Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat

Knowlton­, Nancy­; Rohwer, Forest

doi:10.1086/378684

Cited by 411 publications

(322 citation statements)

References 63 publications

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“…Such results pose interesting questions, including how such microbial communities are maintained, the potential widespread microbial mutualisms that exists in coral reef ecosystems and the important functions these may play in ecosystem health (Knowlton and Rohwer, 2003).…”

Section: Discussionmentioning

confidence: 99%

Changes in coral-associated microbial communities during a bleaching event

et al. 2007

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Environmental stressors such as increased sea surface temperatures are well-known for contributing to coral bleaching; however, the effect of increased temperatures and subsequent bleaching on coral-associated microbial communities is poorly understood. Colonies of the hard coral Acropora millepora were tagged on a reef flat off Magnetic Island (Great Barrier Reef) and surveyed over 2.5 years, which included a severe bleaching event in January/February 2002. Daily average water temperatures exceeded the previous 10-year average by more than 1 1C for extended periods with field-based visual surveys recording all tagged colonies displaying signs of bleaching. During the bleaching period, direct counts of coral zooxanthellae densities decreased by B64%, before recovery to pre-bleaching levels after the thermal stress event. A subset of three tagged coral colonies were sampled through the bleaching event and changes in the microbial community elucidated. Denaturing gradient gel electrophoresis (DGGE) analysis demonstrated conserved bacterial banding profiles between the three coral colonies, confirming previous studies highlighting specific microbial associations. As coral colonies bleached, the microbial community shifted and redundancy analysis (RDA) of DGGE banding patterns revealed a correlation of increasing temperature with the appearance of Vibrio-affiliated sequences. Interestingly, this shift to a Vibrio-dominated community commenced prior to visual signs of bleaching. Clone libraries hybridized with Vibrio-specific oligonucleotide probes confirmed an increase in the fraction of Vibrio-affiliated clones during the bleaching period. Post bleaching, the coral microbial associations again shifted, returning to a profile similar to the fingerprints prior to bleaching. This provided further evidence for corals selecting and shaping their microbial partners. For non-bleached samples, a close association with Spongiobacter-related sequences were revealed by both clone libraries and DGGE profiling. Despite Vibrio species being previously implicated in bleaching of specific coral species, it is unsure if the relative increase in retrieved Vibrio sequences is due to bacterial infection or an opportunistic response to compromised health and changing environmental parameters of the coral host. This study provides the first molecular-based study demonstrating changes in coral-associated bacterial assemblages during a bleaching event on a natural reef system.

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Section: Discussionmentioning

confidence: 99%

Changes in coral-associated microbial communities during a bleaching event

et al. 2007

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“…Corals live in symbiotic relationships with a plethora of organisms, including endosymbiotic dinoflagellate algae (zooxanthellae), bacteria, archaea and fungi (Falkowski et al, 1984;Rohwer et al, 2002;Knowlton and Rohwer, 2003;Reshef et al, 2006). The whole association has been described as a holobiont (Rosenberg et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Climate change affects key nitrogen-fixing bacterial populations on coral reefs

Santos

Carmo

Duarte³

et al. 2014

The ISME Journal

126

111

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Coral reefs are at serious risk due to events associated with global climate change. Elevated ocean temperatures have unpredictable consequences for the ocean's biogeochemical cycles. The nitrogen cycle is driven by complex microbial transformations, including nitrogen fixation. This study investigated the effects of increased seawater temperature on bacteria able to fix nitrogen (diazotrophs) that live in association with the mussid coral Mussismilia harttii. Consistent increases in diazotroph abundances and diversities were found at increased temperatures. Moreover, gradual shifts in the dominance of particular diazotroph populations occurred as temperature increased, indicating a potential future scenario of climate change. The temperature-sensitive diazotrophs may provide useful bioindicators of the effects of thermal stress on coral reef health, allowing the impact of thermal anomalies to be monitored. In addition, our findings support the development of research on different strategies to improve the fitness of corals during events of thermal stress, such as augmentation with specific diazotrophs.

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“…Although commonly presented as a simple model mutualism, technological advances such as scanning electron microscopy and environmental DNA sequencing have demonstrated additional complexity to this symbiosis involving a wide array of microbial symbionts associated with corals. A high diversity of bacteria, archaea, viruses, algae, protozoa and fungi comprise a complex assemblage that, including the coral animal, has been termed the coral holobiont (Rohwer et al, 2002;Knowlton and Rohwer, 2003). These organisms have been found to differ from those in the adjacent water column and represent potentially co-evolved symbionts (Rosenberg et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Coral-associated marine fungi form novel lineages and heterogeneous assemblages

Amend

Barshis²,

Oliver³

2011

The ISME Journal

141

100

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Coral stress tolerance is intricately tied to the animal's association with microbial symbionts. The most well-known of these symbioses is that between corals and their dinoflagellate photobionts (Symbiodinium spp.), whose genotype indirectly affects whether a coral can survive cyclical and anthropogenic warming events. Fungi comprise a lesser-known coral symbiotic community whose taxonomy, stability and function is largely un-examined. To assess how fungal communities inside a coral host correlate with water temperature and the genotype of co-occurring Symbiodinium, we sampled Acropora hyacinthus coral colonies from adjacent natural pools with different water temperatures and Symbiodinium identities. Phylogenetic analysis of coral-associated fungal ribosomal DNA amplicons showed a high diversity of Basidiomycetes and Ascomycetes, including several clades separated from known fungal taxa by long and well-supported branches. Community similarity did not correlate with any measured variables, and total fungal community composition was highly variable among A. hyacinthus coral colonies. Colonies in the warmer pool contained more phylogenetically diverse fungal communities than the colder pool and contained statistically significant 'indicator' species. Four taxa were present in all coral colonies sampled, and may represent obligate associates. Messenger RNA sequenced from a subset of these same colonies contained an abundance of transcripts involved in metabolism of complex biological molecules. Coincidence between the taxonomic diversity found in the DNA and RNA analysis indicates a metabolically active and diverse resident marine fungal community.

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Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat

Cited by 411 publications

References 63 publications

Changes in coral-associated microbial communities during a bleaching event

Changes in coral-associated microbial communities during a bleaching event

Climate change affects key nitrogen-fixing bacterial populations on coral reefs

Coral-associated marine fungi form novel lineages and heterogeneous assemblages

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