Detection and biosynthesis of puffer fish toxin from bacterial culture for novel medical application

Abstract

Tetrodotoxin (TTX), commonly known as puffer fish toxin, is one of the most lethal neurotoxins. Recent studies demonstrated that, besides puffer fish, TTX is widely distributed amongst a diversity of animals, which indicates TTX has an exogenous microbial origin, rather than being produced by puffer fishes. Due to its specific blocking action towards voltage gated sodium channel that can cease the transmission of action potential, TTX has the potential to develop as a drug lead candidate for local anesthetics or analgesics. In the present study, it aims to investigate a novel direction for the acquisition of TTX through fermentation technology using the TTX producing microbes isolated from the puffer fish. Also, the development of detection methods of TTX for the quantification of toxin in the culture medium and for the clinical diagnosis of TTX in poisoned patients. In order to study the production of TTX in the culture medium by TTX producing bacteria, several detection methods of TTX have been studied. Our research group has developed the use of traditional mouse bioassay for the measurement of TTX culture medium without much purification. Another biological based method for the detection of TTX is a tissue culture assay using neuroblastoma cell line (ATCC, CCL 131). HPLC is a chemical method exploited for TTX detection. HPLC with post column modification using fluorescent detector was developed and it was commonly used for the detection of TTX in research area. However, the detection would denature TTX into C-9 compound which preparative HPLC was not feasible. Therefore, our research group developed the use of HPLC with UV detector for TTX measurement. By using the novel developed heptansulfonic acid (HSA)-based buffer as mobile phase with UV detector at 197nm, TTX could be measured with a detection limit of lOng/ml. Also, under this HPLC UV detection system, we have developed a solid phase extraction system of TTX for the measurement of TTX in the urine of TTX poisoned patient. There was a TTX poisoning outbreak in Hong Kong last winter and the urine samples were collected from the Queen Mary hospital. TTX was detected in the urine sample and it was found to correlate to the severity of patient's clinical symptoms with urinary creatinine correction. For the production of TTX using TTX producing bacteria, puffer fish organs were used as screening targets for TTX producing bacteria and the screened bacteria were identified using MIDI system. Several species of bacteria including Bacillus-cereus, Raoultella-terrigena, Pseudomonas-putida, Microbacterium-arabinogalactanolyticum and Serratia-marcescens were studied for the production of TTX using fermentation. Our result suggested that aerobic condition is more favorable to the growth of TTX producing bacteria and TTX was produced in higher concentration in this condition. Shake flask and fermenter with different carbon sources, salt concentrations and the addition of puffer fish organ extracts into addition to the Ocean Research Institute (ORI) medium were used to study the growth and the TTX accumulation profile of different TTX producing bacterium. The result suggested that a suitable carbon source specific to the bacteria species could significantly enhance the growth of the bacteria. Fermenter study was done to provide a monitored pH and dissolved oxygen condition to study the growing pattern, the consumption of carbon source and the TTX accumulation profile of the TTX producing bacteria. It was found that the addition of puffer fish ovary extract would enhance the TTX production. Therefore, we proposed that some proteins inside the extract were involved in the production of TTX. Total proteins of the puffer fish ovary were extracted and added to the ORI culture medium in a fermenter study. The result of the fermenter study with the addition of total protein suggested that protein extract of puffer fish organ could affect the production of TTX from mouse bioassay analysis. In conclusion, a novel detection and purification method of TTX in urine and bacterial culture medium were developed. Potential TTX producing bacteria were screened from puffer fish organ. The nutrient requirement, growing condition, growing pattern and the TTX accumulation profiles were studied in shake flasks and fermenter. Puffer fish ovary extract and its protein were found to up regulate the production of TTX in the screened TTX producing bacteria.