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Applied and Environmental Microbiology, April 2006, p. 3016-3020, Vol. 72, No. 4
0099-2240/06/$08.00+0 doi:10.1128/AEM.72.4.3016-3020.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Fluorescence In Situ Hybridization and Spectral Imaging of Coral-Associated Bacterial Communities
T. D. Ainsworth,1*
M. Fine,1,2
L. L. Blackall,3 and
O. Hoegh-Guldberg1
Centre for Marine Studies, The University of Queensland, St. Lucia, QLD 4072, Australia,1
The Leon Recanati Institute for Maritime Studies, University of Haifa, Mount Carmel, Haifa 31905, Israel,2
Advanced Wastewater Management Centre, The University of Queensland, St. Lucia, QLD 4072, Australia3
Received 6 December 2005/
Accepted 17 January 2006

ABSTRACT
Microbial communities play important roles in the functioning
of coral reef communities. However, extensive autofluorescence
of coral tissues and endosymbionts limits the application of
standard fluorescence in situ hybridization (FISH) techniques
for the identification of the coral-associated bacterial communities.
This study overcomes these limitations by combining FISH and
spectral imaging.

INTRODUCTION
Microbial communities of corals play substantial roles in normal
and perturbed coral physiological states. Recently, studies
using phylogenetic analysis have demonstrated high microbial
diversity associated with coral tissues (
8,
16,
29,
32,
33,
41) and coral mucus (
29). Coral microbial communities appear
highly complex; they are distinct from those in the water column,
are coral species specific, are spatially and temporally stable,
and have roles in the physiological function of the coral holobiont
(
16,
29,
32,
33). Putative roles include nitrogen fixation,
carbon fixation, nutrient accumulation, antibiotic production,
pathogen protection, and prevention of fouling and colonization
(
13,
33,
36,
41). Yet to better understand the complexity of
the coral microbial community, we need to know the architecture
of the coral-microbe association. Understanding how microorganisms
interact with corals is important, given that they are increasingly
implicated in coral disease and reef degradation. Fluorescence
in situ hybridization (FISH) is widely applied in diverse and
complex microbial systems (
2) where traditional microbial studies
are limited. It is estimated that as few as 0.1% of environmental
microbes can be isolated in pure culture; in situ studies overcome
this limitation (
1,
18,
39).
Extensive autofluorescence has been the major limitation to the application of FISH in coral studies. Coral tissues are highly fluorescent due to the presence of pocilloporins (green fluorescent protein-like molecules) (14, 15, 34) and high densities of endosymbiotic dinoflagellates containing chlorophyll (22, 42). This extensive autofluorescence confounds coral microbial FISH studies, as image analysis is unable to resolve the sources of fluorescence (12). Bythell et al. (9) conducted the first study of FISH using enzyme amplification, previously reported to provide a 10- to 20-fold increase in signal intensity (26, 39). The study of Bythell et al. (9) was able to distinguish coral-associated bacterial communities; however, autofluorescence and nonspecific probe binding confounded image quality. Subsequently, Wegley et al. (40) used peptide nucleic acid probes for visualizing Archaea within coral tissue slurries. While the technique appeared effective for enumeration of probe binding, cellular morphology and image clarity were low. While the authors examined the binding potential of the probes with microbial cultures, controlling for sources of fluorescence emission such as coral tissue fragments and nonspecific probe binding were not considered. Amann et al. (2) suggested that improvements with peptide nucleic acid probes are confounded by nonspecific binding; therefore, the reliability of this method is questionable when it is applied to complex coral tissue slurries where confirmation of cell type and sources of fluorescence are not available. Rowher et al. (33) noted that there is yet to be a clear picture of the ecological roles of the diverse coral microbial associates. The present study describes a method that can address these questions by characterizing the architecture of the coral-bacteria association.
Recently, spectral imaging has been applied to plant research where tissue autofluorescence is a limiting factor (5, 6). Spectral profile images enhance the ability to interpret a fluorescent image by analyzing the spectral emission curve data of each pixel, thus providing an added dimension for image analysis (6, 43). Spectral imaging provides a means of distinguishing sources of fluorescence emission, allowing coral autofluorescence and FISH probe-fluorochrome emissions to be distinguished. Our study applied conventional FISH techniques and spectral imaging to accurately visualize the architecture of bacterial communities associated with reef-building corals.
Branching (Acropora aspera, Acropora formosa, and Acropora nana) and tabulate (Acropora cytherea, Acropora clatharata, and Acropora hyacinthus) acroporids, as well as nonacroporids (Seriatopora hysterix and Stylophora pistillata), were collected from Heron Island on the Southern Great Barrier Reef (23°44'17"S, 151°91'25"E), Australia. Corals were collected from March through September 2004 (at a depth of 1 to 8 m), transported to the Heron Island Research Station, and held in flowthrough seawater aquaria prior to fixation in 4% (wt/vol) paraformaldehyde in sterile phosphate-buffered saline (1) for 12 h. Samples were embedded in 1.5% (wt/vol) agarose (9) prior to decalcification with 20% (wt/vol) EDTA in phosphate-buffered saline (37). Tissues were processed sequentially through 70%, 80%, 95%, and 100% ethanol and three xylene and three paraffin washes, each for 40 min, prior to paraffin embedding. Serial tissue sections (4 µm) were collected onto Superfrost Plus slides (Menzel, Germany). Visualization of bacterial communities associated with coral tissues and lesions was conducted with the bacterial probe suite EUBmix (3, 11) using a conventional FISH protocol (3, 4, 18). Sequential adjacent tissue sections were probed with bacterial group probes (Table 1). All oligonucleotides were labeled with Cy3 (Thermo Electron Corp.). The hybridization was conducted in buffer (0.9 M NaCl, 0.01% sodium dodecyl sulfate, 0.01 M Tris-HCl, pH 7.2) for 1.5 h at 46°C, followed by a 10-min wash in prewarmed buffer (0.08 M NaCl, 0.01% sodium dodecyl sulfate, 0.01 M Tris-HCl, 0.05 M EDTA). Image analysis was conducted on a Meta 510 confocal scanning laser microscope (Zeiss, Germany) with the Zeiss Image Browser software. Several coral tissue sections treated with the FISH protocol without the application of probe were used for spectral profiling of autofluorescence without confounding sources of fluorochrome fluorescence. This was repeated for coral species to determine variability in fluorescence profiles. Coral tissue sections washed with 4% paraformaldehyde-fixed cultures of Escherichia coli were used as positive controls for the combination FISH and spectral imaging procedure.
The application of spectral imaging successfully separated coral
and endosymbiont autofluorescence from the probe fluorochrome,
thereby overcoming previous autofluorescence problems that limited
in situ analysis. The success of spectral imaging of the autofluorescence
was evident by distinguishing the fluorescence conferred by
EUBmix-Cy3-labeled oligonucleotides hybridized to individual
E. coli cells. Individual
E. coli cells coating coral tissues
sections could be easily distinguished from the background fluorescence
(Fig.
1).
The FISH technique and spectral imaging were successfully applied
to visualize and identify bacterial communities associated with
predation lesions of corals. Individual bacterial cells and
communities of bacteria associated with the lesion created by
predation of
A. formosa by the snail
Drupella sp. were identified.
The mixed bacterial community formed a mat that penetrated the
coral gastroderm and tissue layers and coated the epithelium
(Fig.
2). Two morphologically distinct bacterial communities
(filamentous and coccoid) were associated with the predation
lesion and identified as belonging to the

-proteobacteria and
Cytophaga-Flavobacterium (Fig.
2). A small population consisting
of

-proteobacteria was identified associated with the surface
of the coral tissue coating a region of epithelial tissue away
from the lesion area. Nonspecific binding was not evident within
this study, with no binding of the HGC69a, LGC354, or ß-proteobacteria
(BET42a) probes on sequential sections. This study also identified
bacterial aggregates associated with coral tissues. EUBmix universal
bacterial probes marked large ovoid inclusions associated with
the gastroderm and mesenterial filaments of the coral tissues,
and subsequently these were consistently identified as

-proteobacteria
(Fig.
3). Previously, bacterial aggregates within coral tissues
have been described using standard histopathological techniques
as large basophilic bodies of up to 40 µm or more associated
with tissue layers (
27,
28,
35). Interestingly, using 16S rRNA
gene sequencing, Rowher et al. (
33) consistently found a

-proteobacterium
that they designated PA1 in over 50
Porites asteroides colonies
sampled and speculated that this bacterium was the one observed
as ovoid aggregates by Santavy and Peters (
35). The lack of
available and reliable technology previously prevented detailed
analysis of these aggregates within the context of the coral
holobiont, but this problem has been overcome with this technique.
This study's consistent identification of

-proteobacterial aggregates
in branching corals supports the speculation of Rowher et al.
(
33) and indicates the wider presence of

-proteobacteria across
scleractinian corals.
FISH technology allows for spatial and temporal analysis of
bacterial community variability (
7), and its application to
coral microbial ecology can begin to address questions on the
stability and role of bacterial communities. Jones et al. (
19)
conducted FISH, limiting excitation wavelengths to the red/far-red
regions of the spectrum, with coral tissue slurries for confirmation
of 16S rRNA sequence analysis and quantification of coral disease-associated
microbial communities but did not conduct image analysis, nor
did the investigators address the structural arrangement of
the microbial communities and interaction with coral tissues.
Importantly, the authors noted a difficulty in differentiating
disease-causing organisms from secondary invaders (
19), a problem
that could be addressed by investigating the structural environment
of the disease lesions and adjacent regions. The bacterial populations
identified within this study are some of the most abundant oceanic
bacterial groups and are involved in a wide range of functions
(
10,
20,
21). Yet investigating the spatial arrangement of microbial
communities around lesions and tissues can allow the differentiation
of pathogens, lesion colonizers, and persistent microbial communities.
Previous studies utilizing FISH for investigating coral microbial ecology have been limited in determining community interactions by autofluorescence, poor image quality, and probe specificity. This study demonstrates that FISH combined with spectral imaging is a rapid and powerful tool to assess the microbial architecture of reef-building corals. With increasing disease and stress of scleractinian corals (17, 31, 38), the timely description of this technique allows for localization and identification of coral-associated bacterial community changes, suggesting a central role in the future analysis of microbial communities.

ACKNOWLEDGMENTS
We are grateful for support provided by the GEF Coral Reef Targeted
Research Program (
www.gefcoral.org), the Australian Research
Council Centre of Excellence for Coral Reef Studies, and the
Centre for Advanced Light Microscopy at the University of Queensland.

FOOTNOTES
* Corresponding author. Mailing address: Centre for Marine Studies, The University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia. Phone: 617 3379 6858 Fax: 61 7 3365 4755. E-mail:
t.ainsworth{at}uq.edu.au.


REFERENCES
1 - Amann, R., J. Snaidr, M. Wagner, W. Ludwig, and K. H. Scleifer. 1996. In situ visualization of high genetic diversity in a natural microbial community. J. Bacteriol. 178:3496-3500.[Abstract/Free Full Text]
2 - Amann, R., B. M. Fuchs, and S. Behrens. 2001. The identification of micro-organisms by fluorescence in situ hybridisation. Curr. Opin. Biotechnol. 12:231-236.[CrossRef][Medline]
3 - Amann, R. I., B. J. Binder, R. J. Olson, S. W. Chisholm, R. Devereux, and D. A. Stahl. 1990. Combination of 16S rRNA-targeted oligonucleotide probes with flow cytometry for analyzing mixed microbial populations. Appl. Environ. Microbiol. 56:1919-1925.[Abstract/Free Full Text]
4 - Amann, R. I., W. Ludwig, and K.-H. Schleifer. 1995. Phylogenetic identification and in situ detection of individual microbial cells without cultivation. Microbiol. Rev. 59:143-169.[Abstract/Free Full Text]
5 - Berg, R. H. 2004. Evaluation of spectral imaging for plant cell analysis. J. Microsc. 214:174-181.[CrossRef][Medline]
6 - Bezanilla, M., A. Pan, and R. S. Quatrano. 2003. RNA interference in the moss Physcomitrella patens. Plant Physiol. 133:470-474.[Abstract/Free Full Text]
7 - Bouvier, T., and P. A. del Giorgio. 2003. Factors influencing the detection of bacterial cells using fluorescence in situ hybridisation (FISH): a quantitative review of published reports. FEMS Microbiol. Ecol. 44:3-15.
8 - Breitbart, M., R. Bhagooli, S. Griffin, I. Johnston, and F. Rowher. 2005. Microbial communities associated with skeletal tumors on Porites compressa. FEMS Microbiol. Lett. 243:431-436.[CrossRef][Medline]
9 - Bythell, J. C., M. R. Barer, R. P. Cooney, J. R. Guest, A. G. O'Donnell, O. Pantos, and M. D. A. Le Tissier. 2002. Histopathological methods for the investigation of microbial communities associated with disease lesions in reef corals. Lett. Appl. Microbiol. 34:359-364.[CrossRef][Medline]
10 - Cottrell, M. T., and D. L. Kirchman. 2000. Natural assemblages of marine proteobacteria and members of Cytophaga-Flavobacter cluster consuming low- and high-molecular-weight dissolved organic matter. Appl. Environ. Microbiol. 66:1692-1697.[Abstract/Free Full Text]
11 - Daims, H., A. Brühl, R. Amann, K.-H. Schleifer, and M. Wagner. 1999. The domain-specific probe EUB338 is insufficient for the detection of all bacteria: development and evaluation of a more comprehensive probe set. Syst. Appl. Microbiol. 22:434-444.[Medline]
12 - Dickinson, M. E., G. Bearman, S. Tille, R. Lansford, and S. E. Fraser. 2001. Multi-spectral imaging and linear unmixing add whole new dimensions to laser scanning fluorescence microscopy. BioTechniques 31:1272-1278.[Medline]
13 - Dobretsov, S., and P.-Y. Qien. 2004. The role of epibiotic bacteria from the surface of the soft coral Dendronephthya sp. in the inhibition of larval settlement. J. Exp. Mar. Biol. Ecol. 299:35-50.[CrossRef]
14 - Dove, S. G., M. Takabayashi, and O. Hoegh-Guldberg. 1995. Isolation and partial characterisation of the pink and blue pigments of pocilloporid and acroporid corals. Biol. Bull. 189:288-297.[Abstract]
15 - Dove, S. G., O. Hoegh-Guldberg, and S. Rangananthan. 2001. Major colour patterns of reef-building corals are due to a family of GFP-like proteins. Coral Reefs 19:197-204.
16 - Frias-lopez, J., A. L. Zerkle, G. T. Bonheyo, and B. W. Fouke. 2002. Partitioning of bacterial communities between seawater and healthy, black band diseased, and dead coral surface. Appl. Env. Microbiol. 68:2214-2228.[Abstract/Free Full Text]
17 - Harvell, C. D., C. E. Mitchell, J. R. Ward, S. Altizer, A. P. Dobson, R. S. Ostfeld, and M. D. Samuel. 2002. Climate warming and disease risks for terrestrial and marine biota. Science 296:2158-2162.[Abstract/Free Full Text]
18 - Hugenholtz, P., B. M. Goebel, and M. R. Pace. 1998. Impact of culture-independent studies on the emerging phylogenetic view of bacterial diversity. J. Bacteriol. 180:4765-4774.[Free Full Text]
19 - Jones, R. J., J. Bowyer, O. Hoegh-Guldberg, and L. L. Blackall. 2004. Dynamics of a temperature-related coral disease outbreak. Mar. Ecol. Prog. Ser. 281:63-77.[CrossRef]
20 - Jorquera, M. A., M. Lody, Y. Leyton, and C. Riquelme. 2004. Bacteria of subclass
-proteobacteria associated with commercial Argopecten purpuratus (Lamark, 1819) hatcheries in Chile. Aquaculture 236:37-51.[CrossRef] 21 - Kirchman, D. L. 2002. The ecology of Cytophaga-Flavobacteria in aquatic environments. FEMS Micro. Ecol. 39:91-100.
22 - Lesser, M. P. 2004. Experimental biology of coral reef ecosystems. J. Exp. Mar. Bio. Ecol. 300:217-252.[CrossRef]
23 - Manz, W., R. Amann, W. Ludwig, M. Wagner, and K.-H. Schleifer. 1992. Phylogenetic oligonucleotide probes for the major subclasses of proteobacteria: problems and solutions. Syst. Appl. Microbiol. 15:593-600.
24 - Manz, W., G. Arp, G. Schumann-Kindel, U. Szemzyke, and J. Reitner. 2000. Widefield deconvolution epifluorescence microscopy combined with fluorescence in situ hybridisation reveals the spatial arrangement of bacteria in sponge tissue. J. Microbiol. Methods 40:125-134.[CrossRef][Medline]
25 - Manz, W., R. Amann, W. Ludwig, M. Vancanneyt, and K.-H. Schleifer. 1996. Application of a suite of 16S rRNA-specific oligonucleotide probes designed to investigate bacteria of the phylum Cytophaga-Flavobacter-Bacteroides in the natural environment. Microbiology 142:1097-1106.[Abstract/Free Full Text]
26 - Moter, A., and U. B. Gobel. 2000. Fluorescence in situ hybridisation (FISH) for direct visualisation of microorganisms. J. Micro. Methods 41:85-112.
27 - Peters, E. C., J. J. Oprandy, and P. P. Yevich. 1983. Possible causal agent of "white band disease" in Caribbean acroporids corals. J. Invertebr. Pathol. 41:394-396.[Medline]
28 - Peters, E. C. 1984. A survey of cellular reactions to environmental stress and disease in Caribbean scleractinian corals. Helgol. Meeresunters. 37:113-137.
29 - Ritchie, K. B., and G. W. Smith. 1997. Physiological comparison of bacterial communities from various species of scleractinian corals. Proc. 8th Int. Coral Reef Symp. 1:521-526.
30 - Roller, C., M. Wagner, R. Amann, W. Ludwig, and K.-H. Schleifer. 1994. In situ probing of gram positive bacteria with high G+C content using 23S rRNA-targeted oligonucleotides. Microbiology 140:2849-2858.[Abstract/Free Full Text]
31 - Rosenberg, E., and Y. Ben-Haim. 2002. Microbial diseases of corals and global warming. Environ. Microbiol. 4:318-326.[CrossRef][Medline]
32 - Rowher, F., M. Breitbart, J. Jara, F. Azam, and N. Knowlton. 2001. Diversity of bacteria associated with the Caribbean coral Montastrea franksi. Coral Reefs 20:85-95.[CrossRef]
33 - Rowher, F., V. Seguritan, F. Azam, and N. Knowlton. 2002. Diversity and distribution of coral-associated bacteria. Mar. Ecol. Prog. Ser. 243:1-10.[CrossRef]
34 - Salih, A., A. Larkum, G. Cox, M. Kuhl, and O. Hoegh-Guldberg. 2000. Fluorescent pigments in corals are photoprotective. Nature 408:850-853.[CrossRef][Medline]
35 - Santavy, D. L., and E. C. Peters. 1997. Microbial pests: coral disease in the western Atlantic. Proc. 8th Int. Coral Reef Symp. 1:607-612.
36 - Shashar, N., A. T. Banaszak, M. P. Lesser, and D. Amrami. 1997. Coral endolithic algae: life in a protected environment. Pac. Sci. 51:167-173.
37 - St. John, J. A., K. T. Tisay, I. W. Caras, and B. Key. 2000. Expression of EphA5 during development of the olfactory nerve pathway in rat. J. Comp. Neuorol. 416:540-550.
38 - Sutherland, K. P., J. W. Porter, and C. Torres. 2004. Disease and immunity in Caribbean and Indo-Pacific zooxanthellate corals. Mar. Ecol. Prog. Ser. 266:273-302.[CrossRef]
39 - Wagner, M., M. Horn, and H. Daims. 2003. Fluorescence in situ hybridisation for the identification and characterisation of prokaryotes. Curr. Opin. Microbiol. 6:302-309.[CrossRef][Medline]
40 - Wegley, L., Y. Yu, M. Breitbart, V. Casas, D. I. Kline, and F. Rohwer. 2004. Coral-associated Archaea. Mar. Ecol. Prog. Ser. 273:89-96.[CrossRef]
41 - Williams, W. M., A. B. Viner, and W. J. Broughton. 1987. Nitrogen fixation (acetylene reduction) associated with the living coral Acropora variabilis. Mar. Biol. 94:531-535.[CrossRef]
42 - Yokouchi, H., H. Takeyama, H. Miyashita, T. Maruyama, and T. Matsunaga. 2003. In situ identification of symbiotic dinoflagellates, the genus Symbiodinium with fluorescence-labelled rRNA-targeted oligonucleotide probes. J. Microbiol. Methods 53:327-334.[CrossRef][Medline]
43 - Zimmerman, T., L. Rietdorf, and R. Pepperkork. 2003. Spectral imaging and its applications in live cell microscopy. FEBS Lett. 546:87-92.[CrossRef][Medline]
Applied and Environmental Microbiology, April 2006, p. 3016-3020, Vol. 72, No. 4
0099-2240/06/$08.00+0 doi:10.1128/AEM.72.4.3016-3020.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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