Improved detection of toxic chemicals by Photobacterium phosphoreum using modified Boss medium

A bioluminescent bacterium Photobacterium phosphoreum has been used widely as an indicator of pollutants where the presence of toxic chemicals decreases light output. The optimum conditions for the growth and bioluminescence of P. phosphoreum KCTC 2852 were investigated using modified Boss medium and two environmental conditions (pH and temperature). Optimized conditions that supported growth of P. phosphoreum with high bioluminescence intensities were: NaCl (20g/L), glycerol (2.5g/L), peptone (1.0g/L), and yeast extract (1.0g/L). Growth and bioluminescence gradually increased as pH increased reaching a maximum at pH 7.0. The maximum temperature for growth and bioluminescence was 20°C. Based on these optimum conditions for bioluminescence, a continuous culture reactor of P. phosphoreum was operated. During the continuous operation, the optimized medium maintained bioluminescence with a high relative light unit (RLU) around 13,600 for more than 120h. When zinc (0.5mg/L) was added to the reactor, an EC₅₀ was observed in 15min. The detection limit was improved by using the modified Boss medium since the modified Boss medium contained less organic matter which minimizes the complexation and precipitation of heavy metals compared to other enrichment media with high levels of organic matter.