A study on cobalt adaptation and memory retention of freshwater bacteria isolates

Çıtır, Gözde
The mucus-dwelling bacteria previously isolated from the surface of a freshwater fish species (Alburnus alburnus from Lake Mogan, Ankara), were studied to discover their cobalt resistance. The minimum inhibitory concentrations (MIC) were determined for a total of thirty six bacterial isolates. The results of the resistance studies led us to design experiments on adaptation to cobalt and subsequent memory retention. Three selected isolates were exposed to an inhibitory cobalt concentration as a mixed culture and individually. The delayed formation of colonies along with competitive exclusion of one of the isolates in the mixed culture were recorded. The delay for colony formation was followed up for liquid culture conditions. After some of our isolates acclimated to cobalt and started to exhibit constant time of growth period, it is assumed that they were adapted. We regarded adaptation as a result of memory formation. Next, we did a further study to find out how long this memory could be retained via serial multiple passages in cobalt free medium. We expressed our observations quantitatively by measuring the growth by using spectrophotometer and by performing viable counts. Interestingly, where there was a high CFU, the photometric values were very low. We interpreted the finding such that the presence of cobalt above tolerance limits were causing size reduction in the cells. So that their presence was underestimated by optic devices in visible range. Our study hinted that freshwater bacteria was adapting cobalt in a memory based mechanism and able to retain this memory for some time.


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Citation Formats
G. Çıtır, “A study on cobalt adaptation and memory retention of freshwater bacteria isolates,” M.S. - Master of Science, Middle East Technical University, 2010.