Matthias Bock, Ulrike Münzner
Institut für Biophysik, Humboldt-Universität zu Berlin, Germany
Bioluminescent microorganisms were cultivated on sea fish.
Materials and Methods
Four sardines, captured in the northeast atlantic, were bought at Kaisers, a local supermarket. The fishs‘ throats and bellies had been cut open, but the intestines were still inside and intact. As the fish had layed on ice behind the sales counter for several days, it was already aged, such that for human consumption it was not suitable anymore. It had, most importantly, never been deep-frozen though.
Saline water was mixed from mediterranean sea salt (without iodide) and supply water. The amount of salt was chosen relying on taste. The fish were put on a plate and soused with saline water until they were half covered. After that we carefully put the fishs‘ intestines on the outside of the bellies, to also get them in contact with the saline water.
Because of the slightly disturbing smell the plates were incubated on the balcony. Ambient temperature was about 8°C. The plate was covered by a mesh to reduce contamination.
After 6h of incubation the small intestines especially of one fish showed up weakly glowing. This fish also showed one comparably strong glowing spot, which appeared to be inside the beginning of the small intestine. Apparently the intestines had been damaged, as some of the intestinal content had diluted into the water. The skins showed no luminescence. We stirred the medium and wet’nd the skins with it.
After 30h we observed extraordinary strong luminescene on all four fish. On the skins we observed permanent blue glowing, especially in the border area between fish and water, possibly because of surface tension or pleasant growth conditions with respect to humidity, nutrients and oxygen presence. Physical stability indicated the formation of a biofilm.
Additionally to the skins, also the water, which had taken a rather red-brown color, exhibited a greenish homogenous luminescence, especially when mechanically stimulated (shaken or stirred). While the skin luminescence was more intense, both sorts of luminescence were clearly visible to the eye, even at weak artificial lighting. The luminescene in the water only lasted for about a minute after stimulation.
After 54h the luminescence had significantly reduced. The water was not glowing anymore and only on the skin of one fish there was still luminescence visible. At the same time all fish showed signs of rotting.
We consider it possible, that the mechanically stimulatable bacteria in the water were of a different species than the permanently glowing ones on the fish skin (Dinoflaggelates and Aliivibrio fischeri respectively). In any case, we are almost certain, that all glowing organisms originate from the content of the small intestine. This is in accordance with the hypothesis, that sea bacteria glow in order to be found and eaten in the darkness, populating the nutrients which are prefered by their hosts in their respective intestines, and being spread through these hosts‘ excrements.
As we aim to establish sustainably growing and glowing populations, we need to find out more exactly, which conditions and nutrients they prefer. We believe, that the process of rotting is disadvantageous for the growth of luminescent microorganisms. Our next step will be selection and cultivation on pepton trypton agar, as this is an established medium for cultivation of luminescent bacteria. This way we may be able to select for glowing species, which is necessary because of the corrupting species that seem to quickly populate the rotting fish.