Survivability of Wild-Type and Genetically Engineered Thermosynechococcus elongatus BP1 with Different Temperature Conditions

Thermosynechococcus elongatus BP1 is a thermophilic strain of cyanobacteria that has an optimum growth at 57°C, and according to previous analysis by Yamaoka et al, T elongatus BP1 cannot survive at a temperature below 30°C. This suggests that the thermophilic property of this strain may be used as a natural biosafety feature to limit the spread of genetically engineered (GE) organisms in the environment if physical containment fails.

To further explore the growth and survivability range of T elongatus BP1, we report a growth and survivability assay of wild-type and GE T elongatus BP1 strains under different conditions.

Wild-type and GE T elongatus BP1 cultures were prepared and incubated in the laboratory (high temperatures and constant light source) and greenhouse conditions (lower/varied temperatures and sunlight) for 4 weeks. The cell density was monitored weekly by measuring the optical density at 730 nm (OD730). To assess the survivability, a sample of each culture was added to fresh media, placed in laboratory conditions (42.2°C and 30 µE m^–2 s^–1) in multi-well plates and observed for growth for up to three weeks. Lastly, the number of viable cells were determined by plating a diluted sample of the culture on solid media and counting colony-forming units (CFU) after 1 day, 2 weeks and 4 weeks of incubation in laboratory or greenhouse conditions.

Our experimental results demonstrated that growth was hindered but that the cells did not entirely die within 2 to 4 weeks at warm temperatures (31.42°C-36.27°C). The study also showed that 2 weeks of exposure to cool temperature conditions (15.44°C-25.30°C) was enough to cause complete death of GE T elongatus BP1. However, it took 2 to 4 weeks for the wild-type T elongatus BP1 cells to die.

This study revealed that the thermophilic feature of the T elongatus BP1 may be used as an effective biosafety mechanism at a cool temperature between 15.44°C and 25.30°C but may not be able to serve as a biosafety mechanism at warmer temperatures.