Pathogenicity of a Highly Exopolysaccharide-producing Halomonas Strain Causing Epizootics in Larval Cultures of the Chilean Scallop Argopecten purpuratus (Lamarck, 1819)
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2008Metadata
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Rojas, Rodrigo
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Pathogenicity of a Highly Exopolysaccharide-producing Halomonas Strain Causing Epizootics in Larval Cultures of the Chilean Scallop Argopecten purpuratus (Lamarck, 1819)
Abstract
Mass mortalities of larval cultures of Chilean
scallop Argopecten purpuratus have repeatedly occurred in
northern Chile, characterized by larval agglutination and
accumulation in the bottom of rearing tanks. The exopolysaccharide
slime (EPS) producing CAM2 strain was
isolated as the primary organism from moribund larvae in
a pathogenic outbreak occurring in a commercial hatchery
producing larvae of the Chilean scallop Argopecten
purpuratus located in Bahía Inglesa, Chile. The CAM2
strain was characterized biochemically and was identified
by polymerase chain reaction amplification of 16S rRNA as
Halomonas sp. (Accession number DQ885389.1). Healthy
7-day-old scallop larvae cultures were experimentally
infected for a 48-h period with an overnight culture of the
CAM2 strain at a final concentration of ca. 105 cells per
milliliter, and the mortality and vital condition of larvae
were determined by optical and scanning electron microscopy
(SEM) to describe the chronology of the disease.
Pathogenic action of the CAM2 strain was clearly
evidenced by SEM analysis, showing a high ability to
adhere and detach larvae velum cells by using its “slimy”
EPS, producing agglutination, loss of motility, and a
posterior sinking of scallop larvae. After 48 h, a dense
bacterial slime on the shell surface was observed, producing
high percentages of larval agglutination (63.28±7.87%) and
mortality (45.03±4.32%) that were significantly (P<0.05)
higher than those of the unchallenged control cultures,
which exhibited only 3.20±1.40% dead larvae and no
larval agglutination. Furthermore, the CAM2 strain
exhibited a high ability to adhere to fiberglass pieces of
tanks used for scallop larvae rearing (1.64×105 cells
adhered per square millimeters at 24 h postinoculation),
making it very difficult to eradicate it from the culture
systems. This is the first report of a pathogenic activity on
scallop larvae of Halomonas species, and it prompts the
necessity of an appraisal on biofilm-producing bacteria in
Chilean scallop hatcheries.
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