"Never Waste A Good Crisis"

Pocillopora meandrina, aka Cauliflower coral; image courtesy of the National Park of American Samoa, and found here.

To date, all studies that have investigated coral-microbial (bacterial and archaeal) interactions have looked at adults.  But inquiring minds want to know...when (and how) does this non-random association occur?  Is it a vertical (parent to child) or horizontal (selectively taken up from the surrounding water) process?  Amy Apprill, who is clearly a masochist hardworking graduate student, collected oocyte bundles, freshly spawned eggs, and planulae from Pocillopora  meandrina and employed a variety of molecular techniques to get at this question.  P. meandrina is already known to package zooxanthellae into it's eggs and sperm, so it's as good a lab rat as any to look for vertical transmission of other microbes.  However, as you will see from the abstract below, bacteria were not detected inside tissue until the coral babies were planulae, making a case for horizontal rather than vertical transmission:

Associations between healthy adult reef-building corals and bacteria and archaea have been observed in many coral species, but the initiation of their association is not understood. We investigated the onset of association between microorganisms and Pocillopora meandrina, a coral that vertically seeds its eggs with symbiotic dinoflagellates before spawning. We compared the bacterial communities associated with prespawned oocyte bundles, spawned eggs, and week old planulae using multivariate analyses of terminal restriction fragment length polymorphisms of SSU rRNA genes, which revealed that the composition of bacteria differed between these life stages. Additionally, planulae raised in ambient seawater and seawater filtered to reduce the microbial cell density harbored dissimilar bacterial communities, though SSU rRNA gene clone libraries showed that planulae raised in both treatments were primarily associated with different members of the Roseobacter clade of Alphaproteobacteria. Fluorescent in situ hybridization with an oligonucleotide probe suite targeting all bacteria and one oligonucleotide probe targeting members of the Roseobacter clade was used to localize the bacterial cells. Only planulae greater than 3 days old were observed to contain internalized bacterial cells, and members of the Roseobacter clade were detected in high abundance within planula tissues exposed to the ambient seawater treatment. We conclude that the onset of association between microorganisms and the coral P. meandrina appears to occur through horizontal uptake by planulae older than 79 h, and that uptake is preferential to members of the Roseobacter clade and potentially sensitive to the ambient seawater microbial community.

Apprill, A., H.Q. Marlow, M.Q. Martindale, and M.S. Rappe (2009). The onset of microbial associations in the coral Pocillopora meandrina.  The ISME Journal, doi: 10.1038/ismej.2009.3

Lophelia pertusa, image credit:  http://www.ipsl.jussieu.fr/~jomce/acidification/

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This week I received an email from Christina Kellogg (USGS) that was addressed to 'Deep-coral people (and shallow-water friends)' about her recently published manuscript titled 'Culture-Independent Characterization of Bacterial Communities Associated with the Cold-Water Coral Lophelia pertusa in the Northeastern Gulf of Mexico'.   

Chris is a friend of CoralMicrobes.org - and is contributing to this blog, for which I am (as one of her shallow colleagues) quite grateful!  So regardless of your personal depth (or temperature preference), go and take a look at her article.  To get you started, here is the abstract:   

Bacteria are recognized as an important part of the total biology of shallow-water corals. Studies of shallow-water corals suggest that associated bacteria may benefit the corals by cycling carbon, fixing nitrogen, chelating iron, and producing antibiotics that protect the coral from other microbes. Cold-water or deep-sea corals have a fundamentally different ecology due to their adaptation to cold, dark, high-pressure environments and as such have novel microbiota. The goal of this study was to characterize the microbial associates of Lophelia pertusa in the northeastern Gulf of Mexico. This is the first study to collect the coral samples in individual insulated containers and to preserve coral samples at depth in an effort to minimize thermal shock and evaluate the effects of environmental gradients on the microbial diversity of samples. Molecular analysis of bacterial diversity showed a marked difference between the two study sites, Viosca Knoll 906/862 (VK906/862) and Viosca Knoll 826 (VK826). The bacterial communities from VK826 were dominated by a variety of unknown mycoplasmal members of the Tenericutes and Bacteroidetes, whereas the libraries from VK906/862 were dominated by members of the Proteobacteria. In addition to novel sequences, the 16S rRNA gene clone libraries revealed many bacterial sequences in common between Gulf of Mexico Lophelia corals and Norwegian fjord Lophelia corals, as well as shallow-water corals.  Two Lophelia-specific bacterial groups were identified: a cluster of gammaproteobacteria related to sulfide-oxidizing gill symbionts of seep clams and a group of Mycoplasma spp.  The presence of these groups in both Gulf and Norwegian Lophelia corals indicates that in spite of the geographic heterogeneity observed in Lophelia-associated bacterial communities, there are Lophelia-specific microbes.

I find the 'unknown mycoplasmal members' of these communities really interesting.

You can find the article here:

Kellogg, C.A., J.T. Lisle, and J.P. Galkiewicz.  2009.  Culture-independent characterization of bacterial communities associated with the cold-water coral Lophelia pertusa in the northeastern Gulf of Mexico.  Applied and Environmental Microbiology  75(8):2294-2303.