| A strain of a prokaryote(Qingdao prokaryote, QDP) was isolated from moribund scallops Chlamys farreri. QDP could reproduce independently in minimal essential medium (MEM, adding 2.2% NaCl and 5% calf serum) or heart-brain infusion(adding 2.2% NaCl). Colorless, transparent and small dots colonies could be observed under microscope (150×) formed by QDP. QDP was Gram-negative, and round or near-round in shape. It included two kinds of particles, matured and unmatured particles. The unmatured particles were less than 100nm in diameter, and the diameter of matured particles ranged from 60nm to 4000 nm or above. The relatively small cells contained nucleoid, ribosome and vacuole, but no cell-wall has been found. The relatively big cells contained cell-wall, cytoplasmic membrane and one or several irregular transparent vacuoles inside each cell, but no nucleoid and ribosome were observed. The densities in QDP varied with self-development, and were higher at the cumulative reproduction.A method of sucrose density gradient centrifugation with filtration was created for QDP isolation from moribund scallops. The optimal temperature, pH, and NaCl were about 23℃, 7.4 and equal to MEM. QDP was found in the ultrathin section of lesion tissue of the scallop.The extracting nucleotide could be denatured by RNase A. DNA was not found from the extracting nucleotide. The 16S rRNA gene could be amplified by RT-PCR, but not PCR, and it was a 1430 BP stretch. The highest similarity values of 16S rRNA gene with some bacteria from 6 families were about 95-95.47%.Two experiments were conducted to methodically document pathogenicity in C. farreri, which were different pathogen concentrations at the same temperature and the same pathogen concentration at different temperatures. Results indicated that QDP, which could cause heavy infection in Farrer's scallop, was one of the causative agent of the Farrer's scallop mortalities, and the temperature (23℃or above) was a key environmental factor. |
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