MICROBES
Elizabeth A. Dinsdale
San Diego State University, San Diego, CA, USA
Definition
Microbes are microscopic organisms. Many organisms fit
into this size category, including, Bacteria, Archaea, Fungi,
Protists, etc. The definition provided here uses microbes to
describe Bacteria and Archaea. These two groups are unicellular organisms, which do not contain a nucleus and
rarely harbor membrane-bound organelles. Both Bacteria
and Archaea were classified together as Prokaryotes, but
this classification is no longer considered appropriate,
because these two groups evolved from separate lineages.
Microbial association with corals: holobiont
Corals exist as a community of multiple organisms that
work together, termed the coral holobiont (Knowlton and
Rohwer, 2003). These organisms include the coral animal,
microbes, Fungi, endolithic algae, and zooxanthellae
(Rohwer et al., 2002, Wegley et al., 2004). Microbes associated with corals are diverse, numerous and provide many
functions (Kushmaro et al., 1996; Frias-Lopez et al.,
2002). Microbes form species-specific associations
(Rohwer et al., 2001); however, some taxonomic variation
occurs between reefs (Littman et al., 2009).
Functional role of microbes
Metagenomic analysis shows that microbes possess a
gene complement that allows them to perform a diverse
variety of functions (Wegley et al., 2007). Coral associated
microbes have the genes to breakdown complex sugars
and proteins, reflecting the types of carbohydrates
excreted by the coral animal. Nitrogen fixation, ammonia
assimilation, and nitrate/nitrite ammonification are functions that the coral associated microbes can conduct and
these would enhance nitrogen recycling with in the
holobiont and potentially supplement supplies of nitrogen
to the zooxanthellae. Coral associated microbes possessed
multiple pathways involved in sulfur cycling. Microbes
associated with Dimethylsulfoniopropionate (DMSP)
breakdown are also common within the coral holobiont
(Raina et al., 2009). Since sulfur is an essential element
in the biosynthesis of amino acids, the microbial community maybe playing a pivotal role in the coral growth.
Other mutualistic benefits provided by the microbes
include, the release of secondary metabolites, such as antibiotics (Castillo et al., 2001).
Microbial role in coral stress
Changes in microbial complement associated with changes
in environmental conditions may exacerbate coral stress.
Corals exposed to four stressors, including increased
organic carbon, inorganic nutrients, temperature, and
reduced pH, showed a variation in their associated microbial assemblage. Genes including those associated with
virulence, stress response, sulfur and nitrogen metabolism,
motility, and chemotaxis increased within the microbial
community of stressed corals. The microbial taxonomic
component associated with the stressed coral was dominated by species often associated with disease, including
many Bacteriodetes and Fusobacteria (Vega Thurber
et al., 2009).
Microbial role in altering environmental
conditions
Apart from symbiotic microbes, corals are influenced by
the microbes present in their surroundings, such as those
in the water column or in the substratum. Microbiolization
of the water column was a feature of coral reefs influenced
by high levels of human activity (Dinsdale et al., 2008).
On a coral reef with little to no fishing or human habitation
microbial numbers were low and their gene complement
matched that of a balanced autotrophic/heterotrophic community (Dinsdale et al., 2008). On reefs with higher levels
of fishing and human population, microbes were highly
abundant and dominated by heterotrophic microbes, many
of which were similar to known pathogens. The increase in
pathogenic-like microbes was correlated with an increase of
unhealthy corals (Dinsdale et al., 2008, Sandin et al., 2008).
Bibliography
Castillo, I., Lodeiros, C., Nunez, M., and Campos, I., 2001. In vitro
evaluation of antibacterial substances produced by bacteria isolated from different marine organisms. Revista de Biología Tropical, 49, 1213–1221.
Dinsdale, E. A., Pantos, O., Smriga, S., Edwards, R. A., Angly, F.,
Wegley, L., Hatay, M., Hall, D., Brown, E., Haynes, M., Krause,
L., Sala, E., Sandin, S. A., Thurber, R. V., Willis, B. L., Azam, F.,
Knowlton, N., and Rohwer, F., 2008. Microbial ecology of four
coral atolls in the Northern Line Islands. PLoS ONE, 3, e1584.
Frias-Lopez, J., Zerkle, A. L., Bonheyo, G. T., and Fouke, B. W.,
2002. Partitioning of bacterial communities between seawater
and healthy, black band diseased, and dead coral surfaces.
Applied and Environmental Microbiology, 68, 2214–2228.
Knowlton, N., and Rohwer, F., 2003. Multispecies microbial mutualisms on coral reefs: The host as a habitat. American Naturalist,
162, S51–S62.
Kushmaro, A., Loya, Y., Fine, M., and Rosenberg, E., 1996. Bacterial infection and coral bleaching. Nature, 380, 396–396.
Littman, R. A., Willis, B. L., Pfeffer, C., and Bourne, D. G., 2009.
Diversities of coral-associated Bacteria differ with location, but
not species, for three acroporid corals on the Great Barrier Reef.
Fems Microbiology Ecology, 68, 152–163.
Raina, J. B., Tapiolas, D., Willis, B. L., and Bourne, D. G., 2009.
Coral-associated bacteria and their role in the biogeochemical
cycling of sulfur. Applied and Environmental Microbiology,
75, 3492–3501.
Rohwer, F., Breitbart, M., Jara, J., Azam, F., and Knowlton, N.,
2001. Diversity of bacteria associated with the Caribbean coral
Montastraea franksi. Coral Reefs, 20, 85–91.
Rohwer, F., Seguritan, V., Azam, F., and Knowlton, N., 2002.
Diversity and distribution of coral-associated Bacteria. Marine
Ecology Progress Series, 243, 1–10.
MICROBES
697
Elizabeth A. Dinsdale
San Diego State University, San Diego, CA, USA
Definition
Microbes are microscopic organisms. Many organisms fit
into this size category, including, Bacteria, Archaea, Fungi,
Protists, etc. The definition provided here uses microbes to
describe Bacteria and Archaea. These two groups are unicellular organisms, which do not contain a nucleus and
rarely harbor membrane-bound organelles. Both Bacteria
and Archaea were classified together as Prokaryotes, but
this classification is no longer considered appropriate,
because these two groups evolved from separate lineages.
Microbial association with corals: holobiont
Corals exist as a community of multiple organisms that
work together, termed the coral holobiont (Knowlton and
Rohwer, 2003). These organisms include the coral animal,
microbes, Fungi, endolithic algae, and zooxanthellae
(Rohwer et al., 2002, Wegley et al., 2004). Microbes associated with corals are diverse, numerous and provide many
functions (Kushmaro et al., 1996; Frias-Lopez et al.,
2002). Microbes form species-specific associations
(Rohwer et al., 2001); however, some taxonomic variation
occurs between reefs (Littman et al., 2009).
Functional role of microbes
Metagenomic analysis shows that microbes possess a
gene complement that allows them to perform a diverse
variety of functions (Wegley et al., 2007). Coral associated
microbes have the genes to breakdown complex sugars
and proteins, reflecting the types of carbohydrates
excreted by the coral animal. Nitrogen fixation, ammonia
assimilation, and nitrate/nitrite ammonification are functions that the coral associated microbes can conduct and
these would enhance nitrogen recycling with in the
holobiont and potentially supplement supplies of nitrogen
to the zooxanthellae. Coral associated microbes possessed
multiple pathways involved in sulfur cycling. Microbes
associated with Dimethylsulfoniopropionate (DMSP)
breakdown are also common within the coral holobiont
(Raina et al., 2009). Since sulfur is an essential element
in the biosynthesis of amino acids, the microbial community maybe playing a pivotal role in the coral growth.
Other mutualistic benefits provided by the microbes
include, the release of secondary metabolites, such as antibiotics (Castillo et al., 2001).
Microbial role in coral stress
Changes in microbial complement associated with changes
in environmental conditions may exacerbate coral stress.
Corals exposed to four stressors, including increased
organic carbon, inorganic nutrients, temperature, and
reduced pH, showed a variation in their associated microbial assemblage. Genes including those associated with
virulence, stress response, sulfur and nitrogen metabolism,
motility, and chemotaxis increased within the microbial
community of stressed corals. The microbial taxonomic
component associated with the stressed coral was dominated by species often associated with disease, including
many Bacteriodetes and Fusobacteria (Vega Thurber
et al., 2009).
Microbial role in altering environmental
conditions
Apart from symbiotic microbes, corals are influenced by
the microbes present in their surroundings, such as those
in the water column or in the substratum. Microbiolization
of the water column was a feature of coral reefs influenced
by high levels of human activity (Dinsdale et al., 2008).
On a coral reef with little to no fishing or human habitation
microbial numbers were low and their gene complement
matched that of a balanced autotrophic/heterotrophic community (Dinsdale et al., 2008). On reefs with higher levels
of fishing and human population, microbes were highly
abundant and dominated by heterotrophic microbes, many
of which were similar to known pathogens. The increase in
pathogenic-like microbes was correlated with an increase of
unhealthy corals (Dinsdale et al., 2008, Sandin et al., 2008).
Bibliography
Castillo, I., Lodeiros, C., Nunez, M., and Campos, I., 2001. In vitro
evaluation of antibacterial substances produced by bacteria isolated from different marine organisms. Revista de Biología Tropical, 49, 1213–1221.
Dinsdale, E. A., Pantos, O., Smriga, S., Edwards, R. A., Angly, F.,
Wegley, L., Hatay, M., Hall, D., Brown, E., Haynes, M., Krause,
L., Sala, E., Sandin, S. A., Thurber, R. V., Willis, B. L., Azam, F.,
Knowlton, N., and Rohwer, F., 2008. Microbial ecology of four
coral atolls in the Northern Line Islands. PLoS ONE, 3, e1584.
Frias-Lopez, J., Zerkle, A. L., Bonheyo, G. T., and Fouke, B. W.,
2002. Partitioning of bacterial communities between seawater
and healthy, black band diseased, and dead coral surfaces.
Applied and Environmental Microbiology, 68, 2214–2228.
Knowlton, N., and Rohwer, F., 2003. Multispecies microbial mutualisms on coral reefs: The host as a habitat. American Naturalist,
162, S51–S62.
Kushmaro, A., Loya, Y., Fine, M., and Rosenberg, E., 1996. Bacterial infection and coral bleaching. Nature, 380, 396–396.
Littman, R. A., Willis, B. L., Pfeffer, C., and Bourne, D. G., 2009.
Diversities of coral-associated Bacteria differ with location, but
not species, for three acroporid corals on the Great Barrier Reef.
Fems Microbiology Ecology, 68, 152–163.
Raina, J. B., Tapiolas, D., Willis, B. L., and Bourne, D. G., 2009.
Coral-associated bacteria and their role in the biogeochemical
cycling of sulfur. Applied and Environmental Microbiology,
75, 3492–3501.
Rohwer, F., Breitbart, M., Jara, J., Azam, F., and Knowlton, N.,
2001. Diversity of bacteria associated with the Caribbean coral
Montastraea franksi. Coral Reefs, 20, 85–91.
Rohwer, F., Seguritan, V., Azam, F., and Knowlton, N., 2002.
Diversity and distribution of coral-associated Bacteria. Marine
Ecology Progress Series, 243, 1–10.
MICROBES
697