGGE in coral microbiology,
the knowledge about the nature of coral-microbe interactions is growing by leaps and
bounds to address questions about the makeup and dynamics of coral microbial
assemblages.
16.3 Bacterial Diversity Associated with Coral Reef
Ecosystem
Bacteria are omnipresent and corals are no exception. They have coexisted ever
since the early stages of evolution. They represent all conceivable modes of interactions—mutualism, parasitism, and commensalism. These interactions together
influence the ecosystem directly or indirectly. It is well known that corals and bacteria synergistically affect each other’s physiology and metabolism. Their interactions are important for the primary productivity of the most ecosystems.
In general, corals provide mainly three niches to bacteria each of which has a
distinct bacterial population. These include the surface mucus layer, the coral tissue
(including the gastrodermis cavity), and the calcium carbonate skeleton (Bourne
and Munn 2005; Koren and Rosenberg 2006; Rosenberg et al. 2007) (Fig. 16.4).
The diversity of coral-associated bacteria has been reasonably well documented in
these niches using both culture-dependent and culture-independent techniques
(Rohwer et al. 2002; Bourne and Munn 2005; Wegley et al. 2007; Dinsdale et al.
2008; Thurber et al. 2009; Cook et al. 2013). These studies indicate that it is common for a single coral to house many of the known divisions of bacteria such as
Gammaproteobacteria, Alphaproteobacteria, Cyanobacteria, Firmicutes, and
Bacteroidetes (Littman et al. 2009; Bayer et al. 2013). Moreover, the various coral
niches are reported to be colonized by distinctive species (Sweet et al. 2011; Agostini
et al. 2012), and environmental disturbances can alter coral microbial communities
16 Role of Bacteria in Coral Ecosystem
endosymbiotic dinoflagellates, bacterial and viral associates of polyp, and dinoflagellates (Rohwer et al. 2002). Coral polyps are composed of two layers of cells, the epidermis and gastrodermis, covered by a surface mucus layer and connected to a large,
porous calcium carbonate skeleton (Rosenberg et al. 2007). The symbiotic dinoflagellate from the genus Symbiodinium is a photosynthetic associate that resides inside the
membrane-bound vacuoles within specialized cells of the polyp. They are the main
source of carbon nutrition as they translocate approximately 60–80% of their photosynthate to the coral host, allowing the holobiont to thrive in nutrient-poor waters
(Tremblay et al. 2012). These dinoflagellate endosymbionts contribute significantly to
the physiological attributes of the coral holobiont as these associations are dynamic
and flexible. Corals can expel their dinoflagellate symbionts and acquire new strains
(or even clades) of Symbiodinium that may be more effective in aiding holobiont to
respond under environmental stress conditions (Little et al. 2004). The flexible associations of the dinoflagellates with coral encouraged researchers to investigate flexibility of the interactions between corals and the bacteria. With the incorporation of
new high-throughput techniques like metagenomics, DGGE in coral microbiology,
the knowledge about the nature of coral-microbe interactions is growing by leaps and
bounds to address questions about the makeup and dynamics of coral microbial
assemblages.
16.3 Bacterial Diversity Associated with Coral Reef
Ecosystem
Bacteria are omnipresent and corals are no exception. They have coexisted ever
since the early stages of evolution. They represent all conceivable modes of interactions—mutualism, parasitism, and commensalism. These interactions together
influence the ecosystem directly or indirectly. It is well known that corals and bacteria synergistically affect each other’s physiology and metabolism. Their interactions are important for the primary productivity of the most ecosystems.
In general, corals provide mainly three niches to bacteria each of which has a
distinct bacterial population. These include the surface mucus layer, the coral tissue
(including the gastrodermis cavity), and the calcium carbonate skeleton (Bourne
and Munn 2005; Koren and Rosenberg 2006; Rosenberg et al. 2007) (Fig. 16.4).
The diversity of coral-associated bacteria has been reasonably well documented in
these niches using both culture-dependent and culture-independent techniques
(Rohwer et al. 2002; Bourne and Munn 2005; Wegley et al. 2007; Dinsdale et al.
2008; Thurber et al. 2009; Cook et al. 2013). These studies indicate that it is common for a single coral to house many of the known divisions of bacteria such as
Gammaproteobacteria, Alphaproteobacteria, Cyanobacteria, Firmicutes, and
Bacteroidetes (Littman et al. 2009; Bayer et al. 2013). Moreover, the various coral
niches are reported to be colonized by distinctive species (Sweet et al. 2011; Agostini
et al. 2012), and environmental disturbances can alter coral microbial communities
16 Role of Bacteria in Coral Ecosystem