U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007-3065

August 2007 Printed on recycled paper

Phage Therapy for Florida Corals?

Introduction

Coral disease is a major cause of reef decline and a 

significant problem in the Florida Keys (fig. 1). Of the 

many diseases and syndromes that have been described, 

very few so far have been linked to a specific pathogen 

(disease-causing organism). In all but one of those cases, 

the pathogen is a bacterium as shown in table 1.

A grant from the Mote Marine Laboratory Protect Our 

Reefs program is allowing the U.S. Geological Survey 

(fig. 2) to conduct a preliminary study that will look at 

applying phage therapy to diseased corals in the Florida 

Keys.

Disease Pathogen Type

Aspergillosis Aspergillus sydowii Fungi

Black band Mixture of cyanobacteria 

and sulfur-cycling bacteria

Bacteria

Bacterial bleaching Vibrio shiloi Bacterium

Vibrio coralliilyticus Bacterium

White plague type II Aurantimonas coralicida Bacterium

White pox Serratia marcescens Bacterium

Table 1. Coral diseases and the microorganisms that cause them.

Figure 1. A star coral (Montastraea annularis) affected by white 

plague type II, a disease caused by the bacterium Aurantimonas 

coralicida. (Photograph by Ginger Garrison, USGS.)

Figure 2. U.S. Geological Survey microbiologist Christina Kellogg 

near a large colony of healthy star coral in the Florida Keys. 

(Photograph by Peter Richardson.)

Prepared in cooperation with the Mote Marine Laboratory Protect Our Reefs program

Much effort and money are being directed toward 

cataloging coral diseases, mapping locations of coral 

diseases, determining causes of coral diseases, and 

measuring rates of coral demise. Very little research is 

being directed at ways to prevent or stop coral diseases. 

What is Phage Therapy?

The term “phage” is a shortened version of the word 

“bacteriophage,” which literally means “bacteria eater.” 

Bacteriophages are viruses that only infect bacteria 

(fig. 3). Phages are typically very specific, with each 

phage only able to recognize and infect a single bacterial 

strain. Phage therapy is the use of these bacteriophages 

as biocontrol agents to treat bacterial infections. Phage 

therapy was first developed in the 1930s to treat human 

bacterial infections, but the discovery of antibiotics made 

it obsolete in the Western world. However, the Soviet 

Union continued to study and test phage therapy and 

successfully used this treatment against agricultural pests, 

to treat livestock, and even in humans, both topically and 

internally. With the increase in antibiotic resistance, 

interest in phage therapy has been renewed. The U.S. 

Food and Drug Administration recently approved the use 

of phage therapy to treat packaged meat in an effort to 

eliminate potential food-poisoning bacteria like 

Salmonella.
are preparing to move to the next phase of the study which 

involves testing the phage therapy treatment on diseased 

corals in aquarium experiments. A similar study was just 

conducted in the Red Sea using corals and bacteriophages 

native to that region, and the treatment was a success. 

As a result, prospects are good for using the bacteriophages characterized from Florida waters to treat diseased 

corals on the Florida reef tract–the only coral reef in the 

continental United States.

Several factors about phage therapy make it a promising 

treatment option for coral diseases:

• Environmental safety—These bacteriophages already 

occur naturally in the marine environment, so their use 

does not introduce any foreign substances to the system.

• Specificity—As mentioned above, most bacteriophages 

are specific to one strain or species of bacterium, so 

treating a coral with one or more bacteriophages will 

only affect the target (for example, the bacteria causing the disease). In contrast, using antibiotics (which 

are non-specific) would affect all of the bacteria on a 

coral (both the disease-causing bacteria and the good 

bacteria) as well as the coral animal, the zooxanthellae, 

bacteria in the surrounding seawater and sediment, and 

other nearby marine organisms.

• Self limiting—Because bacteriophages need the 

bacterial host to reproduce, the virus particles will only 

persist as long as the bacteria being targeted are present; 

therefore, when the pathogen disappears, the viruses 

stop producing and eventually decay. This is another 

way that phage therapy is environmentally safe.

Hunting for Phages

A typical drop of seawater contains about 

10 million viruses, most of them bacteriophages. 

Phage therapy involves trying to find very specific 

viruses that infect a particular coral pathogen. To 

accomplish this, large volumes of water (40-80 liters) 

are passed through a filtration system that allows the 

water molecules to pass through, but retains and recycles 

any particles, concentrating the virus community in the 

sample. After concentrating that community almost 

100 times, the virus-containing samples are mixed with 

the target bacterium (coral pathogen) and incubated on 

nutrient agar plates. The bacteria will grow on the agar, 

and any viruses able to infect and kill the bacteria will 

appear as clear spots on the agar plate (areas where 

bacteria are not growing). These clear spots are then 

picked and purified, and the viruses they contain are 

characterized. Some examples of characterization 

methods include looking at the viral particles under a 

transmission electron microscope (TEM) to see their 

morphology (fig. 3), determining which type of nucleic 

acid (RNA or DNA) the particles contain, and using 

restriction enzymes to make nucleic acid finger prints 

to compare patterns between particles and to size the 

genomes.

Ongoing Research

The scope of the Protect Our Reefs project was to 

screen Florida reef environments for bacteriophages 

specific for coral diseases and then characterize these 

viruses. This work has been performed. Now researchers 

Figure 3. A transmission electron microscope (TEM) was used 

to take these images of bacteriophages. The top two images are 

phages that infect the bacterium Aurantimonas coralicida (cause 

of white plague type II disease) and the bottom two images are 

phages that infect the bacterium Vibrio coralliilyticus (cause of 

bacterial bleaching disease).

Contact information:

Christina A. Kellogg, Ph.D.

U.S. Geological Survey

Florida Integrated Science Center

600 4th Street South

St. Petersburg, FL 33701

Phone: (727) 803-8747 ext. 3128

Fax: (727) 803-2031

Email: ckellogg@usgs.gov

http:// /pubs.usgs.gov/fs/2007/3065/

Additional information about 

USGS coral microbial ecology 

research is available at:

http://coastal.er.usgs.gov/coral-microbes/