Production level of tetrodotoxin in Aeromonas is associated with the copy number of a plasmid.
Tetrodotoxin (TTX) has been identified from taxonomically diverse organisms. Artificial synthesis of TTX has been reported, but the biosynthetic pathway of TTX remains elusive. In this study, we found TTX producing ability was associated with the copy number of plasmid pNe-1 in Aeromonas strain Ne-1 during fermentation, suggesting that at least one gene encoding a TTX-synthesis enzyme is located on this plasmid. Compared with bacterial genomes, plasmids are small and easier to screen for genes associated with TTX biosynthesis. The approximately 100 kb genome of pNe-1 was sequenced. The plasmid contains 60 complete open reading frames (orfs) of which 32 (53.3%) encode hypothetical proteins. Seven genes are related to the type IV secretion system (T4SS) and 2 genes are related to transposons, indicating that the TTX-producing bacterium Aeromonas might have the ability to transfer the TTX biosynthesis gene via the conjugation and contagion of plasmid pNe-1. In addition, we unexpectedly found that Aeromonas Ne-1 contains unknown TTX-degrading materials, indicating there is a homeostatic mechanism to maintain a stable amount of TTX in the bacterium. These results will help us to better understand TTX biosynthesis, the bacterial origin of TTX, and TTX degradation.
Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China.
Jing
J
Liu
Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China.
Fen
F
Wei
College of Food Science & Technology, Shanghai Ocean University, Shanghai 201306, China.
Ying
Y
Lu
Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China.
Tinglong
T
Ma
College of Food Science & Technology, Shanghai Ocean University, Shanghai 201306, China.
Jing
J
Zhao
Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China.
Xiaoling
X
Gong
Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China. Electronic address: blbao@shou.edu.cn.
Baolong
B
Bao
D000333:Aeromonas / Q000378:metabolism*; D056915:DNA Copy Number Variations; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification*; D005798:Genes, Bacterial; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013779:Tetrodotoxin / Q000096:biosynthesis*; D000069319:Type IV Secretion Systems / Q000235:genetics / Q000378:metabolism
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D000069319:Type IV Secretion Systems; D013779:Tetrodotoxin
Plasmid copy number; Plasmid genome; TTX biosynthesis; TTX degradation; TTX-producing bacteria