Behavior of Surface Adsorbed Bioluminescent Bacteria
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Behavior of Surface Adsorbed Bioluminescent Bacteria Satoshi Sasaki School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura, Hachioji, Tokyo 192-0982, Japan ABSTRACT Characteristics of surface-adsorbed bioluminescent bacteria were examined. The bacteria were expected to function as an oxygen probe inside the biofilm. Luminescent behavior of the bacteria inside a typical biofilm was observed. Adsorption characteristics as well as the luminescence intensity change through the desorption process were investigated. INTRODUCTION In the field of biofilm research, it is important to know the chemical environment around the bacterium. Bioluminescent bacteria, Photobacterium kishitanii, are known to emit blue-green light [1]. As the light emission reaction consumes oxygen as substrate, the intensity of bioluminescence is affected by the dissolved oxygen concentration. Luminescence from a single bacterial cell can be measured using a photodetector such as EM-CCD camera. P. kishitanii do not produce harmful material that might possibly affect the metabolism of biofilm-forming bacteria. It is presumably reasonable to use P. kishitanii as an oxygen probe inside the biofilm. In this study, bioluminescent characteristics of P. kishitanii adsorbed on a glass surface or embedded in alginate gel were examined, aiming at the use of the bacteria as an oxygen probe. EXPERIMENT At first, P. kishitanii was tested if it grows in the Pseudomonas aeruginosa boifilm. Over the small colonies of P. kishitanii formed on a marine-agar plate, the liquid culture of P. aeruginosa was dropped. Growth of the both bacteria as well as the luminescence were simultaneously observed. Secondly, adsorption characteristics of P. kishitanii on a positively charged glass surface were examined. P. kishitanii cells were washed by Milli-Q water and the suspension with different cell density were dropped on the glass. After incubation, the glass surface was washed gently with Milli-Q water. Number of adsorbed cells was counted for each concentration, and a possible mechanism of the adsorption was discussed. Finally, luminescence characteristics of the P. kishitanii adsorbed glass were examined. The bacteria-adsorbed glass was placed in marine broth and the time course of the luminescent intensity was recorded. RESULTS AND DISCUSSION In the first experiment, liquid culture of P. aeruginosa was dropped on the P. kishitanii colony. After overnight incubation at room temperature (ca. 25°C), most of the P. kishitanii colonies were covered with P. aeruginosa biofilm. Luminescence from P. kishitanii seemed not
to be affected by the biofilm. This might be due to the small thickness of the biofilm. Part of the P. kishitanii colony was distorted by the growth of the biofilm. Results were shown in Fig. 1. In the second experiment, the cell adsorption mechanism seemed to be well described by the Freundlich-type model [2]. The meaning of the parameters obtained after a simple calculation is now examined. In the third experiment, two types of ce
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