More comments on RWD
Ernesto_J_QUINTERO at umail.umd.edu
Wed Nov 12 21:52:00 EST 1997
I have been following the RWD debate for some time now and as a marine
microbiologist, I would like to make some comments on a couple of items on
Microbes can degrade/dissolve mineral surfaces (metals, rocks, etc.) by
several different mechanisms. Microbial induced corrosion is a topic that
has been (and still is) subject to a great amount of research.
Bacterially-mediated solubilization of minerals has been used by the mining
industry for decades for precious metal recovery and is also a source of
"natural" heavy metal pollution in abandoned mining sites.All these
processes have 2 things in common: they occur over an extended period of
time (weeks to months), they are usually localized to small areas (mm in
This also appears to be the case for the example cited recently concerning
the ectomycorrhizal fungi hyphae penetrating granitic rock (See Rock-eating
fungi, Nature, Oct. 1997, 389:682-683) as a possible mechanism for coral
matrix degradation in RWD. It was cited in this paper that "hyphal tips
producing millimolar concentrations of organic acids could dissolve
calcium-rich plagioclase feldspars to form pores at rates of 0.3-30
micrometers/year". This process is too slow to account for the rapid
degradation of the coral skeleton observed in RWD cases (inches/day); it
would need to be several orders of magnitude more efficient to cause such
injuries. The putative fungal pathogen responsible for RWD would have to be
using a different, yet to be described, mechanism to dissolve the calcium
carbonate in corals.
It was mentioned in a recent posting that the coral matrix in RWD wounds was
"eroded, not broken". Did the microscopic examination of the matrix reveal
any pores and/or fungal hyphae penetrating the matrix?
The suspected etiologic agent of RWD must fulfill Koch's postulates (or a
modified subset of them if the causative agent cannot be grown in pure
culture) in order for it to be recognized as the causative agent of the
1. The organism should be present in all animals suffering from the disease
and absent from all healthy animals.
2. The organism must be grown in pure culture outside the diseased animal
host (not always possible in the case of pathogens with complex lifecycles,
viruses and nonculturable bacteria)
3. When such a culture is inoculated into a healthy susceptible host, the
animal must develop the symptoms of the disease.
4. The organism must be reisolated from the experimentally infected animal
and shown to be identical to the original isolate.
All 4 postulates were fulfilled in the recognition of Vibrio AK-1 infection
as the causative agent of bleaching of the Mediterranean coral Oculina
patagonica (Kushmaro et al. 1997. Mar. Ecol. Prog. Ser. 147:159-165), and a
modified subset of them met in the recognition of a bacterial pathogen as
being responsible for coralline lethal orange disease (CLOD) of crustose
coralline algae (Littler & Littler, 1995. Science 267:1356-1359).
If the putative fungal pathogen responsible for RWD is proving to be a
fastidious organism, does the transfer of a plug/core from a site of RWD
infection to a healthy coral result in infection of the new subject? Does
the addition of antimycotic agents to microcosms containing infected
individuals stop the progress of the infection?
It would be interesting to PCR-amplify (with fungi-specific primers) the
nuclear 18S, 5.8S and/or internal transcribed spacer (ITS) regions of the
ribosomal RNA genes (rDNA) of the fungi found in RWD wounds to: a) Sequence
and obtain information on the molecular phylogeny of the microorganism, b)
obtain an RFLP fingerprint or unique DNA sequences suitable for probe design
to ascertain if the same putative etiologic agent is found in RWD material
collected from different specimens/locations.
My intention in posting the above comments is to contribute to the
scientific discussion on this topic, and should not be construed as a
personal affront or meant to impugn the opinion or research of other groups.
I would appreciate immensely if somebody could please point me to a
published reference on Aspergillus infection of sea fans. Thanks in
Ernesto J. Quintero, Ph.D.
Senior Research Scientist
Oceanix Biosciences Corp.
Hanover, MD 21076
Email: eq1 at umail.umd.edu
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