Black band disease is a

coral disease Coral diseases, comprising the diseases that affect corals, injure the living tissues and often result in the death of part or the whole of the colony. These diseases have been occurring more frequently in the twenty-first century as conditions beco ...

in which

corals Corals are marine invertebrates within the class (biology), class Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important C ...

develop a black band. It is characterized by complete tissue degradation due to a pathogenic

microbial consortium A microbial consortium or microbial community, is two or more bacterial or microbial groups living symbiotically. Consortiums can be endosymbiotic or ectosymbiotic, or occasionally may be both. The protist ''Mixotricha paradoxa'', itself an endosym ...

. The mat is present between apparently healthy coral tissue and freshly exposed coral skeleton.

Appearance

Black band disease was first observed on reefs in Belize in 1973 by A. Antonius, who described the pathogen he found infecting corals as '' Oscillatoria membranacea'', one of the

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

. The band color may be blackish brown to red depending on the vertical position of a cyanobacterial population associated with the band. The vertical position is based on a light intensity-dependent photic response of the

l filaments, and the color (due to the cyanobacterial pigment

phycoerythrin Phycoerythrin (PE) is a red protein-pigment complex from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptophytes, accessory to the main chlorophyll pigments responsible for photosynthesis.The red pigmen ...

) is dependent on the thickness of the band. The band is approximately thick and ranges in width from to White specks may be present on surface, at times forming dense white patches. The pathogenic

microbial mat A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...

moves across coral colonies at rates from to a day. Tissue death is caused by exposure to a

hypoxic Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

-rich microenvironment associated with the base of the band.

Composition

The black band microbial consortium consists of an assortment of

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

and non-photosynthetic

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

that co-exist

synergistically Synergy is an interaction or cooperation giving rise to a whole that is greater than the simple sum of its parts. The term ''synergy'' comes from the Attic Greek word συνεργία ' from ', , meaning "working together". History In Christi ...

. The consortium has three functionally and physically dominant members as well as numerous

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ic members whose role in the disease is as yet unknown. The three functionally dominant members are populations of cyanobacteria and sulfide-oxidizing and

sulfate-reducing bacteria Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...

. The black band disease microbial consortium is structurally and functionally identical to cyanobacterial-dominated microbial mats found in other illuminated, sulfide-rich environments

Taxonomy

Several species of cyanobacteria have been found associated with black band disease, the most well-known of which is ''

Phormidium corallyticum ''Phormidium'' is a genus of cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly for ...

''. Sulfide-oxidizing bacteria, dominated by ''

Beggiatoa ''Beggiatoa'' is a genus of ''Gammaproteobacteria'' belonging the order ''Thiotrichales,'' in the ''Pseudomonadota'' phylum. This genus was one of the first bacteria discovered by Ukrainian botanist Sergei Sergei Winogradsky, Winogradsky. During ...

'' spp.,Ducklow and Mitchell, 1979. "Observations on naturally and artificially diseased tropical corals:scanning electron microscope study". ''Microbial Ecology'', Vol.5, pp.215-223 are present in well-developed bands and exhibit visible vertical migrations within the band matrix (Richardson, 1996; Viehman and Richardson, 2006). When present on the band surface ''Beggiatoa'' appears white due to intracellular inclusions of stored elemental

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

. Sulfate-reducing bacteria dominated by ''

Desulfovibrio ''Desulfovibrio'' is a genus of Gram-negative sulfate-reducing bacteria. ''Desulfovibrio'' species are commonly found in aquatic environments with high levels of organic material, as well as in water-logged soils, and form major community member ...

'' spp. are present at the base of the band and are responsible for producing high concentrations of sulfide within the band matrix.Carlton, R.G. and L.L. Richardson, 1995. "Oxygen and sulfide dynamics in a horizontally migrating cyanobacterial mat: Black band disease of corals". ''FEMS Microbiology Ecology'', Vol18, pp. 155-162. Light microscopic observation of black band reveals motile (gliding) filaments of ''P. corallyticum'' that are 4 mm wide, with one round end and one narrow (sharply tapering) end. Also present are gliding ''Beggiatoa'' filaments (1–4 mm wide) that are non-pigmented but contain highly refractive intracellular granules of elemental sulfur. Numerous

gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

bacteria (small rods) are also present but not identifiable using light microscopy. The bacterial population has been characterized using molecular techniques and was found to contain over 500 species of bacteria that are different from bacterial communities found in the water column, healthy coral tissue, or dead coral skeleton.Frias-Lopez, J., A. Zerkle, G. Bonheyo and B. Fouke (2002). "Partitioning of bacterial communities between seawater and healthy, black band diseased and dead coral surfaces". ''Applied and Environmental Microbiology'', Vol. 68, pp 2214-2228Cooney, R.P., O. Pantos, M. D. A. Le Tissier, M. R. Barer, A. G. O´Donnell, and J. C Bythell (2002) "Characterization of the bacterial consortium associated with black band disease in coral using molecular microbiological techniques". ''Environmental Microbiology'', Vol 4 (7), pp 401, Jul 2002. The functional role of this diverse population of bacteria is not known. Black band disease affects 42 species of coral in a worldwide distribution. The only known reservoir is within cyanobacterial

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

s that are present on sediments in depressions of healthy black band disease susceptible corals. Black band disease significantly affects boulder star coral in the reef ecosystem, allowing for more staghorn coral to grow.

References

External links

NOAA website on coral (public domain)World Conservation Monitoring Centre Global Coral Disease Database
{{DEFAULTSORT:Black Band Disease Coral diseases Animal bacterial diseases

Appearance

Composition

Taxonomy

See also

References

External links