NOCARDIA CRASSOSTREAE SP, NOV., THE CAUSAL AGENT OF NOCARDIOSIS IN PACIFIC OYSTERS

Seven strains of bacteria were isolated from Pacific oysters, Crassost rea gigas, with a focal or systemic disease. The strains were aerobic, Gram-positive, acid-fast, produced a mycelium which fragmented into i rregular rod-like elements, had a peptidoglycan containing meso-diamin opimelic acid, arabinose and galactose as major sugars, mycolic acids with 46-58 carbon atoms and G+C-rich DNA, All of these properties are consistent with the classification of the organisms in the genus Nocar dia. A partial sequence of the 16S rRNA gene of isolate NB4H was deter mined following isolation and cloning of the PCR-amplified gene. The s equence was aligned with those of representative mycolic-acid-containi ng taxa and a phylogenetic tree was generated using the neighbour-join ing method, It was evident from the phylogenetic tree that the three s trains tested, RB1, OB3P and NB4H, were identical and belonged to the Nocardia otitidiscaviarum rRNA sub-group, The biochemical, chemical, m orphological and physiological properties of the isolates were also es sentially identical and served to distinguish them from representative nocardiae, It is, therefore, proposed that the strains isolated from the diseased Pacific oysters be assigned to a new species, Nocardia cr assostreae, The type strain is NB4H (= ATCC 700418).