327
16.4.2 Coral-Associated Bacteria as a Pathogen
Over the past several decades, the decline in coral reef has been observed. Various
bacterial pathogens have been found responsible for this decline. These pathogens
cause diseases such as coral bleaching and black band disease, to name a few
(Rosenberg et al. 2007; Pratte 2013). Coral diseases are linked to various environmental stresses such as temperature increase, water pollution, and many other
anthropogenic activities which altogether make coral animal susceptible to infections by pathogens (Roder et al. 2014). For instance, the decline in the Caribbean
populations of the elkhorn coral A. palmata is due to environmental stress resulting in bleaching, and the disease has been reported. They showed a decrease in
antibiotic activity of bacterial isolates from the mucus and tissue of A. palmata
during a summer bleaching event and were dominated by members of the genus
Vibrio which are the common pathogens of coral diseases (Ritchie 2006). Another
study by Rypien et al. (2010) observed that members of the Gammaproteobacteria
particularly Vibrionales and Alteromonadales had high antagonistic activity
against other coral bacteria. Other than antimicrobial activity against coral native
bacteria, there are several ways by which these bacteria cause coral diseases such
as by producing high radical oxygen species (ROS) scavenging compounds and
enzymes which enable them to thrive on the oxidative-stressed coral surface
resulting from the metabolic activities of zooxanthellae and associated microbes.
Moreover, according to several studies, these antioxidant enzymes are related to
virulence such as superoxide dismutase in V. shiloi, which aid in its pathogenicity
(Munn et al. 2008). Siderophore-producing bacteria are also known to cause coral
disease by competing with the host and its associated microorganisms for iron
which is a limiting nutrient present in very low concentration in the marine environment. Siderophore is known to play a dual role in the infectious process. These
are by enhancing the growth of the invading pathogen and inhibiting host defense
system (Autenrieth et al. 1991). However, in the middle of the negative role of
coral pathogens, a study by Marhaver et al. (2013) suggested the importance of
pathogenic and opportunistic bacteria in structuring the reef community by mortality of nearby conspecific coral recruits (Fig. 16.6).
16.5 Recent Technologies to Study the Role of Bacteria
in Coral Ecosystem
Various biotechnological techniques are required to study the role of bacteria in the
coral ecosystem. These techniques include biochemical methods, microbiological
methods, and molecular techniques. With recent advancement and easy accessibility, molecular methods based on targeting DNA, RNA, and proteins have gained
much popularity among researchers to explore diverse bacteria and their functional
role in coral holobiont. Below, we reviewed some of the advance molecular techniques used in coral-bacterial research.
16 Role of Bacteria in Coral Ecosystem
16.4.2 Coral-Associated Bacteria as a Pathogen
Over the past several decades, the decline in coral reef has been observed. Various
bacterial pathogens have been found responsible for this decline. These pathogens
cause diseases such as coral bleaching and black band disease, to name a few
(Rosenberg et al. 2007; Pratte 2013). Coral diseases are linked to various environmental stresses such as temperature increase, water pollution, and many other
anthropogenic activities which altogether make coral animal susceptible to infections by pathogens (Roder et al. 2014). For instance, the decline in the Caribbean
populations of the elkhorn coral A. palmata is due to environmental stress resulting in bleaching, and the disease has been reported. They showed a decrease in
antibiotic activity of bacterial isolates from the mucus and tissue of A. palmata
during a summer bleaching event and were dominated by members of the genus
Vibrio which are the common pathogens of coral diseases (Ritchie 2006). Another
study by Rypien et al. (2010) observed that members of the Gammaproteobacteria
particularly Vibrionales and Alteromonadales had high antagonistic activity
against other coral bacteria. Other than antimicrobial activity against coral native
bacteria, there are several ways by which these bacteria cause coral diseases such
as by producing high radical oxygen species (ROS) scavenging compounds and
enzymes which enable them to thrive on the oxidative-stressed coral surface
resulting from the metabolic activities of zooxanthellae and associated microbes.
Moreover, according to several studies, these antioxidant enzymes are related to
virulence such as superoxide dismutase in V. shiloi, which aid in its pathogenicity
(Munn et al. 2008). Siderophore-producing bacteria are also known to cause coral
disease by competing with the host and its associated microorganisms for iron
which is a limiting nutrient present in very low concentration in the marine environment. Siderophore is known to play a dual role in the infectious process. These
are by enhancing the growth of the invading pathogen and inhibiting host defense
system (Autenrieth et al. 1991). However, in the middle of the negative role of
coral pathogens, a study by Marhaver et al. (2013) suggested the importance of
pathogenic and opportunistic bacteria in structuring the reef community by mortality of nearby conspecific coral recruits (Fig. 16.6).
16.5 Recent Technologies to Study the Role of Bacteria
in Coral Ecosystem
Various biotechnological techniques are required to study the role of bacteria in the
coral ecosystem. These techniques include biochemical methods, microbiological
methods, and molecular techniques. With recent advancement and easy accessibility, molecular methods based on targeting DNA, RNA, and proteins have gained
much popularity among researchers to explore diverse bacteria and their functional
role in coral holobiont. Below, we reviewed some of the advance molecular techniques used in coral-bacterial research.
16 Role of Bacteria in Coral Ecosystem