For decades, the large-scale mortality of salmonine fishes in the Laurentian Great Lakes and Baltic Sea from thiamine (vitamin B1) deficiency has presented an unsolved mystery in aquatic ecosystem management. Recent studies have shown that this thiamine deficiency results from the consumption of clupeid prey containing thiaminase I, an enzyme that degrades available thiamine, yet conditions that influence thiaminase I levels in fish remain poorly characterized. We have pursued laboratory experiments with bacterial cultures and two model organisms to evaluate the hypothesis that bacterial production of thiaminase I is responsible for this problem in fisheries and aquatic ecosystem management. Recent discoveries in molecular biology and structural chemistry guided development of our hypothesis that bacteria living within aquatic organisms regulate the production of thiaminase I, which subsequently leads to thiamine deficiency in fish and consumers of fish. Our lab experiments have focused on two lines of investigation to evaluate this hypothesis: 1) Altering culture conditions to influence thiaminase I production in culture experiments with five types of thiaminase-I producing bacteria, and 2) manipulating environmental conditions in aquaria with two model organisms (quagga mussels, Dreissena rostriformis, and goldfish, Carassius auratus) in order to alter thiaminase I levels in these organisms.
Results/Conclusions
Published gene sequences of thiaminase-I producing bacteria show this enzyme consistently coded for in an operon associated with thiamine-producing enzymes, preceded by a 5' end non-coding sequence with a proposed secondary structure that may regulate translation. Corresponding culture experiments with these bacteria have supported this expectation, based on our observation that thiaminase I production can be turned on and off by regulating levels of thiamine in the bacterial culture media. Whole organism experiments with quagga mussels reared in aquaria with water containing a variety of antibiotics - including chloramphenicol, erythromycin and gentamycin sulfate - have shown that thiaminase I in mussel tissue can be increased or decreased in response to specific antibiotics, though each of these antibiotics has a different effect in magnitude, direction and timing. Experiments with goldfish have also shown that levels of thiaminase I in these fish increase through ontogeny after an initial absence of this enzyme within eggs.