大黄鱼结节病病原菌—诺卡氏菌的鉴定及其系统发育分析

Identification and phylogenetic analysis of a strain of Nocardia,A pathogen of large yellow croakers(Larimichthys crocea) with tuberculosis

一株分离自浙江台州、舟山海水网箱养殖患结节病大黄鱼(Larimichthys crocea)的病原菌,经生理生化试验及形态结构观察显示,该菌株革兰氏阳性,好氧,具有弱抗酸性,菌体呈长或短杆状,或细长分枝状,过氧化氢酶阳性、氧化酶阴性,还原硝酸盐,不水解酪素、黄嘌呤、酪氨酸、淀粉和明胶,能以柠檬酸盐为唯一碳源生长。对其16S rRNA基因进行PCR扩增、测序和系统发育分析,结果表明,该菌株与诺卡氏菌属的菌株亲缘关系最近,与鱼诺卡氏菌(Nocardia seri-oleaJCM 3360T)的16S rRNA基因序列相似性达99.9%。据此鉴定结果认为,该菌株为鱼诺卡氏菌(Nocardia seri-olea)。

A pathogenic bacterium was isolated from large yellow croaker, Larimichthys crocea, with white nodules, 0.1-0.2 cm in diameter, scattered on the heart, spleen and kidney. The bacteria were aerobic, Gram-positive, acid-fast, bead-like or long, slender, filamentous rods, and formed weakly pigmented, tan/ yellow and white adherent colonies 1-2 mm in diameter on Lowenstein Jensen medium （LJM） and tryptic soy agar （TSA） respectively. The organism was found to be catalase-positive, oxidase-produced, and could reduce nitrate and aesculin but not degrade xanthine, tyrosine, casein, starch and gelatin. It could utilized the citrate as sole carbon source but not mannitol, arabinose and sorbitol. A almost complete 16S rRNA gene sequence of the 16S rRNA gene of the bacteria was determined following PCR amplification and sequencing. The GenBank Accession No. is AY846841. The sequence was aligned with those available for nocardiae and phylogcnetic trees inferred using N-J method. The organism and the type strain of Nocardia seriolea JCM 3360^T（Z36925） consistently formed a monophyletic clade with a distant sequence similarity of 99.9 %. Base on the morphological, physiological, biochemical properties and Phylogenetic Analysis, the pathogenic organism was identified as Nocardia seriolea.